Microbiology of Commercially Sterile and Shelf-Stable Products 

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MICROBIOLOGY OF THERMALLY PROCESSED 

COMMERCIALLY STERILE AND SHELF-STABLE MEAT 

AND POULTRY PRODUCTS 

To understand the microbiology of thermally processed commercially sterile and 

shelf-stable meat and poultry products you must first be familiar with the 

microbiology of meat and poultry, as well as some basics of processed food 

microbiology in general. In this section you will learn about microorganisms of 

significance in thermally processed commercially sterile and shelf-stable 

products, the sources of these microorganisms, the conditions affecting their 

growth and inactivation, and the specific microbiology of acidified and low-acid 

“canned” (commercially sterile) foods. You will learn more about the specific 

microbiology of other shelf-stable meat and poultry products such as dry and 

acidified/fermented products in the section on the Microbiology of Shelf-Stable 

Dried Meats. 

The objectives of this section are for you to be able to: 

1. Recognize pathogens of concern for thermally processed commercially 

sterile and shelf-stable products and distinguish them from spoilage 

organisms. 

2. Identify conditions affecting microbial growth and related control methods. 

3. Identify causes of canned food spoilage. 

Introduction to the Microbiology of Food Processing 

All raw foods normally contain microorganisms that will eventually cause spoilage 

unless they are controlled or destroyed. Food preservation is a competition 

between the human species and microorganisms – we attempt to preserve the 

food, the microorganisms attempt to destroy it (by breaking down the food for its 

own consumption) in order to survive. Many of the thousands of microorganisms 

that have been discovered and identified perform some useful function. Without 

microorganisms, we would not have some of the tasty foods we enjoy, such as 

breads, cheese, wine, beer, sauerkraut and other fermented foods, including 

many sausages. Vanilla, olives, tea and chocolate are other products that 

include a microbial fermentation step. In addition, these microorganisms are 

needed to make products useful to industry and medicine, such as enzymes, 

antibiotics, glycerol and other alcohols. Still other types of microorganisms have 

the ability to break down organic matter and return it to the earth in a recycling 

process to form food for plants, which in turn provide food for animals. Without 

such microorganisms, the earth would accumulate dead animals, leaves and 

other non-decayed matter – all of which would have eliminated life on earth long 

ago. 

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However, it is also true that most diseases of humans, animals or plants are 

caused by specific microorganisms. The microorganisms that can cause illness 

are known as pathogens. The pathogen, or the substances it produces, must 

invade the human, animal or plant body to cause illness. Fortunately, 

comparatively few of the tens of thousands of known microorganisms are harmful 

to humans. While many diseases can be transmitted from person to person or 

from animals to humans, only a few can be transmitted through foods. Although 

it is becoming recognized that the vast majority of cases of food borne illnesses

are caused by viruses such as hepatitis A and noroviruses (67% of all cases of food 

borne illness, according to one analysis), bacterial agents, such as Salmonella and 

Campylobacter, are most frequently identified as the cause of illness because we 

have a much greater understanding of how to isolate and identify them. 

Significant Microorganisms in Food Processing 

There are many different ways to classify and group microorganisms, including 

groupings based on microscopic appearance, the materials they can use as 

foods, the byproducts resulting from the breakdown of these foods, their 

tolerance to oxygen, their growth temperatures, and their resistance to such 

destructive agents as heat and chemicals. The microorganisms of primary 

concern to the food processor are generally molds, yeasts and bacteria, because 

they can grow in the food and cause spoilage. Processors are also concerned 

about viruses and parasites in foods, although they are not capable of growing in 

the food and do not cause spoilage. Bacteria, viruses and parasites are of 

particular concern because a number of them cause illness. A brief review of the 

significant groups of microorganisms in food processing follows. 

►Molds 

Molds exhibit some of the characteristics of the higher plants. They are multiple 

cell organisms forming tubular filaments. Molds demonstrate branching and 

reproduce by means of fruiting bodies, called spores, which are borne in or on 

aerial structures. Their mycelia, or intertwined filaments, may resemble roots. 

They are many times larger than bacteria and somewhat longer than yeasts. 

Molds are widely distributed in nature, both in the soil and in the dust carried by 

air. Under suitable conditions of moisture, air and temperature, molds will grow 

on almost any food. The black or green discoloration that appears on moldy 

bread is familiar evidence of such growth. Molds are also able to survive on a 

wide variety of substances not normally thought suitable for the support of life. 

These include concentrated solutions of some acids and water containing minute 

quantities of certain salts, as well as on building structures. Molds grow readily 

on the walls and ceilings of buildings where there is high humidity and 

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considerable moisture condensation. Mold growth can even occur in 

refrigerators, because molds are much more tolerant to cold than to heat. Molds 

can grow at reduced water activities (aw) and can be a problem in improperly 

processed dry and semi-dry fermented products, as discussed later. 

Molds are capable of consuming acids, thereby raising the pH of products. Their 

growth in foods has, on very rare occasions (and never in meat or poultry 

products), removed the acid conditions that inhibit growth of Clostridium

botulinum, a food borne pathogen discussed later in this section. 

Most molds have little heat resistance and cannot survive the thermal processes 

for low-acid canned foods. Some molds produce a type of spore (ascospore) 

that is more resistant to heat, but these spores are much less resistant than the 

spores that are the target of processes for low-acid and acidified canned foods; 

these heat-resistant molds have not caused problems in meat and poultry 

products. Therefore, molds are present in canned meat and poultry products 

only as a result of gross under-processing or as a post-processing contaminant. 

Since molds must have oxygen to grow, only slight growth can occur unless the 

food container has an opening to the outside environment. 

Mold growth in thermally processed commercially sterile and shelf-stable foods 

has to date not been shown to present a public health problem. In fact, mold is 

used in the ripening process of some sausages, as will be discussed in other 

sections. 

►Yeasts

Another microorganism of importance to food preservation/spoilage is yeast. 

Yeasts are single cell, microscopic living bodies, usually egg-shaped. They are 

smaller than molds, but larger than bacteria. Their greatest thickness is about 

1/2,000 of an inch. Yeasts reproduce mainly by budding. A small bud forms on 

the parent yeast cell and gradually enlarges and breaks off into another yeast 

cell. A few varieties reproduce by forming spores within a special cell; later these 

spores may form new yeast cells. 

Yeasts are widely found in nature and are particularly associated with liquid 

foods containing sugars and acids. They are quite adaptive to adverse 

conditions such as acidity and dehydration. Like molds, yeasts are more tolerant 

to cold than to heat. Compared to bacterial spores, yeasts and their spores 

possess little resistance to heat. Most yeast forms are destroyed on heating to 

170oF (77oC). Spoilage may result from the presence of yeast in canned food, 

but if this happens, gross under-processing or leakage must be suspected. 

Usually the growth of yeasts results in the production of alcohol and large 

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amounts of carbon dioxide gas, which swells the container. 

Yeast growth in processed foods does not present a public health problem. 

►Viruses 

Virus particles are so small they cannot be seen by the standard light 

microscopes used in laboratories – a special electron microscope is needed to 

see these microorganisms. A virus particle is composed of either RNA or DNA 

enclosed in a coat of protein, sometimes with an outer envelope containing lipids 

(fats). (Deoxyribonucleic acid (DNA) is a nucleic acid which carries genetic 

instructions for the biological development of all cellular forms of life and many 

viruses. Ribonucleic acid (RNA) transmits genetic information from DNA to 

proteins, and carries the genetic instructions for many viruses.) Viruses lack the 

enzymes and other components needed to replicate. Thus, viruses cannot 

multiply in food – they can only replicate themselves in suitable living host cells. 

Viruses transmitted by food are produced in the human body and shed in the 

feces. Of particular concern for foods are the hepatitis viruses and noroviruses. 

These latter viruses have been mentioned in many news stories in recent years 

for causing large outbreaks of vomiting illnesses at large gatherings and on 

cruise ships. Viruses get into food through contaminated water and infected food 

handlers with poor hygienic practices. 

Viruses are not heat resistant, with most having resistance similar to non-spore 

forming bacteria (see below). Hepatitis A virus is somewhat more resistant, but 

is still inactivated at 185°F (85°C). Avian influenza virus, which can infect 

chickens, turkeys, pheasants, quail, ducks, geese, and guinea fowl, as well as a 

wide variety of other birds, has been known to infect humans, but it is not 

transmitted through foods, nor is exotic Newcastle disease virus, which also 

causes a highly contagious poultry disease. Heating to at least to 161.6°F (72°C) 

internal temperature is considered adequate to inactivate both these viruses. 

The Human Immunodeficiency Virus (HIV) which causes the disease AIDS

(Acquired Immune Deficiency Syndrome) is a severe public health problem. AIDS

has never been shown to be transmitted by food or drink. Individuals who are 

known to be infected with the virus can handle food safely if they observe basic 

sanitation precautions for food handling and take care to avoid injury when

preparing food. As with any food handler, should an injury occur, food 

contaminated with blood should be discarded for aesthetic as well as safety

reasons. Employees should be restricted from handling food if they have evidence

of infection or illness that would otherwise require that they not handle food. 

Viruses are not a concern in thermally processed commercially sterile and shelfstable meat and poultry products. 

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►Parasites 

The parasites of concern in the production of meat and poultry products include 

worms and protozoa. Some of them are large enough to be seen with the naked 

eye, whereas others are microscopic. Parasites cannot multiply in food, only in a 

host cell, and they are not heat resistant. 

Parasitic worms of public health importance are the beef and pork tapeworms 

(Taenia saginata and Taenia solium, respectively) and the roundworm that 

causes trichinosis (Trichinella spiralis, also referred to as trichinae) found in pork. 

These small cysticerci (refered to as Cysticercus cellulosae) are approximately 6- 

18mm wide by 4 - 6mm in length when found in the muscles or subcutaneous 

tissues (the normal sites for the larvae of this parasite). The cysticerci may 

however be found in other tissues, such as those of the central nervous system, 

where they may grow much larger up to several cm in diameter. 

Muscle and organs of animals with severe tapeworm infection are usually visually 

detected by government inspection personnel or by plant employees through 

evidence of the immature stages (larval stage in a cyst known as a cysticercus) 

of tapeworms, which are 6- 18 mm wide by 4 – 6 mm in length when found in the 

muscles. Such product cannot be further processed for human consumption. 

When the cysts are less severe or evident, infected meat may enter the human 

food chain, however illness will not occur if meat is properly cooked. Humans 

consuming undercooked meat infected with these tapeworms become ill with 

taeniasis generally after the mature stages of the tapeworms, which develop from 

the cysticercus, invade the intestinal tract. Most cases of infection with adult 

worms are without symptoms. Some persons may experience abdominal pain, 

weight loss, digestive disturbances, and possible intestinal obstruction. 

Taeniasis may last many years without medical treatment. However, people can 

get a more serious illness called cysticercosis by consuming food or water 

contaminated with the eggs of T. solium (pork tapeworm). Worm eggs hatch and 

the larvae then migrate to various parts of the body and form cysts (cysticerci). 

This can be a serious or fatal disease if it involves organs such as the central 

nervous system, heart, or eyes. Symptoms may vary depending on the organ or 

organ system involved. For example, an individual with cysticercocis involving 

the central nervous system (neurocysticercosis) may exhibit neurological 

symptoms such as psychiatric problems or epileptic seizures. Death is common. 

Trichinella spiralis is an intestinal worm that produces larvae that migrate to and 

encyst in muscles of a number of animals, particularly swine. Humans 

consuming infected pork that is undercooked get ill from the cysts, which then 

live in the muscles of the human hosts. The first symptoms are nausea, 

diarrhea, vomiting, fever, and abdominal pain, followed by headaches, eye 

swelling, aching joints and muscles, weakness, and itchy skin. In severe 

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infections, persons may experience difficulty with coordination and have heart 

and breathing problems. Death may occur in severe cases. 

Parasitic protozoa of concern in meat processing include Cryptosporidium 

parvum and Toxoplasma gondii. Cryptosporidium is typically transmitted to 

humans from fecal material of animals, primarily cattle, via contaminated water or 

occasionally, food. The organism is destroyed by boiling water. Toxoplasma 

gondii is carried by cats but can infect many warm-blooded animals. A form 

known as the oocyst is shed and can sporulate and survive in soil and other 

environments for extended times; the sporulated oocyst is infectious to all warmblooded hosts. When ingested, the sporulated oocysts go through several forms, 

eventually forming cysts in tissue such as muscle. These cysts are infective if 

ingested. Toxoplasma can cross the placenta and affect the fetus, resulting in 

blindness and more serious effects in the brain. 

Parasites are readily destroyed at cooking temperature and are not a major 

concern in thermally processed commercially sterile meat and poultry products 

since they are subjected to temperatures well in excess of what is needed to 

destroy parasites. Parasites are a concern with respect to shelf-stable products 

that are not cooked. For example, trichinae are a concern with respect to shelfstable products, such as dried sausages, containing pork. We’ll discuss this 

further in the module for the microbiology of shelf-stable dried meats. 

►Bacteria

Bacteria are the most important and troublesome of all the microorganisms for 

the food processor. Bacteria are single-celled living bodies so small that 

individually they can be seen only with the aid of a microscope. They are among 

the smallest living creatures known. The cells of bacteria vary in length from 

1/25,000 to 1/1,000 of an inch. The number of these tiny microorganisms that 

could be placed on the head of a pin would equal the population of New York 

City! Viewed with a microscope, bacteria appear in several shapes or forms, but 

are primarily either round in shape (called “cocci”) or rod-shaped (called “rods”). 

Reproduction of bacterial cells

Bacteria reproduce by division, which microbiologists call fission. When a 

bacterial cell is ready to divide, the cell material gradually increases until its 

volume is almost doubled. The cocci shapes become oval while rod shapes 

stretch to nearly twice their length. The cell then constricts in the middle. This 

constriction deepens until the cell contents are held in two distinct compartments 

separated by a wall. These two compartments finally separate to form two new 

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cells, which are duplicates of the former cell and each other. Since the 

reproduction of bacteria increases the numbers, it is often referred to as “growth.” 

Experiments conducted to determine the growth rate of bacteria under favorable 

conditions have found that each cell divides, on the average, about every 20 or 

30 minutes. At this rate of cell division, each single cell will produce four cells at 

the end of the first hour. At the end of two hours, each cell will have produced 16 

new cells. After 15 hours, each parent cell will have produced 1,000,000,000 

(one billion) cells identical to the original. For example, if there were 75,000 

bacteria per square inch on a conveyor belt, by the end of one hour there could 

be 300,000 bacteria per square inch of that belt. At the end of a three-hour shift, 

the bacteria count per square inch of belt surface could be 4,800,000. 

Bacterial growth becomes limited without a constant supply of available fresh 

food. Also, large numbers of bacteria result in an accumulation of substances 

that are byproducts of bacterial growth and that also inhibit growth. With 

cessation of growth due to pollution of their environment, the cells may die. 

However, if the microorganism is a type that forms resistant but dormant spores, 

these cells can remain alive under conditions that kill other cells. 

Sporeforming and non-sporeforming bacteria 

Bacteria can be divided into two groups based on their ability or inability to form 

spores. Practically all of the round-shaped bacteria (cocci) and many of the rodshaped bacteria cannot form spores; thus they are classified as nonsporeformers. However, a number of the rod-shaped bacteria have the ability to 

produce a spore within the cell (endospore). Spores are a dormant stage in the 

normal growth cycle of these organisms. They have the ability to survive a wide 

range of unfavorable conditions. The primary function of most spores is to 

ensure the survival of the organism through periods of environmental stress. 

Spores have been compared to plant seeds because they will germinate and 

grow when conditions are suitable. The major sporeforming bacteria are species 

of Clostridium and Bacillus. Cells of non-sporeformers and the cells of 

sporeformers that have not formed spores are referred to as “vegetative cells.” 

These cells generally have little resistance to heat, drying and other unfavorable 

conditions. 

When formed in yeasts and molds, spores represent reproductive bodies, but 

bacterial spores are a resting stage in the growth cycle of these organisms. 

When a bacterial spore germinates, it is simply the same organism continuing its 

growth process. 

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Resistance of spores to the environment 

In general, bacterial spores are extremely resistant to heat, cold and chemical 

agents. Some bacterial spores can survive in boiling water – 212oF (100oC) – for 

more than 16 hours. The same organisms in the vegetative state and the nonsporeforming bacteria will not survive heating in boiling water. 

As a general rule, spores that successfully resist heat are also highly resistant to 

destruction by chemicals. There are bacterial spores that can survive more than 

three hours in sanitizing solutions normally used in a food processing plant. On 

the other hand, vegetative cells (non-sporeforming bacteria and the vegetative 

cell form of sporeformers) are readily destroyed by these sanitizing agents. The 

purpose of sanitizing is not to sterilize surfaces (to remove all bacteria), so the 

survival of spores under appropriate sanitation practices is not a concern – they 

will be present in low numbers and will be inactivated or controlled in the final 

product. 

Bacterial hazards of concern in meat and poultry 

Of the microbiological hazards of concern in meat and poultry, the most 

important are bacteria. Illness from meat and poultry is primarily caused by 

bacterial pathogens. The pathogens that are most likely to be found in livestock 

(cattle, sheep, and swine) and poultry (chicken and turkey) include Salmonella, 

Campylobacter, and Listeria monocytogenes. Listeria monocytogenes also is 

widespread in the environment. Escherichia coli is also found in livestock and 

poultry, but most strains are not pathogenic; the pathogenic E. coli of primary 

concern is known as E. coli O157:H7 and is found in beef. (Although the 

organism has occasionally been found in chickens and pigs, it has not been 

known to cause illness from those animals.) Yersinia enterocolitica is a pathogen 

most commonly associated with pork; only certain serotypes (strains) are 

pathogenic. Clostridium perfringens can also be found in meat and poultry; the 

spores may survive cooking and grow to high numbers in foods due to 

temperature abuse. Clostridium botulinum is rare in meats. When present, it is 

there in very low numbers (estimates are 0.1 spore to 7 spores per kg meat). 

Bacillus cereus is another sporeformer of concern in meat and poultry products, 

especially those containing spices, which is a common source of the spores. 

All of these pathogens have been implicated in food borne disease outbreaks 

associated with the consumption of meat and poultry products in which these 

hazards were not properly controlled. Proper cooking or thermal processing, 

fermentation, cooling, and storage of food can destroy and/or prevent growth of 

these bacteria. 

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Sources of Microorganisms 

Raw materials and ingredients are the primary sources of microorganisms that 

must be addressed in the production of thermally processed commercially sterile 

and shelf-stable products. Although muscle tissue is generally considered to be 

sterile, raw meat and poultry become contaminated during slaughter and further 

processing. The ultimate source for pathogens in raw meat and poultry is 

apparently-healthy animals that may shed these bacteria in their feces. While 

dressing the carcasses during the slaughter process, these bacteria may be 

transferred from the hide, skin, feathers, gastrointestinal tract and other offal to 

the carcass, causing contamination. This is also a major source of spoilage 

microorganisms. 

Soil or water can be a common source of food borne microorganisms and 

spores. Vegetables become contaminated during production, with those that 

grow close to or through the soil usually having high numbers of bacteria and 

bacterial spores, including spores of C. botulinum. Contaminated water used for 

irrigation has also been a source of pathogens on vegetables. Dried herbs and 

spices can be a primary source of sporeformers, since the spores will survive for 

extended times in the dehydrated product. Soy and milk protein ingredients can 

also be sources of spores. 

Contamination can also come from the processing environment. Utensils such 

as knives used in slaughter and fabrication, workers hands and gloves, 

equipment, and occasionally aerosols with dust and other particles carrying 

microorganisms can all contribute to the microbial load of products. 

Contaminants may be present on containers and other packaging materials, 

although this is generally not a likely source of pathogens. Proper sanitation of 

the environment and protecting containers from environmental contamination can 

prevent these from being major sources of contamination such that they will 

negatively impact thermally processed commercially sterile and shelf-stable 

products. 

Conditions Affecting Microbial Growth 

The following information focuses on bacteria, since we are most concerned with 

bacterial pathogens; however, much of it is applicable to yeasts and molds as 

well. It is not applicable to parasites and viruses, since they do not grow in food. 

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►Nutrient Requirements

A suitable food supply is the most important condition affecting growth of 

bacteria. Every living cell requires certain nutrients to multiply. These include 

solutions of sugars or other carbohydrates, proteins and small amounts of other 

materials such as phosphates, chlorides and calcium. If the food supply is 

removed, bacteria will not multiply. 

►Moisture Requirements

The concentration of moisture and its availability in a food (referred to as water 

activity, or aw) are important factors to prevent microbial growth. The bacterial 

cell has no mouth, and therefore its food must be in a soluble form to enter the 

cell through the cell wall. Without sufficient available moisture, the inflow of food 

and the outflow of food residues and cell body fluids would be impossible. Later 

we will discuss how bacterial growth can be prevented by controlling the amount 

of moisture available to the bacteria. 

►Oxygen Requirements

Some bacteria – called aerobes – require free oxygen in order to survive. For 

others, called anaerobes, the reverse is the case – the smallest quantity of free 

oxygen prevents their growth. The majority of bacteria – called facultative 

anaerobes – are neither strict aerobes nor strict anaerobes, but can tolerate to 

some degree either the presence or absence of oxygen. 

►pH Requirements 

The term pH designates the acidity or alkalinity of an aqueous solution. 

Scientifically, pH is the negative logarithm of the hydrogen ion concentration. 

The pH scale ranges from 0 to 14, with pH 7 being neutral. Numbers smaller 

than 7 indicate an increase in hydrogen ion (more acid) and numbers greater 

than 7 indicate a decrease in hydrogen ion concentration (more basic, or 

alkaline). All bacteria have an optimum (most favorable) pH range for growth 

(generally around neutral pH), as well as a minimum below which the organism 

will not grow (and where the organism may die) and a maximum above which it 

cannot grow. The pH of foods can be adjusted to help control microbial growth, 

as will be described later. 

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►Temperature Requirements

As with pH, all bacteria have an optimum temperature range for growth. 

Temperatures below and above the optimum for each group adversely affect the 

growth of the organism; all bacteria have a minimum and a maximum 

temperature below or above which the organism cannot grow. Bacterial groups 

bear names that indicate their relationships to temperature – psychrophile, 

psychrotroph, mesophile, thermophile. 

The psychrophilic and psychrotrophic group

The terms psychrophile and psychrotroph are sometimes used interchangeably, 

but the groups are distinguished by their optimum growth temperatures and 

temperature ranges. Both psychrophiles and psychrotrophs grow over the 

temperature range of subzero to 68°F (20°C). True psychrophilic bacteria 

(“psychro” for “cold,” “phile” for “loving”) have an optimum temperature of 59°F 

(15°C) and cannot grow above 77°F (25°C). Psychrotrophic bacteria generally

grow best at around 77°F (25oC), or even mesophilic temperatures (see below), 

but can grow slowly in or on food at refrigerator temperatures (around 40oF 

(4oC)). These organisms are primarily responsible for spoilage of refrigerated 

foods. L. monocytogenes and some strains of C. botulinum (C. botulinum type E 

and non-proteolytic strains of type B and F) are considered to be psychrotrophs. 

None of these bacteria – except perhaps the strains of C. botulinum – is of 

concern to low-acid or acidified canned foods. 

The mesophilic group

Mesophilic bacteria grow best at temperatures of 86oF to 104°F (30oC to 40°C) 

(the normal range of warehouse temperatures, depending on geographic 

locations), although some mesophiles grow well at higher temperatures such as 

116oF (46.7oC). All of the bacteria that affect food safety grow within this 

mesophilic temperature range, although some may be considered psychrotrophic 

as well. The sporeforming organism C. botulinum is a member of this group, 

although some strains are considered psychrotrophs (see above). 

The thermophilic group

Thermophiles (“thermo” for heat, “phile” for loving) are bacteria that grow at high 

temperatures. Thermophilic bacteria are found in soil, manure, compost piles, 

and even hot springs. Many are sporeforming bacteria and are divided into two 

groups based on the temperature at which the spores will germinate and grow. If 

the spores will not germinate and grow below 122oF (50oC), the bacteria are 

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called obligate thermophiles, i.e., the high growth temperature is an absolute 

requirement. If growth occurs at thermophilic temperatures of 122o to 150oF 

(50oC to 66oC) and at lower temperatures – e.g., about 100oF (38oC) – the 

bacteria are called facultative thermophiles, meaning they have the ability to 

grow at both temperature ranges. 

Some of the obligate thermophiles can grow at temperatures up to 170oF (77oC). 

Laboratory tests have indicated that the spores of these bacteria are so heatresistant that they can survive for more than 60 minutes at temperatures of 250oF 

(121oC). Thermophilic bacteria are not pathogenic and do not produce toxins 

during spoilage of foods; therefore, they do not affect food safety. 

►Interaction of Factors 

The level of a single growth-limiting factor to inhibit a microorganism is usually 

determined under conditions under which other factors that could influence 

growth are optimal. When other factors are not optimal, the organism will not be 

able to grow at the minimum or maximum level of another factor. For example, 

when the water activity is lower, the pH range at which an organism can grow is 

more limited. When the pH is lower, the water activity that limits growth will be 

higher. The presence of preservatives can affect the pH at which an organism

grows; growth may take longer at lower temperatures when preservatives are 

present. With that in mind, let’s look at some of the control methods for 

microorganisms in foods. 

Control Methods for Microorganisms 

►Control of Bacteria by Temperature 

Bacterial growth can be controlled by keeping food at temperatures below the 

minimum or above the maximum for the organism to grow. Thus, refrigeration, 

freezing and hot holding can be used to control growth. However, the most 

effective use of temperature to control microorganisms is to kill them with heat. 

The amount of heat needed to inactivate the microorganisms of concern will be

dependent on the specific microorganism (the species and whether or not it is in 

the spore form), the number of microorganisms to be inactivated, and the food 

product in which the microorganism is heated (and factors of the food such as its 

pH, aw, the presence of preservatives such as nitrite). 

The thermal resistance of microorganisms is generally expressed using D- and zvalues. The D-value is the time in minutes at a constant temperature to destroy 

90% (or 1 log) of the organism present; the z-value is the number of degrees 

between a 10-fold change (1 log cycle) in an organism’s resistance. For 

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example, if an organism has a D-value of 5 minutes at 140°F and a z-value of 

10°F, then the D-value at 130°F will be 50 minutes and the D-value at 150°F will 

be 0.5 minutes. If there are <100,000 microorganisms present in a sample, then 

a process that delivered a 5-D reduction (also called a 5-log reduction) to the 

sample would result in <1 microorganism remaining. We will refer to this logreduction concept again in the section on thermal processing of commercially 

sterile products and in the section on the microbiology of shelf-stable dried 

meats. 

In general, low-acid commercially sterile products will require high temperatures 

that are achieved by processing under pressure to inactivate the organisms of 

concern. Acidified meat and poultry products can be processed at lower 

temperatures, since only vegetative cells must be inactivated; the pH prevents 

germination and outgrowth of the spores. In canned cured products, the 

presence of nitrite and salt reduces the amount of heat needed to achieve 

commercial sterility (heat kills the vegetative cells of pathogens; salt and nitrite 

prevent germination and outgrowth of spores). In most canned products it is not 

the pathogen of concern that determines the amount of heat needed but rather 

the spoilage microorganisms, which are more heat resistant than the pathogens. 

If these organisms are not inactivated, the product will not be shelf-stable. In 

most instances, this provides a wide margin of safety with respect to survival of 

pathogens in the product. 

►Control of Bacteria by pH

As noted above, microorganisms can be controlled by reducing the pH below the 

minimum for growth of the organism. An “acidified low acid product” is defined 

by FSIS as a canned product which has been formulated or treated so that every 

component of the finished product has a pH of 4.6 or lower within 24 hours after 

the completion of the thermal process unless data are available from the 

establishment’s processing authority demonstrating that a longer time period is 

safe. Proper acidification is necessary to prevent the growth of C. botulinum. 

Unlike processes for low-acid foods that destroy C. botulinum spores, processes 

for acidified foods depend upon the pH of the food to prevent this organism from 

growing. The final equilibrium pH of an acidified food must be 4.6 or lower to 

prevent growth of C. botulinum However, since some microorganisms can cause 

illness at very low levels (e.g., Escherichia coli O157:H7), preventing growth 

alone will not provide a safe product. Reduced pH can be combined with other 

factors to control the pathogens of concern. For example, a reduced pH, 

combined with a mild heat treatment, is used to achieve commercial sterility in 

acidified meat and poultry products such as pasta sauces containing meat. The 

role of pH in conjunction with other factors in the production of 

acidified/fermented meat and poultry products will be covered in the sections on 

Principles of Preservation of Shelf-Stable Dried Meat Products and the 

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Microbiology of Shelf-Stable Dried Meats. The pH values for representative 

canned meat and poultry products are shown in Table 1. 

Table 1 – pH values of representative canned meat and poultry products 

Food pH

Beans with wieners 5.7 

Beef chili 5.6 

Beef stew 5.4-5.9 

Chicken and dumplings 6.4 

Chorizos 5.2 

Corned beef 6.2 

Corned beef hash 5.0-5.7 

Ham 6.0-6.5 

Spaghetti and meatballs 5.0 

Spaghetti sauce with beef 4.2 

Sloppy Joe 4.4 

Vienna sausage 6.2-6.5 

Acidification procedures 

To produce products with a pH of 4.6 or less, acidification must be properly 

carried out. While there are several methods to obtain properly acidified foods, 

one commonly used with meat products is direct batch acidification. Ingredients 

are mixed in a kettle, and acid or, more commonly an acid food, is added directly 

to the batch. (An elevated temperature may improve the rate of acid penetration 

into solid particles.) The pH of the batch is checked before the material is sent 

from the batch kettle to the filler. If the particle size is small enough, the product 

pH will be below 4.6 at this point. With larger particles, the product may not 

reach the desired pH until later; however a pH taken at this point can be used to 

determine that the acidification process is under control. Another method that is 

used for acidification of meat products is the addition of acidified brine, such as 

with pickled pigs’ feet. Other methods will be discussed in the section on 

Principles of Thermal Processing. 

Determination of pH

The most important factor in the production of acidified foods is the timely 

attainment and maintenance of a pH level that will inhibit the growth of 

C. botulinum spores. To achieve this goal, it is necessary to measure pH. 

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Although pH can be measured using colorimetric methods (dye solutions and pH 

paper) or by titratable acidity, the recommended method for determining pH is 

the electrometric method using a pH meter. The pH meter measures the 

electrical potential developed between a glass and a reference electrode when 

they are immersed in a solution. USDA currently requires the electrometric 

method to be used any time pH is specified as a critical factor for a scheduled 

process. 

The sensing elements used with pH meters are called electrodes. Combination 

electrodes contain both a glass and reference electrode in a single probe. They 

come in a number of different sizes and conformations, which increases the 

applications of this type of electrode. For example, flat-surface electrodes are 

useful for measuring the surface pH of a solid sample; long, thin electrodes may 

be inserted in tubes for measuring pH of small sample volumes or inserted into 

the process stream for continuous monitoring of pH. Unbreakable electrodes 

should be used in food processing plants to minimize the chances of 

contaminating food. For best results, pH meters should be operated in 

accordance with manufacturer's instructions; the manufacturer’s 

recommendations should be followed for care and maintenance of all pH 

electrodes. 

Once the unit has been turned on and allowed to warm up, the meter should be 

properly standardized (calibrated) using two buffers to cover the pH range of 

interest, such as one at pH 4.0 and the other at pH 7.0. The meter should be 

standardized (1) before any food pH measurements are taken and (2) at least 

once an hour following that. More frequent standardization and cleaning may be 

necessary with some products that contain oil, grease or fats. 

The sample to be tested must be properly prepared, which is dependent on the 

type of product to be evaluated. Homogeneous products, such as sauces, 

require little preparation. Products that consist of solid and liquid components

should have the solid components tested separately to determine if they have 

been properly acidified. One means of sample preparation is to transfer a portion 

of the solid component to a screen, rinse it with a small volume of distilled water 

(10-20 ml), and thoroughly blend before taking a pH. Sufficient tests must be 

made to ensure that the finished equilibrium pH of the product is not higher than 

4.6. These tests indicate whether the acidification process is sufficient to bring 

the product to the appropriate pH. 

Electrodes should be rinsed between samples and after use. The purpose of 

rinsing is to prevent cross-contamination between samples that could result in 

errors in pH values for products. Rinsing with distilled water is recommended. 

However, if enough sample is available, rinsing with a portion of the next sample 

to be measured and throwing away the rinse solution is the best way to prevent 

cross-contamination. If distilled water is used, the water should be blotted – not 

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wiped – off the electrodes. If the electrode is rinsed with the next sample, this 

step is not necessary. Electrodes should not be wiped, because wiping could 

implant a charge on the electrode causing it to drift. Oil and grease from 

samples may coat or clog elements; therefore, electrodes should be cleaned with 

ethyl ether or acetone in accordance with the manufacturer's instructions, and the 

instrument should be re-standardized frequently. If the primary use is to test high 

fat/oil products, special electrodes are available. 

►Control of Bacteria by Water Activity (aw)

For thousands of years people have dried fruits, meats and vegetables as a 

method of preservation. It was also discovered that the addition of sugar would 

allow preservation of foods such as in the production of candies and jellies. Salt 

preservation of meat and fish has been extensively practiced over the ages. 

As late as 1940, food microbiologists thought that the percentage of water in a 

food product controlled microbial growth, but gradually they learned that it is the 

availability of the water that is the most important factor influencing growth. The 

measure of the availability of water in a food is made by determining the water 

activity. Water activity is usually designated with the symbol “aw.” 

When substances are dissolved, there is substantial reaction between the 

substance and the water. A number of the molecules of the water are bound by 

the molecules of the substances dissolved. All of the substances dissolved in the 

water reduce the number of unattached water molecules and, in this way, reduce 

the amount of water available for microbial growth. The extent to which the water 

activity is lowered depends primarily on the total concentration of all dissolved 

substances. Thus, if some ingredient – such as sugar, salt, etc. – is added to 

food, it competes with the bacteria for available water. The water-binding 

capacity of a particular dissolved ingredient influences the amount of water left 

for the growth of bacteria. 

Meat or poultry containing products with a water activity of 0.85 or less are not 

covered by the USDA canning regulations (9 CFR 318 Subpart G (meat) and 381 

Subpart X (poultry)) even if they are in hermetically sealed containers. 

The aw is the ratio of the vapor pressure of a substance to the vapor pressure of 

pure water, and is equal to the equilibrium relative humidity divided by 100. 

Thus, aw is a fraction between 0 and 1.00, with the aw of pure water being 1.00.

A measurement of aw on a food provides information as to which types of 

microorganisms are most likely to cause spoilage and how close the aw is to the 

safety limits. Most bacteria, yeasts and molds will grow above a water activity of 

0.95 (See Table 2), and most foods have a water activity above this level. 

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Spores of C. botulinum are generally inhibited at an aw of about 0.93 or less. 

(For more information on the effect of aw on C. botulinum, see the section on salt 

under Control by Chemicals below.) Therefore if the amount of water available to 

spores is decreased to a point where they are inhibited and mild heat treatment 

is applied to destroy the vegetative cells, we have a method of preservation for 

products whose quality is sensitive to high heat. 

Table 2 – Minimum aw requirements for microorganism growth 

Microorganism Minimum aw For Growth

Most molds (e.g., Aspergillus) 0.751

Most yeasts 0.882

C. botulinum3 0.93 

Staphylococcus aureus4

 0.85 

Salmonella 0.94 

Listeria monocytogenes 0.92 

1

 some strains – 0.61 

2

 some strains – 0.62 

3

 Proteolytic strains, 10% NaCl 

4

 Minimum for toxin production is higher.

Examples of foods preserved with mild heat and reduced aw are some cheese 

spreads, peanut butter, syrups, jams and jellies, and many meat products. The 

water activity of some common foods is shown in Table 3. 

Table 3 – Water activity of some common foods 

Food aw

Perishable and canned foods (including 

meats, vegetables, fish and milk) 0.95-1.00 

Liverwurst 0.96 

Some cheese spreads 0.95 

Some cheeses and cured meats 0.91-0.95 

Chorizos 0.92 

Many fermented sausages 0.87-0.91 

Semi-moist pet food 0.83 

Salami 0.82 

Chocolate syrups 0.75-0.83 

Jams 0.75-0.80 

Peanut butter – 15% total moisture 0.70 

Jerky ≤0.80 

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It is apparent that as far as C. botulinum is concerned, a water activity of 0.85 

provides a large margin of safety. Studies with this organism show that an 

accurate water activity of 0.93 plus pasteurization will give commercial sterility. 

However, some questions exist about the precision or accuracy of the 

instruments and methods used to determine water activity and about some 

factors that control water activity. Therefore, if water activity between 0.90 and 

0.93 plus pasteurization is used to control commercial sterility, data must be 

obtained and records kept showing that the process yields commercial sterility. 

Methods for determining aw

Several methods exist for determining the water activity of a food. One 

commonly used method is an electric hygrometer with a sensor to measure 

equilibrium relative humidity (ERH). As noted above, the equilibrium relative 

humidity above the food in a closed container divided by 100 is a measure of the 

available moisture – the water activity. The instrument was actually devised by 

weathermen, and the sensors are the same as those used to measure relative 

humidity in air. A dew point instrument is also commonly used to measure aw. 

This instrument measures the temperature at which condensation occurs on a 

cooled mirror in the headspace of the sample chamber. The aw is computed by 

converting sample and mirror temperatures to vapor pressures and calculating 

the ratio, which is the aw. 

In determining the aw using an electric hygrometer, 30-90 minutes may be required for the water vapor (relative humidity) to reach equilibrium in the 

headspace above the food in the closed container. A dew point instrument is 

usually much faster – generally only 5 minutes. Generally the formulation of the 

product to give the required aw is predetermined and very accurately controlled at 

the time of processing. For products that have a reduced aw due to reduction in 

moisture (e.g., through a drying process), following proper procedures can be 

critical. Determination of aw in a laboratory is often used to verify that the 

formulation and other steps that reduced product moisture were correctly carried 

out and the appropriate aw was achieved. Samples of the final product should be 

checked as frequently as necessary to ensure that the appropriate water activity 

is being achieved. 

►Control of Bacteria by Chemicals 

Chemicals (often called preservatives, antimicrobial compounds, or 

antimicrobials) may be added to foods to inhibit microbial growth or to kill 

microorganisms. However, at normal levels of use (which must be approved by 

regulatory agencies such as FDA and FSIS), most chemicals cause inhibition 

rather than inactivation. Acids and their salts (e.g., lactic acid, sodium lactate), 

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nitrites, some phosphates, and sodium chloride (salt) are common chemicals 

added to meat and poultry. In order to produce a commercially sterile or shelfstable product, chemicals are usually combined with other factors such as heat 

or reduced aw. 

Salt 

 

For example, salt has been used to preserve meat products (i.e., salt-cured 

meats). Salt, which lowers the aw, is often supplemented with other ingredients, 

such as nitrites, that aid in spoilage prevention. In all cases the salt is necessary 

to inhibit the growth of sporeforming bacteria, such as C. botulinum, and only 

enough heat is applied to kill the non-heat resistant vegetative cells. Strains of 

C. botulinum that grow in a suitable food containing 7 percent salt are known. 

For example, toxin was produced in experimentally produced turkey frankfurters 

with an aw of 0.956 (7% NaCl) in 12 days at 27°C (81°F). The growth of these 

strains, however, is inhibited at a concentration of 10 percent, which is equivalent 

to a water activity of 0.935, when all other conditions are optimum. If conditions 

are not optimum for growth (e.g., low pH or temperature) then less NaCl is 

required to inhibit growth. For example, growth of C. botulinum may occur at an

aw of 0.96 (6.5% NaCl) at pH 7.0, but if the pH is reduced to 5.3, growth will be 

inhibited at an aw of 0.97 (5% NaCl). The actual salt content of a meat product is 

not as important in inhibiting C. botulinum as the brine concentration (percent of 

salt in the aqueous portion of the meat). Toxin production is inhibited at a brine 

level exceeding 9.0%. 

Nitrite

When direct addition of nitrite was approved for meats in 1925, it was believed 

that the sole function was for color development. However, within a few years 

scientific studies began to demonstrate the antimicrobial effects of this 

compound. Numerous studies now document the efficacy of nitrite in inhibiting 

growth and toxin production by C. botulinum in meat systems. However, studies 

also determined that there was little or no effect of nitrite on bacterial growth at or 

above neutral pH. In spite of large amounts of research, there is still not a 

complete understanding of how nitrite controls C. botulinum in meat products. 

Nevertheless, it is now recognized that nitrite inhibition is due to a combination of 

factors, not nitrite alone. 

►Control of Bacteria by Combinations of Factors 

As has been noted above for chemicals, combinations of inhibitory factors that 

individually are insufficient to control microorganisms can often be effective. This 

has sometimes been referred to as the hurdles concept – if enough hurdles or 

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barriers are included, bacteria will not be able to overcome the hurdles and grow. 

Commercially sterile, canned cured meats are preserved by thermal destruction 

of vegetative cells of microorganisms, partial destruction of microbial spores and 

inhibition of the surviving spores by the effects of salt, nitrite, and possibly other 

additives such as ascorbate/isoascorbate. 

The hurdle approach is used for many fermented meat products – curing 

chemicals such as nitrite and salt, reduced aw due to drying, reduced pH due to 

fermentation, and, in some cases, mild heat processes result in a safe and shelfstable product. This will be covered in much more depth in the sections on shelfstable products. 

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Workshop: Microbiology of Commercially Sterile and ShelfStable Products 

The following questions are multiple-choice questions. Circle the answer(s) you 

believe to be correct; some questions have more than one answer. 

1. Microorganisms that can grow in food and cause spoilage include _____ . 

a. viruses 

 b. bacteria 

 c. molds

 d. yeasts 

 e. parasites 

2. A psychrotrophic non-sporeforming pathogen that can grow at refrigerator 

temperatures is ___. 

a. Clostridium botulinum 

b. Bacillus cerus

 c. Clostridium perfringens

 d. Listeria monocytogenes

3. Controlling microorganisms in foods can be achieved by _______ . 

a. temperature 

b. pH 

c. acidification 

d. water activity 

4. The pH established to provide safety with respect to C. botulinum is ____ . 

 

a. 4.6 

 b. 4.7 

 c. 4.8 

 d. 4.9 

5. Spores of C. botulinum are generally inhibited at an aw of about ___or 

less. 

 

a. 0.98 

 b. 0.85 

 c. 0.93 

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6. Reducing the water activity of a food product to 0.85 would have the best 

potential for inhibiting ________ . 

 

a. bacteria 

 b. mold 

 c. yeast 

7. Bacteria that can survive adverse conditions caused by heat, cold and 

chemical agents are __________ . 

 a. psychrotrophic bacteria 

 b. facultative bacteria 

 c. sporeforming bacteria 

8. Acidified low-acid foods are products with a pH less than or equal to ____. 

 

 a. 4.6 

 b. 4.2 

 c. 3.8 

9. When low water activity is used to preserve a food, the most important 

factor controlling microbial growth is 

 

a. the amount of available water in the product. 

b. the total water content. 

c. a scheduled process approved by a processing authority with 

supporting data. 

10. Thermophiles are bacteria that grow best 

 

a. at temperatures of about 80 ̊F to 98 ̊F (27 ̊C to 37 ̊C). 

b. at temperatures of about 122 ̊F to 150 ̊F (50 ̊C to 66 ̊C). 

c. in acid media. 

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The Microbiology of Low-Acid Canned Foods 

►Clostridium botulinum 

The pathogen of primary concern for low-acid foods in hermetically sealed 

containers is not among those typically associated with illness from other meat 

and poultry products, such as Salmonella – it is the sporeforming bacterium 

Clostridium botulinum. The term “clostridium” indicates an organism that is able 

to grow in the absence of air or oxygen and is a sporeformer. The term 

“botulinum” comes from the Latin word “botulus,” meaning sausage, because the 

organism was first isolated from a sausage that had produced the illness now 

called “botulism.” 

Clostridium botulinum (C. botulinum) is of great concern to home and commercial 

canners because (1) when it grows it can produce a potent toxin, (2) it can be 

isolated from soil or water practically everywhere in the world, (3) it is the 

pathogen with the greatest heat resistance due to its ability to produce heat 

resistant spores, and (4) canning foods provides an anaerobic environment 

favorable to growth of the organism if it has not been destroyed by the process. 

As noted before, the ability to form spores enables C. botulinum to survive a wide 

range of unfavorable conditions, such as heat and chemicals. The spores 

survive many heat processes that kill other pathogens of concern in meat and 

poultry. In fact, certain types of C. botulinum spores are able to survive five to 10 

hours in boiling water. (As you will learn later, processes to kill C. botulinum are 

on the order of 250°F for 3 minutes, compared to, for example, 157°F for 15 

seconds to kill Salmonella in certain cooked meat and poultry products.) Oxygen 

is excluded from sealed containers, thus providing the anaerobic environment for 

spores to germinate, become vegetative cells, multiply and produce toxin when 

the foods are stored at temperatures that allow growth. It is important to 

recognize that it is not the spore that produces the toxin, but the vegetative cell. 

If spores are present but prevented from forming vegetative cells, as in acidified 

foods, toxin will not be produced. 

Certain strains of C. botulinum are called putrefactive because this term 

describes the odor produced during their growth. These strains require proteins 

to grow (they are proteolytic) and they grow best at temperatures between 86oF 

(30oC) and 98oF (37oC), although growth can occur at any temperature between 

50oF (10oC) and 104oF (40oC). Other strains, which are non-proteolytic, are 

more dependent on carbohydrates, such as sugars and starch, for growth and do 

not produce putrefactive odors. Some of these strains are associated with 

marine environments; they grow best at 64-77°F (18-25°C) and have a minimum 

growth temperature of 38oF (3.3oC). Their spores will not withstand heating to 

212oF (100oC). 

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Because C. botulinum spores are found everywhere, any raw food may be 

contaminated with them (although, as was noted before, the organism is rare in 

meats, and at low levels – 0.1 to 7 spores/kg – when present in meats). 

However, it is only when the vegetative form of the organism grows in a food that 

the toxin or poison is produced. Although the spores are heat resistant, the toxin 

is not. The toxin can be inactivated by boiling temperatures – 212oF (100oC). 

Heat processes for low-acid canned meat and poultry are designed, at a 

minimum, to produce a product that is safe with respect to C. botulinum. 

Microbial inhibitors and pH can impact the processes needed to inactivate 

C. botulinum. Inclusion of sodium nitrite and sodium chloride in meat and poultry 

products (e.g., commercially-sterile, canned cured meats) can lower the thermal 

process required to produce a commercially sterile product that is stable at room 

temperature. For example, processes equivalent to 0.4-0.6 minutes at 250°F 

(121°C) are common for commercially sterile, cured luncheon meats containing ~ 

150 ppm ingoing nitrite and 5.0-5.5% brine strength. These processes may 

range from 0.1 to 1.5 minutes depending on nitrite, brine strength and other 

factors (compared to processes of 3.0 minutes for uncured products). (It should 

be noted that there are both perishable and commercially sterile cured meat and 

poultry products packed in hermetically sealed containers. If the products are not 

commercially sterile, they are not subject to the canning regulations.) Reducing 

the pH can also lower the process required, even when the product is not 

acidified to a pH that produces an acidified food (see below). 

►Other Microorganisms Important in Low-Acid Canned Foods 

Although heat processes for thermally processed commercially sterile foods are 

designed to destroy any microorganisms of public health significance, we are 

also concerned about other microorganisms that could grow in the product under 

normal storage conditions and result in adulterated product. As will be discussed 

when we get to the principles of thermal processing, processes designed to 

ensure commercial sterility of low-acid canned foods usually target Clostridium

sporogenes or similar organisms (putrefactive anaerobes). Because spores of 

C. sporogenes have higher heat resistance than those of C. botulinum, 

processes targeted to destroy spores of C. sporogenes will also destroy 

C. botulinum spores. 

Note that commercial sterility is not the same as absolute sterility – there may be 

viable microorganisms present in commercially sterile products. Spores of 

thermophilic bacteria such as Bacillus stearothermophilus or Clostridium

thermosaccharolyticum, if present, can survive processes that achieve 

commercial sterility. However, these organisms, which are not harmful to 

humans, cannot grow under normal conditions of storage. If product is properly 

cooled and stored, generally the spores are not exposed to the high 

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temperatures they require for germination and growth. Although canned foods 

are not generally processed to inactivate thermophiles, one exception to this is 

hot-vended products. Products that will be held hot in vending machines will be 

exposed to temperatures at which thermophiles can grow and will receive higher 

processes to ensure thermophilic spoilage does not occur. 

The Microbiology of Acidified Canned Foods 

Meat and poultry products to which acids or acid products have been added to 

reduce the pH to 4.6 or below are called acidified foods. Spores of C. botulinum

do not germinate and grow out in foods that have a pH below 4.8; a pH of 4.6 is 

set for acidified foods to provide a margin of safety. Heat processes for acidified 

foods target organisms other than C. botulinum, since the pH prevents its growth. 

The safety of acidified meat and poultry products is achieved by controlling the 

pH to 4.6 or less and applying a mild heat treatment to inactivate the vegetative 

cells of pathogens (e.g., Salmonella, E. coli O157:H7 and C. botulinum). 

However, achieving commercial sterility of these products requires treatments 

that inactivate yeast, mold and bacteria, including some sporeformers, that could 

grow in the product. The type of organism to be destroyed by the process will 

depend on the pH of the product. If the pH is below 4.2, only vegetative cells 

need be considered; however, if the pH is 4.2-4.6, processes may need to take 

into account sporeforming organisms such as Bacillus coagulans and the butyric

acid anaerobes (e.g., Clostridium pasteurianum and Clostridium butyricum). For 

more information on these organisms see the later section on Spoilage by AcidTolerant Sporeformers. 

The Microbiology of Shelf-Stable, Canned, Cured Meats 

The safety and stability of shelf-stable, canned, cured meat products (e.g., 

canned hams and luncheon meats) are related primarily to the concentrations of 

salt (sodium chloride, NaCl) and nitrite and the thermal process acting 

synergistically. These products only receive mild heat treatments, relying on 

NaCl and nitrite to inhibit surviving sporeformers, in particular C. botulinum. The 

inherent low levels of spores in these products also contribute to ensuring safety 

and shelf stability. 

Canned Food Spoilage 

►Indications of Microbial Spoilage

Most bacteria produce gas when allowed to grow in a canned food. This gas 

causes the containers to swell. Exceptions are the flat-sour sporeforming 

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organisms, which produce acid and sour the food without producing gas, leaving 

the container ends flat. These organisms are an economic but not a public 

health problem. 

The most obvious indicator of spoilage in processed food is a swollen container – 

bulging at one or both ends. This implies that the food has possibly undergone 

spoilage by the action of gas-forming bacteria. Consumers are advised by public 

health officials, food trade associations and regulatory agencies not to use any 

container with a bulged end or ends, even though the swelling may be of 

non-microbial origin. 

The appearance and odor of the container contents may also indicate spoilage. 

If the product is broken down and mushy, or if a normally clear brine or syrup is

cloudy, spoilage may be suspected. In jars, a white deposit may sometimes be 

seen on the bottom or on pieces of food. This is not always a sign of spoilage, 

as starch sometimes precipitates from certain foods. 

Bacterial decomposition of thermally processed product may result from one of 

six causes: 

1. Incipient spoilage – growth of bacteria before processing; 

2. Contamination after processing – leakage of bacteria into the container; 

3. Inadequate heat processing; 

4. Growth of thermophilic bacteria in the processed food; 

5. Spoilage by acid-tolerant sporeforming bacteria; and 

6. Spoilage due to improper curing. 

The last two causes of spoilage are specific to products with reduced pH and to 

cured products, respectively. In addition, there can be non-microbial causes of 

spoilage. 

►Incipient Spoilage (Spoilage Before Processing)

Processed food is sometimes held too long between filling or closing the 

containers and thermal processing. Such delays may result in growth of bacteria 

normally present in the food and the initiation of spoilage before the retorting 

process. This type of spoilage is referred to as “incipient spoilage.” The 

microorganisms that grow will be killed by the process; with sufficient time, 

sporeformers may germinate and form vegetative cells that will be killed. 

Typically incipient spoilage manifests itself as low or no vacuum in the container 

and a slight change in pH of the product. Generally no viable microorganisms 

are recovered in subculture media. Although the product presents no risk to 

public health, if there is sufficient growth, the product may be considered to be 

adulterated (e.g., if the product characteristics are changed). The degree of 

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spoilage depends on the specific product and the time and temperature 

conditions during the delay. For example, if the product has been heat treated 

(e.g., cooked) prior to container filling, there may be low levels of bacteria 

present such that holding product for several hours may result in bacterial 

increases that are not significant. Products that contain inhibitors, those that are 

held at lower temperatures (e.g., below 70°F) or those that are filled hot (above 

microbial growth temperatures) may also demonstrate only limited bacterial 

growth for several hours. 

The loss of vacuum that can result from growth of microorganisms in sealed 

containers held too long prior to retorting may lead to extensive internal 

pressures in the containers during retorting. The build-up of internal pressure 

strains the container seams or seals and increases the potential of leaker 

spoilage. Some containers may actually buckle or rupture, rendering them 

unusable. Steps should be taken to avoid such a delay before retorting the 

containers. 

►Contamination After Processing (Leakage)

Leaker spoilage – or post-processing contamination with microorganisms – 

usually shows up rapidly as swollen containers. It may take several weeks until 

all spoilage has ceased. If many swells are present, a small percentage of flat, 

spoiled containers (flat-sours) may be expected, and normal appearing cans 

should be examined with this potential in mind. Leakage is generally due to 

inadequately formed seams, container damage or cooling water contaminated 

with large numbers of microorganisms. 

While theoretically leakage could result in post-processing contamination with 

pathogens, this is unlikely in plants operating under good manufacturing 

practices. Incidents of typhoid fever resulted from consumption of meat products 

(imported into the UK from Argentina in the 1950s and 1960s) that were 

contaminated when cans were cooled using river water contaminated with 

sewage. Recontamination with C. botulinum has occurred with seafood, but not 

meat products. Based on existing reports of food borne disease for which 

package defects are alleged or proven to have contributed to the problem, the 

probability of post-process contamination with organisms of public health 

significance is extremely low. In fact, it was estimated in 1984 that the probability 

of botulism from container leakage is about one chance in every 260 billion cans 

of food consumed (or one potential botulism incident about every 9 years). The 

report concluded that this probability compares well to the risk associated with

the minimum acceptable thermal process for low-acid canned foods. 

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►Inadequate Heat Processing

The term “inadequate heat processing” (also referred to as under-processing) is 

almost self-explanatory. Heat processes for thermally processed food are 

designed to destroy any microorganisms of public health, as well as non-health, 

significance that could grow in the product under normal storage conditions. In 

many instances, the product receives sufficient heat to inactivate pathogenic 

sporeformers such as C. botulinum, with the more heat resistant spoilage 

organisms surviving and spoiling the product. However, if the heat process is 

inadequate to destroy C. botulinum, the situation can be very hazardous, since 

botulinum toxin could be produced and, if the product is consumed, cause 

botulism in the consumer. 

Botulism is the disease caused by ingestion of the toxin produced when 

C. botulinum grows in a food. Symptoms include, dry mouth, dizziness, and 

weakness, generally within 12-48 hours after consumption of the toxin. Nausea 

and vomiting may also occur. Neurologic symptoms follow, including blurred or 

double vision, inability to swallow, difficulty in speech, descending weakness of 

skeletal muscles and, ultimately, respiratory paralysis. Untreated, this can lead 

to death. 

A heat process may be inadequate for a variety of reasons, including but not 

limited to the following:

1. If the time and/or temperature (or its equivalent) specified in the 

scheduled heat process for the particular product in the particular size of 

container is not used. 

2. If the scheduled heat process was not established properly. 

3. If the scheduled heat process is not properly applied because of some 

mechanical or personnel failure. 

4. If one or more of the scheduled process critical factors is not met. 

5. If the formulation is changed such that the critical factors change. 

►Thermophilic Spoilage

Generally, the higher the temperature at which a sporeforming organism can 

grow, the greater the heat resistance of its spores will be. Thus, the spores of 

thermophilic bacteria usually have a greater heat resistance than the spores of 

mesophilic bacteria. The spores of thermophilic bacteria are so resistant to heat 

that heat processes designed to kill the mesophilic bacteria may not be adequate 

to destroy thermophilic bacteria. In order to prevent thermophilic spoilage, the 

product must be properly cooled, preferably below 105oF (41oC), after thermal

processing and held below 95oF (35oC). Thermophiles may grow in equipment 

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that contacts food if the temperature is within their growth range. Consequently, 

product should always be held at 170oF (77oC) or above or at room temperature 

or below to prevent the growth of thermophiles. 

For meat and poultry products containing ingredients known to be a source of 

thermophiles (e.g., such as sugar, starch and/or spices) where thermophilic 

spoilage may be a problem, prudent processors will use ingredients that the 

supplier guarantees are free of thermophilic bacteria or that meet specifications 

for thermophiles for canning processes. This is particularly important if the 

product is to be hot-vended. This is the responsibility of the establishment, as it 

is a quality issue, not one of safety. 

►Spoilage by Acid-Tolerant Sporeformers 

As noted above, acidified foods (those products with a pH 4.6 or below) do not 

require a severe thermal process to assure product safety. Therefore a variety of 

acid-tolerant sporeformers may survive the process. A thermal process 

scheduled for acidified foods is designed to inactivate a certain level of these 

sporeformers. Their survival is typically a result of excessive pre-processing 

contamination. Sometimes underprocessing, either due to inadequate 

processing or process deviations, may also result in survival of these acidtolerant sporeformers. The organisms of spoilage significance are butyric-acid 

producing anaerobes and aciduric flat sour sporeformers. 

The butyric-acid producing anaerobes, such as Clostridium butyricum and 

Clostridium pasteurianum, are mesophilic sporeformers that produce butyric acid 

as well as carbon dioxide and hydrogen. The spores are capable of germination 

and growth at pH values as low as 4.2-4.4 and consequently are of spoilage 

significance in acidified foods, particularly if the pH is above 4.2. In products 

where the pH is not low enough, spoilage by butyric acid anaerobes may be 

controlled by either further acidification of the product or by increasing the 

thermal process. Growth of these organisms in foods is characterized by a 

butyric odor and the production of large quantities of gas. Occasionally strains 

will be encountered that can grow at a pH lower than 4.2. If these strains are 

present in high numbers, the heat process may be inadequate and spoilage may 

occur. 

Aciduric “flat sours” are facultative anaerobic sporeformers that seldom produce 

gas in spoiled products. The ends of spoiled cans remain flat; hence the term 

“flat sour.” Spoiled products have an off flavor that has been described as 

“medicinal” or “phenolic.” These organisms have caused spoilage in acid foods 

such as tomato products (by Bacillus coagulans) and could cause problems in 

meat products with tomato sauces if the sauces are prepared from fresh 

tomatoes. (The problem is unlikely if the tomato ingredients are previously 

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processed to inactivate these organisms, as with commercially sterile products). 

It may be necessary to ensure that the thermal process is adequate to inactivate 

an expected number of spores, which can be determined through bacteriological 

surveys. Pinpointing the ingredient that is contributing the most to the total spore 

load may prove beneficial in process control. For example, proper handling of

vegetables prior to use, such as washing and culling, may help to reduce spore 

loads. 

Most food processing operations do not provide anaerobic conditions; therefore, 

heavy build-up of acid-tolerant anaerobic sporeformers seldom occurs. This is 

one reason why “dead ends” (“dead legs”) must be avoided in processing lines. 

However, when this does occur, under-sterilization spoilage can result because 

of the heavy load of spores in the product. The spoilage pattern within the 

affected lots is often spotty and scattered, more typical of post-processing 

spoilage that is due to container leakage, than of the pattern expected from 

sporeformers that survive a thermal process. Thermal processing records and 

other processing parameters usually give no indication of any irregularities. In 

most cases, the problem can be identified only by investigation at the factory, 

which includes a bacteriological survey, plus the absence of demonstrable 

leakage and package defects in the spoiled containers. 

►Spoilage Due to Improper Curing 

As was noted before, canned cured meat and poultry products are made 

commercially sterile by the interrelationship of salt, nitrite, heat and low levels of 

spores. Spoilage due to underprocessing in canned cured meats is rare, and is 

usually the result of improper curing rather than inadequate heating. The heat 

processes for canned cured meat and poultry products are not designed to 

inactivate mesophilic sporeformers, as their outgrowth will be inhibited by salt 

and nitrite. Reduced levels of salt or nitrite can result in spoilage, as the heat 

treatment may be inadequate for product containing these lower levels. 

►Non-microbial Spoilage 

Spoilage in canned foods can sometimes occur as the result of container 

deterioration; this may at times result from chemical interactions of the food and 

the container. To avoid this type of spoilage, the packer must be aware of the 

impact of container, processing, and product chemistry variables on the corrosion 

shelf life of the container. Container deterioration may result in swollen 

containers resulting from the production of hydrogen (“hydrogen swells”) or in 

leaking containers due to pinholes or cracks. 

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Non-microbial spoilage rarely results in a health hazard. However, in high acid 

products where detinning of containers has occurred, there have been instances 

of illness due to high levels of tin (>200 ppm), which can cause acute toxicity 

(nausea, vomiting, cramps and diarrhea). This has not been a problem in meat 

and poultry products. 

There are four main types of corrosion inside plain tinplate containers: normal

corrosion, rapid detinning, pitting corrosion and cosmetic corrosion. The normal 

corrosion process is slow, even detinning of the tinplate surface. The canned 

product will have a minimum shelf life of about 2 years. Rapid detinning involves 

rapid tin dissolution of the tinned surface and pitting corrosion involves rapid 

dissolution of iron, with or without tin dissolving. These two forms of corrosion 

lead to either hydrogen swells or perforations. Cosmetic corrosion problems, 

such as sulfide staining, are not of public health significance, but consumers may 

reject the pack for aesthetic reasons. 

Meat and poultry products are usually packed in enameled cans rather than plain 

tinplate. Corrosion inside enameled cans is localized at fractures in the coating 

where the plate is exposed to the product. There are five main manifestations of 

corrosion in coated cans – 1) normal corrosion, 2) pitting corrosion, 3) underenamel corrosion and enamel flaking, 4)stress corrosion cracking and 5) sulfide 

black corrosion. The normal corrosion process involves iron dissolution from 

small pores, and the corrosion shelf life will exceed 18-24 months. Pitting 

corrosion involves rapid iron dissolution from the container walls at coating 

defects. Under-enamel corrosion is detinning or staining through the coating at 

areas where the coating has lost adhesion. Stress corrosion cracking involves a 

reaction between the container and stress inducing components in the product. 

Cracks through the container have been observed in as little as 4 months. 

Sulfide black corrosion involved rapid iron dissolution through the coating with 

black deposits forming about 24 hours after processing. Sulfide black 

discoloration is a type of cosmetic corrosion that is objectionable to the 

consumer. 

External corrosion involves rusting, detinning or staining of the outside walls of 

the container. It rarely leads to perforations from the outside in. Filiform 

corrosion involves tunneling through the walls of the can. It occurs at the scratch 

defects in the coating on the outside of cans. It sometimes leads to pinholes in 

the container. 

►Determining the Cause of Spoilage 

Analysis of spoilage of commercially sterile canned food products requires 

expertise to conduct the analysis and to appropriately interpret the results. The 

isolation of microorganisms from spoiled product does not necessarily mean they 

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are the cause of spoilage. For example, if acidified foods are cultured in neutral 

laboratory media, microorganisms that are present in the product but are 

inhibited by the pH may grow out. These are of no significance since they cannot 

grow in the product due to its pH. Likewise, if other inhibitors are present in 

product, culturing in laboratory media may dilute the inhibitors such that 

microorganisms which are viable in the product but prevented from growing can 

grow in the media. Again, it is unlikely that these organisms are significant with

respect to spoilage of the product. Thus, microbiological examination of products 

intended to be commercially sterile requires a trained analyst following accepted 

procedures such as those outlined in the USDA/FSIS Microbiology Laboratory 

Guidebook for examination of heat processed, hermetically sealed (canned) 

meat and poultry products or the equivalent. 

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Workshop: Microbiology of Canned Products 

The following questions are multiple-choice questions. Circle the answer(s) you 

believe to be correct; some questions have more than one answer. 

1. Commercial sterility refers to applying a heat treatment to a low-acid 

canned food designed to destroy pathogens and spoilage organisms 

capable of growing in the product at normal storage conditions. What is 

the pathogen of greatest concern in a low-acid canned food? 

a. Clostridium botulinum 

b. E. coli O157:H7

c. Clostridium perfringens

d. Listeria monocytogenes

2. Certain types of Clostridium botulinum spores 

a. produce a potent toxin. 

b. are able to survive for 5 to 10 hours in boiling water. 

c. produce toxin that cannot be inactivated by boiling at 212 ̊F 

(100 ̊C). 

3. Clostridium botulinum is 

a. an anaerobic, sporeforming bacterium. 

b. a mesophilic acid-tolerant microorganism. 

c. a thermophilic microbe. 

4. Botulism is an illness that can be caused by 

 

a. eating spores of Clostridium botulinum or other food spoilage 

organisms. 

b. eating vegetative cells of Clostridium botulinum which may be 

found in raw meat and spices. 

c. eating food in which vegetative cells of Clostridium botulinum have 

grown and produced toxin. 

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5. Incipient spoilage in canned foods is caused by 

a. holding closed containers too long before retorting. 

b. under processing. 

c. post-process contamination, especially from dirty cooling water. 

6. Thermophilic bacterial spores 

a. are less heat resistant than mesophilic bacterial spores. 

b. are never present in low-acid canned foods. 

c. may not be destroyed during the heat process for low-acid foods. 

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Workshop: Spoilage of Canned Foods Case Study

(Note: This is a simplified training example only.) 

While walking through the warehouse of Uncle Sam’s Canned Goods Company, 

you and the warehouse supervisor notice several cases of canned beef stew that 

look wet. The QA manager is called to the warehouse to inspect the problem. 

Upon opening the cases he finds several cans that are swollen or leaking. He 

pulls out the swollen and leaking cans, along with several of the normal-looking 

flat cans. He then sends some of the sample cans to Microtesting, Inc., a 

microbiology laboratory that specializes in analyses of canned food products. 

You send the remaining samples to the FSIS laboratory in Athens, Georgia. The 

lot of product is placed on hold pending the laboratory results. 

Upon receipt of the samples on Friday afternoon at 4:45pm, the diligent 

laboratory technician at Microtesting, Inc., begins analysis of the samples. The 

laboratory sends back preliminary results to the QA manager the following week. 

The laboratory results listed below are four possible “what-if” scenarios. Please 

read the possible scenarios then answer the following questions. 

Microbiological Results Container Evaluation 

Scenario #1 Thermophilic microorganisms were 

identified. 

No container defects 

were detected. 

Scenario #2 Mixed culture of rods and cocci 

were identified. 

No sporeformers or heat resistant 

microorganisms were recovered. 

Can exam revealed false 

seam on packer’s end. 

Scenario #3 Mesophilic organisms with spores 

were identified. 

No container defects 

were detected. 

Scenario #4 No viable bacteria (sporeformers or 

non-sporeformers) were recovered. 

Hydrogen gas was 

detected. 

►Questions 

1. Which of these scenarios, if any, suggests microbiological problems due 

to potential under-processing? Why? 

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2. Which of these scenarios, if any, suggest post-process contamination? 

Why? 

3. Which of the scenarios, if any, is indicative of microbial spoilage that has 

the potential for an adverse public health consequence? 

Why? 

4. Which of the scenarios, if any, is indicative of detinning of the can interior? 

Why? 

5. After receiving the results indicated in Scenario #1, Uncle Sam’s decides 

to sort and remove the swollen and leaking cans from the lot and release 

the normal cans. 

The lot of cans are incubated in an unair-conditioned trailer held at 110-

120 ̊F and checked weekly. After 6 weeks there are no additional swollen 

containers. Since the cause of spoilage was the growth of thermophilic 

microorganisms, the plant manager believes that it is acceptable to 

release the flat containers. The plant microbiologist wants to conduct a 

simple test to determine the pH of random samples before making the 

decision to release. Why? 

6. Is every swollen can an indication of an adverse public health 

consequence? Why or why not? 

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Principles of Thermal Processing 

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PRINCIPLES OF THERMAL PROCESSING 

The “canning” of foods has been practiced for almost 200 years, but the science 

supporting the canning process has been understood for only about half of that 

time. In this section we will discuss the theory and science that forms the basis 

for the development and application of thermal processes to low-acid and 

acidified foods packaged in hermetically sealed containers. This section will 

identify and review some of the major factors affecting thermal processing of 

canned food products. 

The objectives of this section are for you to be able to: 

1. define commercial sterility; 

2. identify who can establish a thermal process; 

3. identify the components in establishing a thermal process; 

4. identify factors that impact the thermal process; and 

5. recognize a process deviation. 

The Scheduled Process

As mentioned in the Introduction Section, “canned” products are treated with heat 

to make them commercially sterile. The condition of commercial sterility (or 

shelf-stability as it is characterized in the FSIS Canning Regulations -9 CFR 

318.300 and 9 CFR 381.300) is recognized as follows: 

Commercial Sterility – The condition achieved by application of heat, 

sufficient alone or in combination with other ingredients and/or 

treatments, to render the product free of microorganism capable of 

growing in the product at nonrefrigerated condition (over 50°F or 

10°C) at which the product is intended to be held during distribution 

and storage. 

A condition of commercial sterility will result in products that are safe to eat 

because the pathogens of concern are destroyed or inactivated. The product will 

remain shelf-stable as long as the container is intact because any spoilage 

organism that favors the environmental conditions within the container (i.e., 

anaerobic) and normal storage temperatures (i.e., mesophilic bacteria) are also 
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destroyed with the thermal process. The current FSIS Canning Regulations 

(9 CFR 318.300 and 9 CFR 381.300) refer to this condition as shelf-stability, but 

in this course we will refer to “canned” products as being commercially sterile to 

avoid confusion with the dry and semi-dry meat and poultry products that are 

also shelf-stable. 

The application of heat to make a product commercially sterile is conducted in a 

controlled manner; this has been traditionally called the scheduled process or 

process schedule. The FSIS Canning Regulations (9 CFR 318.300 and 9 CFR 

381.300) require that scheduled processes be established by a processing 

authority. A processing authority is a person or organization having expert 

knowledge of thermal processing requirements for foods packed in hermetically 

sealed containers and having adequate facilities to make these process 

determinations. 

The scheduled process, as designed by a processing authority, if properly 

executed, will produce a commercially sterile product. The scheduled process, 

includes thermal processing parameters such as initial temperature of the 

product, the process temperature and the process time, plus any other critical 

factors that may affect the attainment of commercial sterility. Critical factors may 

include any characteristic, condition or aspect of a product, including formulation, 

container, preparation procedures, or processing system that affect the 

scheduled process. We will discuss critical factors again later in this section. 

Processing authorities use their knowledge of food microbiology (specifically, 

thermobacteriology), heating characteristics of food, and processing systems as 

the basis for process schedule establishment. Contrary to other cooked meat 

and poultry products, the cook process for commercially sterile products is 

controlled by monitoring the process parameters (such as process temperature 

and time) rather than monitoring a temperature of the product. Temperature and 

time are easily controlled and monitored to ensure delivery of a proper thermal 

process. 

For low-acid canned foods (those with a pH greater than 4.6), the thermal 

process focuses on the destruction of the spores of certain sporeforming 

bacteria. (These have been discussed in the previous section). The target 

pathogen for low-acid canned foods is Clostridium botulinum (specifically the 

spores of the organism.) Failure to destroy these spores, followed by 

germination and growth, can lead to the production of the deadly botulinum toxin, 

an extremely potent neurotoxin. Low-acid canned food processes that assure 
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the destruction of C. botulinum spores are adequate to protect human health; 

however, as noted previously, a more substantial process, or a commercial 

sterility process, is required to destroy spores of other microorganisms that could 

germinate and grow under normal storage and handling conditions and cause 

economic spoilage. The target for commercial sterility is typically C. sporogenes, 

an organism very similar to C. botulinum but with a higher heat resistance. 

Thermal processes for acidified foods are targeted toward vegetative cells of 

microorganisms and are generally significantly milder than those applied to lowacid foods. This is primarily because spores of microorganisms such as 

C. botulinum will not germinate due to the acid nature in the product. Keeping 

the spores from germinating will prevent the growth of the vegetative cells of 

C. botulinum and subsequent toxin production. In distinguishing between 

acidified and low-acid foods, the standard used is a pH of 4.6 (greater than 4.6 is 

low-acid and less than or equal to 4.6 is acid or acidified). Typical thermal 

processes for acidified foods will maintain the commercial sterility of a product as 

long as good sanitation and GMPs are followed. Lack of pH control for an 

acidified food can lead to problems if the pH is high enough to allow surviving 

spores of C. botulinum to germinate and produce toxin. 

Determining the scheduled process with the proper temperature and process 

time needed to produce commercially sterile products has been the subject of 

years and years of study in the canning industry. Sound process determinations 

depend upon good knowledge of the : 

1. nature of the product and how it heats; 

2. container in which the product is packed; 

3. details of the thermal processing procedures used; and 

4. characteristics of the target microorganisms such as growth, survival, and 

thermal resistance. 

These four factors are related to the thermal resistance of the microorganisms 

and the heating characteristics of the product. Utilizing all this information, the 

processing authority will establish a thermal process that will specify the amount 

of time at a specific temperature necessary to ensure the destruction of 

C. botulinum and spoilage organisms that may be present. 
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Establishing a Thermal Process 

As mentioned previously, the processing authority will base the establishment of 

a thermal process for a particular food product on two separate factors: 1) the 

thermal (also known as heat) resistance of the microorganism of choice in that 

food and 2) the heating characteristics of the product. In simplified terms, the 

processing authority needs to know 1) how much heat and for how long is 

necessary to destroy microorganisms in the food product and 2) how fast does 

the product heat (in the case of conventional canning) or how does the product 

flow (in the case of aseptic processing). The combination of these two factors is 

used to establish the thermal process. 

The establishment of the thermal process will also depend upon the method of 

processing: conventional canning or aseptic processing. As noted in the 

Introduction section, in conventional canning, the product is filled into the 

container, the container is hermetically sealed, and the container and product are 

thermally processed at a specified time and temperature to achieve commercial 

sterility. For aseptic processing, packages or packaging material and the food 

product are sterilized in separate systems. Product sterilization involves heating 

a pumpable product to a sterilizing temperature and holding it at that temperature 

for sufficient time to sterilize the product. The packaging materials are sterilized 

with heat, chemicals, radiation or a combination. The sterile package is then 

filled with sterile product, closed and hermetically sealed in a sterile chamber. 

Once a process has been established for a particular food, it is specific for that 

particular set of parameters regarding formulation, preparation, thermal 

processing system, container, etc. Since a seemingly insignificant change in any 

of these parameters could result in under-processing, it is important that 

processes not be altered without consultation with a processing authority. 

Thermal Resistance of Microorganisms 

The thermal resistance of microorganisms (vegetative cells or spores) is 

dependent upon a number of factors: 1) the growth characteristics of the 

microorganisms, 2) the nature of the food in which the microorganisms are 

heated, and 3) the kind of food in which the heated microorganisms are allowed 

to grow. Because of the variability of any biological entity, thermobacteriology is 

a highly complex science, and variations in any of these factors can affect the 

heat resistance of microorganisms. 
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►Thermal Death Time (TDT) Tests 

The amount of heat required to destroy microorganisms in a product can be 

determined through thermal death time (TDT) tests. TDT tests are conducted by 

thermobacteriologists in a laboratory. Very few food processing establishments 

have the facilities to conduct TDT tests on-site. The instrumentation and 

equipment used for TDT tests include TDT retorts, tubes, and/or cans; 

three-neck flask, oil baths, sealed plastic pouches, and/or capillary tubes. The 

equipment and instrumentation used will depend on the type of product being 

tested – whether it is low-acid, acidified, thick puree, solid or a liquid. 

TDT tests involve heating a known amount of microorganisms in a buffer solution 

or food at several temperatures and for several time intervals at each 

temperature. The results from the TDT tests are used to calculate D- and zvalues. These values are used to define the heat resistance of the 

microorganisms of concern.

►Determination of D- and z-values 

In conducting TDT tests, the thermal characteristics (D- and z-values) of the 

microorganisms will be determined. The D-value is defined as the time at a 

particular temperature required to reduce a known number of microorganisms by 

90% or to result in a 1-log reduction. This is also termed the decimal reduction 

time because exposure for this length of time decreases the population by 90%, 

thus shifting the decimal point in the number of microorganisms remaining one 

place to the left. For example, if you had 100,000 spores and if exposing them to 

a temperature of 240°F for 3 minutes reduced the count to 10,000 spores, the 

D240°F would be 3 minutes. 

The D-value decreases as the temperature increases, since it takes less time to 

destroy the microorganisms at the higher temperature. By determining the Dvalues at various temperatures, a z-value can be determined from the slope of 

the line that results from plotting the log of D-values versus temperature. The zvalue, indicative of the change in the death rate based on temperature, is the 

number of degrees between a 10-fold change (1 log cycle) in an organism’s 

resistance. As an example, suppose that z = 18°F and the D232°F = 3 minutes. 

The D250°F would be 0.3 minutes. (Because 232°F + 18°F = 250°F and 3 minutes 

/ 10 = 0.3 minutes.) Both D- and z-values are indirectly used to establish thermal 
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processes. 

►“Minimum Health” and Commercial Sterility Processes 

Traditionally, a 12D process for spores of C. botulinum has been used to assure 

public health protection for low-acid canned foods. This has been based on 

historical data indicating that a heavy load of C. botulinum spores in a canned 

food product would be 1012 spores; therefore, a 12D reduction would provide a 

one-in-a-billion chance that a spore would survive in a canned food. For all 

practical purposes the 12D process is very conservative, as it is highly unlikely 

that spore loads of C. botulinum would approach these levels, especially in meat 

and poultry products. (Remember, Clostridium botulinum is rare in meats, and 

when present is there in very low numbers - 0.1 spore to 7 spores per kg meat.) 

A typical D-value for C. botulinum spore destruction in many foods is ~0.2 

minutes at 250°F; therefore, a 12D destruction would be ~2.4 (=12 x 0.2) minutes 

at 250°F. (A value of 3 minutes is sometimes used to incorporate a margin of 

safety.) However in some products, the components of a food (or ingredients in 

a formulated food) can have adverse or beneficial effects on the thermal 

destruction of spores and will impact the D-values. For example, if 3 minutes at 

250°F is needed to ensure public health at pH of 6.0, 2.0 minutes may be 

sufficient if the food is acidified to pH 5.3. (See discussion of Fo values on the 

next page.) Processing authorities refer to the times and temperatures needed 

to inactivate C. botulinum as “minimum health” processes because this is what is 

necessary for public health protection. 

In order to attain commercial sterility, a thermal process more strenuous than that 

required for public health protection must be provided. Commercial sterility 

means the condition achieved in a product by the application of heat to render 

the product free of microorganisms capable of reproducing in the food at normal 

non-refrigerated conditions of storage and distribution. A commercial sterility 

process will destroy other spores in addition those of C. botulinum. These 

spores, if not destroyed, have the potential to grow under normal storage and 

handling conditions and cause economic spoilage, even though they pose no 

public health risk. A 5D destruction of C. sporogenes spores (such as PA3679) 

is the target for commercial sterility. This 5D process for C. sporogenes spores 

is more lethal than a 12D process for C. botulinum spores due to the fact that 

spores of C. sporogenes are more heat resistant than spores of C botulinum. 

In order to compare thermal processes calculated for different temperatures, a 
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standard Fo value is assigned for each product. This Fo value is the time in 

minutes (at a reference temperature of 250°F and with a z = 18°F) to provide the 

appropriate spore destruction (minimum health protection or commercial sterility). 

 As previously noted, using D- and z-values, this reference value at 250°F can be 

converted to other temperatures. Due to a variety of factors (e.g., influence of 

the food on the destruction of spores) different foods will have different Fo values. 

 For example, if an Fo of 6 minutes is needed to ensure commercial sterility at pH 

of 6.0, an Fo of 4 minutes may be sufficient if the food is acidified to pH 5.3. In 

cured meat products containing 150 ppm nitrite and 3-4% brine (% NaCl X 100/ 

% NaCl + % water), an Fo of 0.3–1.5 minutes may be sufficient to render the 

product commercially sterile. 

Fo values are already established for many food products. However, there are 

times, such as for novel formulas of food products, when TDT work may be 

needed to determine D- and z-values and appropriate Fo values for spores of 

C. botulinum and C. sporogenes for a specific product. In the absence of TDT 

data on a specific formulation, a processing authority will apply a conservative Fo

that is known to result in a safe product. 

Product Heating Data Determinations 

Processing authorities determine product heating characteristics through the use 

of heat penetration tests. The rate at which a product heats can be measured 

using devices to monitor the rate of change in temperature of the food as it is 

being heated within the container (heat penetration studies). These 

determinations are made with a temperature sensor or thermocouple located in 

the product at the slowest heating region of the container. The slowest heating 

region will depend on the type of product, container size, processing method and 

the heat transfer mechanism. Typical heat transfer mechanisms in canned foods 

are convection (heat current flowing within the container as experienced in 

canned broths), conduction (molecule to molecule as experienced in corned beef 

hash), and combinations (for example, convection then conduction due to 

thickening of the product as maybe experienced in formulated products such as 

chicken and dumplings). The number of containers per run and the number of 

runs necessary to ensure the data are adequate depends on the variability of the 

product and the processing system. When either demonstrates significant 

variability, additional containers/runs may be required to ensure confidence in the 

process. 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

The need to simulate the worst case scenario likely to occur when producing 

product cannot be overstated, because the thermal process is controlled by 

monitoring and controlling the process parameters rather than with the actual 

temperature of the product. The processing authority will review variables in 

product preparation such as changing a starch or protein in the formulation, filling 

procedures, rehydration procedures, etc., to determine the impact on the heating 

rate of the product. More viscous product, higher fill weights, or improperly 

rehydrated product can all affect the heating rate of the product. If the heat 

penetration tests do not account for this effect or if the establishment can not 

control for these variations, the result could be under-processed product. 

The heating characteristics of the product aseptically processed are also 

important. For aseptic processing, the heated product flows at a constant rate 

through tubing of a specified length; it is the flow characteristics of the product 

that determine whether certain particles in the fluid stream move through the 

tubing faster than others. The speed of the fastest moving particles (which 

remain at the elevated temperature for the shortest time) and the temperature of 

the flowing product determine the heat (lethality) attained by the product. 

Process Schedule Calculations 

For conventionally canned products, the process authority will calculate a 

process using the product heating data and the thermal resistance data for the 

significant spoilage organisms or organisms of public health consequence 

expected to be present in the product. These mathematical procedures combine 

the Fo value that provides commercial sterility with the factors that define the 

product heating rate. There are several acceptable methods for calculating 

thermal processes. Some of the more common methods are the General 

Method, the Ball Formula Method, and the NumeriCALTM Method. 

For aseptically processed products, the process authority will calculate a process 

using the flow characteristics of the product and the thermal resistance data for 

the significant spoilage organisms or organisms of public health consequence 

expected to be present in the product. The resulting process schedule will 

indicate a specific sterilization time or residence time at a specific temperature. 

The residence time is directly related to the rate of flow of the fastest moving 

particle/fluid stream through the system. 

Although the method of characterizing the product heating rate is different for 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

conventionally canned and aseptically processed products, the Fo value for a 

particular food is the same in either processing method. 

ACIDIFIED FOODS

Products that are high acid (have a low pH) or are acidified to a pH of 4.6 or less 

do not require a high temperature process. The foods may be processed at the 

temperature of boiling water – 212°F (100°C) – or lower. The thermal process is 

designed to destroy vegetative cells and some spores of low heat resistance. 

The product’s low pH (4.6 or less) will prevent the remaining spores from growing 

out. 

To produce products with a pH of 4.6 or less, acidification must be properly 

carried out. Here are some methods to obtain properly acidified foods. 

1. Blanch the food ingredients in an acidified aqueous solution. To acidify 

large food particulates, the particulates could be blanched in a hot acid bath. The 

ability to obtain a properly acidified product is dependent upon blanch time and 

temperature, as well as the type of and concentration of acid. 

2. Immerse the blanched foods in an acid solution. That is, blanch the 

product in the normal steam or water blancher. Then, dip it into an acid solution, 

remove it from the acid solution and place it into containers. Proper acidification 

depends upon how well the product is blanched, the concentration of the acid 

and the contact time. 

3. Direct batch acidification. This is normally the best way to acidify fluid 

material. Ingredients are mixed in a kettle, and acid is added directly to the batch. 

(An elevated temperature may improve the rate of acid penetration into solid 

particles.) The pH of the batch is checked before the material is sent from the 

batch kettle to the filler. 

4. Add acid foods to low-acid foods in controlled portions. Essentially, this 

is how a formulated product such as pasta sauce is made. Components in the 

sauce, such as meat or onions, are low-acid foods, while the tomato sauce is an 

acid food. The acid food is mixed with the low-acid food to get an acidified food 

product. The formulation, including the proportion of tomato sauce to low-acid 

components, is critical to obtain uniform and accurate control of pH of the 

finished product. 

5. Directly add a predetermined amount of acid to individual containers 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

during production. This involves addition of acid pellets, known volumes of acid 

solution, or some other means for direct acidification of each container. This is 

probably the most inaccurate and least consistent method of acidification, 

because acid addition to a given container may be overlooked. Although this is a 

permissible way to acidify, it is not recommended and it is not used for meat and 

poultry products. 

Processes for acidified foods may involve a hot-fill-hold process or the 

conventional canning process. Hot-fill-hold processing involves filling the product 

hot, sealing the container, then holding filled containers for a period of time at or 

above a certain temperature before cooling. Acidified products may also be 

processed in a pasteurizer, atmospheric cooker or retort for a given period of 

time to destroy the target microorganisms. The processing authority will calculate 

a process using pH, fill temperature, and the thermal resistance data for the 

significant spoilage organisms. 

INOCULATED TEST PACK

It is possible and sometimes desirable (e.g., with new products or new 

processing systems) to confirm the calculated process by means of inoculated 

test packs. In this procedure, the test product is prepared under commercial 

plant operating conditions. Appropriate test microorganisms of known heat 

resistance are added to the product. (It is undesirable to use C. botulinum

spores in processing plants processing low-acid canned foods due to the risk 

associated with the potential toxin production.) The product is inoculated with a 

known number of microorganisms and is then subjected to various processing 

times at one or a number of different processing temperatures. The product is 

then incubated at an appropriate temperature for growth of the test organism. 

Product that received a process inadequate to destroy the added 

microorganisms will show evidence of spoilage. A satisfactory process is 

demonstrated by the absence of spoilage. Substantial agreement between 

calculated processes and those determined by inoculated packs furnishes the 

strongest possible assurance of the adequacy and safety of a particular process. 

 

Occasionally, due to peculiarities of the thermal processing systems or the 

product, reliable heating data cannot be obtained. Under these circumstances, 

consideration may be given to using an inoculated pack alone to establish a safe 

thermal process.
Principles of Thermal Processing 

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Process Deviations

A deviation in processing (or a process deviation) occurs whenever an actual 

thermal process is less than the scheduled process (or process schedule) or 

when any critical factor does not comply with the requirements for that factor as 

specified in the process schedule. Common causes of process deviations for 

traditional canning operations include failure to meet initial temperature, process 

time, or retort temperature requirements or failure to meet any other specified 

critical factor. For aseptic processing and packaging systems, deviations can 

result from improper hold tube temperature, flow rate, or package sterilization; 

breach of the aseptic zone; etc. According to FSIS regulations (9 CFR 318.308 

and 381.308) deviations involving meat and poultry products may be handled in 

accordance with a HACCP plan for canned product that addresses hazards 

associated with microbial contamination or alternative documented procedures 

that will ensure that only safe and stable product is shipped in commerce. 

Otherwise, deviations must be handled in accord with procedures specified in 

paragraph (d) of the regulations. 

Product involved in deviations identified during processing may be immediately 

reprocessed using the full scheduled process, may be given an appropriate 

alternate process established in accordance with FSIS regulations, or may be 

held for later evaluation by a processing authority to determine its safety and 

stability. It should be kept in mind that, in some cases, the original process may 

change the heating characteristics of the processed product (e.g., thickening due 

to starch). For this reason it is a good idea to consult with the processing 

authority to assure that the reprocess is adequate for the product and conditions 

of use. 

Upon completion of the evaluation of the process deviation, the establishment 

maintains a complete description of the deviation along with all necessary 

supporting documentation; a copy of the evaluation report; and a description of 

any product disposition actions, either taken or proposed. Product handled in 

accordance with paragraph (d) of the regulations shall not be shipped from the 

establishment until the inspection personnel have reviewed all of the information 

submitted and the product disposition actions. 

If an alternate process schedule is used that is not on file with the inspector or if 

an alternate process schedule is immediately calculated and used, the product 

shall be set aside for further evaluation as noted above. 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

Product involved in process deviations that are identified through review of 

processing and production records shall be held and the deviations evaluated by 

a processing authority in accord with the requirements noted above. If product 

involved in a deviation is destroyed, destruction shall be conducted in 

accordance with FSIS regulations. 

FSIS regulations also require the maintenance of a process deviation file. The 

establishment shall maintain full records regarding the handling of each 

deviation, regardless of the seriousness of the deviation. Such records shall 

include, at a minimum, the appropriate processing and production records, a full 

description of the corrective actions taken, the evaluation procedures and results, 

and the disposition of the affected product. Such records shall be maintained in 

a separate file or in a log that contains the appropriate information. The file or log 

shall be retained for no less than one year at the establishment, and for an 

additional 2 years at a suitable location. The file or log shall be made available to 

inspection personnel upon request. 
Principles of Thermal Processing 

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Workshop: Process Letter Review

Note: This is a simplified example prepared for instructional purposes only. 

Review the following process letter and answer the questions. 

1/24/2005 

Dr. John Smith 

Food Safety Manager 

Uncle Sam’s Canned Goods Company 

1234 E. Canning Plant Rd 

Somewhere, ST 12345-1234 

Dear John, 

Based on the heat penetration data that you provided to us, we would 

recommend the following thermal processes for your Chili No Beans in 300X407 

metal cans. 

Processing Conditions 

Product: Chili No Beans 

Processing System: Water Immersion with Container 

Rotation 

Container Size: 300x407 metal cans 

Least Sterilizing Value (Fo) 5.3 

Critical Factors:

Fill weight of fully soaked beans: 10.0 ounces 

Container orientation: Vertical 

RPM: 18-20 

Headspace (inches): 10/16 

Product: Preparation method and Formulation

Minimum come up time (minutes): 13 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

Process Time in Minutes 

Process Time (minutes at Retort Temperature (°F)) 

Initial Temp. (°F) 250 251 252

90 40 39 38

100 39 38 37

110 38 37 36

120 38 37 36

These processes are designed to produce a commercially sterile product 

provided that all processing and packaging operations are completed 

satisfactorily. Please give us a call if you have any further questions. 

Sincerely yours, 

Kelly White 

Senior Scientist, TPA, Inc. 

Questions: 

1. What are the critical parameters that will need to be controlled by Uncle 

Sam’s Canned Goods Company when processing this product? 

2. There are several errors on the process letter. Please identify the errors 

or information that needs to be clarified. 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

3. What would be the impact if the headspace requirement was not met? 

4. What would be the impact if the beans were not soaked? 

5. What process time would Uncle Sam’s Canned Goods Company use if the 

product initial temperature was 115°F and the retort was operated at 

252°F? 

Uncle Sam’s Canned Goods Company has set the following as the operating 

process for this product: 

Minimum IT = 100oF 

Minimum Retort Temperature = 252oF 

Minimum Process Time = 40 minutes 

6. Would the operating process result in a higher or lower Fo than the 

scheduled process? Why would the firm use an operating process rather 

than a schedule process? 
Principles of Thermal Processing 

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FSRE Shelf-Stable 

7. Which of the following situations is a processing deviation? 

IT = 90oF 

RT = 250oF 

Process Time = 40 

minutes 

IT = 100oF 

RT = 251oF 

Process Time = 42 

minutes 

IT = 112oF 

RT = 249oF 

Process Time = 42 

minutes 
nomenclature

 Institute For Thermal Processing Specialists

NOMENCLATURE FOR STUDIES IN THERMAL PROCESSING

Various symbols have been employed to represent measured and derived variables in the applications of 

thermal processing science. The overall objective of these guidelines is to recommend a standard system 

of nomenclature for thermal processing applications. The following recommendations are to be 

considered voluntary guidelines. While this does not preclude the use of other symbols, these 

guidelines have been developed by consensus of the Institute for Thermal Processing Specialists and 

should be given serious consideration for adoption by individuals involved in thermal processing studies

aw - Water activity defined as the ratio of the partial pressure of water above a food to 

the water vapor pressure of pure water above a food (p) to the water vapor pressure of pure 

water (po) at a given temperature (aw= p/po)

A - Frequency factor in the Arrhenius equation, K = A exp (-Ea/RT) where T is 

expressed in Kelvin

c - Cook rate, c = 10(T - Tx)/z

C - Concentration of a nutrient or chemical component

 - Cook value used to relate a high temperature thermal process to an 

equivalent process at stove top temperatures, generally applied with T=100°C (212°F) 

and a z-value related to quality attributes

DT - Decimal reduction time equal to the time at a given temperature, T, for a 

survivor curve to traverse one log cycle or equivalently, to reduce a microbial 

population by 90%, t = DT(log No - log N)

Ea - Activation energy in the Arrhenius equation, K = A exp(-Ea/RT), Ea= 

1.8*2.303*R*Tx*T/z where Tx and T are expressed in Kelvin

f - Temperature response parameter equal to the time for the linear section of a 

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nomenclature

heating or cooling curve plotted on semi-log coordinates to traverse one log cycle

f2 - Temperature response parameter of the second straight line segment of a broken 

heating curve

fc - Temperature response parameter derived from the cooling curve

fh - Temperature response parameter derived from the heating curve

F - Time intercept from a thermal death time curve (log tgmvs T) at T = Tx

 - Accumulated lethality to reflect the total lethal effect of heat applied; 

expressed as equivalent minutes at a specific reference temperature for a specific zvalue, = DT(log No - log Nf

) = DTYN; may also be referred to as F-biological

Fc - Accumulated lethality in the cooling phase

Fh - Accumulated lethality in the heating phase

Fi - Factor relating the lethality at the retort temperature to lethality at the reference 

temperature, Fi

 = 10(Tx - Tr)/z

Fo - Accumulated lethality when Tx = 121.1°C (250°F) and z = 10 C° (18 F°)

Fs - Integrated lethal or degradative capacity of heat received by all points in a 

container during a process

 - Accumulated lethality at an iso-j surface

g - Unaccomplished temperature difference, g = Tr - Tc

gc - Unaccomplished temperature difference at the end of the heating period, gc = Tr - 

Tic

gbh - Unaccomplished temperature difference at the intersection of fh and f2 for a broken 

heating curve

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gih - Initial unaccomplished temperature difference, gih = Tr - Tih

 - Unaccomplished temperature difference at an iso-j surface

Ir - Ratio of the log of the straight line survivor curve zero intercept to the initial spore 

count (No)

jc - Cooling lag factor, jc = (Tw - Tpic)/(Tw - Tic)

jcl - Cooling lag factor associated with an iso-j surface

jh - Heating lag factor, jh = (Tr - Tpih)/(Tr - Tih)

k - Reaction rate constant for base 10 logarithms

K - Reaction rate constant for base e (natural) logarithms; death rate constant in the 

Arrhenius model, K = 2.303/D

L - Lethal rate expressed as minutes at the reference temperature per minute at the 

product temperature, L = 10(T - Tx)/z

m - Unaccomplished temperature difference during cooling, m = Tc - Tw

mic - Value of m at the beginning of the cooling cycle, mic = Tic - Tw

n - Number of samples

N - Number of surviving microorganisms

No - Initial number of viable spores or vegetative cells before heat is applied, initial 

bioburden

Nf - Final number of surviving spores or vegetative cells after heat is applied

Nmp - Most probable number of survivors in a thermal resistance experiment

Ns

 - Number of microbial cells remaining after a preservation treatment to a 

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specified probability of finding a non-sterile unit; end point process specification

pH - The degree of acidity or alkalinity of a water solution

 - Pasteurizing value used in place of F-value for pasteurizing processes

P - Pasteurizing value defined as the accumulated lethality when Tx= 60°C (140°F) and 

z = 10 C°(18 F°)

R - Number of negative responses in a thermal resistance experiment

R - Universal gas constant, 1.987 cal/mol×K, 8.314 J/mol×K where K refers to Kelvin 

temperature units

t - Time

tB - Ball's process time, tB = tp + 0.42 tc simple heating, tB= fh(log jhgih-log gc) broken 

heating, tB= fhlog jhgih+(f2 - fh)log gbh- f2log gc

tc - Come-up time is the time between the start of heating and the time when the retort 

reaches processing temperature

tD - Time when the first sample exhibiting no growth is observed in a thermal death time 

(TDT) experiment

tp - Process time is the time from the end of the come-up period to the end of heating, 

defined as tp = tB - 0.42 tc in the Ball Formula Method

tS - Time when the last sample exhibiting growth is observed in a thermal death time 

(TDT) experiment

tbh - Time measured from tB = 0 to the intersection of fh and f2 for a broken heating 

curve

tgm - Geometric mean time, square root of (tS * tD)

T - Temperature

Tc - Container center or coldspot temperature

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nomenclature

Tic - Product temperature at the start of the cooling cycle

Tih - Initial product temperature measured before heating

Tpic - Pseudo-initial cooling temperature determined by extrapolating the linear portion of 

a cooling curve to the start of cooling

Tpih - Pseudo-initial heating temperature determined by extrapolating the linear portion of 

a heating curve to time, tB = 0

Tr - Retort temperature

Ts - Mass average temperature

Tw - Cooling water temperature

Tx - Reference temperature

U - Sterilizing value in terms of minutes at the heating medium temperature, U = FoFi = 

Fo/L

Uc - Sterilizing value for the cooling phase

Uh - Sterilizing value for the heating phase

YN - Spore-log reduction, YN = log No - log Nf

Ys - Spore-log reduction to reach a specified probability of finding a non-sterile unit, Ys= 

log No - log Ns

z - Number of degrees of temperature required for the thermal death time curve 

(log F vs. T) or thermal resistance curve (log DT vs T) to traverse one log cycle, z = (Tx

- T)/(log FT - log FTx) or z = (Tx - T)/(log DT - log DTx)

a - Thermal diffusivity, a =thermal conductivity/(specific heat * density), is 

inversely proportional to fh where the proportionality constant is related to the container 

geometry

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nomenclature

r - Fraction of total lethality delivered during heating, r = Uh/(Uh + Uc) or r = Fh/( Fh

+Fc)

• The Institute for Thermal Processing Specialists is a non-profit organization established 

exclusively for the purpose of fostering education and training for those persons interested in 

procedures, techniques and regulatory requirements for thermal processing of all types of food or 

other materials, and for the communication of information among its members and other 

organizations.

• Part of the mandate of the IFTPS Committees is to develop protocols to be used as guides for 

carrying out the work of thermal processing specialists. This is the first such protocol prepared by 

the Committee on Temperature Distribution and reviewed extensively by members of the Institute. 

The protocol has been approved by the Board of Directors. This document may be photocopied 

in its entirety for use. 

• Single copies of the protocol, as well as information on membership in IFTPS may be obtained 

from: Institute for Thermal Processing Specialists, 304 Stone Rd. W. Ste. 301, Guelph, ON N1G 

4W4 Phone: (519) 824 6774 Fax: (519) 824 6642, E-Mail: info@iftps.org

 

 

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1

FOOD SCIENCE 4075

LAB_____

THERMAL PROCESS CALCULATION

WARNING: Thislab contains at least 28 pages - you may not want to print the entire thing - just

what you need.

PURPOSE: Demonstrate the techniques involved in determining the processing time and

temperature for canned food products.

MATERIALS: Two food products; one heavy, semisolid and one more liquid, cans,

thermocouples, multipoint recorder, retort, sealer

PROCEDURE: In order to determine the processing time for a certain size container with a

'specific' product; two things must be known: (1)the lethality of the microorganisms which may cause spoilage; and (2)the manner of heat penetration in the

canned product. For non-acid foods the organism in question is Clostridium

botulinum and the thermal lethality of this organism is well documented. For acid

foods any number of other organisms become more important,some of which are

even more resistant thanC.botulinum. All that remains is to determine the manner

of heat penetration into the product in the specific size container.

1. Install copper-constantan thermocouples into the sides of the can. The thermocouples

must be placed at the coldest point in the can. For heavy thick products, the coldest point

isthe geometric center ofthe can. For very dilute water-like products, because of convection heating the cold point is below the geometric center of the can and is determined by

experimentation. As a general rule, with smaller cans (eg. 303 x 406) the cold point is

about 0.75 inch above the bottom, assuming the can is standing upright. For large

containers (like a No. 10) the cold point is about 1.5 inches above the bottom.

2. Fill two cans with each product, exhaust and seal in a closingmachine. Place cans upright

into the retort and attach the thermocouple extension wires. Connect the other ends of the

wires to a data logger or multipoint recorder for temperature recording.

3. Set temperature controls on retort and begin the process. Note when steam wasturned on

(mark on the chart paper or circle data logger time). Also note time when venting is

finished and when retort operating temperature RT is achieved, as measured by the

mercury-in-glass thermometer. [It is convenient to also use a stopwatch here to measure

the time between steam on and time when operating temperature isreached on the glass

therrmometer. This will be used later for determining adjusted 0.] Rapid heating products

should be scanned rapidly (every minute or so) while slower heating products can be

scanned at longer intervals. Continue heating until the can temperatures are within about

2 degrees of the retort temperature. Turn off steam (noting the time) and begin cooling
2

cycle. When cans are about 100-120°F, open retort and remove.

4. Prepare a table of “time after steam on” versus can temperature in convenient time units.

For example,for conduction heated foods you might use 2, 4 or 8 minute increments. For

convection heated foods, you might use 0.5 or 1 minute increments. If there are two

samples of each product, just average the temperatures of the two samples at each time

reading. To determine the process timing points, you can use the times printed on the data

logger tape or, if using a multipointrecorder, you must determine the times using the chart

speed and the gage lines on the paper. For instance, if the chart speed was 15 inches per

hour and the chart gradations are 0.5 inch, then each gradation represents 2 minutes.

Time=0 isthe point at which steam was turned on. The time at which the retort reaches

the operating temperature asindicated on the mercury-in-glassthermometeristhe "comeup time".

5. There are two ways of calculating the process time for a product: the graphical method;

and the formula method (SEE ATTACHMENT - for complete descriptions, and then

some!). We will use the formula method. The heat penetration data is plotted on 3 or 4

log cycle semi-log graph paper - 3 cycle paper is included as the last page of the

attachments or you may purchase semi-log paper at the book store - eg. National Brand

Engineering Form 12-183. Temperature (IN DEGREES F) is plotted on the log scale and

time (IN MINUTES) on the linearscale. Note: For plotting this data, the paper is inverted

(i.e. turned upside down) compared to the normal way semi-log paper is used. Start

numbering the log cycles on the Y-axis (on the leftside) with the temperatures beginning

at the top line and continuing downward. See example listed as Fig. 1 in the attached

sheets. The very top line should be 1°F lower than the retort temperature. For example

iftheRT=245/F then the first line would be 244/F. Proceed with temperatures downward

--- remember this is log paper so there will be a step change every 10 lines.

The lower linear time scale (X-axis)should begin in the lower left corner with time 0. On

the right hand side (Y2-axis), if not already printed for you[but upside down], number the

typical log valuesstarting with 1.0 on the top line which represents 1°F below RT. Proceed

downward to 1000 for 3 log cycle paper. This axis represents degrees below retort

temperature. If the axes are labeled correctly then values on the left scale should be equal

to the retort temperature minus the values on the right scale directly across.

Plot the points from your table on the chart paper. Try to draw a line through the maze of

dots so that it is within 1 degree or so of all points. Hopefully the plot will be mostly a

straight line except for an initial lag in the first 5 minutes or so and a tail which trails off

upward or sideward near the end (you can disregard these points). You will need at least

6 to 10 points to get a reasonable estimate of the regression line. Some products exhibit

a broken curve heating in which two intersecting lines must be drawn through the points

(see Fig. 2 in attached sheets). Pray that this does not happen for your product.

We need to get two data points from this plot: j, the lag factor; and fh, the slope.

6. First determine "corrected 0 time". To do this you must find the total time it took for the
3

retort to “come up” to the operating temperature from “time on”. Find the time on the X

axis which represents 0.60 of the total come-up time in the retort after steam-on (or

conversely 0.40 of the come-up time before steam-up). Draw a vertical line upward from

this point until it intersects the straight line you drew in step 5. The temperature at the

point of intersection can be read from the temperature scale at the left and this value is

subtracted from the retort operating temperatureRTto get jI. Alternatively, jI can be read

directly from the scale on the right which is degrees below RT. The initial temperature of

the product in the can before retorting isIT. First calculate I = RT-IT, then calculate j = jI/I

from the jI ofthe graph and I from the previous calculation. The value j must be corrected

if cans are small and the product is a conduction heated type. To do this, multiply the

calculatedvalueby the appropriate "Correctionfactorsforj" found in the attachedhandout

= jcorrected. 

7. To determine fh count the minutes required for the drawn regression line to pass through

one log cycle (change by a factor of 10 eg.from 10 to 100 or 5 to 50) of temperature on the

left scale. Remember this is 3 log cycle paper.

8. Tocalculate the processing time we will assume C. botulinum isthe problemorganismand

we will want a desired value F250 or Fo=2.45 min. Find Fi for the actual operation

temperature [if not 250°F] used from table 4 in handout. Then calculate

(fh/U) = fh/ (Fo x Fi)

with this value of (fh/U) go to table 3 and find the value of log g corresponding to the fh/U.

9. The processing time (BB) in minutes is found by 

BB = fh [log (jcorrected x I) - log g]

SOME CAUSES OF UNRELIABLE HEAT PENETRATION DATA 

The following is a partial list of some factors that have been associated with unreliable heat

penetration data.

1. Thermocouple readings not continued for a sufficient length oftime to adequately

define heating rate or rates.

2. Heat penetration test conducted in a retort load of commercial production and

stopped at the end of the scheduled process for quality determinations,ratherthan

continued long enough to obtain sufficient data.

3. Frequency of readings not sufficient to obtain accurate heating rate or rates.

4. Erroneous temperatures received as a result of inadequate electrical grounding of

potentiometer.

5. No initial temperatures taken on the test cans.

6. No notation of retort come-up time, or a come-up time significantly different from
4

that used in commercial practice.

7. Multiple thermocouples in small cans of product.

8. No coldspot study, or insufficient number of replicates at the coldspot

thermocouple location.

9. No time notation on temperature recorder.

10. No notation of "steam on" for test.

11. No free lead reference.

12. No mercury thermometer readings.

13. Erratic processing temperature control during test.

14. Critical factors associated with product and processing system not recorded and

controlled.

15. Large temperature disagreement between thermocouple free lead and mercury

thermometer.

16. Initial temperature oftest canssignificantly differentfrom that used in commercial

production.

17. In agitating retorts, rotation speed incompatible with commercial production.

18. No complete can-position study in rotating-cage retorts.

19. Excessive delay in running test after containers are sealed.

20. Product for tests not prepared according to procedures used commercially forraw

product preparation or condition.

21. Large difference in processing temperatures between heat penetration tests and

commercial practice.

22. One unexplained abnormally-slow-heating can within a group of cans.

23. Erratic and illogical thermocouple readings.

24. No readings taken until processing temperature is reached.

DISCUSSION QUESTIONS:

1. What are some factors which influence thermal resistance of micro-organisms?

2. What are some factors which influence heat penetration into a canned product?

3. How is thermal resistance determined? 
5

F0'

1

log& 1

(250& T)

(18)

ATTACHMENT

Plotting Heat Penetration Curve

Heat penetration data are usually plotted on three cycle semilogarithmic paper. Temperature is represented on the logarithmic scale

and time on the linear scale. If the graph paper is inverted, the temperatures can be plotted directly as shown in Figure 1 for a straight

line heating curve and in Figure 2 for a broken heating curve.

The temperatures should be numbered from the top down starting with 1E be low the retort temperature. The time divisions should

be numbered from left to right starting with 0 and ending with the time at which the test was ended.

Plot the temperatures for the corresponding time. Inspect the data plotted. Simple heating curves consist of a lower portion which

rises slowly in temperaturetime. This is the lag when the container outside is heating rapidly but the product in the cold zone is not

receiving heat. When the product in the cold zone begins to receive heat, the temperature rises logarithmically. For straight convection

or conduction heating products, a single straight line can be drawn to the data points. This fine is known as the heat penetration curve.

PROCESS CALCULATIONS

The symbols used here are consistent with those used in the industry for many years. it is assumed that time and temperature data

have been obtained by heat penetration tests or that heat penetration factors for the product involved are available. Values for the

parameters m+g and z have been taken as 180EF and 18EF, respectively. All tables and graphs are based on these values. See definition

of terms and symbols at end of this chapter.

Methods of Analyzing Data

After time and temperature data for a given product in a given can size have been obtained by heat penetration studies, these data

may be analyzed by either of two methods:

(1)The "general" or "graphical" method.

(2)The "formula" method.

The two methods of determining process times or levels are based on identical principles but the mechanics or procedures used are

different. Each method has its own advantages. The choice of methods may be governed by the following conditions:

The graphical method is used when it is desired to measure the exact sterilizing value of a process, when such conditions as come-up

time, cooling water temperature, or the holding time after processing but before water cooling are different from normal retorting

procedures. This method is also adapted to conditions when the heat penetration curve cannot be represented by one or two straight lines

within the lethal temperature range on semi-logarithmic paper. It is not readily adapted to the calculation of processes when the retort

temperature and/or initial temperature are different from those under which the heating data were obtained. Time and temperature data

during the cooling cycle as well as the heating cycle must be recorded in order to use the graphical method. The graphical method is

not applicable to air cooled products.

The formula method is used when the heat penetration curve can be represented by not more than two straight lines on semilogarithmic paper. The formula permits evaluating processes for retort and initial temperature conditions differing from those under

which the heating data were obtained. In the case of heating curves represented by one line only on semi-log paper, the heat penetration

factors can be converted to different can sizes. The various methods of calculating processes win be described in detail.

Standards

It is first necessary to set up a standard sterilizing value. The greatest interest in processing canned foods is with low-acid products.

With such foods, 250EF has been generally established as the reference temperature and the lethal heat expressed in terms of minutes

at 250EF. This reference temperature will be used here.

The Graphical or General Method

As mentioned above, the lethal heat of a process is expressed in minutes at 250 degrees F. One minute at 250 degrees F or an

equivalent amount of heat is defined as one unit of sterilizing value. The symbol for sterilizing value is Fo.

Temperatures other than 250EF have lethal heat. Under conditions used here. one minute at 250EF is equivalent to 10 minutes at

232EF or 100 minutes at 214EF. In other words. for each 18E drop in temperature the time necessary to obtain the equivalent bacterial

destruction increases ten times.

The lethal ratio (Fo/t) or the sterilizing value effective in one minute at other temperatures (T) can be expressed mathematically as:

Lethal rate values in the range 200EF to 260EF are shown in Table 1.
6
7
8

Table 1

LETHAL RATES

(For z equals 18)

TEMP (tenths of degrees F)

°F. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

190 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.001 0.001

191 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

192 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

193 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

194 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

195 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

196 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

197 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

198 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

199 0.001 0.001 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002

200 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002

201 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002

202 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002

203 0.002 0.002 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003

204 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003

205 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.004 0.004

206 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004

207 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.005 0.005

208 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005

209 0.005 0.005 0.005 0.005 0.006 0.006 0.006 0.006 0.006 0.006

210 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.007 0.007 0.007

211 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.008 0.008

212 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.009 0.009

213 0.009 0.009 0.009 0.009 0.009 0.009 0.010 0.010 0.010 0.010

214 0.010 0.010 0.010 0.010 0.011 0.011 0.011 0.011 0.011 0.011

215 0.011 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.013 0.013

216 0.013 0.013 0.013 0.013 0.014 0.014 0.014 0.014 0.014 0.014

217 0.015 0.015 0.015 0.015 0.015 0.016 0.016 0.016 0.016 0.016

218 0.017 0.017 0.017 0.017 0.018 0.018 0.018 0.018 0.018 0.019

219 0.019 0.019 0.019 0.020 0.020 0.020 0.020 0.021 0.021 0.021

220 0.022 0.022 0.022 0.022 0.023 0.023 0.023 0.024 0.024 0.024

221 0.024 0.025 0.025 0.025 0.026 0.026 0.026 0.027 0.027 0.027

222 0.028 0.028 0.029 0.029 0.029 0.030 0.030 0.030 0.031 0.031

223 0.032 0.032 0.032 0.033 0.033 0.034 0.034 0.035 0.035 0.035

224 0.036 0.036 0.037 0.037 0.038 0.038 0.039 0.039 0.040 0.040

225 0.041 0.041 0.042 0.042 0.043 0.044 0.044 0.045 0.045 0.046

226 0.046 0.047 0.048 0.048 0.049 0.049 0.050 0.051 0.051 0.052

227 0.053 0.053 0.054 0.055 0.056 0.056 0.057 0.058 0.058 0.059

228 0.060 0.061 0.062 0.062 0.063 0.064 0.065 0.066 0.066 0.067

229 0.068 0.069 0.070 0.071 0.072 0.073 0.074 0.075 0.075 0.076

230 0.077 0.078 0.079 0.080 0.081 0.083 0.084 0.085 0.086 0.087

231 0.088 0.089 0.090 0.091 0.093 0.094 0.095 0.096 0.097 0.099

232 0.100 0.101 0.103 0.104 0.105 0.107 0.108 0.109 0.111 0.112

233 0.114 0.115 0.117 0.118 0.120 0.121 0.123 0.124 0.126 0.128
9

234 0.129 0.131 0.133 0.134 0.136 0.138 0.139 0.141 0.143 0.145

235 0.147 0.149 0.151 0.153 0.154 0.156 0.158 0.161 0.163 0.165

236 0.167 0.169 0.171 0.173 0.176 0.178 0.180 0.182 0.185 0.187

237 0.190 0.192 0.194 0.197 0.200 0.202 0.205 0.207 0.210 0.213

238 0.215 0.218 0.221 0.224 0.227 0.230 0.233 0.236 0.239 0.242

239 0.245 0.248 0.251 0.254 0.258 0.261 0.264 0.268 0.271 0.275

240 0.278 0.282 0.285 0.289 0.293 0.297 0.300 0.304 0.308 0.312

241 0.316 0.320 0.324 0.329 0.333 0.337 0.341 0.346 0.350 0.355

242 0.359 0.364 0.369 0.373 0.378 0.383 0.388 0.393 0.398 0.403

243 0.408 0.414 0.419 0.424 0.430 0.435 0.441 0.447 0.452 0.458

244 0.464 0.470 0.476 0.482 0.489 0.495 0.501 0.508 0.514 0.521

245 0.527 0.534 0.541 0.548 0.555 0.562 0.570 0.577 0.584 0.592

246 0.599 0.607 0.615 0.623 0.631 0.639 0.647 0.656 0.664 0.673

247 0.681 0.690 0.699 0.708 0.717 0.726 0.736 0.745 0.755 0.764

248 0.774 0.784 0.794 0.805 0.815 0.825 0.836 0.847 0.858 0.869

249 0.880 0.891 0.903 0.914 0.926 0.938 0.950 0.962 0.975 0.987

250 1.000 1.013 1.026 1.039 1.053 1.066 1.080 1.094 1.108 1.122

251 1.136 1.151 1.166 1.181 1.196 1.212 1.227 1.243 1.259 1.275

252 1.292 1.308 1.325 1.342 1.359 1.377 1.395 1.413 1.431 1.449

253 1.468 1.487 1.506 1.525 1.545 1.565 1.585 1.605 1.626 1.647

254 1.658 1.690 1.711 1.733 1.756 1.778 1.801 1.824 1.848 1.872

255 1.896 1.920 1.945 1.970 1.995 2.021 2.047 2.073 2.100 2.127

256 2.154 2.182 2.210 2.239 2.268 2.297 2.326 2.356 2.387 2.417

257 2.448 2.480 2.512 2.544 2.577 2.610 2.644 2.678 2.712 2.747

258 2.783 2.818 2.855 2.891 2.929 2.966 3.005 3.043 3.082 3.122

259 3.162 3.203 3.244 3.286 3.328 3.371 3.415 3.459 3.503 3.548

260 3.594 3.640 3.687 3.734 3.782 3.831 3.881 3.930 3.981 4.032

261 4.084 4.137 4.190 4.244 4.299 4.354 4.410 4.467 4.524 4.583

262 4.642 4.701 4.762 4.823 4.885 4.948 5.012 5.076 5.142 5.208

263 5.275 5.343 5.412 5.481 5.552 5.623 5.696 5.769 5.843 5.919

264 5.995 6.072 6.150 6.229 6.310 6.391 6.473 6.556 6.641 6.726

265 6.813 6.901 6.989 7.079 7.171 7.263 7.356 7.451 7.547 7.644

266 7.743 7.842 7.943 8.046 8.149 8.254 8.360 8.468 8.577 8.687

267 8.799 8.913 9.027 9.143 9.261 9.380 9.501 9.624 9.747 9.873

268 10.000 10.129 10.259 10.391 10.525 10.661 10.798 10.937 11.078 11.220

269 11.365 11.511 11.659 11.809 11.961 12.115 12.271 12.429 12.589 12.751

270 12.915 13.082 13.250 13.421 13.594 13.769 13.946 14.125 14.307 14.491

At the slowest heating point within the container. there is a gradual rise in the temperature. the rate being dependent on the physical

characteristics of the product. There will be some lethal effect during each minute of the process; the amount during this interval is

dependent upon the temperature at that time. These values are obtained from Table 1 and they can be added to obtain the total effective

lethal heat of the process.

Heat penetration time and temperature data are usually recorded at some convenient time interval and can be set up in four columns

as shown in Table 2. In the third column is added the sterilizing value effective in one minute (lethal rate) at the temperature indicated.

The sum of Fo values in the third column will be the sterilizing value of the process if the temperature observation had been made of each

minute of the process. When temperature observations are not made each minute of the process. lethal rate values must be extrapolated

from the known Fo per minute values. as shown in the fourth column.
10

TABLE 2 HEAT PENETRATION DATA

CONDUCTION HEATING - 211 x 304 CAN

Come-Up Time: 10 minutes Retort Temperature: 240EF

Heating time Temperature Lethal Rate 3 F0/min Cooling time Temperature Lethal Rate 3 F0/min

IT 160 0 71 237.8 0.21 0.21

6 164 0 72 235.9 0.165 0.165

12 174 0 73 232.7 0.109 0.109

18 195 0.001 0.003 74 228.7 0.066 0.066

21 201 0.002 0.006 75 223.8 0.035 0.035

24 208 0.005 0.015 76 218 0.017 0.017

27 214 0.01 0.03 77 212 0.008 0.008

30 218.5 0.017 0.058 78 206 0.004 0.004

33 222.5 0.028 0.084 79 199 0.001 0.001

36 225.5 0.041 0.123 80 192 0.001 0.001

39 228 0.06 0.18 85 157 0 0

42 230 0.077 0.231 90 132 0 0

45 232 0.1 0.3 95 115 0 0

48 233.5 0.121 0.363 100 102 0 0

51 234.6 0.138 0.414 105 94 0 0 

54 235.3 0.153 0.459 0.616

57 236.4 0.176 0.528

60 237 0.19 0.57

63 237.6 0.205 0.615 Heating time F0 = 5.089

66 238 0.215 0.645 Cooling time F0 = 0.616

69 238.4 0.227 0.227 Process F0 = 5.705

70 238.5 0.23 0.23

70 steam off 5.089

The lethal rate figures can be plotted against time on coordinate paper to obtain a lethal rate curve as shown in Figure 3. Since the

vertical distance on this curve at each minute represents the F0 effective in that minute. it follows In other words. the sterilizing value

is proportional to the area under the curve. that the total sterilizing value is equal to the sum of all the vertical distances for every minute

of the process. It is necessary to measure the area under the curve in order to determine process sterilizing value. This can be done

by Simpson's rule. or with method of counting the small squares or with an instrument called a planimeter. The area in square inches

must be multiplied by a factor to be converted to Fo units. This factor is found by determining the area of a unit sterilization area such

as ABCD shown in Figure 3.

 The product of the height and width of this area in terms of F0 per minute and time is unity. The factor to be multiplied by the

square inch area under the lethal rate curve is the reciprocal of the square inch area of the unit sterilization rectangle. This means that

if the area under the curve is 6.5 square inches. Fo equals 6.5 divided by 0.5 equals 13.

The procedure for determining the length of a process for a known sterilizing value is quite similar except that instead of measuring

area for a known length of process. the process is found to yield a known area under the curve. For example. suppose a process is wanted

having a sterilizing value of 10. previous experience having shown that this value gives satisfactory results. It is necessary then to find

the time that would yield an area of 5 square inches under the lethality curve. Inspection of the curve would lead us to believe that this

time would not be far from 65 minutes. We will. therefore. estimate the cooling curve from 65 minutes which we can do fairly accurately

by drawing it parallel to the actual cooling curve from 78 minutes. Now. we will measure the area under this 65 minute curve by one

of the methods previously described. and we find it to be 4.56 square inches. Since this process fails to give us 5 square inches. or 10

Fo units under the curve. we know that 65 minutes is not quite enough. Actually. we need not go further than this as it is almost a
11

certainty that the next higher practical process. i.e.. 70 minutes. would yield at least 5 square inches. We check these though. and find

the area under the 70 minute curve to be 5.85 square inches or 11.7 Fo units. We could of course. interpolate between 65 and 70 minutes

to get a more exact time. but for practical purposes we will select 70 minutes.

It should be emphasized again that the results obtained by this method are valid only when the initial and retort temperature

conditions are the same as those of the heat penetration tests. If the heat penetration curve can be represented by one or two straight lines

on semi-log paper. it is possible to make corrections for these factors. but in this case. the graphical method is not the recommended one.

Either the formula method or the nomogram method is better suited for such a calculation.

Effect of 3 Degrees F Errors in Retort Temperature on

Fo Value of Heating Phase of Typical Processes

for 303 x 406 Cans

Initial Process Retort

 Product Temp. Time Temp. Fo

(°F) (min) (°F) (min)

Green beans 120 20 237 2.0

 in brine 240 3.0

243 4.7

Cream-style 140 95 237 3.2

 corn 240 4.4

243 6.2

The Formula Method

The first step in calculating processes by the formula method is to plot the time-temperature data on semi-log paper. time being

plotted as abscissae and temperature as the logarithmic ordinate. Zero time is the time at steam on. The time at which the retort reaches

processing temperature is noted as come-up time. Three cycle semi-log paper generally provides a convenient range for plotting the data.

Actually. the temperatures plotted are the retort temperature minus the can temperature. Instead of making these subtractions it is

more practical to turn the semi-log paper upside down and plot can temperatures directly. The temperature on the top line is one degree

below retort temperature. At the bottom of the first log cycle the temperature is 10 degrees below retort temperature and at the bottom

of the second log cycle. 100 degrees below.

Either one straight line (simple heating curve) or not more than two straight lines (broken heating curve) are drawn through the

points in the lethal temperature range (above 210EF). An attempt should be made to pass the straight lines within 1 degree of all the

points rather than fit them by any geometric mean method.

Having drawn the lines on the graph paper. factors must be determined that will describe the positions. Simple and broken heating

curves will be discussed separately.
12

Simple Heating Curve

A plot of a simple heating curve is shown in Figure 1. From this plot we obtain two factors used in calculating processes. These

factors are j (lag factor) and fh (slope).

In making a heat penetration test. some time is required in bringing retort to processing temperature. It will be obvious that the

come-up time does not have the heating value of the processing or holding temperature but that its heating value would be more than

0 minutes. Conventionally. the heating value of the come-up me is taken as 0.42 of the come-up time. This means the corrected

beginning of process is not when the retort reaches process temperature but 0.4 of the come-up time before steam-up or 0.6 of the come-up

time after steam-on. With a 10 minute come-up. the corrected 0 is at 6 minutes on the time scale. It is necessary make this correction

because retort come-up times will vary over comparatively wide limits and. unless means are provided for correcting these to the come-up

time will always have to be specified with the heat penetration curve. If because of the long come-up time it is necessary to make

allowance for come-up 0.4 of the come-up can be subtracted from the calculated process or the sterilizing value is the sought unknown

0.4 of the come-up time is added to process time.

Having determined the corrected zero time. a vertical line is drawn at this value on the time scale and crossing the extended straight

line drawn through the time-temperature plotted. The point where these two lines cross will be a certain number of degrees below the

retort temperature and this value is called "jI". A temperature value can be read on the left side temperature scale corresponding to the

point the lines cross and this value subtracted from the retort temperature. If a degree-below-retort-teperature scale is marked on the right

hand side of the graph paper, the value of "jI" can be read from this scale directly.

(1) I = RT-IT

The retort temperature (RT) is the retort temperature obtained during the heat penetration test. and the initial temperature (IT) is

the center temperature of a particular can for which the time_temperature data are plotted.

Then:

(2) j = jI/I

Thiss value of j remains constant for the given product; it does not change when converting the heating data to another can size.

With smaller cans of conduction heating products. a correction to the j value is advisable to compensate for heat conducted into the

product by the thermocouple wires and fittings. These corrections are discussed by Ecklund in his article. "Correction Factors for Heat

Penetration Thermocouples". (Food Technol. 10:43-44. 1956). The following table gives correction factors for j.
13

Correction factors for “j”

Use on conduction heating products only

Can Size Multiply "j" factor by:

202 x 214 1.36

211 x 400 1.16

300 x 407 1.10

307 x 409 1.06

The second heat penetration factor obtained from the graph of a simple heating curve is fh. This factor is the time in minutes for

the straight line drawn through the time-temperature plots to pass through one logarithmic cycle. A log cycle is the distance between

any two points on the logarithmic ordinate in which the number of degrees below retort temperature increases ten times. For example.

the distance can be from 1 to 10. 3 to 30. 10 to 100 or 20 to 200 as read on the right hand side of the graph sheet.

With the values of j and fh obtained from the graph of the heating data. the sterilizing value (Fo) of a process can be determined or

the process time in minutes (BB) can be calculated for a desired Fo value.

To calculate Fo we use the following equations:

(3) logg log jI B

f

B

h

= −

(4) F

f

(f / U)F

o

h

h i

=

In equation (3) the values of j and fh have already been determined. BB (process time) is known and I = RT-IT. RT is a retort

temperature at which the product will be processed and IT is the initial temperature that will be encountered under commercial canning

conditions. These values are substituted in equation (3) and the value of "log g" calculated. The value of "g" is the number of degrees

below retort temperature at the slowest heating point in the container at the end of the process. In order to simplify calculations. the log

g is used in the equations.

For each value of log g there is a corresponding value of the term fh/U. This relationship is shown in Table 3. The term "Fi" is

related to the retort temperature. It can be calculated by the equation:

(5) F

RT

i =

 −











−

log ( ) 1 250

18

Values of Fi for various retort temperatures are listed in Table 4.

The proper value of Fi for the retort temperature is selected and substituted in equation (4) along with fh/U (found from Table 5 for

the corresponding value of log g) and fh. The Fo value obtained will be the sterilizing value of the process.

To calculate BB we use the following equations:

(6) fh / U

f

F F

h

o i

=

×

(7) BB = fh(log jI − log g)

In equation (6). fh is from the heat penetration curve. Fo is the desired sterilizing value and Fi is obtained from Table 4 for the

particular retort temperature involved. With these values. fh/U is calculated. From the relationship of fh/U and log g shown in Table 3.

the value of log g can be found which corresponds to the value of fh/U calculated in equation (6).

This value of log g is substituted in equation (7). The values of j and fh are from the heat penetration curve and I again is RT-IT.

The value of BB calculated would be the process time in minutes.






13

TABLE 4

Fi VALUES FOR VARIOUS RETORT TEMPERATURES (°F.)

RT Fi RT Fi R T Fi

214 100.00 233 8.799 252 0.7743

215 87.99 234 7.743 253 0.6 813

216 77.43 235 6.813 254 0.5995

217 68.13 236 5.995 255 0.5275

218 59.92 237 5.275 256 0.4642

219 52.75 238 4.642 257 0.4085

220 46.42 239 4.085 258 0.3594

221 40.85 240 3.594 259 0.3163

222 35.94 241 3.163 260 0.2783

223 31.63 242 2.783 261 0.2449

224 27.83 243 2.449 262 0.2154

225 24.48 244 2.154 261 0.1896

226 21.54 245 1.896 264 0.1668

227 18.96 246 1.668 265 0.1468

228 16.68 247 1.468 266 0.1292

229 14.68 248 1.292 267 0.1136

230 12.92 249 1.136 268 0.1000

231 11.36 250 1.000 269 0.0880

232 10.000 251 0.8799 270 0.0774







1

10

100

1000
HP_protocol

 Institute For Thermal Processing Specialists

PROTOCOL FOR CARRYING OUT HEAT PENETRATION STUDIES

Various methods and equipment may be employed in order to collect accurate heat penetration data. The 

overall objective of these guidelines is to recommend procedures for carrying out heat penetration studies 

for establishing thermal processes necessary to produce commercially sterile foods packaged in 

hermetically sealed containers. The following recommendations are to be considered voluntary guidelines. 

While this does not preclude the application of other methods and equipment for collecting heat 

penetration data, these guidelines have been developed by consensus of the Institute for Thermal 

Processing Specialists and should be given serious consideration for adoption as methodology by 

individuals performing heat penetration studies.

1. NOMENCLATURE

t - Time

tc - Retort come-up time is the time between the start of heating and the time when the retort 

reaches processing temperature (at times referred to as CUT)

tp - Process time is the time from the end of the come-up period to the end of heating (at 

times referred to as the operator's process time)

T - Temperature

Tc - Container center or coldspot temperature (at times referred to as CT)

Tr - Retort temperature (at times referred to as RT)

Tw - Cooling water temperature (at times referred to as CW)

2. TERMINOLOGY

2.1 Ballast Containers: Containers may be required to fill the retort during heat penetration 

studies to simulate production retort conditions. Type, shape and size of containers should be 

the same as used for the intended process. Material used for filling containers could be the 

file:///C|/iftps/protocols/hp_protocol.htm (1 of 15)6/5/2004 8:27:21 AM
HP_protocol

test product, or any suitable material having heating characteristics similar to that of the test 

product, or in some circumstances, water.

2.2 Cooling Time: Time required following the introduction of the cooling medium to 

decrease the internal temperature of the product to a specified value, commonly 35 to 45o C 

(95 - 110o F).

2.3 Critical Factors: Physical and chemical factors that can influence the thermal response 

of a product to a thermal process, the variation of which may influence the scheduled 

process, including: container, product, retort and processing conditions.

2.4 Fill, Drain and Net Weights: Fill weight is the weight of solids prior to processing; drain 

weight, the weight of solids after processing; and net weight, the weight of all product in a 

container

2.5 Heat Penetration Curve: Plot of the logarithmic difference between either retort 

temperature and product temperature (heating curve) or product temperature and cooling 

medium temperature (cooling curve) versus time.

2.6 Mercury-in-Glass Thermometer (MIG): Generally used as the retort reference 

temperature device and regulated for that application by government agencies in some 

countries. Other temperature measuring devices may be calibrated against a MIG retort 

thermometer which has been calibrated against a traceable temperature standard.

2.7 Resistance Temperature Detector (RTD): Thermometry system based on the positive 

change in resistance of a metal sensing element (commonly platinum) with increasing 

temperature

2.8 Temperature Measuring Device (TMD): Device used for measuring temperature, 

including: thermometers, thermocouples, RTDs and thermistors.

2.9 Thermistor: TMD manufactured from semiconductor materials which exhibits large 

changes in resistance proportional to small changes in temperature. Thermistors are more 

sensitive to temperature changes than thermocouples or RTDs and are capable of detecting 

relatively small changes in temperature.

2.10 Thermocouple: TMD composed of two dissimilar metals which are joined together to 

form two junctions. When one junction is kept at an elevated temperature as compared to the 

other, a small thermoelectric voltage or electromotive force (emf) is generated which is 

proportional to the difference in temperature between the two junctions.

3. DESIGN OF A HEAT PENETRATION STUDY

The purpose of a heat penetration study is to determine the heating and cooling behavior of a 

product/package combination in a specific retort system for the establishment of safe thermal 

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processes and evaluating process deviations. The study must be designed to adequately and 

accurately examine all critical factors associated with the product, package and process which 

affect heating rates. Numbers of containers per test run, and number of test runs to account for 

statistical variability are important and discussed in sections 5.11 and 5.12. Before commencing a 

heat penetration study, an evaluation of retort temperature and heat transfer uniformity, at times 

referred to as a heat or temperature distribution study (IFTPS, 1992), should have been completed. 

A goal in conducting these studies is to identify the worst case temperature response expected to 

occur in commercial production as influenced by the product, package and process. 

4. FACTORS AFFECTING HEATING BEHAVIOR

Several product, process, package and measurement related factors can contribute to 

variations in the time-temperature data gathered during a heat penetration test. 

Establishment of a process requires expert judgment and sound experimental data for 

determining which factors are critical and the effect of changing those factors both within and 

beyond established critical limits. The list of items addressed in this section is extensive, but 

should not be assumed to cover all possible factors. Quantitative data on variability should be 

recorded where appropriate and all pertinent data should be documented to better 

understand and account for possible variations in heat penetration behavior. 

4.1 Product:

4.1.1 Product formulation and weight variation of ingredients should be 

consistent with worst case production values. Changes in formulation may 

necessitate a new heat penetration study.

4.1.2 Fill weight used for heat penetration studies should not be less than the 

maximum declared on the process schedule. Excess product may be expressed 

as percent overfill.

4.1.3 Solids content should be measured for nonhomogeneous products both 

before and after processing. Solids content deposited in a sieve should be 

weighed and expressed as a percentage of total weight. Note: Addition of 

compressed or dehydrated ingredients may result in increased drained weight.

4.1.4 Consistency or viscosity of semi-liquid or liquid components should be 

measured before and after processing. Flow behavior will change with type and 

concentration of thickening agent (starch, gums, etc.), temperature and shear 

rate. Changes may be reversible or irreversible which may be important when 

reprocessing product.

4.1.5 Size, shape and weight of solid components should be measured before 

and after processing.

4.1.6 Integrity and size of solid component clusters may change during 

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processing and affect temperature sensor placement in the product and 

coldspot location.

4.1.7 Methods of product preparation prior to filling should simulate commercial 

practice. For example, blanching may cause swelling, matting or shrinkage 

which could influence heat penetration characteristics.

4.1.8 Product matting or clumping may change heat penetration characteristics 

and influence coldspot location. Also caution should be exercised with sliced 

products which may stack together during processing.

4.1.9 Rehydration of dried components, either before or during processing, is a 

critical factor which may influence heat penetration behavior, as well as process 

efficacy with respect to spore inactivation. Details of rehydration procedures 

should be recorded during the heat penetration study.

4.1.10 Product may heat by convection, conduction or mixed convection/

conduction depending on its physical properties. Some foods exhibit complex 

(broken) heating behavior. Product may initially heat by convection, then due to 

a physical change in the product, change to conduction heating behavior. For 

example, for products such as soups which contain starch, the change in 

heating behavior may be due to starch gelatinization at a particular temperature. 

Small variations in product formulation or ingredients may cause the transition 

from convection to conduction heating to occur at a different temperature and 

related time. Special care should be taken to identify and control specific 

product and process variables related to the heating rates of these products.

4.1.11 Additional product characteristics such as salt content, water activity, pH, 

specific gravity, concentration of preservatives, and methods of acidification 

may influence heat transfer or microbiological resistance and should be 

recorded.

4.2 Container:

4.2.1 Manufacturer and brand name information should be recorded in case 

information related to filling, sealing or processing is required.

4.2.2 Container type (metal cans, glass jars, retort pouches, semi-rigid 

containers), size and dimensions should be recorded.

4.2.3 Nesting of low profile containers can influence heating behavior. Heat 

penetration studies on jumble loaded retorts (no racks or dividers) should 

include tests conducted on stacks of nested cans as well as single cans.

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4.2.4 Container vacuum and headspace should be recorded for rigid containers. 

For flexible and semi-rigid containers the volume of residual gases in the 

container should be determined. Entrapped gases may create an insulating 

layer in the container causing a shift in the coldspot location and a decrease in 

the heating rate. Controlled overpressures during processing have been found 

to reduce these effects. 

4.2.5 Maximum thickness of flexible packages (pouches) has a direct 

relationship to the coldspot temperature history with thicker packages heating 

more slowly. Heat penetration studies should be carried out at the maximum 

specified package thickness.

4.2.6 Container orientation (vertical or horizontal) within the retort may be a 

critical factor for some product/package combinations and should be studied 

where appropriate. Changes in container orientation may also influence vent 

schedules and come-up time.

4.2.7 Postprocessing examination of test containers for abnormalities should be 

conducted with special emphasis on the slowest and fastest heating containers. 

It is strongly recommended that flexible packages be carefully examined 

following processing to identify the thermocouple junction location. If the 

intended sensing location has shifted, it is likely that heat penetration data 

collected are not reliable.

4.3 Method of Fill:

4.3.1 Fill temperature of the product should be controlled. It will affect the initial 

temperature which may influence some heat penetration parameters (lag factor, 

retort come-up period). This may constitute a critical control point for a process, 

particularly for products which exhibit broken heating behavior.

4.3.2 Fill and net weights may influence heating rates both in still and rotary 

cooks. Information on variability may be found in statistical process control and 

product quality control records.

4.3.3 In most cases, controlling headspace by determining net weight is not 

sufficient due to possible variations in the specific gravity of the food product. 

Care should be taken to avoid incorporation of air which would affect the 

headspace vacuum. In rotary processes, container headspace is a critical 

control point since the headspace bubble helps mix the product during agitation.

4.4 Closing or Sealing: Closing or sealing equipment should provide a strong, hermetic seal 

which is maintained during the thermal process. Vacuum in cans and jars for most canned 

foods is recommended to be between 35-70 kPa (10-20 in-Hg) measured at room 

temperature. Vacuum is affected by variables such as: headspace, product temperature, 

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entrapped air, and vacuum efficiency of the closing equipment. Some products such as 

vegetables vacuum packed in cans may have a minimum vacuum as a critical control point. 

For others packed in flexible or semi-rigid containers, vacuum setting will influence the 

residual air content in the package, also constituting a critical control point.

4.5 Retort System: The type of retort system used may have a significant influence on 

the heating rates of products processed in the retort. Results from a heat penetration 

test should be reported with reference to the retort type and conditions existing at the 

time of testing.

4.5.1 Retort come-up time should be as short as possible consistent with 

obtaining satisfactory temperature distribution. Laboratory size retorts may be 

used for development work on heat penetration behavior. Results will be 

conservative when the smaller retorts have shorter come-up times and cool 

more quickly than production retorts. After development, the thermal process 

should, if physically possible, be verified in an appropriate production retort.

4.5.2 Racking systems may be used to separate layers of cans or jars; constrain 

the expansion of semi-rigid and flexible containers; provide support and 

circulation channels for thin profile containers; and ensure maximum pouch 

thickness is not exceeded. Care should be taken to understand the influence of 

a specific rack design on retort performance and heat transfer to containers.

4.5.3 Still batch retort systems vary in operation based on: type of heating 

medium(steam, steam/air, water immersion, water spray); orientation of the 

retort (vertical, horizontal); method of heating medium agitation (fans, pumps, air 

injection); and other factors which may influence the heating behavior.

4.5.4 Rotational batch retort systems (axial, end-over-end) are designed to 

rotate (or oscillate) entire baskets of product during processing. Container 

agitation may provide faster rates of heat penetration to the container coldspot 

as compared to still cooks. However, while this is true for some containers, it 

may not be so for all containers within a load and caution must be exercised to 

identify the slowest heating containers. This may entail a detailed can-position 

study. It is recommended that during initial testing, data be collected at small 

time increments (15 s) particularly for viscous fluids where the coldspot may 

move in relationship to a fixed thermocouple during rotation, producing 

erroneous results. Slip-ring connectors should be cleaned and thermocouple 

calibration verified at regular intervals. Critical factors in these retorts include: 

headspace, product consistency, solids to liquid ratio, initial temperature, 

container size, rotational speed and radius of rotation.

4.5.5 Continuous retort systems may move containers through the processing 

vessel along a spiral track located at the outside circumference of a horizontal 

retort shell or be carried through a hydrostatic retort in chain driven flights. 

Regardless of the configuration, it becomes difficult or impossible to use 

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thermocouples to collect heat penetration data in these systems. Data may be 

obtained using self-contained temperature measurement and data storage 

modules in the commercial vessel or by using process simulators.

5. TEMPERATURE MEASUREMENT AND DATA ACQUISITION

5.1 Data Acquisition System: Accuracy and precision of the data acquisition system 

(datalogger) used for heat penetration studies will affect temperature readings. Dataloggers 

are typically comprised of a multi-channel temperature measuring and digital data output 

system. Calibration of a data acquisition system should include verification of the data 

acquisition rate, since errors in the time base would result in erroneous data.

5.2 Type of Thermocouple: The most common TMDs used in thermal processing are 

duplex Type T (copper/constantan) thermocouples with Teflon insulation. Common 

configurations are flexible wires (20-, 22- or 24-gauge) and rigid needle types. Details on 

thermocouples and connecting units are available in Bee and Park (1978) and Pflug (1975).

5.3 Type of Connectors and Associated Errors: Connectors used in a thermocouple 

circuit are fittings attached to a thermocouple within which electrical connections are made. 

Several types of connectors are available for specific applications and thermocouple type. 

Caution must be exercised to avoid certain sources of error which may be associated with 

the use of connectors and extension wires. These include: disparity in thermal emf between 

thermocouples, connectors and extension wires; temperature differences between two wire 

junctions; and reversed polarity at the thermocouple-extension wire junction. Thermocouple 

connectors should be cleaned frequently with metal cleaner to assure good electrical contact 

and prevent errors in thermocouple readings. Similar concerns should be addressed when 

using RTDs and thermistors.

5.4 Thermocouple Calibration: Thermocouples should be calibrated against a traceable 

calibration standard (thermometer, RTD, thermistor). Inaccuracies in temperature 

measurements may result in errors in process evaluation; hence, frequent calibration is 

essential to provide reliable data. Factors affecting calibration include: worn or dirty slip-rings, 

improper junctions, metal oxidation, multiple connectors on one lead, and inadequate 

datalogger cold junction compensation. As a consequence, thermocouples should be 

calibrated in place as part of the complete data acquisition system. Some precautions when 

using thermocouple based data acquisition systems include: minimizing multiple connections 

on the same wire; cleaning all connections; grounding the thermocouples and recording 

device; slitting thermocouple outer insulation outside the retort to prevent flooding of 

datalogger or data recording device (see NFPA, 1985, or ASTM, 1988 for illustrations); and 

using properly insulated thermocouple wires.

5.5 Positioning of Thermocouple in the Container: The method of inserting a 

thermocouple into a container should result in an airtight, watertight seal which should be 

verified after testing. Thermocouple sensing junctions should be positioned in the slowest 

heating component of the food product and situated in the slowest heating zone within the 

container. During insertion of the thermocouple, caution must be taken to avoid physical 

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changes to the product. Also, the method employed for mounting the thermocouple into the 

container should not affect the container geometry which could influence heat penetration 

characteristics. Flexible or rigid thermocouples may be inserted into rigid, flexible and semirigid containers using compression fittings or packing glands. For flexible containers, NFPA 

(1985) provides illustrations of thermocouple positioning into a solid particulate and several 

thermocouple positioning devices to ensure the thermocouple remains in a fixed position 

within the container. The most appropriate device for a particular application will depend 

upon the product, racking system, container type and sealing equipment. Leakage may be 

detected by weighing the container before and after processing to determine changes in 

gross weight. If there is leakage caused by improperly mounted thermocouples, data 

collected for that container should be discarded. Note: Ecklund (1956) reported correction 

factors for heat penetration data to compensate for errors associated with the use of 

nonprojecting, stainless steel receptacles. While not reported in the literature, this may also 

be a concern with other fittings.

5.6 Type and Placement of Containers: The type and size of container used in the heat 

penetration study should be the same as that used for the commercial product. The racking 

and loading of rigid (cans), semi-rigid (trays and cups) and flexible (pouches) containers 

should simulate commercial practice. Test containers should be placed at the slowest heating 

location in the retort, as determined by temperature and heat transfer distribution studies.

5.7 Temperature of the Heating Medium: TMDs should be positioned so as to prevent 

direct contact with racks or containers and identified according to their specific location in the 

retort. A minimum of two thermocouples is recommended for retort temperature 

measurement: one situated close to the sensing bulb of the retort MIG thermometer, the 

other located near the test containers. In addition, at least one thermocouple should be 

placed near the sensor for the temperature controller when that location is remote from the 

location of the MIG thermometer bulb.

5.8 Retort Pressure: Overpressure conditions during processing will influence package 

expansion by constraining the expansion of headspace gases. This may be beneficial by 

improving heat transfer to food in flexible and semi-rigid containers or detrimental by 

restricting the size of the headspace bubble in rotary processes. For steam/air retorts, 

overpressure conditions are also related to the steam content of the heating medium at a 

particular processing temperature which may influence heat transfer conditions within the 

retort. In addition, cooling without overpressure may result in depressurization within a 

container upon collapse of steam at the end of a process, leading to accelerated decreases 

in temperature for fluid foods.

5.9 Coldspot Determination: The location of the slowest heating or coldspot in a container 

is critical to establishing a process. For a conduction heating product in a cylindrical can with 

minimal headspace, the geometric center of the can is considered to be the slowest heating 

spot. Generally, if a larger headspace is included, the coldspot may shift closer to the top of 

the can due to the insulating effect of the headspace which may be significant if the height-todiameter ratio of the can is small. The coldspot location in vertically oriented cylindrical cans 

containing products which heat by natural convection may be near the bottom of the 

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container. Products which exhibit broken heating behavior may have a coldspot which 

migrates during heat processing as the physical properties of the product change. The use of 

containers with different geometries or constructed from different materials may have 

differing effects on coldspot locations. A coldspot location study should be completed to 

determine the slowest heating location for a specific product/package/process combination. 

Usually, the coldspot location will be determined from a series of heat penetration tests 

employing several containers with thermocouples inserted at different locations. Alternatively, 

more than one thermocouple per container may be used; however, multiple thermocouples 

may influence heating behavior, especially for products in smaller containers. In all cases, 

care should be taken to determine the "worst case" anticipated during production. Careful 

judgment, based on a number of preliminary experiments, must be exercised to ensure the 

coldspot location has been identified.

5.10 Initial Product Temperature: Measurement of initial product temperature should be 

taken immediately prior to testing.

5.11 Number of Containers per Test Run: A heat penetration test should evaluate at least 

10 working thermocouples from each test run (NFPA, 1985). If the retort cannot 

accommodate this quantity, the number of replicate test runs should be increased.

5.12 Number of Test Runs: Replication of heat penetration test runs is important in order to 

obtain results which account for run-to-run, product, container and process variability. After 

initial coldspot determination tests are completed and all critical factors have been 

determined, at least two full replications of each test are recommended. Should results from 

these tests show variation, a minimum of a third test is recommended. Variation in the results 

is expected and quite common, especially for products which are non-homogeneous or 

exhibit complex heating behavior. Variability is generally evaluated based on plots of the 

heating and cooling curves and/or lethality calculations and should be considered when 

identifying or predicting the slowest heating behavior of a process.

6.0 SUMMARY OF DOCUMENTATION

The following provides a summary of details which may be incorporated in a checklist and 

documented in their entirety or partially as deemed appropriate for a specific study. Other 

factors not listed in this section may also be relevant. 

6.1 Pre-test Documentation:

6.1.1 Product Characteristics 6.1.1.1 Product name, form or style, and packing 

medium

6.1.1.2 Product formulation and weight distribution of components

6.1.1.3 Net weight and volume

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6.1.1.4 Consistency or viscosity of the liquid component

6.1.1.5 Size, shape and weight of solid components

6.1.1.6 Size of solid component clusters

6.1.1.7 pH of solid and liquid components

6.1.1.8 Methods of preparation prior to filling (ingredient mixing methods, special 

equipment)

6.1.1.9 Matting tendency

6.1.1.10 Rehydration of components

6.1.1.11 Acidification procedures

6.1.1.12 Other characteristics (% solids, density, etc.)

6.1.2 Container Description

6.1.2.1 Container material (brand name and manufacturer)

6.1.2.2 Type, size and inside dimensions

6.1.2.3 Container test identification code

6.1.2.4 Maximum thickness (flexible container)

6.1.2.5 Gross weight of container

6.1.2.6 Container nesting characteristics

6.1.2.7 Slowest heating or coldspot location in container

6.1.3 Data Acquisition Equipment and Methodology

6.1.3.1 Identification of datalogging system

6.1.3.2 Thermocouple and connector plugs maintenance

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6.1.3.3 Thermocouples and connectors numbered

6.1.3.4 Electrical ground checked

6.1.3.5 Thermocouples placed in heating medium and readings compared with 

a reference TMD

6.1.3.6 Type, length, manufacturer and identification code of thermocouples and 

connectors

6.1.3.7 Thermocouple location in container

6.1.3.8 Positioning technique for thermocouple

6.1.3.9 Calibration data for each thermocouple

6.1.4 Fill Method

6.1.4.1 Fill temperature of product

6.1.4.2 Fill weight of product

6.1.4.3 Headspace

6.1.4.4 Filling method (comparison to commercial process)

6.1.5 Sealing Operations

6.1.5.1 Type of sealing equipment

6.1.5.2 Time, temperature, pressure and vacuum settings (if applicable)

6.1.5.3 Gas evacuation method

6.1.5.4 Can vacuum

6.1.5.5 Volume of residual gases in flexible containers

6.1.6 Retort System

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6.1.6.1 Retort system: still or rotary (end-over-end, axial, oscillatory)

6.1.6.2 Reel diameter (number of container positions) and rotational speed

6.1.6.3 Can position study data for batch rotary retorts

6.1.6.4 Heating medium (steam, steam/air, water immersion, water spray) and 

flow rate

6.1.6.5 Circulation method for water or overpressure media

6.1.6.6 Temperature distribution records

6.1.6.7 Retort venting schedule

6.1.6.8 Retort identification number

6.1.7 Loading of Retort

6.1.7.1 Loading or racking system details

6.1.7.2 Location of test containers in retort (slowest heating zone)

6.1.7.3 Container orientation

6.1.7.4 Location of thermocouples for retort temperature

6.1.7.5 Use of ballast containers to ensure fully loaded retort (some retort 

systems)

6.1.7.6 Selected time interval for data logging system

6.1.8 Additional Information

6.1.8.1 Date

6.1.8.2 Test identification

6.1.8.3 Processor and location

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6.1.8.4 Individual(s) performing heat penetration test

6.2 Test-Phase Documentation:

6.2.1 Test run identification

6.2.2 Initial temperature of product at the start of heating

6.2.3 Time heating starts

6.2.4 Time vent closed and temperature, if applicable

6.2 5 Temperature indicated on MIG thermometer

6.2.6 Time retort reaches set point temperature (tc)

6.2.7 Pressure from a calibrated pressure gauge or transducer

6.2.8 Time process begins

6.2.9 Time cooling begins (pressure cooling, if applicable)

6.2.10 Time cooling ends

6.2.11 Rotation speed (if applicable)

6.2.12 Cooling water temperature

6.2.13 Any process irregularities or inconsistencies

6.3 Post-Test documentation:

6.3.1 Container net and gross weight check for leakage

6.3.2 Thickness of container

6.3.3 Location of the thermocouple and whether or not it is impaled in a food 

particle

6.3.4 Measurement of container vacuum (rigid metal and glass) or residual air 

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content (flexible and semi-rigid containers)

6.3.5 Post-processing product characteristics: syrup strength, appearance, 

viscosity, headspace, drained weight, pH, consistency, shrinkage, matting, 

clumping

6.3.6 Container location and orientation (jumble pack)

7. LITERATURE CITED

ASTM. 1988. Standard Guide for Use in the Establishment of Thermal Processes for Foods 

Packaged in Flexible Containers. F 1168-88. American Society for Testing and Materials, 

Philadelphia, PA.

Bee, G.R. and Park, D.K. 1978. Heat penetration measurement for thermal process design. Food 

Technol. 32(6): 56-58.

CFPRA. 1977. Guidelines for the Establishment of Scheduled Heat Processes for Low-Acid Foods. 

Technical Manual No. 3. Campden Food Preservation Research Association, Chipping Campden, 

Gloucestershire, UK.

Ecklund, O.F. 1956. Correction factors for heat penetration thermocouples. Food Technol. 10(1): 43-

44.

IFTPS. 1992. Temperature Distribution Protocol for Processing in Steam Still Retorts, Excluding 

Crateless Retorts. Institute for Thermal Processing Specialists, Fairfax, VA.

NFPA. 1985. Guidelines for Thermal Process Development for Foods Packaged in Flexible 

Containers. National Food Processors Association, Washington, DC.

Pflug, I.J. 1975. Procedures for Carrying Out a Heat Penetration Test and Analysis of the Resulting 

Data. University of Minnesota, Minneapolis, MN.

• Prepared by The Committee on Heat Penetration Institute For Thermal Processing 

Specialists Approved for Publication Nov. 10, 1995

• The Institute for Thermal Processing Specialists is a non-profit organization established 

exclusively for the purpose of fostering education and training for those persons interested in 

procedures, techniques and regulatory requirements for thermal processing of all types of food or 

other materials, and for the communication of information among its members and other 

organizations.

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• Part of the mandate of the IFTPS Committees is to develop protocols to be used as guides for 

carrying out the work of thermal processing specialists. This is the first such protocol prepared by 

the Committee on Temperature Distribution and reviewed extensively by members of the Institute. 

The protocol has been approved by the Board of Directors. This document may be photocopied 

in its entirety for use. 

• Single copies of the protocol, as well as information on membership in IFTPS may be obtained 

from: Institute for Thermal Processing Specialists, 304 Stone Rd. W. Ste. 301, Guelph, ON N1G 

4W4 Phone: (519) 824 6774 Fax: (519) 824 6642, E-Mail: info@iftps.org

 

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OPERATIONS IN THE THERMAL PROCESSING 

AREA

OPERATING PROCESSES

9 CFR 431.5(a) requires that a LACF manufacturer post the operating processes and 

venting procedures to be used for each product and container size being packed in a 

conspicuous place near the processing equipment, or place the processes where they 

are readily available to the retort operator and to the Consumer Safety Inspector (CSI). 

During the CSI’s verification checks, it must remember that the firm’s operating 

process may be different than the firms scheduled process for the same product. Many 

firms employ an operating process of one to two degrees above their filed scheduled 

process temperature and one to two minutes longer then the filed process time to 

compensate for minor fluctuations in the steam supply and possible improper 

employee setting or reading of timing devices. This process is called the firm's 

operating process. If the operating process exceeds the scheduled process, a drop of

time or temperature below the operating process is not a process deviation if the drop 

is not below the scheduled process. The firms scheduled process should be used to 

evaluate the thermal process for that product.

INITIAL TEMPERATURE

Initial temperature (I.T.) is defined in 431.5(c) as the average temperature of the 

contents of the coldest container to be processed at the time the thermal processing 

cycle begins, as determined after thorough stirring or shaking of the filled and sealed 

container.

The initial temperature of the contents of one container to be processed must be 

determined with sufficient frequency to ensure that the temperature of the product is no 

lower than the minimum initial temperature specified in the filed scheduled process. 

The regulations do not require that the initial temperature of each retort load of product 

be checked. The closer that a firm operates to the minimum initial temperature in the 

filed scheduled process the more critical measurement of the initial temperature at 

frequent intervals becomes.

When initial temperature is measured in those products which incorporate frozen 

ingredients extra care may need to be taken to insure that the temperature reading is of 

the (average) temperature of the contents of the container and not just the temperature 

of the covering liquid. Initial temperature may have a significant effect on the thermal 

process delivered to the product, and the effect may be determined only through the 

analysis of process establishment data for that product.

Initial temperature is normally determined using a dial, electronic or other type of hand 

held thermometer. Glass stem thermometers are normally not used to determine initial 

temperature because of the potential risk of breakage. Firms have attempted to use 

pyrometers to measure initial temperature with mixed results. The use of pyrometer's 

to measure the outside temperature of a container to determine the initial temperature 
of a process requires adequate studies by the firm to document a correlation between 

outside container temperature and the actual product initial temperature in the 

container.

When determining the initial temperature of containers being processed by steam, a 

container is normally selected from one of the first containers going into the bottom 

layer of the first retort crate. This container is then set aside where it is not subject to 

extreme changes in temperature. At the time that the retort lid is closed and the steam is 

turned on the initial temperature in the container is determined. This same procedure is 

normally acceptable for all batch type retort systems except as noted. For those retort 

systems using water to cushion the fall of containers into the retort, or where water is in 

the retort prior to the addition of the containers, provisions must be made to insure that 

the temperature of the water does not lower the initial temperature of the containers. In 

those instances where water comes in contact with the containers prior to beginning the 

thermal process, the initial temperature of the process may be either the temperature of

the contents of the container or the temperature of the water in the retort, whichever is 

the lowest. In systems that use cushion water, such as the crateless retort system, the 

initial temperature may be the temperature of one of the last containers to enter the 

retort, if the cushion water is maintained at a high temperature. For continuous retort 

systems a container should be obtained just prior to entry into the retort system for 

initial temperature determination.

Line breakdowns and processing delays may cause the initial temperature in containers 

to fall below the minimum scheduled initial temperature. During inspections of LACF

manufacturers the investigator should determine the firm’s procedures for handling 

product in the event of thermal processing delays. When a product is placed into a retort 

that has to be cooled to restart the process, or to move the product to a second retort for 

processing, a new initial temperature may have to be determined.

CRITICAL FACTORS-MEASUREMENT EQUIPMENT

A variety of equipment is used to measure critical factors including: scales, 

thermometers, gauges, and consistency-meters or devices. The accuracy of the 

equipment must be documented by the LACF manufacturer. There is no specific 

requirement in the LACF regulations that equipment used for the measurement of 

critical factors be checked for accuracy and calibrated as necessary. Good 

judgment however dictates that equipment used to measure critical factors be 

accurate. The investigator can determine the accuracy of scales, thermometers and 

gauges used to determine critical factors by making comparison measurements 

during the factory inspection. It is suggested that the manufacturing firm also 

make accuracy checks on their scales and thermometers on a routine basis and that 

records of these checks be made. If a thermometer used to determine initial 

temperature or a scale used to determine fill weight is found to be out of 

calibration, the thermal process for the product for which the device was used may 

be in question back to the date that the measuring device was last checked for 

accuracy.
TIMING DEVICES

Devices used to time retort thermal processes must be accurate. Pocket and wrist 

watches are not considered satisfactory for timing purposes. Even though wrist and 

pocket watches may be accurate, one problem noted with the use of wrist watches is 

that several people involved in separate portions of the thermal process may use wrist 

or pocket watches with different times of the day. When this happens the thermal 

processing records do not correspond to each other. A large wall clock which can be 

read from all areas of the thermal processing room is the best method for timing 

thermal processes. If more than one clock is used in the thermal processing area they 

both should be set to the same time of day. During the inspection of LACF

manufacturers the accuracy of the timing clock should be checked with an accurate 

stop watch.

431.5(d) states digital clocks may be used if the operating process and the venting 

schedule have a 1 minute or greater safety factor over the scheduled process and venting 

schedule. If the digital clock reads out to the second this requirement is not necessary. 

When timing clocks are read, the method used must be conservative to insure that the 

time of vent, come up time, the time of thermal processing, and other operations are 

carried out for the required time interval. Except in those instances where automatic 

equipment is used to record times, the operator normally records operations in the 

thermal processing area in full minutes (e.g., 7:15). If time is not recorded to the 

second that the operation takes place then the operator must record the time for the 

beginning of the operation at the next full minute and the time for the end of the 

operation to the last full minute to insure that the full required time for an operation is 

achieved (e.g., if the retort vent is turned on at 07:10:15, the operator would record 

07:11 and if the retort vent was turned off at 07:10:15, the operator would enter 07:10). 

Operations in the retort room must be monitored during the inspection to insure that 

timing of the operations are accurate. Use of a stop watch by the investigator insures 

that accurate time intervals are measured.

CONTROL OF RETORT TRAFFIC

431.5(b) defines that traffic in the retort room and processing area must be controlled to 

prevent unprocessed LACF from circumventing the thermal process. The retort area 

should be designed so that product enters one end of the processing area and leaves the 

opposite end. This can be done in several ways depending upon the retort system in use. 

For batch retort systems a routine procedure should be designed by the firm to stage 

unprocessed product in an area separate from processed product. When multiple vertical 

retorts are arranged in rows or rings, the product should enter the row or ring at a 

different location than product exits the ring or row. In systems using continuous 

conveyors or chains to move the product through the retort system the entry and exit of 

product should be physically separated if possible to prevent the mixing of processed 

and unprocessed containers. Containers which are found to be on the floor or off of 

normal conveying equipment should be destroyed.

Crates and containers of LACF products must be identified in a manner which will 

readily identify the status of the product. One method of identifying the status of LACF

product containers is through the use of thermal indicators. Thermal indicators are 
placed on the containers, on one container in a retort crate, or on the retort crate itself. 

Thermal indicators may be impregnated onto a paper tag to be attached to a retort crate, 

painted onto the surface of a container or crate, incorporated into a tape to be placed 

onto a container or crate, or incorporated into an ink jet spray which is applied by the 

can manufacturer or canning firm. Some container manufacturing firms incorporate 

thermal ink into a container manufacturing code which is placed on each container. 

Thermal indicators can be purchased to meet the temperature range of the thermal 

process being used. Thermal indicators do not however indicate that an adequate 

thermal process has been applied to the LACF product, only that the product has been 

subjected to a heat source. The thermal indicators should be examined following 

processing and written records of changes in thermal indicators should be made. In lieu 

of thermal indicators the firm can use other effective means of visually distinguishing 

between processed and unprocessed containers.

STEAM SUPPLY

Although other methods of heating LACF are being developed, steam is the 

predominant heating medium used to process LACFs. The steam may be used to 

directly or indirectly heat the products or containers. Steam in modern canneries is 

normally produced in remote steam boilers. Two common types of steam boilers or 

generators found in canneries are the fire-tube and water-tube. Smaller boilers of the 

"packaged" boiler type are almost always fire-tube boilers, and in physical appearance 

are unusually long and relatively low. Such boilers are often referred to as "scotchmarine" or "marine" type boilers. Larger boilers which have been constructed in place 

are almost always water-tube boilers, and are usually nearly square and quite high,

some times 4 or 5 stories high. The fire-tube boiler is operated at pressures normally 

under 150 psi. One advantage of the fire-tube boiler is the large water storage capacity. 

Because of this feature, wide and sudden changes in steam demand are met with little 

change in pressure. Watertube units on the other hand are capable of considerably higher 

overloads. Boilers may be fired using a variety of fuels including, natural gas, liquid 

propane gas, fuel oil, coal and wood. The method of firing the boiler may have an 

impact on the steam pressure supply and recovery time.

Boiler or steam generator capacities are normally listed in terms of horsepower or lbs of 

steam per hour. The term horsepower is defined as the ability of the unit to change 

approximately 34 lbs of water at 212° F to 34 lbs of steam at 212° F. If boiler capacity 

is given in pounds of steam per hour it can be converted to equivalent number of horse 

power by dividing by 34.5. The rated capacity of a boiler is not an absolute measure of 

the amount of steam that can be generated. Fire tube boilers may be operated at 135 to 

150% of the rated capacity and water tube boilers may be operated at 150 to 200% of 

capacity. Operation of the boiler depends upon proper maintenance of the boiler. A 

boiler with heavily encrusted scale in the tubes or one which is not properly fired may 

not be able to even meet the rated capacity of the boiler. This is usually beyond the 

ability of the investigator to determine.

Steam pressures in the main steam line (header) may vary depending upon the 

operation of the boiler(s) and the demand upon the steam supply. Boilers are normally 

operated by either of two methods, use of modulating burners, or on-off operation of 
the boiler. Modulating control is normally used in larger installations. Small plants 

usually operate by on-off operation of one boiler; if additional boilers are used they are 

normally fired at a fixed rate. The pressure gauge on the main steam line should be 

watched over a period of time to determine if there are large fluctuations in steam 

pressure. Modulated systems will normally have only small variations in the steam 

supply; however the variation in on-off systems can be quite large. A reserve steam 

capacity is sometimes obtained by operating the boilers at a high pressure (150 psi) and 

using a reducing valve to reduce the steam pressure to (100 psi) at the retort steam 

supply header.

Steam header pressure at the retorts of 100 to 125 psi is recommended for best 

performance. Lower steam pressures can provide for adequate operation of retort 

systems if the steam supply valve and plumbing of the retorts is carefully selected. 

Temperature distribution testing in the retort system should be performed on these 

systems to document adequate operation under the highest plant steam demand. The 

greatest steam demand for retort systems normally occurs when the maximum number 

of steam retorts are being vented or during the heating or come-up period of other retort 

systems. A standard three or four crate vertical still steam retort can require from 2,500 

to 6000 lbs of steam per hour (depending upon the size of the steam inlet) during 

venting. One-fourth to one-half of the total steam demand of the retort is required for 

venting. The steam demand of the retort rapidly drops to 100 to 150 lbs per hour after 

the vent is closed and the retort reaches processing temperature. Other retort systems 

have similar peak demands during the initial heating phases of the retort and product. 

The steam supply to the retorts must take into consideration the maximum number of 

retorts to be vented or brought to processing temperature at one time and any other 

equipment, such as blanchers, steam kettles, steam peelers, and steam exhaust boxes, 

which may have a steam demand at the same time. The steam demand of the entire 

plant should be taken into consideration during the establishment of venting and comeup schedules for retort systems. Fluctuations in the header steam pressure should be 

correlated with fluctuations in retort temperatures, long vent periods and long come-up 

times in the retort systems.

Most boiler systems require the addition of water treatment chemicals to prevent the 

buildup of scale on the boiler tubes and to prevent corrosion in the boiler system. When 

the steam comes into contact with the LACF, through direct injection of the steam into 

the food; during the exhausting of containers in a steam exhaust box; through injection 

of steam into the headspace of containers to form a vacuum, or through any other 

means, the boiler additives must be approved for use as a food additive and labeled for 

that use as per 21 CFR Part 173.310, Boiler Water Additives.

THERMAL PROCESSING SYSTEMS INSTALLATION AND 

INSTRUMENTATION

Although retort systems vary from still batch type retorts to more complex continuous 

retorts, employ different heating mediums during processing, and may use control 

systems ranging from operator to computer controls; there are still basic equipment 

requirements specified in the LACF regulations 431.6 that are applicable to all retort 
systems.

MERCURY-IN-GLASS (MIG) THERMOMETER

Each retort system used for the thermal processing of LACF(s) must be equipped with 

a MIG thermometer as per 431.6(a)(1)(i). This is emphasized in the LACF regulations

by being repeated for each specific retort system covered 

431.6(a)(1)(ii) allows other temperature-indicating devices, such as resistance 

temperature detectors, used in lieu of mercury-in-glass thermometers, provided they 

meet know, accurate standards for such devices when tested for accuracy.

The MIG thermometer is the reference instrument for all temperature readings, 

including vent temperatures, come-up temperatures and process temperature during the 

processing of LACF(s).

The regulations require that the MIG thermometer be graduated in divisions which are 

easily readable to 1° F (1/2° C) and whose temperature range does not exceed 17° F (8° 

C) per inch (2.54 cm). The thermometer may be graduated in 2° F (1° C) divisions as it 

is possible to read a MIG thermometer graduated in this manner to the nearest 1° F 

(1/2° C). The LACF regulations require that MIG thermometers be tested for accuracy 

upon installation, and at least once per year after that. It is important that the MIG 

thermometer be tested/calibrated at the operating temperature of the retort system (i.e. 

240° F, 250° F, 260° F etc.) and if possible in the heating medium used in the retort. If 

the retort is operated at more than one processing temperature or over a wide range of 

temperatures the MIG thermometer should be checked at all of the temperatures 

normally used for processing LACF(s). The MIG thermometers should be tested 

against a thermometer that can be traced back to an NIST (National Institute of 

Standards and Technology) Standard thermometer. The standard thermometer should

also be checked for accuracy on a routine basis. Documentation should be available for 

the calibration of the standard thermometer used and its last check for accuracy. The 

accuracy of the standard thermometer should be checked at least once every 3 years

depending upon how it is handled and stored.

One way that firms using steam for thermal processing can check their MIG 

thermometers is to use a cross made of 3/4 inch pipe for holding the thermometers with 

1/16 inch holes drilled in the fittings to provide for a flow of steam past the 

thermometer bulb. The cross is then mounted on a retort or steam manifold with a 

certified standard thermometer in the center and one MIG retort thermometer to be 

tested in each of the two outside arms. The thermometers are then allowed to heat to 

equilibrium for 10 to 15 minutes. If an adjustment is needed the face plate screws are 

loosened and the face plate is adjusted on the MIG thermometers. After the adjustment 

another reading is taken to insure that the thermometer is now reading the same as the 

standard MIG thermometer.

The installation of the standard thermometer in the retort next to the MIG thermometer 
to be checked and the use of a circulating laboratory oil bath are also acceptable 

methods used to check MIG thermometers for accuracy.

Records should be kept of the accuracy check of all MIG thermometers which include 

the date of the last check, the person performing the check, the standard used, the 

method used, and the amount of correction needed to bring the thermometer back into 

calibration. The regulations recommend that each thermometer be identified with a tag, 

seal or through some other means that identifies the date on which the last accuracy test 

was made. The MIG thermometer must at least be identified in a manner that will allow 

the thermometer to be matched with the thermometer calibration records.

MIG thermometers that have a divided column, that are broken, or which can not be 

adjusted must be repaired or replaced immediately.

The MIG thermometer must be installed in a manner that it can be easily read, without 

the operator having to go to extraordinary measures, such as entering a steam flow, 

touching hot equipment, or climbing a ladder to make the reading. If it is difficult for 

the MIG thermometer to be read, the operator will be more likely to use the recording 

chart or some other method to obtain temperature readings, not the MIG as required by 

the regulations.

TEMPERATURE RECORDING DEVICE

The LACF regulations in 413.6(a)(2) require that each retort system be equipped 

with an accurate temperature-recording device. This has been interpreted to mean that 

the recording device provides a continuous record of the temperature in the retort 

system during thermal processing. Common systems found use circular or strip charts 

which are marked with ink pens, electrical sparks, pressure pins, or which are created 

by graph plotters at the time temperature readings are received.

The regulations require that graduations on the temperature-recording device charts 

must not exceed 2° F (1° C) within a range of 10° F (5.5° C) of the processing 

temperature. A working scale of not more than 55° F per inch (12° C per Cm) is 

required within 20° F (10° C) of the processing temperature. A ruler can be used during 

the inspection to determine the firm’s compliance with this part of the LACF

regulations. The object of the chart specifications is to provide a chart which can be 

easily read by the operator and record reviewer. The regulations require that the 

temperature recording chart be adjusted as closely as possible to the reference MIG 

thermometer but to be in no event, higher than the known accurate reference 

thermometer. The working accuracy of most recording devices is at least 1 F (1-1/2o

C). 

In most instances the recording chart can be adjusted to agree with the MIG 

thermometer to within 1 F (1-1/2oC).

The temperature recorder should provide a fine temperature recording line which can be 

easily read to the nearest 1 F (1/2C). A conservative approach should always be taken 

when reading a wide line on a temperature recording curve or line. The temperature 
recorded should always be determined by reading the bottom of the recorded line on the 

temperature chart.

The pen arm on a circular chart recorder should follow the time curve on the chart. 

Failure of the pen arm to follow the time curve indicates that the pen is out of 

adjustment, bent, or that the wrong chart is being used. It is evident that the pen is not 

following the temperate curve on the circular chart when it is noted that the temperature 

curve travels back in time as the pen arm moves up or down on the chart. Some of the 

more common recorders found in use have a mark inside of the chart case for adjusting 

the arc of the pen. The number of the chart to use with the recorder may also be 

stamped inside of the recorder case.

Recorders are driven either by electrical or mechanical wind-up clock mechanisms. If 

driven by a wind up clock the firm must insure that the clocks are wound on a daily 

basis. The recorder chart should be adjusted at the beginning of the production day to 

agree with the time of day. The majority of charts in use can be adjusted to agree at 

least to within 15 minutes of the time of day. The accuracy of the timing mechanism 

should be determined over a designated time interval through the use of stop watch. If 

the timing mechanism is not accurate, the recorder will not provide accurate

temperature recordings of the thermal process.

A means of preventing unauthorized changes to the temperature recorder must be 

provided by the firm. This can consist of a locked recorder box, and/or a posted notice 

from management that only authorized persons are allowed to make changes.

The temperature recorder probe must be installed in the retort in a manner which will 

provide a true recording of the retort temperature. The recorder sensing probe is 

normally installed next to or in the same manner as the MIG thermometer. The recorder 

is then adjusted to the MIG thermometer.

The LACF regulations recommend that each retort system be equipped with a pressure 

gauge that is graduated in divisions of 2 lbs or less. A pressure gauge is necessary for 

observing the pressure during pressure cooling, and processing over-pressure in those 

systems using air or steam to create pressures higher than those created by the system 

temperature. The pressure gauge is also an extra safety device which lets the operator 

know if excess retort pressure is being created.

Vents are large pipes, located opposite the steam entry on steam retorts, used to expel 

the air from the retort prior to beginning the thermal process. Retort systems other than 

steam retorts sometimes identify a purge valve, used for removing air from the system 

to allow for the addition of water to a processing drum or for the rapid introduction of 

steam to a steam-air retort, as a vent valve. The valves on these systems do not serve 

the same function as the vent valve on a steam retort. The operation of the vent or purge 

valve may be critical to the thermal process achieved in the retort system. Bleeders are 

small openings required on steam retorts to remove air from the retort during 

processing, promote circulation, and remove condensate from specific retort systems. A 

bleeder is also necessary to ensure adequate steam flow past thermometer bulbs. They 
should be open at all times during venting, come-up and thermal processing. Bleeders 

must be installed in a manner that allows the operator to observe that they are 

functioning during operation of the retort. 

Mufflers are mechanical devices placed on bleeders or vents of steam retorts to reduce 

the noise of the escaping steam. If mufflers are used the LACF manufacturing firm 

must have information on hand in the form of temperature distribution data or other 

documentation, such as a letter from the manufacturer, that shows that the mufflers do 

not impede the flow of steam.

STEAM CONTROLLERS

Automatic steam controllers are required by the LACF regulations 431.6(a)(3) for all 

retort systems. The automatic steam controller may operate independently of or in 

conjunction with the temperature recorder. Steam controllers are of two main types: 

on/off or modulating. With an on/off system the steam valve is either fully open or fully 

closed. In a system with an on/off steam valve you would expect to find fluctuations in 

the temperature curve produced by the temperature recorder. Modulating systems control 

the steam valve to proportionally supply steam to the system as needed.

One method of retort temperature control found prior to the current LACF regulations 

in some U.S. LACF plants, and still found in LACF plants in foreign countries, is the 

operator manually controlled steam valve. In these retort systems the operator observes 

the steam pressure on a retort pressure gauge and/or the retort temperature on a MIG 

thermometer, or on some other type of thermometer. The steam valve is then opened 

and closed by the retort operator to maintain the required steam pressure or 

thermometer readings. In some plants where this type of control has been used, it has 

been noted that by assigning one operator to each retort, the steam supply to the retort 

can be controlled to provide for a consistent temperature. The retort temperature control 

is dependent upon the operator observing the retort steam pressure and/or temperature 

constantly. This type of steam/temperature control does not meet the requirements of 

this section of the regulation.

The temperature of saturated steam of high quality bears a fixed relationship to its 

absolute pressure (psia). In most instance steam is measured as gauge pressure (psig), 

which has its zero point at 14.7 psia (equivalent to atmospheric pressure at sea level). 

15.1 psig (Pounds per Square Inch Gauge Pressure) of steam at sea level is equal to 

250F. Attachment 1 is a table which provides the corresponding gauge pressure and 

process temperatures at various altitudes. Gauge pressures above those listed for the 

corresponding temperatures may indicate air pockets in a steam retort system.

One of the oldest methods of temperature control in steam retort systems is the use of 

the relationship between steam pressure and temperature in the retort. In this type of 

control system a pressure line is connected between the retort and a steam control 

valve. The diaphragm on the control valve is opposed by a spring which pushes against 

the valve stem and opens the valve. When the steam is turned on to the retort the steam 

pressure in the retort is low and the steam control valve is forced open by the spring 

tension. As the pressure/temperature in the retort rises, steam pressure against the 

diaphragm forces the steam valve to close, and less steam is supplied to the retort. As 
the pressure/temperature in the retort fluctuates the valves opens and closes to modulate 

the steam supply to the retort. This type of controller may provide for adequate 

temperature control if it is well maintained. You will normally see fluctuations in the 

temperature recorder curve as the pressures changes in the retort and steam supply. 

Firms using this type of controller normally operate several degrees above their filed 

scheduled process temperature to account for fluctuations in the temperature in the 

retort.

Control of steam supplies to retorts has been reported using valves which are connected 

to the steam header. One type of valve is actuated in one direction by a lever arm with 

adjustable weights, operating against an opposing fixed spring. In another type the 

valve is set to open a fixed amount by adjusting the compression of a moveable spring, 

operating against an opposed fixed spring. If the steam header pressure does not 

fluctuate appreciably, these will perform satisfactorily. If the header pressure does vary, 

the retort pressure/temperature will vary also; for these valves are essentially steam 

pressure ratio valves.

For example: Assume that the header pressure is 105 psig when a valve of this type is 

adjusted to hold 15 psig (250 F) in the retort. If the header pressure drops to 90 psig at 

any time, the retort pressure will drop to 12.5 psig (245 F).

(P1-P2)/P2 = pressure ratio therefore (105-15)/15 = 6

and (90-15)/X = 6, or X = (90-15)/6 = 12.5 psig

For this reason in those systems which use these types of controllers it is important to 

observe the retorts operate through several cycles to determine if temperature 

fluctuations are being caused by fluctuations in the steam supply. Using this type of 

steam controller to supply steam to more than one retort would not meet the 

requirements of 431.7(a)(3). Fluctuations in temperature control should be documented 

during the inspection. Records should be reviewed to determine if process deviations 

have occurred because of fluctuations in steam supply to the retorts. 

Self-actuated steam supply/temperature control valves which operate directly off of the 

pressure generated in a liquid/vapor filled temperature sensing tube are available for 

temperature control in industrial situations. In this type of control system the vapor 

generated by the heating of the liquid in the temperature sensing bulb is used to exert 

pressure on the diaphragm of the steam control valve. The pressure on the diaphragm is 

opposed by a spring. As the liquid heats up in the sensing tube the gas pushes on the 

valve diaphragm causing the valve to close. As the temperature drops the spring forces 

the valve open. Different liquids are used to fill the sensing tube depending on the 

temperature range to be controlled. The system temperature would be adjusted by 

adjusting the spring tension on the steam control valve. This type of temperature

control is not normally found on retort systems.

One of the most common types of retort temperature control systems found in the U.S. 
is the pneumatic (air to open) steam control valve (Attachment 2). This valve is opened 

by supplying air to a diaphragm which is connected to the valve stem. The valve is 

closed by spring pressure on the valve stem. The valves are air-to-open for safety 

reasons. If the power or air supply fails, the loss of air to the system results in the steam 

valve closing and the retort pressure/temperature falling. These valves are commonly 

connected to a mechanical recorder/controller which controls the supply of air to the 

valve (Attachment 2) when using the mechanical recorder/controller a temperature bulb 

in the retort is connected through a thermal tube to a Bourdon tube located in the 

control panel. The temperature changes in the retort cause the Bourdon tube to expand 

and contract.

Expansion/contraction of the Bourdon tube causes the recording arm to move which 

also controls the amount of air to the control valve. As the temperature in the retort 

rises, the supply of air to the valve diaphragm would be reduced, the spring would force 

the valve partly closed and less steam would be supplied to the retort. As the 

temperature in the retort starts to fall, more air is supplied to the valve diaphragm and 

the valve is forced open, with more steam being supplied to the retort.

Pneumatic air controlled valves are also common in many advanced computer 

controlled retort systems. In these systems the air supply to the steam control valve is 

usually controlled through an electronic solenoid.

With any retort using air for control of the system it is very important that the air supply 

to the instruments and control valves be kept clean and free of oil, water, rust and other 

contaminants. It is ideal for the air supply to the instruments to be separate from the air 

supply to the rest of the plant. This air supply should be equipped with devices for 

keeping the air clean, such as air filters, condensate traps, water drains and oil traps. 

Maintenance of the air supply system on a routine basis is essential to the continued 

accurate operation of pneumatic air controls.

A simple mechanical/electrical control system for an electronic solenoid operated steam 

control valve may consist of a temperature dial to set the selected retort temperature, a 

temperature sensing element in the retort which is connected to a Bourdon tube or some 

other type of expanding gas or liquid sensor, and a steam supply valve which is 

controlled by air, an electric solenoid or rotary motor. These systems act much the same 

way that a thermostat in your house would be used to control the temperature. As the 

set temperature in the retort is reached the expansion of the liquid/gases in the 

temperature sensing element causes the Bourdon tube to expand, expansion of the tube 

causes electrical contacts to open or close, depending upon the design of the control

mechanism. As the electrical contacts close an electrical source is supplied to an 

electronic solenoid or motor to operate the valve. This type of system may supply steam 

in an on/off fashion instead of proportionally.

A similar type system would replace the Bourdon Tube with a solid state electronic 

temperature controller using a thermocouple or resistance temperature devices (RTD) to 

sense the temperature in the retort. The solid state electronic circuits would then be set 

to control the retort at the selected operating temperature through the use of an 

electronic solenoid, solenoid/air or electric motor operated steam control valve. The 
solid state circuits may provide for on/off or proportional operation of the steam valve 

depending upon the control system and manufacturer.

In systems using RTDs or thermocouples a low level electrical signal is sent to a 

control mechanism. It is important not only for a firm to properly calibrate the 

RTD/thermocouple but to insure that the electrical signal sent to the sensor is not 

interfered with. The circuits (wires) used to transmit the signal to the signal convertor 

or sensor must be designed and installed to prevent electrical interference on the circuit. 

Electrical interference on the circuit can cause false readings to be received from the 

RTD/thermocouple. The firm should have in place a system for routine calibration and 

maintenance of RTD's and thermocouples including the complete control circuit.

MECHANICAL/ELECTRICAL TIMED RETORT CONTROL SYSTEMS

Addition of a manually set electrical/mechanical clock to the pneumatic air/electrically 

controlled valve systems mentioned above provides for timing of the retort thermal 

process. An additional mechanical/electrical clock for the timing of the vent cycle on 

steam retorts further automates the system. These systems are designed so that both a 

time and temperature must be reached for venting; the process timing does not start 

before the process temperature is reached, and the process ends after the set process 

time has been reached. These systems still require the observation and manual recording

of MIG thermometer readings and processing times.

In 1948 Taylor Instrument Co. supplied the LACF industry with the first fully 

automatic controlled retort systems. Other manufacturers have introduced similar 

systems since that time. These systems use electronic/mechanical clocks, stepping 

switches electronic relays, pressure switches, solenoid valves and temperature sensors 

to provide for automatic/pneumatic control of vent valves, bleeder valves, cooking 

times, over-pressure, cooling water, cooling times, and draining of the retort. The 

operators function is to set the process time, the thermal process temperature, and the 

vent times to meet those of the operating thermal process. In order to start the process 

the operator only has to push a start button. The control of the retort thermal process is 

then through the controller. The system may be equipped with a series of lights which 

indicate when the steam is turned on, when the process is up to temperature (start of 

thermal process) and when the retort is in the cooling phase. The operator is still 

required to observe and manually record MIG thermometer temperature readings, 

processing times, vent times and other factors critical to the process. At the end of the 

process the timing clocks are automatically reset to the preselected times. The system is 

then ready for the next thermal process.

Because these systems are fully automatic, including the operation of the bleeder 

valves, maintenance of the system is often neglected. Failure to adequately maintain the 

system can result in failure of bleeder valves, vent valves and system controls to 

operate properly. When these types of retort control systems are encountered the 

investigator must observe the operation of the system through several cycles to insure 

that all control valves are operating properly, that bleeder valves are fully open and 
functional during the venting and thermal processing cycles, and that scheduled process 

time and temperature parameters are being met.

Cam operated control systems have been used by U.S. and European equipment 

manufacturers to automatically control retort processing including processing 

temperature, pressure, processing times and cooling times. In these systems a cam is cut 

out of plastic, metal or some other durable material. As the cam is turned by an 

electrical/mechanical clock a cam follower rides upon the cam and operates a series of 

electrical sensing switches. The electrical switches are used to operate electrical and/or 

pneumatic control valves which supply steam and air to the retort or serve other 

functions such as venting of the retort. Care has to be taken to cut the correct profile in 

the cam to provide the correct thermal process. As the cam wears the profile may 

change, changing the thermal process.

European manufactures such as LaGarde and Stock have used card readers to control 

retort temperature, retort pressure and process timing. In these systems a card made of 

plastic, metal or paper is either cut or punched to a certain profile for each thermal 

process. The card is then placed in a card reader. In the LaGarde system the card is read 

by a light source. As the card passes through the reader the light source activates limit 

switches. In the Stock system the card comes into contact with the limit switches as is 

passes through the card reader. The limit switches control the signals sent to the control 

valves which may be either electronically or pneumatically controlled. The profile of 

the cards are very important. Care has to be taken to punch or cut the correct profile for 

each thermal process. If the profile is not cut correctly for the process the correct 

process will not be provided. The cards also become worn or damaged during use and 

care must be taken to maintain the cards in good working condition.

DIGITAL ELECTRONIC CONTROLLERS

In recent years digital electronic controllers have replaced the relays and sensing 

switches of mechanical/electrical control systems. Digital control systems may range 

from the single-loop controller to complex high-end computer systems.

If the process to be controlled consists of numerous sequential (logical) steps, the 

controlling device can be a first-level computer device called a logic controller. The 

logic controller may be set up as a single loop controller.

A single loop controller would be responsible for controlling one function such as 

temperature in the retort. The controller loop would be programmed to control the retort 

temperature within set temperature parameters. The loop would consist of the 

microprocessor controller, a sensor, and actuator for the steam valve and a 

digital/analog signal converter. The simple single loop controller contains Read Only 

Memory (ROM) which is manufactured into the controller or programmed into the 

controller by using Programmable Read Only Memory (PROM), Erasable 

Programmable Read Only Memory (EPROM), or Electronically Erasable 

Programmable Read Only Memory (EEPROM). PROM is field programmable by the 

manufacturer or customer one time only by burning out fuses in the PROM 

microprocessor chips. EPROM is electronically programmed by the manufacturer or 
user. EPROM microprocessor chips can be reprogrammed by exposing the chip to an 

ultraviolet light source which resets the original chip configuration. EEPROM 

microprocessor chips can be reprogrammed by electronically erasing the memory on 

the chip. ROM is normally used to control processes where the options of the customer 

or operator do not need to be changed.

Random Access Memory (RAM) using battery backed volatile memory components is 

another type of memory component. This memory requires a power supply but lends 

itself to modification and reprogramming. Advanced microprocessor or computer 

systems would normally use a combination of ROM and RAM to program control of 

retort functions.

A more advanced system would use a programmable logic controller (PLC) which 

would allow the operator or firm to alter the control limits of the controller. This type of 

controller would use algorithms (a programmed procedure for solving a problem) to 

control the loop. Algorithms are written to provide the microprocessor with a logical 

sequence of events for solving a problem.

Control of multiple parameters such as temperature, pressure, rotation, etc may be 

controlled by installation of several loop controllers controlled by one PLC,

microprocessor or computer.

With the advancement of technology, defining the differences between 

microprocessors, minicomputers and mainframe computers has become more difficult. 

Size is usually the distinguishing factor. The size of the computer needed for control 

depends upon the number of loops to be controlled and whether the system is set up as 

an independent (each retort control system is self standing), centralized (one computer 

controls all retorts), or a distributed system (two or more computers talking to each 

other).

In the independent system each retort would be controlled by its own PLC or 

microprocessor. If one of the retort control systems failed the remainder of the systems 

would continue to operate.

In a centralized system all data would be collected and analyzed by a central 

computer. This provides for quick capture of all processing information and for control 

from a central location. Failure of this control system would mean that all processing

systems would be down.

In the distributed system a PLC or microprocessor can be used for independent control 

of each retort system. The retort microprocessor is then used to supply information to a 

systems computer which captures all retort data for storage and printing. The systems 

computer in turn is used to store process programs and to program the logic controls of 

the microprocessor.

Computer controlled retort systems may be marketed with one or more peripherals 

added to the basic PLC or microprocessor. Peripherals may include: keyboard or key 

pads for programming and entering information, printers for printing stored and 
captured in-process information, personnel computers for programming the PLC, CRT 

(touch screens) for monitoring the process and entering information, and modems 

which allow for connections to remote computers for programming or trouble shooting.

During inspections of LACF manufacturers using computers to control thermal 

processes or to control other factors critical to the process the investigator must 

determine the functions of the computer system.

In many cases LACF manufacturing firms will not have on hand detailed information 

covering the development and validation of the software and microprocessors used on 

their retort systems. Many firms buy the microprocessors as black boxes from the 

equipment vendor. The investigator must then determine the functions of the control 

system in as much detail as possible. It is important to remember that computer 

controlled retort systems must function to provide for control of the thermal process, 

the same as any other type of control system. The mercury-in-glass thermometer is still 

the reference thermometer as per the LACF regulations. The operator is required to 

read and record mercury-in-glass thermometer readings the same as for any other 

control system (these may be entered into a computer record). Each retort system is still 

required to be equipped with a temperature recorder as per the LACF regulations. This 

recorder must provide a continuous record of the thermal process; must meet the 

specifications of the LACF regulations; and must not record a temperature higher than 

the MIG thermometer reading. It is important to determine that the system is 

controlling the retort to meet the requirements of the firms filed scheduled processes for 

time and temperature; that critical factors such as rpm's in agitating retorts and come up 

time in water immersion retorts are being controlled; and that vent times and 

temperatures for steam retorts are being adequately controlled. If the firm has a 

schematic drawing of the control system this should be obtained or the investigator may 

prepare a simplified schematic drawing, which will be helpful in explaining the system 

operations. If the firm does not have detailed information on the microprocessor control 

system the investigator should obtain any limited information that is available. At a 

minimum this would include the vendor and model numbers of the computer control 

system and the functions performed by the computer control system. Observation of the 

system as it operates can be used to determine if critical factors such as RPM, vent 

times, temperatures, pressures, and thermal process times are being adequately

controlled by the microprocessor. This may require observation of the system through 

several thermal process cycles. The investigator should determine who is responsible for 

programming the system, how the system is programmed, the name and number of 

programmable functions, if the programming functions are password or otherwise 

protected and who is responsible for record review and process verification.

It is also important to determine if the operator has the ability to override any of the 

computer control functions. If operator override of computer functions are possible, 

details on how this is done, what overrides are possible, and how this is reflected in the 

thermal process record should be determined.

The investigator should determine how the system handles process deviations during 

thermal processing. If the computer system is able to calculate new processes or chose 

alternate pre-programmed processes the investigator must determine the parameters for 
computing or selecting the alternate process.

During inspections where microprocessor or computers are being used to control thermal 

processes in retorts the CSI should determine at a minimum:

1. The equipment specifications for software and hardware.

2. The critical factors that are controlled by the system.

3. How the critical factors are controlled.

4. How does the firm ensure that the microprocessor or computer is indicating the 

correct information (validation).

5. How, and how often is the equipment calibrated and/or checked for accuracy.

The references "Guide to Inspection of Computerized Systems in Drug Processing" 

Feb. 1983, U.S. Dept. of Health and Human Services, Food and Drug Administration 

and "Software Development Activities" July, 1987, U.S. Department of Health and 

Human Services, Food and Drug Administration, should be used as guides to inspecting 

firms using complex computer controlled retort systems (these guides are currently 

undergoing revision). DEIO also has in process 'Guide to Inspection of Computerized 

Systems in the Food Processing Industry.

An example of a parameter that could be under digital electronic control is pressure in a 

retort, which is normally controlled by adding or releasing air from the retort. A 

common method for pressure control is the use of a pressure sensor to transmit a signal 

to a pressure controller. The pressure controller will then send signals to position the air 

supply and pressure release valves. Control of pressure through addition and release of 

air allows for a more uniform pressure control in the retort. The valves used in pressure 

control may be pneumatic, electric or a combination of these types. Control of other 

factors critical to the proper operation of the retort system, such as water level in water 

immersion retorts, water circulation in cascading & spray water systems, and RPM's in 

agitating retorts may be monitored and controlled by a variety of methods, including 

mechanical, electrical and combination systems.

It is important to remember that the system used must provide assurance that the retort 

system is operating in a manner that the scheduled process will be delivered to the

LACF product.

RETORT VALVES

A variety of valve types may be used on retort systems including:

PLUG COCK VALVE - This valve consists of a tapered plug with a vertical slot which 

fits into a tapered valve body. Full flow is obtained when the opening in the tapered 

plug faces in the direction of flow. When the plug is rotated a quarter of a turn, flow is 

stopped. Opening and closing the valve is usually accomplished by using a wrench or 

lever applied to the valve stem. Plug cock valves are noted on retort bleeders and may 

be used on retort vent lines.

GATE VALVE - Gate valves are full flow valves normally used to start or stop flow. A 
gate (sliding shut-off wedge) within the valve body is raised and lowered through a set 

of threads on the valve stem. The valve is operated by turning the valve stem counter 

clockwise to open the valve and clockwise to close the valve. These valves are usually 

either fully open or fully closed during service. When fully open the gas or fluid flows 

through the valve in a straight line with very little resistance to flow. This feature 

makes the valve ideal for use in the vent lines of steam retorts, where rapid removal of 

air may be important to proper temperature distribution. A gate valve can normally be 

recognized by a long stem, by the number of turns of the valve stem that it takes to 

close the valve (more turns are needed for a gate as compared to a globe valve), and 

sometimes by the appearance of the outside of the valve body (more square when 

compared to a rounded globe valve). If the gate valve cannot be identified in this 

manner the valve stem may have to be removed to identify the type of valve.

GLOBE VALVE - Globe valves are extensively used for the control of flow and where 

positive shut off is required. A globe valve employs an internal seat within the valve 

body. Hand operated globe valves are operated by turning the valve stem counter 

clockwise to open the valve and clockwise to close the valve. Threads on the valve 

stem cause the seal on the valve stem to mate with or move away from the valve seat. 

Close control over flow is readily accomplished. As the fluid or gas moves through this 

type of valve it must change direction. This results in increased resistance to flow. For 

this reason this type of valve is not ideal for venting of steam retorts. Globe valves are 

ideal for use on water and air lines where close control over flow is required. Globe 

valves have a positive shut off feature which can prevent leakage of air and water into 

retorts during processing.

BALL VALVE - Ball valves are quick opening, full flow valves, needing only a quarter 

of a turn to be fully open. A ball with a non-restricting port rides in a valve body on 

plastic non-sticking seats. Ball valves can provide a bubble tight seal. The ball valve 

can be used for full flow (venting), and control (water and air supply) functions on 

retorts.

BUTTERFLY VALVE - Butterfly valves are quick opening, full flow valves which 

employ a metal disk which when rotated on a shaft seals against seats in the valve body. 

Butterfly valves are normally used as throttling valves to control flow. Butterfly valves 

may be found on some of the newer retort systems

DIAPHRAGM VALVE - Diaphragm valves contain a moveable diaphragm within the 

valve body which fits against a valve body seat. When the diaphragm is raised or 

lowered by the valve stem flow is increased or decreased through the valve. Diaphragm 

valves may be found on some of the newer retort systems.

Valves may be operated by hand, pneumatically (by air, steam or other gas), electrically 

(by a solenoid or motor) or by a combination of these methods.

Free flow valves such as the gate or ball valve are normally used on steam retort vent 

lines. The use of globe or other type valves on steam retort vent lines is not prohibited 

by the LACF regulations. If these types of valves are used, temperature distribution 

studies are required to document adequate temperature distribution in the retort prior to 
the start of the thermal process.

Valves which provide a tight seal, such as the globe or ball valve must be used on air 

and water lines to prevent leakage into the retort during thermal processing. Valve seats 

and seals must be maintained to prevent the valves from leaking. During a LACF

inspection the retort should be examined for evidence of leaking water and air valves. 

Some firms may employ the use of double valves on air and water lines to insure that 

no air or water is leaked into the retort during processing.

TEMPERATURE DISTRIBUTION

Temperature distribution is the work performed to ensure that the retort instrumentation 

accurately reflects that adequate temperature distribution has been achieved throughout 

the retort at the time that the sterilization cycle begins. This is accomplished by 

distributing an adequate number of thermocouples or other temperature measuring 

devices (TMDs) throughout the load (external to the containers), and making several 

runs or tests to ensure that temperature differences have been minimized. The number 

of thermocouples (TMDs) to be used is normally limited by the equipment available. A 

minimum of 12 thermocouples has been suggested by The Institute for Thermal 

Processing Specialists. With large retort systems and numerous retort crates a greater 

number of thermocouples may allow for a more extensive test to be completed. At least 

one thermocouple is placed next to the MIG thermometer and used as a reference 

during the study. The worst case situation for temperature distribution normally occurs 

when heat flow to the product is the greatest. The heat absorption rate of a convection 

heating (heat currents are formed in the container) is much higher than a conduction 

heating (heat must penetrate through the material) product. It is normally suggested that 

a convection heating product in the smallest container processed or a special cold water 

pack be used to test temperature distribution in still retorts. Other conditions may 

present the worst case for temperature distribution in a specific retort system or for a 

specific product or container type. This must be documented in the temperature 

distribution study. In some retort systems temperature distribution tests must be

performed for each container type (e.g. glass, metal, plastic), for each container size, for 

each container racking system, for each container shape, for each product produced and 

for each individual retort system.

Acceptable temperature ranges in the retort at the time that the process begins varies 

with retort systems and products. Normally you would expect to find all thermocouples 

(TMDs) within 1oF of the processing temperature at the time the process timing begins 

for still steam retorts. For water immersion retorts you would normally expect to find 

all thermocouples (TMDs) at or above the set point temperature and no greater than a 

2oF degree difference between the minimum and maximum TMD. Other conditions 

may be acceptable to meet the requirements of adequate temperature distribution in a 

particular retort system. These conditions should be documented in the temperature 

distribution study. Equipment and procedures which fail to provide adequate 

temperature distribution in a retort system prior to start of the process must be modified 

to provide adequate temperature distribution.

There must be documentation on hand at the LACF plant, from the processing 
authority, which specifies the come-up procedures (e.g. venting, cut-up time) to be 

employed to ensure adequate temperature distribution is achieved at the time that the 

thermal process or sterilization cycle begins. The firm must employ the same 

procedures during production as were used to establish the temperature distribution in 

the retort.

Among the factors which may affect temperature distribution are:

Initial temperature of the product

Loading configuration (retort crate and retort)

Retort geometry

Steam spreader design

Type of heating media (steam, water immersion, cascading water, water spray, 

steam air etc.)

Circulation of heating medium

Use of agitation

Size, type and location of vent valve in steam retorts

Steam header pressure

In some foreign countries LACF manufacturers attempt to establish the effectiveness of 

the retort by performing heat penetration tests in various areas of the retort, or by 

performing numerous heat penetration tests using a limited number of containers placed 

in different areas of the retort during several different process cycles. This method of 

retort temperature validation has not been accepted by FSIS as being a valid method for 

performing temperature distribution studies. Variations in such things as retort load, 

retort cycles, product fill, and initial temperatures can cause temperature readings 

obtained from thermocouples inside of the containers to vary by several degrees.

A good reference for temperature distribution protocol for steam still retorts has been 

published by the Institute for Thermal Processing Specialists.

Heat penetration, in contrast to temperature distribution, is designed to measure the rate 

of heating of the food product under consideration. In these tests thermocouples or 

other temperature measuring devices are inserted into the containers to measure the 

product heating rate. Not only should the slowest heating container in the test be 

identified, but also the slowest heating zone within any given container. Thus it may be 

necessary to do a preliminary "cold-spot" study to identify the slowest-heating zone 

within the container prior to doing the actual heat penetration test on several containers. 

In addition, the performance of heat penetration work must be based upon adequate 

knowledge of the heat resistance of the microorganism(s) of concern in the specific 

product to be processed. Finally, the heat penetration test must cover all the variables 

expected to be encountered during the course of commercial operation in the plant.

Among the factors which may affect heat penetration results are:

Container position, geometry and heat transfer characteristics.

Type of heating medium

Product factors (e.g. fill weight, viscosity, particle size, percent solids, method 
of preparation)

Equipment factors (e.g. filling method, head space, rotational speed)

The information developed during the heat penetration test is then used along with 

other information such as the heat resistance of the microorganism(s) in question (this 

can be effected by the food being tested), and the numbers of microorganisms expected 

to be present in the product, to calculate a theoretical process.

The theoretical process may be confirmed by using an inoculated pack. In an inoculated 

pack a known amount of an organism with a known heat resistance is placed into each 

container. The containers are then processed at various calculated process times and/or 

temperature(s) and examined for surviving organisms. The objective of the inoculated 

pack method is to determine the time/temperature combination that will kill all of the 

spores added to the product. A similar method called the count reduction method uses a 

procedure which relates the decrease in the numbers of spores from the initial number 

to some final number with process Fo value. Processes may also be established using 

other procedures such as chemical indicators to provide Fo values.

The process should be established by qualified persons having expert knowledge of the 

thermal processing requirements of LACF, and having adequate equipment and 

facilities to make such determinations. All critical factors, including the establishment 

of venting or other come-up procedures to ensure adequate temperature distribution, 

must be investigated by the processing authority. There must be some form of 

documentation on hand at the factory; at least a letter or other similar transmittal from 

the processing authority, which details all factors critical to the delivery of the 

scheduled process.

Should no documentation exist at the plant, every effort should be made to determine 

whether such documentation exists at any location, before leaving the plant.

Should the documentation for the scheduled thermal process be more extensive than a 

letter or other similar document, a preliminary review should be made to determine if 

any of the procedures are questionable (it may not always be possible to accomplish 

this at foreign plants if the documentation is not in English). 

The information from the processing authority should be compared with the operations 

at the firm and with the information which the firm submitted with their scheduled 

thermal process. 

The LACF regulations require that crates, trays, gondolas etc. for holding containers 

must be made of strap iron, adequately perforated sheet metal or other suitable material. 

When perforated sheet metal is used for the bottoms, the perforations should be 

approximately the equivalent of 1 inch holes on 2 inch centers. If divider plates are 

used they should be perforated as above.

Other arrangements can be used as long as there is temperature distribution 

documentation on hand for the equipment in use. It is important for good temperature 

distribution to use a crate with as much open area as possible. The percent open area of 
the crate bottom and the divider plate can be calculated by dividing the total open area 

of the holes by the total area of the bottom or divider plate x 100. A divider plate which 

meets the specification of the regulations (1 inch holes on 2 inch centers) has 

approximately 27% open space. Tightly packed small round containers may cover over 

90% of the divider plate. The holes in divider plates must be carefully designed to 

provide for the maximum heating medium flow between the containers. By using 

closely spaced smaller holes the percent open space can be dramatically increased. The 

crates and divider plates in use should at least be no more restrictive than those used to 

establish the retort operating procedures. When a firm changes the type or design of 

divider plates the effect of the new divider plates must be evaluated by the firms 

processing authority.

If dividers, racks, trays, or other means are used to position flexible containers in place 

they must be designed and employed to ensure even circulation of the heating medium 

around all containers.

Discuss equipment and procedures as they apply to each of the various types of retort 

systems. In addition to the common types of retort systems discussed there are other 

less common types which may be encountered.

When inspecting these systems always review the LACF regulations to determine 

compliance of equipment installation and operation.
1

RETORT SYSTEMS

FOR THERMAL PROCESSING OF LOW-ACID, CANNED FOOD 

(LACF)

Equipment and procedures common to all retort systems has been previously discussed.

The following section will discuss equipment and procedures as they apply to each of the 

various types of retort systems. In addition to the common types of retort systems 

discussed, there are other less common types which may also be encountered.

Always review regulations 9 CFR 431.1-431.12 to determine requirements for equipment 

installation and operations when inspecting these systems.

STILL STEAM RETORTS

Equipment and procedures for pressure processing in steam in still retorts are covered by 

9 CFR 431.6(b)(1) of the LACF regulations.

Still steam retorts (Figures 1 and 6) are identified as vertical, in which the crates are 

lowered by hand or overhead hoist into the retort; horizontal, in which the crates are 

pushed or conveyed into the retort; or crateless (Figure 3), in which the containers drop 

into cushion water in the retort. Vertical retorts vary from small one crate, to retorts 

holding several crates. Vertical retorts are commonly found to be approximately 42 

inches in diameter and to hold 3 or 4 crates of product. Horizontal retorts vary from small 

one crate, to large retorts holding 12 or more crates of product. Retort size normally 

depends upon the size of the firm, the amount of product to be processed at one time, the 

length of the thermal process and the closing capacity of the firm.

Still steam retorts were one of the first types of retort systems used to pressure process 

LACF. Steam under pressure provides a number of advantages for processing LACF 

products in metal containers:

- It is an excellent medium for heat transfer

- Its temperature is easily regulated

- The steam pressure required in the retort in order to achieve the required 

processing temperature serves to counter-balance the pressure built up inside of 

the container during processing.

- Steam can be easily manufactured and held in reserve for immediate use.

- The stored energy property of steam makes it a superior heating medium as 

compared to water or steam-air. The stored energy results from the fact that in the 

manufacture of steam considerable heat (970 B.T.U.'s) is required to change one 

pound of boiling water to one pound of steam at the same temperature. When the 

steam condenses on the containers during processing this latent heat is given up to 

the container. It is important in the operation of still steam retorts to remove air 

from the retort prior to starting the process. Air in the retort acts as an insulator 

around the containers which prevents steam from contacting the container. Air in 
2

the presence of high heat may also cause the containers to rust. Small amounts or 

pockets of air in the retort can cause containers in those areas of the retort to be 

under processed.

-
3

Air is removed from the retort prior to processing through the retort vent and bleeders. 9 

CFR 431.6(b)(1) describes vent plumbing and operating procedures for various vertical

and horizontal still steam retorts. As long as the equipment is installed and operated 

exactly as per the regulations, the vent times and temperatures given are adequate to meet 

the requirements of the regulations for containers in jumble stack (containers randomly 

dropped into the crates) or off-set stack arrangements.

The Grocery Manufacturers Association Bulletin 26L recommends venting schedules 

similar to those found in the regulations. The recommendations found in Bulletin 26L do 

not, however, apply to retort systems which utilize divider plates. Bulletin 26L suggests 

that the venting schedules for still steam retorts using divider plates be obtained from a 

process authority.

Each retort system must be equipped with a steam inlet large enough to provide sufficient 

steam for proper operation of the retort. Steam may enter either the bottom or top portion 

of the retort, but must enter that portion of the retort opposite the vent. This is important 

to provide for adequate circulation of steam and removal of air during the venting of the 
4

retort. It is recommended that the automatic steam control valve be of the same size or 

larger than the steam inlet. This allows the use of the automatic steam controller during 

retort venting. If an automatic steam controller valve of a size smaller than the steam inlet 

line is used, a steam by-pass may be needed during venting and come-up to provide 

enough steam to the retort to rapidly vent the retort. The steam by-pass may be manually 

operated by the retort operator or automatically operated through the retort control 

system. At the time that the retort reaches processing temperature the by-pass valve 

would be closed. Control of retort temperature during processing would be through the 

smaller automatic steam control valve. Use of a smaller automatic steam control valve 

provides for more accurate control of processing temperature with less temperature 

fluctuation.

Steam spreaders which are continuations of the steam inlet line inside of the retort should 

not be larger than the steam inlet line. Steam spreaders are required in horizontal retorts. 

In horizontal retorts, the steam spreader must extend the entire length of the retort. The 

steam spreader should have perforations along the top 90o (that is within 45o on either 

side of top dead center of the spreader). Horizontal retorts over 30 feet long should have 

two steam inlets connecting to the steam spreader. In vertical still steam retorts, a steam 

spreader is not required, however if one is used it should be operational. When used, the 

spreader should be in the form of a cross with perforations along the center line of the 

pipe facing the interior of the retort or along the sides of the pipe. The steam should not 

flow directly onto the retort bottom (this erodes the metal) or directly onto the containers.

Vertical steam retorts are required to have crate supports to prevent the crate from sitting 

upon the steam spreader. 

The number of perforations in steam spreaders should be such that the total cross 

sectional area of the perforations is equal to 1.5 to 2 times the cross sectional area of the 

smallest restriction in the steam inlet. The following table can be used for guidance:

Number of Holes in Steam Spreaders of Steam Inlet Pipe Size

SIZE

HOLES*

(INCHES)

 1”

PIPE

1-1/4”

PIPE

1-1/2”

PIPE

2”

PIPE

2-1/2”

PIPE

3/16 47-62 81-108 111-148 183-244 260-346

1/4 27-36 45-60 62-84 102-137 147-196

3/8 2 1-28 28-37 45-60 66-88

1/2 11-15 15-20 26-36 36-48

*Inside Diameter
5

Vents must be installed in such a way that all air is removed from the retort before timing 

of the process begins. Vents are normally controlled by a gate, plug cock or ball valve, 

which must be fully open during venting. Vents must be installed so that a back pressure 

is not created during venting. Vents must not be connected directly to a closed drain 

system. Vent pipe(s) exits cannot be submerged under water during venting. On those 

retort systems where more than one retort vent pipe from a single retort connects to a 

manifold, the manifold must be of a size that the cross sectional area of the manifold is 

greater than the cross sectional area of all of the connecting vents. The manifold may be 

controlled by one free flowing valve. Where vents from more than one retort or manifold 

pipes are connected to a header, the header must have a cross sectional area at least equal 

to the cross sectional area of the connecting pipes from the maximum number of retorts 

to be vented at one time. The header must not be controlled by a valve. Vent installations 

may differ from the above specifications if the firm has evidence in the form of heat 

distribution data that adequate venting of air is accomplished.

Bleeders are openings in retorts used to remove air entering the retort with the steam, and 

to promote circulation of the steam in the retort. The LACF regulations require that all 

retort bleeders, except thermometer well bleeders, have an inside diameter of no less than 

1/8 inches when fully opened. Thermometer well bleeders are required to have an inside 

diameter no less than 1/16 inch when fully opened. Bleeders must be wide open and emit 

steam continuously during the entire process including the come-up time. The operator 

must be able to observe the operation of the bleeders during processing. If the retort has 

the steam entry in the top of the retort, a bleeder of adequate size must be installed in the 

bottom of the retort to remove the condensate from the retort during processing. The 

condensate bleeder has to be installed in a manner that allows the operator to observe its 

function.

Vertical still retorts are required to have at least one bleeder opposite the steam entry. 

Horizontal retorts are required to have at least one bleeder opening within one foot of the 

outermost location of containers at each end of the retort, and at intervals of no less than 

8 feet along the top of the retort.

As previously noted, each retort system must be equipped with a mercury-in-glass (MIG)

thermometer, a temperature-recording device, and an automatic steam controller. The 

sensing bulbs for the MIG thermometer and the temperature recording device may be 

installed within the retort shell or in an external well attached to the retort. External wells 

or pipes must be connected to the retort through at least a 3/4 inch diameter opening, and 

be equipped with at least a 1/16 inch diameter bleeder to provide for a free flow of steam 

past the thermometer sensing bulb.

Air may be supplied to the still steam retort to provide overpressure during the water 

cooling of containers in the retort. Considerable pressure is built up in the container 

during thermal processing. To prevent buckling (the container ends become permanently 

distorted) of the container overpressure from air or steam is provided during cooling. Air 

overpressure is more easily controlled because the steam tends to collapse in the retort 

headspace. The overpressure must be controlled within limits. Too great a pressure or 
6

cooling for too long will panel (permanently distort the side panels) the containers. The 

air supply line must be equipped with a tight fitting valve (e.g., globe or ball) to prevent 

air leaking into the retort during thermal processing. Generally pressure cooling is needed 

when processing container sizes with diameters above 401 (4 1/16 inches) at 

temperatures greater than 240° F. Smaller containers processed at higher temperatures 

may also require pressure cooling.

CRATELESS RETORTS

Equipment and procedures for crateless retorts, which are still steam retorts (see above), 

are covered by 9 CFR 431.6(b)(1)(ix)(d) of the LACF regulations.

Crateless retort systems are manufactured by Malo Inc., by the FMC Corp. and by others. 

Crateless retort systems are still steam retorts in which the containers are fed directly into 

the retort from a continuous belt (Figure 3). Crateless systems are normally operated in a 

series of from 2 to 6 or more retorts depending upon the firms requirements. One operator 

can normally operate several crateless retorts at one time. Crateless retorts may be up to 8 

feet high and 6 feet in diameter. The capacity of the retort is several times that of the 

normal 3 crate vertical retort (over 10,000 cans for some smaller containers). Container 

size is not limited by the retort design. Prior to filling the retort with containers, the retort 

is filled to approximately half full with preheated cushion water at a temperature which 

will not lower the product temperature below the minimum temperature specified in the 

process schedule. When used, the automatic conveyor system is set to feed the preset

number of containers (depending upon can size) into the retort through the top sliding 

door. A counter counts the number of containers added to the retort. The product 

containers fall into the water to limit container damage. The containers are jumble

stacked in the retort. When the preset number of containers have entered the retort the 

containers are automatically diverted to the next retort to be filled. The hydraulic push 

button operated top sliding door of the retort is then closed. Steam is admitted to the 

retort through a spreader in the top of the retort, forcing out the cushion water which is 

normally collected, reheated, and reused. In some plants the cushion water is gravity 

drained before venting. The drain is left open until all cushion water has been removed 

from the retort and venting conditions met. Newer models of crateless retorts are 

normally equipped with a false bottom door at the exit end (bottom) of the retort. The 

false bottom door is perforated with holes which allow for a flow of steam between the 

false bottom door and the discharge door. The false bottom door also prevents containers 

of product from contacting the condensate which may build up in the bottom of the retort. 

Condensate is removed from the bottom of the retort through a condensate bleeder 

(normally 3/8" or larger) normally located in the bottom door of the retort. A 1/8" bleeder 

is recommended between the false bottom door and the condensate bleeder to provide 

visual assurance to the operator that there is no condensate buildup in the retort during 

thermal processing. Some older systems may still be encountered which do not use a 

false bottom and/or employ a second 1/8" bleeder. These systems should be carefully 

evaluated to determine that the condensate is being removed from the retort during 

thermal processing.
7

After the cushion water has been removed from the retort using the steam forced method, 

the retort is vented for a short period of time (this must be established by a processing 

authority). The processing of the product normally starts when the retort reaches 

processing temperature, but not before a free flow of steam is noted from the 1/8 bleeder 

located between the false bottom door and the discharge door. Failure of condensate 

bleeders to function properly in these retort systems has caused several instances of 

improperly processed LACFs. Condensate buildup in the bottom of the retort may contact 

only a few cans in the bottom of the retort, causing underprocessing of those containers. 

Such a situation can result in a very few cans of underprocessed product in a large lot of 

containers. After the product has been processed cooling water is normally brought into 

the retort to partially cool the product. In some systems, the product is dumped from the 

bottom of the retort into a cooling canal. The discharge door on some systems is below 

the level of the water in the cooling canal. This causes a vacuum to be formed in the 

retort and the cans drift slowly out of the retort into the cooling canal. A chain in the 

cooling canal then moves the container through the cooling water to the unscrambling 

station. In some of the older crateless retort systems, containers were dropped into the 

cooling canal through a vibrating basket on the retort or directly onto a chain conveyor. 

Excessive container damage was sometimes noted in those systems.

 Figure 3
8

STILL WATER IMMERSION RETORTS

Equipment and procedures for pressure processing in water in still retorts are covered by

9 CFR 431.6(c)(1) of the LACF regulations. The requirements for still water immersion 

retort systems (Figures 2 and 4) would also apply to those agitating systems used in the 

still non-agitating mode.

.

Figure 2

Thermal processing of glass, plastic, laminated pouch, and large profile metal containers 

require that an overpressure greater than the pressure created by the retort temperature be 

provided to maintain container integrity. Pressures in the range of 20 to 32 psig are 

normally used for glass containers. When the product in a container is heated to high 

temperatures, pressures exceeding those of the retort can be created in the container. This 

higher pressure is due to the combination of increased vapor pressure and expansion of 

the contents in the container. In the case of small metal cans, the metal can may be able to 

withstand these pressures without permanent distortion of the metal in the can. In the case 

of glass jars and other less durable containers, an overpressure must be used to prevent 
9

the container from venting the contents, or becoming permanently distorted or destroyed. 

The water immersion still retort was first designed for use in processing glass jars. Water 

immersion still retorts are now used to process a variety of containers requiring an 

overpressure. In some cases, the water immersion retort may be used to process small 

metal containers as well. If the water immersion retort is used to process metal containers 

there is some concern with the rusting of containers caused by the addition of air to the 

processing water.

Basically there are four principle differences in a still retort equipped for pressure 

processing in water as compared to a still steam retort:

- Compressed air must be provided to the retort to create the overpressure during 

processing and cooling.

- A pressure control valve must be added to the retort.

- The temperature of the retort must be controlled independently of the pressure.

- The containers are processed and cooled under water.

 

Figure 4
10

The water level in the retort must be maintained to provide water above the top level of 

the containers at all times. It is recommended that the containers be covered by at least 6 

inches of water. If the water level falls below the level of the top containers those 

containers exposed to the steam/air mixture in the top of the retort must be identified and 

set aside for reprocessing or evaluation by a processing authority. A water level indicator 

is required on all water immersion retorts. This can be in the form of a water glass sight 

tube, pet cocks, or mechanical indicator. A low-water alarm (visual & audible) is 

suggested. The operator must observe the water level during processing to insure that the 

water does not drop below the level of the top containers. At a minimum, observations 

should be made and recorded at the start of the process and at the end of the thermal 

process prior to the addition of cooling water to the retort. A non-clogging water tight 

drain valve is required to prevent leakage of water from the retort during processing. It is 

suggested that this valve be screened to protect the valve from being clogged with broken 

glass and other debris.

Heating and circulation of the water to provide for uniform thermal processing 

temperatures in the retort system is important.

Steam introduction into the bottom of vertical retorts can be accomplished in one of 

several satisfactory ways. One way is by using a steam spreader equipped with six pipes 

radiating out from the center with "fish tail" nozzles which direct the flow of steam up 

along the sides of the vertical retort outside of the crates. A second acceptable method is 

to use a 4 legged cross steam spreader in which each pipe is perforated with holes 

directed 15° below horizontal along one side only. The legs are arranged in opposing 

pairs so that the holes face each other to give alternate live and dead quadrants. This 

arrangement provides for circulation of the water in the retort. In horizontal retorts, the 

steam distributor should run the full length of the retort with perforations distributed 

uniformly along the pipe. Several still water immersion retorts of European design inject 

steam directly into the water circulation line to maintain the processing temperature. Any 

of the above, or other methods, are appropriate as long as there is documentation in the 

form of temperature distribution data or other documentation from a processing authority 

that supports the method of heating the water.

Circulation of the water is important to provide uniform temperature throughout the 

retort. Adequate circulation of the processing water by air or pump must be established 

through procedures recognized by a processing authority.

Air is added to the steam supply line prior to the steam spreader in vertical retorts to aid 

in the mixing of the water. As the air is added with the steam, it also prevents steam 

'knock" or "chatter" (a loud bumping sound) in the retort which happens when live steam 

is introduced into water. The air and steam mix to form bubbles out of the steam 

distributor. As the bubble moves up through the water the heat from the steam is lost to 

the water. The air that remains reaches the top of the vertical retort to provide the air 

overpressure. Excess pressure is released through the pressure control valve. A large flow 

of air (15 to 18 cubic feet per minute) is needed during the initial heating and come-up 

phases of the retort. This may be provided through an air bypass line. When the retort 
11

processing temperature is reached the flow of air can normally be reduced to (4 to 5 

CFM). Air flow is normally regulated by placing an orifice in the line which provides a 

certain air flow at a regulated pressure. The air flow to vertical retorts should be 

documented during establishment of the temperature distribution in the retort. The air 

flow should be verified by the establishment using a flow meter at intervals sufficient to 

insure that the retort is operating under the parameters used to establish the temperature 

distribution in the retort.

For horizontal retorts, a water circulation system is recommended. This system uses a 

pump to draw water out of the bottom of the retort through several screened openings 

(suction manifold) and to discharge the water over the entire length of the top of the retort 

through a water spreader. The pump should be capable of circulating the entire volume of 

retort water at least every 4 to 5 minutes. A pilot light is normally used to indicate that 

the pump motor is running. Even though the light indicates that the pump motor is 

running, it does not insure that the water circulation is adequate. Plugged lines, bent 

impellers on the pump and other mechanical problems may not be indicated by the pilot 

light. A flow meter on the circulation line is recommended to provide a true indication of 

water flow in the circulation line. Air must still be added to the horizontal retort to 

provide for the overpressure during processing.

Vertical still water immersion retorts are required to have centering guides, which should 

be installed so as to insure that there is a clearance of approximately 1 1/2" along the side 

of the retort to provide for circulation of the water during thermal processing and cooling, 

in addition to crate supports.

Containers are normally added to vertical retorts that contain water at or near the same 

temperature as the initial temperature of the product. If product in glass jars is subjected 

to water which is too cold, thermal shock may break the containers. If the water in the 

retort is more than 15° F above the temperature of the container, the glass container 

closure may vent product. Water must be added to horizontal retorts after the containers 

are loaded. A separate warm water supply at or near the initial temperature of the product 

which can be used to fill the retorts aids in more rapid production of glass containers. If 

the water added to the retort is below the initial temperature of the containers, measures 

must be taken to insure that the initial temperature in the container is not lowered, or that 

the temperature of the water is used as the initial temperature. Several retort systems use 

hot water storage tanks located above the processing shell. The temperature of the stored 

water is dependent upon the container to be processed, and may range from several 

degrees above the thermal processing temperature for metal cans to only a few degrees 

above the initial temperature of glass containers. Following processing, a portion of the 

processing water is forced back into the upper storage drum and reheated for processing 

the next batch.

Cooling water is normally added to the circulation pump line on horizontal retorts or 

through a cooling ring above the containers in a vertical retort. It is important that glass 

containers are not subjected to a severe thermal shock to prevent glass breakage.

The overpressure must be maintained in the retort until the pressure in the container falls 
12

to levels which do not cause container failure. Overpressure may be critical to the thermal 

process for large profile half steam tray metal container and retortable flexible pouches. 

The overpressure maintains the container profile and holds the container against the 

product allowing for more efficient heat transfer from the container to the product. When 

overpressure is listed as a factor critical to the thermal process, a record of the process 

pressure must be made. The overpressure used during thermal processing should be the 

same as that used during establishment of the thermal process or as recommended by the 

firms processing authority.

It is recommended that the temperature probe in water immersion retorts be located next 

to the MIG thermometer, except in vertical retorts which are equipped with a 

combination recorder/controller. The controller bulb in these vertical retorts must be 

located in the bottom of the retort beneath the lowest crate rest in such a position that the 

steam does not strike it. This should be the coldest spot in the vertical retort. In a 

horizontal retort the recorder/controller probe should be located between the water 

surface and the horizontal plane passing through the center of the retort so that there is no 

opportunity of direct steam impingement on the control bulb.

Some water immersion systems may be set up to process in both steam and water. Those 

systems must be carefully evaluated to insure that they meet the mandatory provisions of 

both sections of the LACF regulations.

CONTINUOUS AGITATING STEAM RETORTS 

Equipment and procedures for processing in continuous steam retorts are covered by 9 

CFR 431.6(b)(3) of the LACF regulations.

These systems provide for continuous container handling with intermittent product 

agitation. Continuous agitating steam retorts are manufactured by FMC (Sterilmatic) in 

the U.S. and Europe and by Stork (Steristork) in Europe. The basic design of both 

systems is similar (Figure 5).

The retort systems are made up of a series of processing vessels called shells. The 

arrangement and number of shells is dictated by the product, production capacity, and

space limitations in the establishment. Common arrangements found include: Two-shell: 

one pressure cooker and one pressure cooler; three-shell: one pressure cooker shell, one 

pressure cooler shell and one atmospheric cooler shell; and four-shell: preheater shell, 

one pressure cooker shell, one pressure cooler shell and one atmospheric cooler shell. 

Specialized systems may have up to seven shells. The shells can be arranged side by side 

or offset end to end depending upon the available establishment space.

Containers are fed mechanically through the series of at least one heating and one cooling 

shell. Within each processing shell is an open, closely fitting rotating reel which runs the 

length of the vessel. Cans are carried horizontally in channels made up of angles, usually 

of stainless steel, welded around the perimeter of the reel. A spiral T-track is welded to 
13

the inside of the shell spaced at intervals slightly larger than the can length. As the reel 

turns the containers are forced against the spiral T which causes the cans to move down 

the length of the retort while being carried by the reel. The containers are fed into the 

processing shell or preheater through a pocket valve; a rotary transfer valve which is 

timed to the reel and designed to prevent loss of steam from the retort (Figure 7).

 Figure 5

 Figure 7

There is a wheel at the exit end of the retort and into a second transfer valve which 

transfers the cans to the next processing or cooling shell while maintaining processing 
14

pressure if needed. All of the shells are driven by one variable speed motor or drive 

mechanism through a series of interconnecting gears to insure that the reels are timed to 

each other. The drive mechanism is required to be locked or protected by a sign that 

states that only authorized persons are to make adjustments.

Because of the physical limitations of the reel and spiral T these retort systems are 

normally limited to a narrow range of can sizes. The length of the can going into the 

retort can not be longer than the maximum distance between the spirals in the T. The 

diameter of the can is limited by the distance between the steps in the reel. The number of 

steps (number of cans around the diameter of the reel) is determined by the can size and 

the diameter of the reel. For the FMC systems these steps are standardized for can sizes 

(unless the system has been altered or custom built). The number of steps can be used 

along with other information to calculate process time.

STEPS PER TURN OF REEL FOR STERILMATIC CONTINUOUS AGITATING 

RETORTS

Can Size

Steps per

Turn of Reel

211 56

300-303 47

307-401 42

404 36

603 24

The container capacity is normally stamped on the end of the shaft of the processing 

shell.

The length of the process is controlled by the capacity of the retort and the speed at which 

the reel is turned. The capacity is determined by the length of the retort shell and the 

number of steps in the reel.

By knowing the retort capacity, the number of steps in the reel and other processing 

information the following formulas can be used to determine reel speed or process time:

Seconds for 10 reel revolutions = (10 rvs) x (60 secs) x reel steps x process time/capacity

Example: (10x60x47x10)/4136 = 68.18 seconds for 10 revolutions

Containers per minute = Capacity/Process Time 

Example: 4136/10 = 413.6 seconds

Revolutions = Capacity/(reel steps x cook time) 

Example: 4136/(47x10) = 8.8 revolutions per minute (RPM)

Seconds for 10 revs = (10 revs x 60 secs x reel steps)/(cans per minute)
15

or (10 revs x 60 sec)/RPM

Example: (10x60)/8.8 = 68.18

The actual process time is determined by using a stop watch and timing 10 revolutions of 

the retort reel. One arm on the retort reel is selected and observed to pass a stationary 

mark on the retort shell for the required number of revolutions. Reel speeds that are too 

fast will cause the product to move through the retort at a faster rate shortening the 

process time. A reel speed that is too slow increases the process time but may reduce the 

agitation of the product and reduce the thermal process given to the product. The process 

is normally designed with the slowest reel speed (minimum agitation) taken into account. 

The rotational speed of the retort shall be specified in the process schedule. The speed 

shall be adjusted as specified, and recorded by the establishment when the retort is 

started, and checked and recorded at intervals not to exceed 4 hours to ensure that the 

correct retort speed is maintained. Alternatively, a recording tachometer may be used to 

provide a continuous record of the speed. If a recording tachometer is used, the speed 

shall be manually checked against an accurate stopwatch at least once per shift and the 

results recorded. A means of preventing unauthorized speed changes on retorts shall be 

provided. For example, a lock or a notice from management posted at or near the speed 

adjustment device warning that only authorized persons are permitted to make 

adjustments are satisfactory means of preventing unauthorized changes.

The standard continuous agitating retort systems are designed to operate over a wide 

range of temperatures up to 275° F (135° C), with custom designs operated at 

temperatures of up to 294° F (146° C).

Steam is fed into the bottom of the sterilizer through a steam manifold to a steam trough 

in the bottom of the retort. The condensate that forms in the bottom of the retort from 

cold containers continuously entering the retort must be removed to prevent the 

condensate from building up and touching the containers. This not only cools the 

containers but may prevent agitation of the product in the containers. Condensate is 

normally removed during venting by opening the drain valve in the bottom of the retort. 

After the retort is up to processing temperature, continuous draining of the condensate is 

through a 3/4 inch drain valve left partly open or through an automatic condensate trap. A 

1/8 inch (minimum) bleeder is required in the bottom of the steam trough to provide 

visual assurance to the operator that there is no condensate buildup in the retort.

Venting of the retort takes place at the beginning of the production period and need not 

be performed again as long as the retort is not cooled. Venting should be performed as 

per the retort manufacturers or processing authority’s instructions. The FMC continuous 

retort is normally vented for 7 minutes to 220° F through the two 2-inch vents located in 

the top portion of the retort shell. If the retort shell has to be cooled for repairs or is 

stopped and cooled for any other reason, the retort must be vented when it is brought

back up to processing temperature.

Air is removed from the retort during processing by the continuous operation of bleeders 
16

which are located within one foot of the outermost product at each end of the retort and 

not more than 8 feet apart along the top of the retort.

Agitation in this system is intermittent axial agitation. The container rotation can be 

divided into three phases (Attachment 7) consisting of fixed reel, sliding rotation, and 

free rotation. The headspace bubble, provided by the gases in the headspace, moves 

through the product to provide agitation and increased rates of heating in the product 

during periods of rotation. Maintaining the headspace filed as part of the process schedule 

insures a headspace bubble. In the fixed reel portion of rotation the container is carried by 

the reel through the top 260° of rotation. During this phase no or little agitation of

products occurs. As the container approaches the lower 140° of rotation in the retort shell,

it starts to contact the spiral "T" welded to the interior of the retort shell and begins to 

turn. This sliding rotation transition phase lasts for approximately 20° of rotation and 

provides some product agitation. As the container enters the lower 100° of rotation (free 

rotation phase), the container contacts the retort shell and rotates freely. The majority of 

agitation occurs in this phase. As the container starts up the side of the retort, sliding 

rotation takes over and changes to the fixed reel phase. Agitation is dependent upon 

control of factors such as: headspace, consistency, reel speed and fill weight which must 

be controlled during processing.

Intermittent agitation will increase the heating rate of the product only if the headspace 

bubble is free to move. Solid pack products will normally not benefit from an agitated 

process. Some manufactures will still use the continuous retort to process products based 

on a non-agitating process because of the convenience of the container handling in the 

continuous system. For products where agitation is not taken into consideration during

establishment of the process, headspace may not be critical to the process.

When checking reel speed there are usually two speeds of concern. During process 

schedule establishment, the minimum reel speed is studied. Then process schedules are

recommended to the manufacturer. When the manufacturing firm sets the retort to meet the 

process schedule, the reel speed may need to be different to meet the process. For example,

the RPM for meeting a time of 15 minutes may be 4.2 RPM whereas the minimum RPM is

3.5. The actual RPM should never be less than the minimum RPM and the actual RPM 

should assure that the process schedule time is achieved.

Following thermal processing in the processing shell, the containers are transferred through 

a pressure transfer valve to either a pressure cooler or an atmospheric cooler depending 

upon process temperature and can size. Some containers can be cooled in a Micro-cool 

valve, where water is sprayed on the containers, to a low enough temperature to allow for 

atmospheric cooling. The pressure cooler and or Micro-cool valve must be operated at a 

pressure at least 2 lbs below that in the processing shell to prevent air and water from being 

forced out of the cooling shell or valve into the thermal processing vessel. The closed 

cooling shell is approximately 2/3 full of water to provide flood cooling of the containers. 

Some systems also use an atmospheric open or half-shell cooler where water is sprayed 

over the containers. The cooling water normally enters the can exit end of the cooling shell 

and flows to an overflow on the can entry end of the cooling shell. This provides for 
17

counter flow cooling of the containers. Additional cold water is added to control the water 

temperature and to maintain the water level in the cooling shell. The temperature of the 

cooling water at the can entry end of the cooler is normally at a very high temperature (> 

200° F) as the hot cans enter the water.

The heating of the cooling water as it passes over the containers tends to drive off chlorine 

if it is used to sanitize the cooling water. A measurable level of chlorine may not be found 

in the cooling water at the water discharge point of the cooler shell. If the quality of the

water in the cooling shells is not maintained by good sanitary practices such as; sanitation 

of the cooling water, routine draining and replacement of the cooling water, and cleaning 

of the cooling shell, excessive microbiological growth in the cooling shells may cause 

post processing contamination.

If the retort jams or breaks down during processing operations, necessitating retort 

repairs, the retort must be operated in a manner that ensures commercial sterility of the 

product. The retort can be operated as a still retort per 431.9(c)(1)(vi)(A)(1). All 

containers can be given a still emergency process using a process supplied by the firms

processing authority. Any containers in the intake transfer valve and any containers in 

transfer valves between processing shells have to be removed, given a still process, 

opened and reprocessed or destroyed. Complete records of the still process must be 

maintained.

If a temperature drop occurs in the retort the temperature drop should be handled per 

431.9(c)(1)(vi)(A)(2). The retort should be equipped with an automatic device to stop the 

reel when the temperature drops to below the specified process temperature. 

If the temperature drop was 10oF or more the reel must be stopped and all of the 

containers must be given a still process as above, discharged and reprocessed, repacked 

and reprocessed or discarded. If the temperature drop was less than 10oF, an authorized 

emergency still process may be used prior to restarting the reel, or container entry to the 

retort can be stopped and authorized emergency agitating process used. Complete records 

of the handling of temperature drops must be made.

These systems may be installed with modifications which will allow unique processing to 

take place. Known system modifications include: the addition of dual spiral construction 

which allows for the processing of two container sizes at the same time using the same 

processing conditions; the use of metal carriers to hold and transport glass containers 

through the system; the use of steam air mixtures to thermally process LACF; and the use 

of the continuous retort system as a water immersion retort with steam over-pressure. 

When modified continuous cookers are encountered, the inspector must insure that the 

retort installation and operation meets the requirements of the firm’s process schedule 

and the LACF regulations.

DISCONTINUOUS AGITATING STEAM RETORTS

Equipment and procedures for pressure processing in steam in discontinuous agitating 

retorts are covered by 9 CFR 431.6(b)(2) of the LACF regulations.
18

These retort systems are batch systems which provide for either continuous axial 

agitation of the product or end over end agitation of the product during thermal 

processing and cooling of the containers. The most common axial agitation batch retort in 

the United States is the FMC Orbital (Orbitort) Sterilizer. This system was designed to 

process large institutional size (603 X 703, #10) cans of medium viscosity products such 

as cream style corn. Other sizes of cans can be processed with modifications to the 

system.

The orbital sterilizer does its pressure processing and cooling in one shell. The sterilizer 

consists of a horizontal retort shell which contains an outer reel to which a spiral has been 

attached, and an inner reel which contains the container channels or steps.

During loading, cans are fed into the retort through a large air-operated gate valve located 

high on the retort wall. The outer spiral reel is locked to the retort shell. The inner reel is 

turning during loading causing the containers to move toward the exit end of the 

sterilizer. 

A counter keeps track of the number of containers loaded into the retort. A second 

counter advances the cans two turns separating processed and unprocessed cans by two 

spiral turns. This is a safety factor to keep unprocessed and processed cans separate. At 

the same time that containers are being loaded, processed containers are being unloaded 

through an air-operated gate valve located low on the exit end of the retort shell. When 

the retort is full the loading/unloading gates are closed, the outer "spiral" reel is locked to 

the inner "channel" reel holding the containers in place during thermal processing and 

cooling.

The retort is vented per the processing authority or equipment manufacturers’

recommendations. Documentation that adequate venting is achieved must be kept on file 

by the processor. At the time that steam is turned on, the drain must be left open for 

sufficient time to remove the steam condensate from the retort, and provision should be 

made for continuing drainage of the condensate during the retort operation. It is important 

to remove the condensate so that the containers do not contact condensate build up in the 

bottom of the retort which could cool the containers during thermal processing.

During thermal processing any air coming in with the steam is removed from the retort 

through bleeders located within one foot of the outermost container on each end of the 

retort and no more than 8 feet apart along the top of the retort or through some other 

arrangement proven to be satisfactory by temperature distribution studies.

At the conclusion of the thermal processing cycle, cooling water is introduced into the 

retort while the containers are still being agitated. When the product is cooled the retort is 

ready for emptying and reloading.

The product agitation in this retort system is produced by forcing the head space bubble 

through the product at very high (approximately 35 RPM) reel speeds (Figure 8). High 

speed rotation is possible because the containers are locked in place. The speed of the 
19

retort must be adjusted as necessary to agree with the speed of the retort listed in the 

process schedule. The rotational speed as well as the process time must be recorded for 

each retort load. A recording tachometer may be used to provide a continuous record of 

retort rotational speed. The accuracy of the recording tachometer shall be determined and 

recorded at least once per shift by checking the retort or reel speed using an accurate 

stopwatch. A means of preventing unauthorized speed changes on retorts shall be 

provided. For example, a lock or a notice from management posted at or near the speed 

adjustment device warning that only authorized persons are permitted to make 

adjustments are satisfactory means of preventing unauthorized changes. 

Figure 8

Factors critical to obtaining the induced agitation in these systems include: maintaining 

the correct headspace, product consistency, minimum machine vacuum in vacuum 

packed products, maximum fill-in or drained weight, and percent solids as specified in

the process schedule.

DISCONTINUOUS AGITATING WATER IMMERSION RETORTS

Equipment and procedures for processing in discontinuous agitating water immersion 

retorts are covered by 9 CFR 431.6(c)(2) of the LACF regulations.

These are batch retort systems which provide for continuous product agitation by 

movement of the head space bubble during thermal processing. Agitation in these 

systems is normally induced through end over end rotation of the container (Figure 8) as 

opposed to the axial rotation of the container in the FMC continuous and orbital retorts 
20

previously discussed. Because of the rotational axis of various containers in the baskets 

during processing, the containers against the outside walls of the basket may receive 

more agitation than those in the center of the basket.

Discontinuous agitating water immersion retorts are manufactured by AlIpax Products 

Inc. in the United States under an agreement with the Maskinfabrikken Phoenix 

subsidiary of the Klinge group in Denmark. Known manufacturers of these systems in 

Europe include: Herman Stock in Germany, Lubeca in Germany, and Phoenix in 

Denmark. All of these systems are or have been available for installation in the United 

States through U.S. distributors. The Stock Rotomat is one which has been distributed for 

a number of years, with numerous installations in the U.S. and world wide.

The majority of these systems operate in a similar manner. These systems can be found 

with a wide variety of valve types and plumbing arrangements. The valves and plumbing 

may be changed for custom installation by the manufacturer or installer of the equipment 

to provide additional functions or for better operation of the system. Many of the early 

Rotomat retorts were equipped with on/off steam control valves which have been 

replaced with modulating steam control valves to provide for better control of the retort 

temperature. Retort systems now entering the U.S. are often modified to meet the U.S. 

requirements for MIG thermometers and instrumentation, and to replace the control 

valves on the retort. The configuration of the retort must be carefully reviewed during 

inspection of these systems.

Discontinuous agitating water immersion retorts can be used for the processing of 

numerous container types including: metal cans, glass jars, and plastic containers and 

unusual container shapes such as semi-rigid plastic bottles, flexible pouches and halfsteam table trays.

The processing system consists of two pressure shells or drums, one sitting on top of the 

other. The top drum is used to store and preheat the processing water. The lower drum is 

the processing drum (Figure 9).

Containers are loaded into crates or specially designed racking systems depending upon 

the container type. The crates are then loaded into a reel within the lower retort shell and 

locked into place during processing.

Water in the upper drum is heated by steam prior to processing. The temperature of the 

stored water is dependent upon the type of container to be processed, and may range from 

several degrees above the thermal processing temperature for metal cans to only a few 

degrees above the initial temperature of glass containers. Storage drum temperature may 

be critical to achieving adequate temperature distribution. To achieve correct temperature 

distribution in the retort, the firm must meet the minimum temperature requirement.
21

Figure 9

Processing in the Rotomat retort system is designed to proceed through a series of 

programmed phases which may consist of several steps within each phase. The steps 

normally encountered include:

- Heating of the upper storage drum

- Sterilization I - in older models this includes dropping the heating water and 

heating the water to processing temperature, in later models this involves only 

dropping the processing water.

- Sterilization II – in earlier models this is the sterilization (hold) phase, in the later 

models this is the heating phase to process temperature.

- Sterilization III – this is the sterilization phase in later models.

- Pressure cool I – this is the initial cooling phase where the process water is 

recaptured

- Pressure cool II – this is the final cooling stages.

- Open door – retort is ready for unloading 

The phases and steps used may vary with the make of retort system used, the model of 

the retort used, the control system used, and the product being processed. It is important 

to determine the retort steps and sequencing during the inspection. This information 

should be compared to the information in the process schedule.

These retorts may be equipped with a wide range of control systems depending upon the 

manufacturer, model and customer specifications including: manual controls, semi-
22

automatic electronic relay controls, electronic card readers, electronic pre-programmed 

logic controls and microprocessor controls.

At the beginning of the sterilizing cycle, water from the pressurized upper drum is 

dropped into the lower processing drum through a connecting pipe and valve. At that 

time, the circulation pump begins to circulate the water by drawing the water out of the 

bottom of the retort through a suction manifold (also called the "circulation channel") and 

returning the water through a distribution manifold in the top of the lower drum. The 

returns located in the bottom of the retort shell should be screened to prevent debris from 

entering the water circulation system. As the water is circulated, it passes through a steam 

injection chamber where live steam is injected into the water to maintain processing 

temperatures.

When water enters the lower drum, air must be expelled to make room for the water. This 

is done through a purge valve (some times called a vent valve by the firm). If the purge 

valve is not open for a long enough time period, air will remain in the lower drum and the 

lower drum will take a longer time to fill with water. If the purge valve is open too long, 

the hot water will flash to steam, and water and steam will be lost out of the purge valve 

lowering the temperature in the processing vessel. This may cause the come-up period to 

be extended to reach processing temperature, and has been reported in some cases to 

affect temperature distribution in the retort system. The length of time that the purge 

(vent) valve is open is determined by the processing authority and normally programmed 

into the retort controls as a set time period.

The come-up time (CUT) prior to processing is very important in this type of retort. 

During the CUT the retort is brought up to processing temperature and the water 

temperature throughout the retort is stabilized at or above the process schedule

temperature. This may require a CUT which extends beyond the time when the 

processing temperature is first reached, as indicated by the retort instrumentation. Usually 

both a time and temperature are required to be met to fulfill CUT requirements. If CUT is 

used in establishing the process schedule, it must be part of the process and controlled as 

a critical factor. If CUT is only critical based on the temperature(s) and time(s) required 

to achieve adequate temperature distribution, it is not part of the process but still must be 

controlled and recorded as part of the processing record. CUT varies by retort model and 

make, and for different products.

In the sterilization (hold) phase, the product is held for at least the minimum time at the 

minimum temperature specified in the process schedule.

When the thermal process is complete cold water is introduced into the lower drum 

through the water distribution system or through a separate pump. This cold water forces 

a portion of the hot processing water back up into the top storage drum where it is 

captured and reheated for the next process.

The water circulation pump is the principle device for insuring adequate temperature 

distribution in the retort. Temperature distribution and heating programs are normally 
23

established at the maximum flow rate. If the water distribution system becomes clogged 

or the pump is damaged or worn, the flow rate may decrease. Severe drops in flow rate 

may be indicated by temperature drops in the retort. However, this may not be the case 

for less severe flow rate changes. Most of the systems are equipped with at least a pilot 

light that indicates that the pump is in operation. Some of the newer systems also 

incorporate a pressure differential alarm, which measures the difference in pressure from 

one side of the pump to the other, and alarms if the pressure differential falls outside of 

preset limits. Neither of the above methods measures the actual water flow in the system. 

A flow-indicting device is recommended for this purpose.

Rotation in the retort may be fixed at one speed, allow for selection of several speeds, or 

may be variable over a wide range of speeds. The newer systems may allow for rotation 

to be in either direction, to provide a rocking motion agitation, and provide for the 

baskets to be in different positions during come-up and processing. The systems are 

normally operated between 6 and 46 RPM. For those systems which do not take agitation 

into consideration when establishing the process, it is still recommended by some 

authorities that the reel be rotated at a minimum speed to enhance mixing of the 

processing water and to maintain proper temperature distribution. Temperature 

distribution must be documented for those systems operated in the still mode. Timing of 

the rotation is done either through the use of a stopwatch and observation of rotation of 

the driving mechanism on the rear of the retort, or through the use of a recording 

tachometer. The accuracy of the recording tachometer shall be determined and recorded 

at least once per shift by checking the retort or reel speed using an accurate stopwatch.

The rotational speed of each retort load must be recorded.

Overpressure during processing (to maintain container integrity) is supplied to the 

majority of these systems by using compressed air. The majority of the retorts are 

equipped with both a valve for supplying additional air and a valve for releasing excess 

pressure (small vent or purge valve). This allows for more uniform control of 

overpressure processing. The Stock systems normally use steam pressure in the upper 

drum to provide over-pressure through a connecting valve to the lower drum. Stock 

systems can also use air for overpressure if requested by the customer. Stock claims that 

when steam is used in the lower shell to provide an over-pressure that deviations are not 

normally caused by lower than normal water levels in the processing shell of agitating 

retorts, as the head space will provide a steam processing medium. There is some 

question as to whether the head space is pure steam or a mixture of steam/air which may 

not provide a uniform temperature. When lower than normal water levels are noted, the 

manufacturer should treat the process as a processing deviation; requiring the 

reprocessing of the product, the destruction of the product or the review of the thermal 

process by a processing authority unless there is documentation on hand to support 

processing with lower than normal water levels.

The majority of the systems noted have been equipped with a water sight glass or 

mechanical indicator of water level in the retort as well as being equipped with electronic 

alarms for low-water levels.

Adequate temperature distribution in the batch agitating water immersion retort is 
24

dependent upon such factors as the proper functioning of the centrifugal pump, rotation 

of the reel, and the number of cages in the retort. A minimum number of cages full of 

containers (e.g. 3 cages in a 4 cage retort) is required to maintain the water level in the 

retort. The number of cages also affects the CUT (come-up time) to the processing 

temperature. If the minimum number of product filled crates are not available the firm 

may use ballast (e.g. containers filled with water) to fill the additional crates required. In 

addition, the open area provided by divider plates or spacers, as well as the cages or racks

themselves, can have an affect on adequate temperature distribution. Any change to a 

more restrictive-to-flow design in any of the above must be validated by new temperature 

distribution studies. Temperature distribution may be affected by container type, 

container size, racking configurations, number of containers in the retort, product being 

produced and many other variations in thermal processing. Because of the many variables 

that can influence temperature distribution in these retorts in some cases each retort, each 

containers type, each racking system and each container size will have to be evaluated to 

determine their effect on temperature distribution.

Delivery of the process schedule is also dependent upon the control of critical factors 

such as: headspace, product consistency, fill-in or drained weights, vacuum in vacuum 

packed products, minimum net weights, percent solids and other critical factors identified 

in the process schedule.

HYDROSTATIC RETORTS

Equipment and procedures for pressure processing in steam in hydrostatic retorts are 

covered by 9 CFR 431.6(b)(4) of the LACF regulations.

Generally the hydrostatic retort can be thought of as a still steam retort operated at a 

constant temperature through which containers are conveyed by a continuous carrier 

chain at a constant rate designed to provide the correct process time (Figure 10).

Figure 10
25

Hydrostatic retorts are manufactured by the FMC Corporation in the U.S. and by Stork 

and others in Europe. Newer designs now offer end over end or axial agitation of the 

product; the use of overpressure for the maintenance of container integrity; the ability to 

process glass and flexible pouches; and water as a heating medium in addition to steam. 

The systems are used for high volume products which need long cook times such as 

condensed soups and pet foods.

The name hydrostatic is derived from the fact that the pressure in the steam dome is 

counter balanced by water in the entry and exit legs of the retort. The higher the water 

level, the higher the pressure and temperature obtained in the steam dome. For example, 

the water height in the water legs must be 37 feet high at sea level to counter balance a 

processing temperature of 250° F (121° C). Operating at temperatures above 250° F will

require a higher water level. The retorts can be operated below the maximum temperature 

as long as the pressure remains high enough to prevent water contact with the containers 

in the steam dome.

Start up procedures for a hydrostatic retort requires venting of the retort and bringing the 

water in the feed legs up to temperature. This procedure takes a longer period of time 

than the venting of still steam retorts. The hydrostatic retort is normally operated for 

periods of up to several weeks and may be shut down and cooled only when required for 

maintenance or repairs.

These retort systems are very large and normally extend several stories into the air. 

Containers are loaded into a horizontal carrier on the continuous chain and conveyed up 

to the inlet leg of the sterilizer. The inlet leg is filled with water which counter balances 

the pressure in the steam dome. The temperature of the water increases as the container 

moves from the top of the inlet leg down toward the steam-water interface at the bottom 

of the leg. Water temperature in the inlet leg may range from ambient to boiling. The feed 

leg may contribute to the process lethality by increasing the initial temperature of the 

product. If process lethality is claimed for the inlet leg of the retort, the water temperature 

in the inlet leg must be carefully controlled. The container is conveyed through the steam 

water interface into the steam dome. The number of times that the carrier passes through 

the steam dome as well as the speed of the carrier determines the process time. Traveling 

from the top of the steam dome to the bottom, and vice-versa, is referred to as one pass. 

Hydrostatic retorts with 2, 4, 6, and 8 passes are common. After traveling through the 

steam dome the containers are conveyed into the exit water leg where the temperature 

decreases as the container passes up the leg. The cans leaving the steam dome are heated 

to a high level and give up their heat to the water in the discharge leg. This results in 

several situations depending upon the design of the retort:

- The water in the discharge leg ranges from 215° F near the steam-water interface 

to 212° F near the top of the leg, and the water quietly boils and steam is 

discharged from the top of the leg.

- Cross circulation pumps are used to pump the hot water from the base of the exit 

leg to the base of the inlet leg and from the top of the inlet leg to the top of the 
26

exit leg, stabilizing the temperatures in the legs.

- Water is pumped from the base of the exit leg through a heat exchanger with the 

cooled water being returned to the top of the exit leg.

Any of the above three methods of operation are acceptable.

As the container exits the leg it is exposed to atmospheric pressure, and it may pass 

through a series of water spray coolers to further cool the product. The conveyor chain 

carries the containers back to near the loading station where the processed product is 

unloaded from the continuous carrier. Because the container inlet and exit are close 

together, care must be taken to insure that unprocessed containers do not become mixed 

with processed containers. Containers found on the floor or elsewhere whose status is 

questionable should be destroyed.

Control of the water levels in the feed and exit legs are important to maintain the 

hydrostatic pressure in the retort. The water level is normally controlled through a 

differential pressure controller which adds water when it is needed and dumps excess 

water from the legs. Water level fluctuation in the feed and exit legs may be caused by 

fluctuations in the feeding and discharge of containers. As more containers are fed into 

the container conveyor more water is displaced from the legs, a lack of production results 

in a lack of containers in the legs and the water level falls.

Hydrostatic retorts have been installed with up to 3 carrier chains operating in the same 

steam dome. This allows for the production of different can sizes at the same temperature 

by adjusting the process time through the speed of the conveyor. Carrier chains designed 

for cans can normally be used to process a number of different diameter cans within 

limits (e.g., 211 - 303, 404 - 603).

Steam is fed into the steam dome, depending upon the manufacturer, either in the center 

or top of the steam dome. Standard temperature or pressure controllers are normally used 

to control the retort temperature. The control of retort temperature through the use of a 

water level float has been used on some European systems.

9 CFR 431.6(b)(4)(i) requires that the MIG thermometer be installed in the retort steam 

dome near the steam-water interface. This should be the coldest spot in the retort dome. If 

the thermal process is based on lethality gained in the feed or exit water legs, a MIG 

thermometer is required to be installed near the bottom temperature recorder in each 

water leg (Figure 11).

9 CFR 431.6(b)(4)(i) requires the installation of additional temperature recorders near the 

top and bottom of each hydrostatic water leg if the process schedule specifies 

maintenance of particular temperatures in the water legs.

9 CFR 431.6(b)(4)(iv) requires the hydrostatic retort to be equipped with at least one 

bleeder 1/4 inch or larger at the top of the steam chamber or chambers at the opposite end 
27

of steam entry. In addition, all bleeders must be arranged in such a way that the operator 

can observe that they are functioning properly.

The carrier conveyor in the hydrostatic retort may be numbered so that the location of the 

carriers can be determined during processing. Carrier location becomes important if the 

retort temperature/pressure falls to a level where the containers contact the water. The 

retort should be equipped with an automatic stop if the temperature drops below the 

minimum process schedule temperature. If the retort is stopped at that point, the operator 

can identify those carriers in contact with the water. The containers in the affected 

carriers can then be set aside for reprocessing, destroyed or held for evaluation by a 

processing authority.

The carrier speed is controlled for each container conveyor through a variable speed 

motor. Carrier conveyor speed may be measured by the number of flights per minute 

using a stop watch or electronically by a sensing probe. Electronic measurement of the 

conveyor speed should be verified by using a stop watch on a routine basis. The correct 

container-conveyor chain speed can be determined in the following manner.

1. The desired carriers-per-minute is determined by dividing the desired process 

time into the number of carriers in steam. Number of carriers in steam = Carriersper-minute Process time in minutes

2. Calculate the actual carriers-per-minute rate by timing 50 carriers with a stop 

watch. Divide this time in seconds into 3,000 to get actual carriers per minute.

3,000/Second for 50 carriers = Carriers-per-minute 

 Figure 11
28

CASCADING WATER RETORTS

Equipment and procedures for processing in cascading water retorts are covered by 9 

CFR 431.6(c)(1)(2) of the LACF regulations. 

Cascading water retorts are known to be manufactured by the Food Processing 

Machinery Division of FMC U.S.A. (Universal and Convenience sterilizers), Lubeca in 

Germany (Lubeca Model LW406 and LW402 G), Herman Stock in Germany (Autovap 

and Rotovap), Phoenix A/S a division of the Klinge Corporation in Denmark (Phoenix) 

and by Barriquand in France (Steriflow). Copies of these retort systems may be made in 

other countries. Custom built cascading water systems may also be encountered.

Figure 12

Cascading water retorts may be either still or end over end agitating batch type retorts. 

They are normally operated with an air over-pressure and may be used to process a wide 

variety of container types including glass, metal, plastic, and flexible pouches.

The Barriquand Steriflow has been the cascading water system most often encountered 

by FSIS.
29

Figure 13

The Steriflow is an over-pressure retort designed to operate at high temperatures, at or 

above 130oC (265° F), at pressures of up to 84 psig (5.9 kg/cm2), with very short cook 

times. The overpressure is supplied by compressed air and controlled separate from the 

retort temperature. The Steriflow uses less water for processing when compared to a 

water immersion retort, (e.g., 100 liters per basket in the standard 1300 mm model retort). 

At the start of processing, the process water is added to the bottom of the retort shell. A 

gate in the bottom front of the retort shell prevents the loss of processing water when the 

retort door is opened. During processing, this water is drawn from a trough in the bottom 

of the retort by a centrifugal pump capable of recirculating the water in the system 

approximately once every 9 seconds. The processing water passes through an indirect 

heat exchanger where steam is used to heat the water to processing temperature. The 

processing water then exits the heat exchanger and enters a water distribution manifold 

above the crates and containers. The processing water is forced through a series of small 

holes (e.g., 4 mm (5/16") on 21 mm (13/16") centers) in the manifold and cascades down 

over the crates and containers. At the conclusion of the thermal process, cold water is 

introduced into the heat exchanger to cool the processing water. The same water used to 

process the containers is used to cool the containers. The cooling water in the heat 

exchanger is never in contact with the containers. This provides for the use of low quality 

water (such as sea water) in the heat exchanger as the cooling medium.
30

Water entry into the water distribution manifold has been noted to be at the center or the 

end of the manifold in different models of the Steriflow. Location of the manifold water 

entry may be important. Temperature distribution studies have indicated that the cold 

zone in the retort may be affected by the location of the water entry.

Process water is normally used throughout a production shift prior to being replaced. 

Small amounts of water may be added prior to each cycle to replace water lost when the 

door is opened and product is removed.

In the standard 1300 mm retort, solid sided, perforated bottom 33" x 34" x 30" high retort 

carts are normally used with perforated dividers [19 mm (3/4") on 25 mm (1") centers] 

between layers. Container orientation is normally vertical. Container orientation, size, 

shape and loading configuration may have an effect on temperature distribution.

Temperature and pressure may be controlled either by a cam programmer on older 

systems, by a microprocessor/computer on newer systems, or by manual control. 

Temperature is normally controlled through a Resistance Temperature Device (RTD) 

located at the exit end of the heat exchanger. A second RTD located at the entry to the 

circulation pump is used to drive the temperature recorder. A MIG thermometer should 

be installed at this location. The entry to the water circulation pump has been selected as 

the location of the coldest water being circulated in the retort during thermal processing. 

Pressure is controlled separately through feed back from a pressure transducer and 

operation of compressed air entry and pressure relief valves.

The production programs for some systems are designed to bring the coldest spot in the 

retort up to thermal processing temperature through a series of time/temperature steps to 

insure that the temperature in the retort is at or above the filed thermal processing 

temperature at the time that the retort thermal process begins. An example of a stepped 

program is as follows:

- Preheat water to 115° C (2390 F).

- Heat from 115° C (239° F) to 137° C (279° F) 6 minutes (must meet both time 

and temperature).

- Heat for 136° C (277° F) 1 minute (time and temperature). This over-shoot 

temperature is used to help achieve adequate temperature distribution in the retort.

- Heat for 135>° C (275° F) 1 minute (time and temperature).

- Heat for 134>° C (273° F) 5 minutes (scheduled operating process temperature).

- Cool

To obtain adequate temperature distribution the system is normally operated with a 

temperature overshoot of at least 1°C above the process schedule temperature.

The stepped program varies with the retort, product and container. This program should 

be part of the firm's process schedule. Documentation that the steps in the come up 

portion of the retort program take place may be difficult. The come-up temperatures 

sensed by the microprocessor may not be the same temperatures displayed by the MIG 
31

thermometer and the temperature recording chart.

There are several areas of concern unique to the water cascade retort systems which 

should be addressed when inspecting these systems.

- The come-up portion of the process must be designed to provide for adequate 

temperature distribution (all parts of the retort are at or above retort temperature at 

the start of the thermal process hold time). The come-up requirements may differ 

from one product to another in the same retort, and from one container type to 

another in the same retort. Ideally temperature distribution studies should be 

performed on each retort model, each product produced, each container type used, 

and on each individual retort installation to determine the come-up procedures. 

The firm should have documented by temperature distribution studies that their 

come-up procedures result in adequate temperature distribution in the retort prior 

to the start of the timing of the process schedule.

- Care should be taken to determine the location of the control and recording 

RTD5. The recording RTD has been noted to be installed in the exit end of the 

heat exchanger. This may provide a recorded temperature higher than the coldest 

temperature in the retort. At least one manufacturer now recommends that the 

control RTD be located after the heat exchanger, with a feed-back RTD located at 

the entry to the circulation pump. The latter RTD also drives the temperature 

recording instrument. Both RTD5 should read at or above the process schedule 

temperature prior to beginning the thermal process timing.

- FDA has noted that the Steriflow is not always equipped with a MIG 

thermometer. When modified for a MIG thermometer, the MIG thermometer 

should be installed in the inlet line of the circulation pump, next to the recorder 

RTD, to monitor the temperature of the return cold water, which is the average 

coldest spot in the retort. MIG thermometer lag will normally be observed during 

the come-up steps.

- Water flow is not normally controlled as a critical factor. A pressure differential 

may be measured between the pressure on the entry and exit ends of the water 

circulation pump. This pressure differential alarms the control system if the set 

limits are exceeded. The pressure differential is a measurement of the differences 

in pressure on the two sides of the pump and may not measure a true water flow. 

The pressure differential will indicate failure of the water pump but may not 

always indicate a clogged water distribution system. A flow measuring device is 

recommended to provide a more accurate measurement of actual water flow in the 

system. Water flow in the system must be the same as that used during 

temperature distribution studies in the retort.

- The holes in the water distribution manifold may become plugged with product or 

mineral deposits. There should be a program in place for routine maintenance and 

cleaning of return ports, the water distribution manifold, and water filter screens if 
32

present. During inspection of these systems, the water distribution manifold 

should be examined to determine if the holes are plugged or have been reduced by 

mineral scale buildup.

- The processing records maintained by the firm must document that operating 

steps required to attain uniform temperature distribution in the retort during 

thermal processing are being met. These steps should be listed as critical factors 

on the firm's process filing form.

The Phoenix cascading water retort operates in a manner similar to the Steriflow. The 

Phoenix retort system is offered in the U.S. by AlIpax Products Inc. Mandeville, La. 

under the name Spray-Pax in still and rotational models.

Cascading water retorts manufactured by Lubeca and Stock in Germany differ from the 

Steriflow in that they offer heating by direct steam injection into the water, or by plate 

heat exchanger as a customer option. Cooling is by addition of cooling water to the retort 

or by indirect cooling through a heat exchanger. A method of recovering process water 

may be provided if cooling water is added to the retort.

The FMC Universal and Convenience Food sterilizers differ from the other cascading 

water retorts in that they utilize a weir arrangement (a small dam used to direct water 

flow) in the container basket to force the heated water to flow over the containers in a 

uniform manner from top to bottom or from one side to the other depending upon the 

container type. The water then overflows the basket and falls back into the bottom of the 

retort where it is picked up by a circulation pump and recirculated through a steam 

injector to reheat the water.

When any of these systems are encountered, it is important to determine if the retort 

system is being operated under the same conditions used during temperature distribution 

testing. The areas of concern for these systems are similar to those for the Steriflow 

including the control probe location.

SPRAY WATER RETORT SYSTEMS

Equipment and procedures for processing in spray water retorts are covered by 9 CFR 

431.6(c)(1)(2) of the LACF regulations. 

Spray Water retort systems are known to be manufactured by the Food Processing 

Machinery Division of FMC U.S.A. (FMC Surdry), Surdry S.L. in Spain (Surdry 

Convac) and in Japan by Hisaka Works Inc. The Hisaka retort is sold in the U.S. by 

Advanced Retort Systems, Inc.
33

Figure 14

Spray water retort systems may be either static or rotary batch, (end-over-end) systems, 

depending upon the make or model (Figure 14 and 15). These retorts are designed to 

process a wide variety of packages including: glass, metal, rigid plastic and flexible 

pouches. They are normally operated with a compressed air over-pressure to maintain 

container integrity during thermal processing.

Spray water retorts differ from the cascading water retort (in which the water falls or is 

sprayed over the top of the containers) in that the water is sprayed over the containers, 

from several different angles to atomize the air used for over-pressure.

In the Surdry retort the spray nozzles are located on four to six manifolds on the top and 

along the sides of the retort. A small amount of water in the bottom of the retort is heated 

by the addition of steam through two steam spreaders located in the bottom of the retort. 

The water is pumped through the system by a high capacity pump. The water sprays 

circulate the steam/air mixture in the retort. The containers are cooled after processing by 

the addition of cooling water to the retort. Instrumentation is normally located in the shell 

of the retort. The MIG thermometer and the temperature recorder probe are located to 

sense the temperature of the steam/air/water mixture in the retort.
34

Figure 15

In the Hisaka retort, spray nozzles are located on manifolds along the sides and in the top 

of the retort. The spray nozzle banks in these retorts can oscillate (back and forward and 

up and down). The water in the retort is heated by means of a heat exchanger using 

steam. When the thermal process has been completed the water and condensate in the 

retort is cooled by the external heat exchanger to cool the product.

The areas of concern with spray water retort systems are similar to those for the water 

cascade type retort system.

1. The process must be designed to provide for adequate temperature distribution. 

The cold spot in the retort must be determined. This may vary with container type 

and arrangement in the retort. Temperature distribution studies should be 

performed on each retort model, each product produced, each container type used, 

each crate or racking configuration used and on each individual retort installation.

2. Care should be taken to determine the location of the control and recording 

instruments. The recording sensing probe must be located where it will provide an 

accurate record of the thermal process. The MIG thermometer must be installed 

where it will indicate the true thermal processing temperature in the retort.

3. Water flow may not normally be directly controlled as a critical factor. A water 
35

flow measuring device is recommended to provide a more accurate measurement 

of actual water flow in the system. Water flow in the system must be the same as 

that used during temperature distribution studies in the retort.

4. The holes in the water distribution sprays may become plugged through clogging 

with product, and through the buildup of mineral deposits. There should be a 

program in place for routine maintenance and cleaning of the water sprays and 

water filter screens if present. During the inspection of these systems the water 

distribution sprays should be examined to determine if the holes are plugged or 

have been reduced by mineral scale buildup.

5. The records maintained by the firm must document that operating steps set-up to 

provide uniform temperature distribution in the retort during processing are being 

met.

When spray water retort systems are encountered, it is important to determine if the retort 

system is being operated under the same conditions used during temperature distribution 

testing.

STEAM-AIR RETORTS

Equipment and procedures for processing in steam-air retorts are covered by 9 CFR 

431.6(d) of the LACF regulations.

Steam-air retorts are normally batch type static or rotary, end-over-end, retorts. Steam-air 

has been used as the heating medium in the Hydrolock (a horizontal continuous feed 

water lock retort) manufactured by the Rexham Corporation, and in at least one 

hydrostatic retort in Japan. These retorts are however the exception and not the rule.

Known manufacturers of batch type steam retorts include: J.L. LaGarde in France 

(Distributed in the U.S. by Stork Food Machinery), Lubeca in West Germany, Marrodan 

in Spain, and Barriquand in France (Steristeam). At one time the Container Machinery 

Corp. built the Truxton Steristar in the U.S. The Steristar steam-air retort is now built by 

Malo. Custom installations of steam-air retorts have been reported and other 

manufacturers may exist. An example of the steam-air retort system is the LaGarde 

steam-air retort (Figure 16).

The steam-air retort uses a mixture of steam and air, which is added to create an overpressure in the retort. The air overpressure allows thermal processing of a wide variety of 

containers including: glass, metal cans, rigid plastic, and flexible pouches. Steam-air 

mixtures, although in a gaseous state similar to 100% steam, when used as a heating 

medium behave more like water. The heat capacity of the steam-air is very small when 

compared to pure steam. As the steam condenses and gives off heat, the air remains. 

Because the retort uses air in the steam mixture, there must be a method of mixing the air 

and steam to prevent the formation of air pockets in the retort and to provide for the rapid 
36

movement of the heating medium over the container surface. Air may provide insulation 

around the container preventing the heat from reaching the container walls in an efficient

manner. A large fan is normally used to rapidly mix the steam-air mixture and to force 

this mixture to flow through the retort and containers during processing.

Figure 16

It is very important to maintain the correct steam-air ratio in this type of retort. The 

steam-air ratio should be the same as that used during studies to determine temperature 

distribution in the retort.

Steam-air retorts are normally operated at steam-air ratios ranging from 75% steam/25% 

air to 95% steam/5% air, depending upon the air over-pressure in the retort. The steam-air 

ratio is normally determined by the processing temperature and the type of package being 

processed.

The pressure in a steam-air retort must be maintained at the correct pressure to prevent 

container distortion and to maintain the correct steam-air ratio. If the amount of steam in 

the steam air ratio drops to too low a level, the energy available to heat the product is 

reduced. If the temperature is maintained by the steam controller, the partial pressure of 

the steam remains constant throughout the process. The pressure of the system is

controlled by releasing over-pressure through a small purge valve and adding compressed 

air as needed.

The percent steam can be calculated using the following formula:
37

Steam pressure PSIA (pounds per square inch actual) = % steam Total system pressure 

psia

Steam pressure PSIA is determined by determining the amount of steam pressure 

generated at a certain temperature [e.g. 240° F generates 10 PSIG (pounds per sq. inch 

gauge)] plus 14.7 PSI (atmospheric pressure at sea level) equals 24.7 PSIA. The total 

system pressure is determined by taking the gauge reading and adding 14.7 PSI. A steam 

air system having a total gauge pressure of 15 lbs operating at 240° F would have 83% 

steam and 17% air mixture.

14.7 PSI atmospheric + 10 PSIG (steam at 240°F) = 24.7 PSIA

15 PSIG + 14.7 PSI atmospheric = 29.7

24.7/29.7=83% steam and 17% air

The LaGarde retort is offered in static or rotational end over end agitation models. The 

LaGarde is normally operated in the following manner:

- Product is placed into the retort in either standard rectangular baskets or crates for 

metal, glass and rigid plastic containers. Special racking trays are used for flexible 

and other containers needing support during processing.

- The retort is purged for 1 to 2 minutes through a large purge (vent) valve, the 

bottom drain or by vacuum to remove excess air from the retort and to enhance 

the steam entry into the retort. Steam is introduced into the retort through steam 

spreaders in the bottom of the retort.

- The fan is turned on to circulate the steam-air mixture. The retort is brought up to 

temperature during a 3-10 minute come-up period. The maximum amount of 

steam is injected at this time. The retort may use a steam bypass valve to provide 

a large flow of steam to the retort.

- A process hold period during which the retort temperature is maintained at the 

correct temperature by the addition of steam through an automatic steam control 

valve. This may be a small steam supply valve used to maintain a more uniform 

temperature. Excess pressure is released through a small purge (vent) valve in the 

retort shell. Compressed air may be added to the rear of the retort to maintain the 

retort over-pressure.

- Pre-cool, at the end of the thermal process a small amount of water may be 

injected into the retort steam-air channels to condense the steam or in some 

models cold water coils located in the retort are used to condense the steam.

- Cooling is then completed by adding water to the retort through top or bottom 

water spreaders. In some of the newer systems plate heat exchangers may be used 

to cool products through indirect cooling.
38

The steam-air mixture is forced through the LaGarde retort by a fixed speed fan located 

at one end of the retort. The steam-air mixture is normally drawn through the basket by 

the fan (an automotive type blade fan in the LaGarde and a squirrel cage type in some 

other systems) and pushed back up along the sides of the retort through channels created 

by welding metal sheets to the top and bottom at each side of the retort. The plates are 

generally referred to as "directional baffles". The space between the plates and the retort 

shell is sometimes referred to as the steam-air "plenum". The flow rate is fixed at 

approximately 30 cubic feet per second. LaGarde states that a temperature overshoot, 

(where the temperature of the retort is operated at several degrees above the required 

product temperature for the first part of the process and as the internal package 

temperature begins to achieve the desired temperature the temperature of the retort is 

reduced) can be used to produce a superior product. This process is reportedly designed 

to achieve shorter processing times and better heat transfer without stressing the container 

by causing high pressure within the containers. If the temperature overshoot is used, it 

must be filed as part of the process schedule.

The Lubeca LW3003 steam-air retort is offered in both static and rotational models. The 

Lubeca differs from the LaGarde in that in addition to using a large fan to mix the steamair mixture this system also pumps the condensate from the bottom of the retort and 

distributes the condensate over the top of the containers. At the beginning of the process,

a small amount of water is added to the bottom of the retort. This water is heated by the 

addition of steam through steam spreaders in the bottom of the retort. A large squirrel 

type ventilator fan pulls air along the bottom of the retort and pushes the air along the top 

of the retort and back through the crates of product. Instrumentation is located in the shell 

of the retort. The temperature of the condensate and water may not be measured or 

recorded during production. Following the thermal process the containers are cooled by 

the addition of cooling water to the retort.

The Barriquand Steristeam retort differs from the LaGarde in that each basket has it own 

circulation fan. The fans are mounted on the side of the retort and circulate the steam-air 

mixture up over the basket and back through the containers. Cooling of product is 

normally through an external heat exchanger or by the addition of cooling water to the 

retort shell at the customer’s option.

The Truxton Steristar is a modified version of the LaGarde. The Steristar may use a 

squirrel cage or an automatic type fan, heavier components, proportional control valves, 

preheated compressed air and a number of other modifications to the LaGarde system. 

Operation of the system is similar to the LaGarde.

Air flow in the steam-air retort system is very important to the maintenance of proper 

temperature distribution during processing. Changes in the container, crate or loading 

configuration can change the air flow in the retort. Steam-air retorts are normally 

operated with a full load of product or with dummy crates of product to fill out the retort 

during the processing of partial loads. In some systems, a baffle may be used to block off 

the retort at the last crate and allow for processing with less than a full retort load. 
39

Temperature distribution studies or other documentation should be on hand to 

demonstrate that adequate temperature distribution is achieved under less than full load 

conditions and with the container/crate configuration being used.

There should be some method for determining that the fan in a steam-air retort is 

operating. A visual inspection of the fan operation should be made on a routine basis. 

Inspection of operation of the fan should be documented.

DURING THE INSPECTION OF ALL THERMAL PROCESSING SYSTEMS, BE 

CERTAIN TO REFER TO THE APPLICABLE SECTIONS OF THE MEAT AND 

POULTRY CANNING REGULATIONS.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New    i

 Institute For Thermal Processing Specialists

GUIDELINES FOR CONDUCTING THERMAL PROCESSING STUDIES

The following recommendations are to be considered voluntary guidelines.  These recommendations

do not preclude the application of other methods and equipment for conducting thermal processing

studies.  These guidelines have been developed by consensus of the Institute for Thermal Processing

Specialists and should be given serious consideration for adoption as methodology by individuals

performing thermal processing studies.

The Institute for Thermal Processing Specialists is a non‐profit organization established exclusively for

the purpose of fostering education and training for those persons interested in procedures, techniques

and regulatory requirements for thermal processing of all types of food or other materials, and for the

communication of information among its members and other organizations.

This document is a compilation and re‐structuring of previously published IFTPS guidance documents.  

Prior documents were modified to follow a common format and were also updated to reflect current

practices.  Common sections amongst previously published documents, such as Retort Survey, were

placed into separate chapters.  Information was added to Chapters on Temperature Distribution, Heat

Transfer Distribution, and Heat Penetration to provide recommendations regarding Data Analyses,

Success Criteria, and Risks, Issues and Other Considerations.

Hyperlinks have been embedded throughout the document to assist the reader in navigating between

different chapters.  Hyperlinks may be identified as underlined, blue text.

Instructions for following hyperlinks in documents

To follow a link to the point being referenced – Press CTRL key + left click on the mouse to move to

referenced item.  Note that the instruction to CTRL + click will also show when the cursor is placed

within a hyperlink.

To return to the place in the document where you were reading – Press ALT key + back arrow(Alt + ←)

(note that using the “backspace” key will not work).

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New    ii

This document was approved for publication in March, 2014 by the IFTPS Board of 

Directors. 

Institute For Thermal Processing Specialists

304 Stone Rd. W., Ste. 301, Guelph. ON N1G 4W4 

P: 519 824 6774 F: 519 824 6642 info@iftps.org 

www.iftps.org

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New    iii

TABLE OF CONTENTS

Chapter 1 – Definitions

Chapter 2 – Test Equipment and Standardization/Calibration

Chapter 3 – Documenting Processing Equipment and Test Conditions

Chapter 4 – Conducting Temperature Distribution Studies

Chapter 5 – Conducting Heat Transfer Distribution Studies

Chapter 6 – Conducting Heat Penetration Studies

Appendices –

A. Literature Cited

B. Documenting Processing Equipment and Test Conditions

C. Temperature Distribution – Data Monitoring/Collection Points by Retort Type

D. Heat Penetration Documentation Checklist

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐1

1 DEFINITIONS

This chapter provides definitions commonly used for thermal processing studies.

TERM DEFINITION

Ballast Containers

These are containers used to fill the retort during thermal processing studies to

simulate production conditions.  Typically, ballast containers for heat penetration,

temperature distribution and heat transfer distribution studies are the same type,

shape and size of containers as used for the intended process.  In some retort

systems, e.g., multi‐basket batch retorts, ballast containers may not need to be the

same in baskets not containing heat penetration and heat transfer distribution

probes.  Material used for filling containers may be the test product, or any suitable

material having heating characteristics similar to that of the test product, or in some

circumstances, water (e.g., temperature distribution).

Broken Heating

Heat transfer characteristic of some foods, particularly those with starches, where

the heat transfer rate changes due to a change in the product as a result of product

heating.  The change in heat transfer rate may represent a change from heating

primarily by convection to heating by conduction.

Calibration To check, adjust, or determine by comparison with a traceable standard the

graduations of a quantitative measuring instrument.

Cassettes/Trays/Racks

A means by which filled packages are held/carried in a retort.  Cassettes/trays/racks

may be loaded into cubes, baskets, or other means to convey filled packages into

and out of a retort.

Cold Spot – Heat Penetration

The cold spot for heat penetration studies is determined experimentally and

represents the slowest heating location within the container.  In the case of non‐

homogenous foods, the slowest heating food particle in the slowest heating location

within the container would be considered to be the cold spot.

Cold Spot – Temperature

Distribution

The cold‐spot for temperature distribution is generally that area of the retort which

is the last area in the retort to reach a minimum processing temperature during

come‐up.

Cold Spot – Heat Transfer

Distribution

The slow/slower to heat location(s) for Heat Transfer Distribution is generally the

location(s) in the retort where heat transfer into the product is the slowest.  This is

indicated by the location with the largest fh value.

Come‐Up Time (CUT)

Come‐up time (CUT) is defined as the time requirement for the reference TID to read

at or above the minimum process temperature AND all TMDs to read within 1F°

(0.5°C) of minimum process temperature within 1 minute of starting the hold time.  

Commercial Sterility

Commercial sterility is defined as the condition achieved by application of heat, or

other treatments that renders the product free of viable microorganisms having

public health significance as well as microorganisms of non‐health significance

capable of reproducing in food under normal non‐refrigerated conditions of storage

and distribution.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐2

Computer Control System Computer used for automation of electromechanical processes.  Also referred to as a

Programmable Logic Controller (PLC).

Conduction A type of heat transfer that may be characterized as one where agitation of the

package with the food does not impact the heat transfer rate.

Convection A type of heat transfer that may be characterized as one where agitation of the

package with the food does impact (positively) the heat transfer rate.

Crateless Retort

A non‐agitating (i.e., still) batch retort wherein cans are sterilized in saturated steam

as a “jumble pack”, without baskets, trays or cassettes. Loading is by dropping cans

from the retort top into a cushion of water and cans are unloaded by gravity

dropping out the bottom into a water canal with a drag chain to drying and packing.

Critical Factors

US‐FDA 21CFR Part 113 defines critical factors as – “any property, characteristic,

condition, aspect, or other parameter, variation of which may affect the scheduled

process and the attainment of commercial sterility”.  Critical factors may include

physical and chemical aspects/parameters associated with the container, the

product, the retort and processing conditions.

fh

The time for the heat penetration curve to traverse one log cycle. Also referred to as

the heating rate index.

Fill, Drained, and Net

Weights

Fill Weight means the weight of solid product in the container before processing and

does not include the weight of the package or cover liquid (if applicable); Drained

Weight is the weight of solids after processing; and Net Weight of a product refers to

the weight of all product in the container including any cover liquid minus the weight

of the container.

Flow Meter An instrument/device/sensor that measures fluid flow rate.

Heat Penetration

Studies conducted to determine and establish a Scheduled Process.  Heat

Penetration studies are typically conducted under “worst case” conditions for

product, package, location, and retort parameters.

Heat Transfer Distribution

Heat transfer distribution studies are used to establish the ability of a retort process

to uniformly mix and distribute the heat transfer medium especially when the heat

transfer into product may be rate limiting.

Heat Input Unit(HIU)

Appropriate material such as a polymer, clay, or food product with

repeatable/definitive thermo‐physical properties, and capable of being used for heat

transfer distribution studies.

Heat Penetration Curve

Plot of the logarithmic difference between either retort temperature and product

temperature (heating curve) or product temperature and cooling medium

temperature (cooling curve) versus time.

Hermetic Seal

The condition which excludes the ingress of microorganisms, filth or other

environmental contaminants that could render the product unfit for consumption or

which could reduce the quality of the product to a level less than intended.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐3

Initial Temperature The average temperature of the contents of the coldest container to be processed at

the time the sterilization cycle begins.

Low‐Acid Canned Food

(LACF)

Any food, other than alcoholic beverages, with a pH >4.6 and a water activity (aw)

greater than 0.85 packaged in a hermetically sealed containers that are thermally

processed and stored at ambient temperatures.

Loading Pattern/Map A depiction showing locations of probes and/or probed containers (e.g., temperature

distribution, heat penetration, and heat transfer distribution) within a retort load.

Nesting/Shingling

Condition that occurs when more than one container is stacked fully or partially on

top of another container.  In the case of pouches, this is referred to as shingling.  

Nesting/shingling may negatively impact heat transfer/heat penetration.

Overpressure

Pressure in excess of that corresponding to saturated steam vapor pressure at a

given temperature and when corrected for altitude.  Overpressure may be necessary

to maintain package integrity during the process.

Packing Gland (Stuffing Box)

Soft rubber or other material that is used to create a tight seal around TMDs/PMDs

that assists in providing a means to penetrate the retort shell without allowing

process media to leak to atmosphere (if applicable).

pH A measure of acidity or alkalinity.  Chemically, pH is defined as the negative log of

the hydrogen ion concentration.

Piping and Instrumentation

Diagram (P&ID)

Diagram which shows the piping of the process flow together with the installed

equipment and instrumentation.

Plenum/Shroud

In a steam/air retort, the plenum/shroud is the space between the retort shell and

the portion of the retort holding the baskets/cassettes.  The function of the

plenum/shroud, usually in conjunction with a fan, facilitates movement of steam/air

through the retort and retort load.

Pocket space Space within a cassette/rack/tray to hold a package.

Pressure Control Sensing

Device Instrument used to control pressure inside the retort.

Pressure Indicating Device

(PID)

Instrument used to monitor pressure inside the retort, e.g., pressure gauge or

pressure transmitter with electronic display.

Pressure Measuring Device

(PMD)

Pressure sensor placed within (or mounted on) the retort to accurately monitor

pressures attained and maintained throughout the applied process.

Process Deviation

A change in any critical factor of the scheduled process that reduces the sterilizing

value of the process, or which raises a question regarding the public health safety

and/or commercial sterility of the product lot/batch.

Process Establishment Scientific procedure to determine the adequate process time and temperatures

required to produce commercially sterile canned products.

Resistance Temperature

Detector(RTD)

Thermometry system based on the positive change in the resistance of a metal

sensing element (commonly platinum) with increasing temperature.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐4

Retort

Any closed vessel or other equipment used for thermal processing.  May also refer to

the act of applying a thermal process to a canned food in a closed pressurized vessel.  

May also be referred to as a “sterilizer”.  The terms “retort” and “sterilizer” are often

used interchangeably.

Retort – Continuous

Rotary/Reel and Spiral

Cooker/Cooler Retorts

In Continuous Rotary/Reel and Spiral Cooker Cooler retorts, cans enter and exit the

processing vessel through mechanical pressure locks. Once in the vessel, cans move

through a spiral track mounted on a reel that is rotating inside a horizontal

cylindrical shell. In one revolution of the reel, cans roll by gravity along the bottom

part of the arc (approximately 90‐120°), which provides most of the product mixing

within the can. The cans are essentially static as they pass through the remainder of

the arc (approximately 240‐270°).

Retort –Hydrostatic

A retort in which total pressure in the sterilization section is determined and

maintained by the hydrostatic pressure of inlet and outlet water columns.  Packages

are continuously conveyed through the machine.

Separator/Divider Sheet

Separator/divider sheets are used to separate layers of packages in a basket/crate.  

These typically contain perforations/holes to help facilitate free movement of the

heat transfer medium.  Materials of construction can vary – metal/stainless steel,

rubber, plastic, and so forth.

Scheduled Process The process defined by the processor as adequate under the conditions of

manufacture for a given product to achieve commercial sterility.

Should Should is used in this document to indicate a recommendation or option for

consideration.

Simple Heating Heat transfer characteristic of some foods where the heat transfer rate is relatively

constant during product heating.  

Slip Ring A device that allows for transfer of the thermocouple voltage signal from a rotating

environment to a stationary electrical contact outside of a retort.

Steam/Air Flow Indicator Indicator located in the retort shell to determine the direction and to measure flow

(cubic feet per minute ‐ cfm) of process media.

Steam/Air Ratio

The steam/air ratio (for isothermal/isobaric conditions of the cook segment) is

calculated by volume by determining the amount of steam pressure at a certain

temperature plus the atmospheric pressure at sea level and dividing that value by

the total absolute Total Pressure of Steam and Air/Nitrogen as indicated by the

retort gauge pressure plus the atmospheric pressure.  For example, using the steam

tables, at 240°F (115.6°C), the absolute saturated steam pressure at sea level is

24.968 psia/1.722 bar (or 10.272 psig and 0.708 bar gauge).  For a process with a

gauge pressure of 15psig (1.034 bar gauge), the absolute pressure at sea level is

29.696 psia (2.048 bar).  This would equate to a steam/air mixture that is 84%

saturated steam (i.e., 24.968/29.696 X 100% or 1.722/2.048 X 100%) and 16%

overpressure air (i.e. 29.696‐24.968/29.696 X 100%).  Note that the altitude of the

processing facility should be considered when converting gauge pressure to absolute

pressure.

Steam/Air Retort A steam/air retort is a batch retort that uses air/nitrogen to provide overpressure.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐5

Steam/Air Retort – Forced

Flow Steam/Air Retort

In a forced‐flow retort, a mixing fan induces a forced convection of the process

heating media by drawing the steam/air mixture through the product and circulating

it through a return plenum.  Steam is introduced between baskets while air over‐

pressure is introduced into the return plenum cavity.

Steam/Air Retort – Air

Make‐up Steam/Air Retort

In this type of retort, small vent valves on the retort remain open after desired

temperature and pressure are achieved and provide continuous venting of the retort

during the heating period.  Air is re‐introduced into the retort as needed to satisfy

over‐pressure requirements while steam is simultaneously added to maintain

temperature.

Steam/Air Retort – Positive  

Flow Steam/Air Retort

In this type of retort, a continuous flow of steam and air are passed through the

vessel to create a homogeneous mixture throughout the retort.  This creates an

overpressure condition in the retort and results in continuous venting of the

steam/air mixture thus creating flow past the containers.

Sterilizer See definition above for Retort.

Sufficient Sampling

Frequency (Data Collection)

As used in this document, sufficient sampling frequency is determined by the

processor and should be frequent enough to confirm that the measured parameter

is within control.

Temperature Control

Sensing Device Device used for controlling temperature in a retort.

Temperature Indicating

Device(TID)

Device used for monitoring temperature, including thermometers, thermocouples,

RTDs and thermistors and generally referred to as the “official” or “reference”

temperature monitoring device on a retort system.  A Mercury‐in‐Glass (MIG)

thermometer is an example of a TID.

Temperature Measuring

Device (TMD)

Device used for measuring temperature, including thermometers, thermocouples,

RTDs, wireless data‐loggers, and thermistors.

Temperature Uniformity and

Stability

Verification of temperature across/within the retort load (uniformity) and over time

(stability) of the process particularly during Cook/Hold.

Thermistor

TMD manufactured from semiconductor materials which exhibits large changes in

resistance proportional to small changes in temperature. Thermistors are more

sensitive to temperature changes than thermocouples or RTDs and are capable of

detecting relatively small changes in temperature.

Thermocouple

TMD composed of two dissimilar metals which are joined together to form two

junctions. When one junction is kept at an elevated temperature as compared to the

other, a small thermoelectric voltage or electromotive force (emf) is generated

which is proportional to the difference in temperature between the two junctions.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐6

Temperature Distribution

Studies conducted in a sterilizer (retort)using distributed temperature measuring

devices (TMD) to establish venting procedures, venting schedules, come‐up

requirements, and temperature stability and uniformity, which are necessary to

establish heating and cooling performance (i.e., temperature uniformity) throughout

the retort.  Temperature distribution studies are typically performed using actual

production retort conditions or parameters.

Tray/Rack See Cassette/Tray/Rack above

Validation

There are multiple definitions of the word “validation”.  In the context of this

guideline document, validation is assumed to mean at least two successive and

successful replicate studies that meet established success/acceptance criteria.

Vent/Venting A vent is a device/valve through which air is removed from a retort.  Venting is the

process by which air is removed.

Verification

In the context of this guidance document, verification is assumed to mean replicate

studies that are intended to confirm a process.  Verification may also be used to

indicate confirmation of the calibration status of process measurement devices used

to collect thermal process data.

Water Activity (aw) Water activity (aw) is defined as the ratio of the partial pressure of water above a

food to the water vapor pressure of pure water at a given temperature (aw= p/po).

Water Cascade Retort

A water cascade retort is defined as one where a small amount of process water is

drawn from the bottom of the retort by a high‐capacity pump and distributed

through metal plate(s) or manifold(s) in the top of the retort.  This process water

cascades down over the retort cassettes, cages or racks in a rainwater or “shower”

fashion, passing over the product containers on the way back to the bottom of the

retort where it is re‐circulated through the heating and distribution system.  

Processing water may be heated using one or more direct or indirect heating

methods including heat exchangers, direct steam injection, or via steam distribution

pipes or spreaders.

Water Immersion Retort

A water immersion retort is defined as one where process water is sometimes

heated in a separate vessel and once the process water reaches the desired

processing temperature, is dropped into the processing vessel.  Water is re‐

circulated during processing.  Sufficient water to completely cover the packages may

be used.  In other cases, packages may only be partially covered with water during

processing.

Water Spray Retort

A water spray retort is defined as one where a controlled amount of process water is

drawn from the bottom of the retort by a high capacity pump and distributed

through spray nozzles located along the top and sides of the retort.  This process

water is sprayed over the retort cassettes, cages or racks in a high‐pressure “mist”

fashion passing over the product containers on the way back to the bottom of the

retort where it is re‐circulated through the heating and distribution system.  

Processing water may be heated using one or more direct or indirect heating

methods including heat exchangers, direct steam injection, or steam distribution

pipes or spreaders.

A sensor/measuring device that is self‐contained (i.e., does not require wires).  These
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     1‐7

Wireless Data‐logger devices typically require programming prior to use and collected data are then

downloaded or transmitted for analyses after use.

%CV

The coefficient of variance is mathematically calculated by dividing the standard

deviation of a set of numbers by the average of the same set of numbers and then

multiplying that quotient by 100.  (%CV = standard deviation/average * 100)

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     2‐1

2 TEST EQUIPMENT AND CALIBRATION OF TEST EQUIPMENT

SCOPE

2.1. The guidelines in this chapter apply to equipment used to collect thermal process data in any

retort system.  The guidelines apply to both internal and external measuring and data collection

systems.   Test equipment used for collecting thermal process data should be suitable for the

purpose of the studies being conducted.  Devices to collect temperature distribution, heat

transfer distribution, and heat penetration data, in general, should be calibrated relative to the

expected test conditions and ranges prior to conducting thermal process studies.  Ideally,

devices should also be calibrated upon completion of thermal process studies.  Process efficacy

and success criteria of thermal processing studies may not be met if sensors and measuring

devices are inaccurately calibrated.

2.2. Biological indicators are not addressed in this chapter.

OBJECTIVE

2.3. The objective of this document is to provide guidance with regard to calibration of test

equipment used to collect thermal process data.

TOOLS, EQUIPMENT, INSTRUMENTATION

2.4. Data Acquisition System – The data acquisition system should be calibrated prior to use.  It

should also be equipped with sufficient channels to accurately monitor and record

temperature/pressure within the process delivery system.  Manual recording of data may be

used if a sufficient sampling frequency can be maintained.

2.5. Temperature Measuring Device (TMD) – TMDs may be thermocouples, wireless data‐loggers, or

other similar devices.  All TMDs must be of sufficient accuracy, size, and length, and in sufficient

quantity, to adequately and accurately monitor the process environment.

2.6. Pressure Indicating Devices – Operational gauges, electronic indicators, and/or wireless data‐

loggers may be used to monitor pressures associated with the retort operation during a test.  

These devices should be calibrated prior to the start of data collection.  Typical pressure

measurements could include: retort vessel pressure, steam line pressure, and other line

pressures that may be critical to the process.

2.7. Reference Temperature Indicating Device (TID) – This may be a retort Mercury‐In‐Glass (MIG)

thermometer or other valid reference temperature measuring device including a digital

thermometer of sufficient accuracy and precision.

2.8. Packing Gland (Stuffing Box) – This is needed for entry of lead wires into the retort when wired

data collection devices are used.  Materials used should be soft enough to provide a tight seal

without over‐tightening and damaging the TMDs.  Examples include Neoprene or other

synthetic materials.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     2‐2

2.9. Slip Ring – This allows for transfer of thermocouple outputs from a rotating environment to a

stationary electrical contact outside of the retort.

2.10.Flow Meters – Where applicable, flow meters may be used to measure flow of process water

during come‐up, heating, and cooling in those systems using circulating pumps.  Flow meters

may be used to measure volume or velocity of air flow in those systems using air for agitation

of heating and cooling media.

2.11.Stopwatch – This is needed to verify rotation rate/speed in systems that have agitation and/or

continuous container handling.

2.12.Heat Input Unit (HIU) – An appropriate material to simulate the product being studied in heat

transfer distribution studies.  Packaged product may also be used as an HIU.

METHODS FOR TEST EQUIPMENT STANDARDIZATION

2.13.Retort Temperature Indicating Device (TID) – The reference temperature measurement device

must conform to applicable regulations.  For example, US‐FDA regulation 21 CFR Part 113

establishes the requirement that temperature indicating devices and reference devices must be

tested against a reference device for which the accuracy is traceable to a National Institute of

Standards and Technology (NIST), or other metrology institute.  The reference device is typically

calibrated for accuracy against a known certified reference device at least annually.  The

preference is to have the Retort TID calibrated near to the time data are collected.  The last

calibration check date should be included in the study documentation.

2.14.Measurement System(s) – Measurement systems include as applicable: thermocouples/TMDs

(with extension wires as applicable), data acquisition system, pressure measurement devices,

and flow meters. The recommendations of the datalogging equipment manufacturer should be

followed or an instrument professional should be consulted regarding the correct grounding

technique to use.

TMD Standardization/Calibration

2.14.1.Prior to conducting thermal process studies, standardization or calibration of test

equipment should be performed.  Thermocouples ideally would be calibrated in the test

retort(s).  All thermocouples, extensions, connections and the specific data logger should

be assembled as they will be used under the actual test conditions. Consideration for

conducting duplicate calibration studies prior to conducting critical thermal processing

studies is recommended.

2.14.2.An acceptable method of calibration is to bundle all TMDs and locate them in close

proximity to the known accurate reference TID, taking care not to inhibit flow of the heat

transfer medium across the reference TID.  The retort is brought up to the same

sterilization set‐point temperature and pressure as defined for the test and the retort is

allowed to equilibrate.  Equilibration time may be dependent upon the specific retort

and/or retort type.  The temperature differences between the reference TID and TMDs are

then calculated and documented.  These differences may be applied as correction factors

for each TMD.  A typical range of correction factors for thermocouples is usually not more
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     2‐3

than 1‐2F° (0.6 – 1.2C°).  Large correction factors may indicate an issue with the TMD that

merits investigation and corrective actions prior to use in thermal processing studies.   

Non‐thermocouple TMDs such as wireless data‐loggers should be within manufacturer’s

specifications at the time of their use provided those specifications are consistent with

conditions of intended use of the TMD.  

2.14.3.Alternatively, TMDs may be calibrated off‐line in an established calibration program

within the temperature range to be used during data collection.  The difference between

the TMDs against the known accurate reference device should be calculated and

documented as part of the study data.  This difference may be applied as correction

factors for each TMD.

2.14.4.Verification of the calibration of all TMDs after completing thermal processing studies is

recommended.  Off‐sets which are substantially different than the pre‐study values should

be evaluated relative to the data that were collected.

Pressure Measurement Devices – Various methods are available to calibrate pressure

measurement devices.  Traditional calibrated and traceable dead weight testers (or their

electronic analogs) are recommended to be used as the primary reference standard against

which pressure gauges, transmitters and data logging devices should be calibrated.  

Regardless of method used, standardization results should be documented as part of the

overall study data package where pressure is part of the process.  Accuracy of pressure

measurement systems should preferably be ≤1% of the calibrated and traceable pressure

reference standards used, in the planned working or operating pressure range of the

processes in which they are to be used.  In addition, the accuracy should satisfy the

applicable following considerations:

2.14.5.For steam/air retort processes, the accuracy of pressure measurements should not result

in calculated intrinsic (unsafe) Steam Air Ratios ≥1% (i.e. richer in steam) for the actual

process value.

2.14.6.For non‐overpressure retort systems (primarily saturated steam), the accuracy of

pressure measurements should not result in an overestimate (unsafe) error of the

equivalent saturated steam temperature (corrected for sea level) of ≥0.2Fo (0.1Co

), if

process temperatures are planned to be calculated from pressure values for any

evaluation or consideration.

Flow Meters – A number of methods may be used to calibrate flow meters.  Regardless of

method used, standardization results should be documented as part of the overall study

data package.   

2.14.7.Fluid flow rates are often determined by flow meters or indirectly by revolutions per

minutes (RPM) of fans, pumps or motors for known/fixed cross section flow areas.

2.14.8.Flow meters (usually mechanical or electronic), direct contact or non‐contact, have

become increasingly specialized and complicated and manufacturers have set up

specialized flow test benches to provide calibration services for their flow meters.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     2‐4

2.14.9.Periodically (e.g., annually), factory electronic flow sensor output should be verified with

volumetric, gravimetric or other approaches (e.g., tachometers, velocity meters, current or

voltage draw) and results compared to calibration data.  Re‐calibration would be needed if

the verification results are not consistent with the calibration data.   

2.14.10.Based on the way flow is measured or imputed, process fluid flow sensor accuracy

should be calibrated for use in production or validation in the operating range of the

process and validations should factor in known off‐sets, errors and calibration

inaccuracies.  Process efficacy and success criteria of thermal processing studies may not

be met if flow meters are inaccurately calibrated.

Stopwatches – Stopwatches typically are received calibrated with an expiration date from the

stopwatch equipment supplier.

Non‐product based Heat Input Units (HIU) – Each HIU used in heat transfer distribution studies

must have a unique identity.

2.14.11.Using either a pilot scale retort or the test retort, a standardization test for a complete

set of HIU (e.g., 12‐24 separate units) should be made using expected operating

parameters (i.e., temperature and pressure) to establish a baseline for the heating

performance as measured by the heating rate index (i.e., fh) prior to use and periodically

during their life expectancy.    

2.14.12.All HIUs within a set should be in close proximity to one another during the

standardization/calibration study.

2.14.13.All TMDs used in conjunction with HIUs must be calibrated prior to calibrating the HIU.

2.14.14.A reasonable means of determining acceptable standardization for the use of a set of

HIUs in heat transfer distribution studies at any time during their life expectancy is to

utilize the statistical measure of coefficient of variance of the fh of the HIUs (%CV =

standard deviation/average * 100%).  A value of less than or equal to 1% would be

acceptable for a set of HIUs to be used to collect heat transfer distribution data.

2.14.15.In addition, each individual non‐product based HIU within a set should always be within

1% of its historical performance as measured by fh for the same

standardization/calibration process.  Once the %CV exceeds 1% for a given HIU relative to

its established baseline, consideration for removing it from service should be made.  A

rationale for using an HIU that falls outside of this recommendation could be based on its

performance in a specific study provided the data collected meet the success criteria

established (i.e., fh %CV ≤5% in a heat transfer distribution study).

Product‐based HIU – Product should be representative of the product heating type (e.g.,

conduction, convection) to be studied during heat transfer distribution tests.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     2‐5

RISKS, ISSUES, AND OTHER CONSIDERATIONS

2.15.To meet the calibration criteria noted above (section 2.14) and to ensure accuracy of test

results, consideration should be given to minimizing errors inherent in any component of the

temperature measuring system.  For example, use of special limits of error (SLE) wire or

premium grade thermocouple wire should be used to make thermocouples.  The use of 3 or 4

wire high accuracy RTD can help to reduce intrinsic error.

2.16.Thermocouple Calibration: Thermocouples should be calibrated against a traceable calibration

standard (e.g., thermometer, RTD, thermistor). Inaccuracies in temperature measurements

may result in errors in thermal process studies; hence, frequent calibration is essential to

provide reliable data. Factors affecting calibration include: worn or dirty slip‐rings, improper

junctions, metal oxidation, multiple connectors on one thermocouple and inadequate data

acquisition system cold junction compensation. As a consequence, thermocouples should be

calibrated in place as part of the complete data acquisition system.  Some precautions when

using thermocouple‐based data acquisition systems include: minimizing multiple connections

on the same wire, cleaning all connections, grounding the thermocouples and recording device,

slitting thermocouple outer and inner insulation outside the retort to prevent flooding of data‐

logger or data recording device (4, 8), and using properly insulated thermocouple wires.

2.17.HIU –The considerations discussed below apply to HIUs other than packaged product.

2.17.1.Inherent variations associated with any HIUs must be considered when selecting the

specific type of HIU, e.g., polymer‐based solid material, bentonite suspensions, and oils.  In

addition, the design and geometry of an HIU must also be considered.

2.17.2.The nature of the process environment (temperature and pressure) may dictate the HIU

material.  The material selected must withstand the operating conditions repeatedly and

reliably.

2.17.3.The geometric design of the HIUs should consider the package(s) general shape in all

dimensions and placement within the package holding system (e.g., rack, trays, baskets) in

order to mimic potential flow restrictions of the process media.  Typically, the HIUs should

be designed to conform to the shape of containers forming the ballast.  

2.17.4.The thermal properties of the HIUs should be verified before and after their last use to

ensure that their properties remain unchanged.  Since material thermal diffusivity relates

indirectly to heating rate index (i.e., fh), thermal property verification could be in the form

of heating rate determination of all HIUs under specific heating conditions before and after

a test.

2.17.5.Factors that can influence standardization/calibration of the HIU materials include:

machining tolerances, seals, air and water residues in the TMD wells, and heat degradation

of the HIU upon repeated use.

2.17.6.HIUs such as bentonite suspensions at different concentrations exhibit different heating

characteristics resulting in convection and conduction (simple or broken heating) profiles.  

Preparation steps should be consistent from batch to batch to minimize inherent errors

(13, 14).
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     2‐6

2.18.When actual packaged product is being used to collect heat transfer distribution or heat

penetration data, a critical assumption is that it is uniform across all test packages.  Any

intrinsic variability in the product would be built into the data collected during its use in specific

thermal processing studies such as heat penetration or heat transfer distribution tests.  This

intrinsic variability would/could eventually affect Process Establishment or meeting Heat

Transfer Distribution Success Criteria.

DOCUMENTATION

Calibration or standardization results should be included in study documentation.  A listing of records

required by US‐FDA regarding calibration records for temperature indicating and reference devices can

be found in 21 CFR Part 113.100.

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     3‐1

3 DOCUMENTING PROCESSING EQUIPMENT AND TEST CONDITIONS

It is important to establish proper documentation regarding the processing equipment used for thermal

processing studies including:  temperature distribution, heat transfer distribution, and heat penetration.  

While processing equipment surveys are not a part of data collection per se, they are important in

identifying retorts that are used for thermal processing studies, documenting study test conditions, as

well as helping plant management realize that projects outside the retort room may have an effect on

processing operations.  

Surveys should be periodically performed on all retorts to ensure that they remain consistently and

properly installed to previously documented conditions.  These may also be an important part of a

plant’s change control program.  Note that USDA requires annual surveys or audits of retort systems.

SCOPE

The guidelines in this chapter are applicable to any retort system.  The listed items for a processing room

survey should not be considered as being “all inclusive”.  Some listed items may not be applicable to the

particular retort/processing system being documented.

OBJECTIVES

The objectives of conducting a retort/processing survey include:

3.1. Documentation of test retort(s).

3.2. Providing documentation to aid in the identification and sometimes the selection of retorts for

temperature distribution, heat transfer distribution, and heat penetration studies.

3.3. Documentation of “as existing” conditions that may then be used as part of an overall change

control program.

ITEMS TO INCLUDE IN THE SURVEY

Retort

3.4. Shell – Physical dimensions of the retort and capacity (e.g., number of baskets, cassettes,

dividers, etc.).  Secure if possible, the retort manufacturer’s or factory blueprints of the retort

and all attendant piping, as well as, any alterations since the retort was originally installed.

3.5. Controls‐ Process controls and installation variations from one retort to another (if any) in the

selected test retort group

3.6. Location of Instrumentation including instrument wells – Size, shape and location of well(s)

used to locate sensors.

3.7. Reference Temperature Indicating Device (TID) – Type, location and calibration status.
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     3‐2

3.7.1.Where used, Mercury‐in‐glass (MIG) thermometer location, temperature range and

increments, length of scale, calibration date, and length of insertion, i.e., the length of the

sensing bulb that is inside either the retort shell or instrument well.

3.7.2.Electronic TID type (e.g., RTD, thermocouple, thermistor, etc.), range, response time,

location, and length of insertion.  If applicable, record if the reference TID is located

directly in the heat transfer medium.

3.8. Temperature Control Sensing Device– Type and location of the temperature control sensing

device.  Describe location of control sensor in relation to the TID sensor and to the steam

distributor.  If applicable, record if the temperature control sensor is located directly in the heat

transfer medium.

3.9. Pressure Control Sensing Device – Type and location of the pressure control sensing device.

3.10.Overflow/purge/vents (air removal)

3.10.1.Valve type and size

3.10.2.Pipe size and connections to drain headers or channels

3.10.3.Vents – location and size of pipes, type and size of valves

3.10.4.Vent manifold or manifold headers – location and size of all pipes and connecting pipes

3.10.5.Bleeders, mufflers – location, number, size and construction

3.10.6.Safety valves – size, type and location

3.10.7.Additional piping or equipment such as condensate removal systems, etc.

3.11.Pressure Indicating Device/Sensor – Note type, range and location of pressure sensors and

gauges.

3.12.Drains including water level dumps, overflows, condensate removal

3.12.1.Valve type and size

3.12.2.Pipe size and length

3.12.3.Note if check valves are used

3.12.4.Note location of the condensate removal system in relation to critical zones, e.g., relation

of condensate drain to the bottom of the cook shell in a continuous rotary/reel and spiral

cooker.

3.13.Steam supply to the retorts

3.13.1.Boiler capacity (horsepower, BTU rating), pressure, and method of firing (gas, oil, coal,

dual capacity).

3.13.2.Header pressure.  This is important to determine that adequate steam pressure and

volume is available for the retorting system.  This part of the survey should be performed

during both peak use and off‐load hours.

3.13.3.Pipe size and length, valve size and types, pressure regulators or reducers, pipe fittings

including steam by‐pass pipes, from the main steam line to the test retort(s)

3.13.4.Size of all connecting steam pipes to the main line, noting all equipment using steam

(e.g., blanchers, exhaust boxes, etc.).

3.14.Steam Introduction into the Retort –
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     3‐3

3.14.1.Type and specifications for the steam distribution system including configuration (e.g.,

fishtail, cross, in‐line, etc.), steam flow piping, size, number and location of steam injection

perforations

3.14.2.Steam injection chamber (if applicable)

3.14.3.Steam injection points – size, type and location

3.14.4.Steam spreader or nozzle – shape, size, location and configuration, number, size and

location of holes in pipe, size of “T”, or any other pipe fittings.

3.14.5.Describe the heating medium (e.g., steam, hot water) and temperature.

3.14.6.Describe the cooling medium (e.g., re‐circulated refrigerated water, ambient well water,

evaporative cooling towers or ponds in re‐circulating cooling water circuits).

3.15.Air or nitrogen supply to and into the retorts

3.15.1.Compressor type, capacity and operating pressure

3.15.2.Type and size of filter, dryer and tank

3.15.3.Line size, pressure, filters and dryers for instrument air

3.15.4.Process air header line size(s), pressure and pressure regulation, if used

3.15.5.Entry location and inlet size, control valve size and type, pressure setting and flow rate

during testing.  Availability to supply instruments.  Indicate if air is heated or air lines are in

close proximity to steam or water lines.

3.15.6.For Overpressure Retorts ‐ Location and size of pipes and valves (type and size) and

method of control.

3.16.Water supply to and into the retorts

3.16.1.Process water supply source, quality, temperature, and controls, if applicable

3.16.2.Cooling water supply source, quality (including microbial control methods), temperature,

and controls, if applicable

3.16.3.Use of any alternate methods of heating processing water

3.16.4.Describe the method used to heat and cool the processing water including type (e.g.,

heat exchanger, cooling tower, etc.)

3.16.5.Location and size of pipes, valve size and type, pump and/or spreader size, type and

location (if applicable)

3.16.6.Water level indicators – where applicable, type (e.g., sight glass, petcock, electronic, etc.)

and location

3.17.Depending upon the retort system, document the following:

3.17.1.Where applicable, water recirculation system including pump type and capacity, location

and sizes and filters of inlet/outlet ports, recirculation line size, flow meter type and

capacity, output rates at operating conditions (e.g., gpm or L/min), rpm, pipe diameter for

pump inlet and outlet and horsepower rating, impeller size

3.17.2.Air flow, orifice size, pressure setting and flow rate, if applicable

3.17.3.Pressure and/or flow switches type, location, and trip point setting, if applicable

3.18.For Steam/Air Retorts

3.18.1.Type and description of circulation and mixing system for steam/air mixing; bleeder(s)

size, type and location
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     3‐4

3.18.2.Air Plenum and fan shroud (if applicable)

3.18.3.Distance (length) from retort shell to plenum material if designed as a “shell in shell”.

3.18.4.Details on fan shroud design and connection to the plenum

3.19.For Water Spray and Water Cascading Retorts

3.19.1.Water spreader(s) size, type and location

3.19.2.Water recirculation system – pump type and capacity, impeller size, motor size, location

and sizes and filters of inlet/outlet ports, recirculation line size, type and capacity of flow

meter

3.19.3.Steam injection points – size, type and location

3.19.4.Heat exchanger – use, size and type

3.19.5.Water distribution Plate(s) (Water Cascade)

3.19.6.Location of water inlet pipe to manifold (e.g., top/center of retort shell, top/rear of retort

shell)

3.19.7.Dimensions of manifold and material of construction

3.19.8.Number, size and location (hole pattern) of holes in water distribution plate; percent

open area of the holes in the water distribution plate should be calculated (Water

Cascade)

3.19.9.Water distribution pipes (Water Spray Retorts)

3.19.10.Entrance location of entrance of water inlet pipe into retort shell

3.19.11.Location of water distribution pipes in relation to circumference of retort interior

3.19.12.Length of pipes, do they extend the length of the retort?

3.19.13.Number, size and location of holes in pipes

3.19.14.If connected to nozzles, describe the nozzle type.  Are nozzles fixed or capable of

oscillation?  Describe if nozzles restrict diameter of the openings.

3.19.15.Describe water flow rate, e.g., liters per minute, gallon per minute, etc.

3.19.16.Process water retention channel or trough in bottom of retort

3.19.17.Note if and how process water is retained for cooling or re‐use

3.19.18.Length, width and depth of water channel or trough

3.19.19.Amount of water (liters or gallons) at start of process and how it is controlled and

measured.

3.19.20.If applicable, location of steam distributors or spreaders in relation to channel or

trough.

3.20.Rotational Equipment – rotational speed indicator and drive system

3.21.Recording Device – Recorder or recorder/controller type and description including: resolution,

parameters recorded, and calibration status.

3.22.Retort Loading Considerations/Loading Equipment

3.22.1.Container information to include material, size and dimensions, orientation for

processing (vertical, horizontal, jumbled), and loading configuration (e.g., layered, nested,

compartmented, offset, etc.)

3.22.2.Maximum number of containers per layer
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     3‐5

3.22.3.Maximum number of cassettes, baskets, or racks per retort

3.22.4.Cassette, basket or rack dimensions, hole size, configuration and spacing in the base

plate and sides of cassettes, baskets or racks

3.22.5.Separator sheet dimension, hole size including open area, configuration, and spacing

3.22.6.Partial load arrangement, if permitted

3.22.7.Water displacement requirements (ballast)

3.22.8.Distance between cassettes, baskets or racks, where applicable

3.22.9.Orientation of the cassettes, baskets or racks in the retort during processing

3.22.10.Percent open area of the cassettes, baskets or racks, if used

3.22.11.Describe basket clamping devices, where applicable

3.22.12.Describe top and bottom plates holding baskets, where applicable

3.23.Other Equipment – Other control or functional equipment installed that might affect the

thermal process study being conducted.  Examples of other types of equipment that should be

noted include:

3.23.1.Sampling ports

3.23.2.Water or condensate level dump valves

3.23.3.Initial charge and make‐up water systems

3.23.4.Insulation and/or jacketing of retort shell

DOCUMENTATION

Results and observations made should be documented and retained for future reference.  The use of

digital images may prove useful.

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     4‐1

4 CONDUCTING TEMPERATURE DISTRIBUTION TESTS

Temperature distribution studies are conducted in a sterilizer (retort) using distributed temperature

measuring devices (TMDs) to establish venting procedures, venting schedules, come‐up requirements,

temperature stability and uniformity, all of which are necessary to establish reproducible and reliable

heating and cooling performance throughout the retort.  Temperature distribution studies are typically

performed using estimated production retort operating conditions or parameters.

SCOPE

4.1. The guidelines in this chapter are applicable to conducting temperature distribution studies in

batch saturated steam, steam/air, water immersion, water spray, and water cascade retorts

operating in both still and agitated modes.

4.2. Crateless retorts are excluded from the guidelines provided in this document.

4.3. Continuous Rotary/Reel and Spiral and Hydrostatic retorts are excluded from the guidelines in

this document.

OBJECTIVES

4.4. The objectives of conducting temperature distribution studies include:

4.4.1.Establishing venting procedures and schedules (where applicable), come‐up requirements,

identifying the existence (if any) of slowest to come to process temperature location(s), as

well as temperature stability and uniformity during the Cook.

4.4.2.Temperature distribution data may also provide insight into the impact of changes made

to processing equipment, utilities, and other identified critical factors (e.g., package size,

type, loading configuration, etc.).

INTRODUCTION and BACKGROUND

4.5. Acceptable temperature distribution is a requirement for process establishment.

4.6. New retorts require temperature distribution studies.  Similarly, retorts that have undergone

extensive repair re‐design, or relocation can be expected to require temperature distribution

studies.

4.7. Consideration should be given to testing all retorts on a regular basis to confirm they continue

to perform as previously tested and documented.  The replacement or normal wear of

components associated with maintaining acceptable temperature distribution also warrant

consideration for performing temperature distribution studies.  These components may

include, but are not limited to:  water circulating pumps, valves and pipes associated with

steam/water flow, steam injectors (fishtails), air orifices, overflow/pressure regulating valves,

spray nozzles, heat exchangers, water distribution plates, and control system changes.  
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     4‐2

4.8. Temperature distribution can vary with individual installations of identical equipment at the

same location.  Consideration should be given to performing temperature distribution in each

individual retort to document variation within individual retorts.

4.9. If appropriate, information taken in the processing equipment survey and an understanding of

plant change control processes, validation, and operation procedures may be used to develop a

reduced testing plan.

4.10.Demonstration of adequate temperature distribution is usually a prerequisite for conducting

heat transfer distribution (where applicable).

MATERIALS, TOOLS, EQUIPMENT

4.11.See Chapter 2 – Test Equipment and Standardization of Test Equipment

METHODS

4.12.Test Retort Selection

4.12.1.Consideration should be given to testing all retorts in a system.  

4.12.2.When appropriate, a reduced testing plan can be developed based on the information

taken in the processing equipment survey (see – Chapter 3, Documenting Processing

Equipment and Test Conditions).  The reasons for retort selection should be documented

in testing records.  The retort(s) selected should represent the one(s) identified as having

the greatest potential for diminished delivery of the critical process utilities such as steam,

air, and water.  Factors that may help identify the test retort (s) include:  retort position

(e.g., at the beginning or end of a line of retorts, furthest from steam header), container

configuration, divider sheet style, type of heat transfer medium, and processing partial

loads.

4.12.3.The results of the processing equipment survey should be verified for completeness and

accuracy prior to the start of tests.

4.13.Test Retort Documentation

4.13.1.Test retort documentation may include photographs, diagrams, and a description of the

operation, condition, and calibration status of sensors/measurement devices.

4.14.Location of Temperature Measuring Devices in the retort

TMDs should be placed in the following locations:

4.14.1.Attached or in close proximity to the reference TID probe.

4.14.2.Attached or in close proximity to the temperature control device, unless the reference

TID and the controller probe are located together.

4.14.3.Located in at least two containers filled with test medium for the purpose of determining

initial product temperatures.  These containers should be located in the positions that are

representative of the potential worst case locations in the retort load.

4.14.4.The lowest of initial temperatures to be encountered during normal commercial

operation should be taken into account in establishing temperature distribution.  The
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     4‐3

initial temperature measured should be considered in the context of retort shell and

basket/crate/rack temperatures which may be lower or higher than the product

temperatures and could have an effect on the total heat load.

4.14.5.An adequate number of TMDs are needed to ensure that the slowest to come‐up to

temperature locations are identified.   A minimum of five (5) TMDs per basket/crate are

typically used.  These should be located in different layers or otherwise separated in each

basket/crate in the initial phase of the temperature distribution study.  The intent is to

determine the slowest to come‐up to temperature location in each basket/crate.  Note

that additional studies with a higher concentration of TMDs in a particular area or zone

may be required to verify that the slowest come‐up to temperature location(s) within the

retort load have been identified.

4.14.6.TMDs should be placed so those measuring junctions are not in direct contact with

containers or other surfaces.  All TMDs must be securely fastened in place to prevent

damage and unplanned movement during the process (particularly in agitating systems).

4.14.7.In subsequent studies, where no changes have been made to the equipment and

previous studies have indicated consistency of cold spot location(s), a reduced number of

TMDs per basket/crate/rack may be sufficient.

4.15.Location of pressure sensor(s)

4.15.1.At least one pressure sensor should be located in the retort shell.  If the operational

pressure sensor has been recently calibrated, it can be used in place of a test device.  

Pressure gauges should also be used to monitor line pressures of steam, air, and cooling

water during a test.

4.16.Location of flow meter(s)

4.16.1.A calibrated flow meter (or alternate method) should be located in a manner to provide

an accurate record of the water circulation flow during the process cycle in systems using

circulation pumps.

4.16.2.A calibrated flow meter (or alternate method) should be located in a manner to provide

an accurate record of the air flow during the process cycle in systems using air for agitation

and mixing of process water.

4.16.3.For steam/air retorts – a calibrated flow meter (or alternative method) may be located in

the return air plenum to provide an accurate record of the steam/air mixture during the

process cycle.  If the circulating fan is equipped with a directional/rotational and rpm

sensing ability of the fan shaft, then the details of the fan motor from the retort survey will

suffice.

4.17.Record of Monitored Locations (TMD Map)

4.17.1.A schematic drawing to show the placement of all monitoring devices within the retort

should become part of the documentation for the temperature distribution tests.

4.18.Preparing Retort with Containers

4.18.1.Container Size – The container size and load density that are likely to be the most difficult

to achieve temperature uniformity are typically selected for temperature distribution

studies.  In many cases this will be the smallest container and/or the densest load in use.  
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In some cases, multiple container sizes, types, configurations and orientations will need to

be tested.

4.18.1.1.Since temperature distribution may vary widely with some systems depending

upon container and type, it may be necessary to study each different container/ type

and loading condition to develop a different come‐up profile for each size/type and

loading condition.

4.18.2.Container Contents – Containers may be filled with water, or the fastest heating product,

for studying retorts that process convection heating products.  For conduction heating

products, the containers should be filled with product, starch suspensions, or other

material that simulates the product.  Regardless of material chosen, caution should be

exercised when heating characteristics may change with multiple heating cycles.  For

water immersion, water spray, or water cascade retorts that use a temperature

“overshoot” in the come‐up profile to help temperature uniformity, use of conduction

heating containers is often the worst case situation, and should be carefully considered.  

Note that stabilization periods at the end of come‐up are not considered to be overshoots.

4.18.2.1.For saturated steam retorts, water may be used for conduction heating products;

however the come‐up times may be somewhat longer than what will occur with

product.

4.18.2.2.Document the reasons for ballast container content selection in test

documentation.

4.18.3.Container Placement Considerations – Containers are placed in the basket/crate in a

manner that is equivalent to the worst‐case situation as seen in the commercial operation.  

The worst‐case may be the maximum number of containers per layer, actual number of

layers, maximum load density, loading pattern, maximum fill of pocket space, and other

conditions that result in the densest load.  Where vertical channelling is possible, this

condition should be considered in the temperature distribution test design.  These aspects

may need to be evaluated through additional testing to ensure that the worst‐case has

been defined.  

4.18.4.Container Organization – This includes aspects related to baskets, divider sheets, trays,

racks, and other means of holding or configuring packages in the retort.

4.18.4.1.The separator or divider sheets should be the same as those to be used in

production.  If more than one type of separator or divider sheet is used in

production, then the dividers with the smallest percent open area should be used. If

additional dividers are used on either the top or the bottom of the container load,

this procedure must be duplicated for the test.

4.18.4.2.For a tray or rack that is used to hold and/or separate containers, the design of the

tray or rack that will be used in production must be used for temperature

distribution studies.

4.18.4.3.Variations in basket/crate/rack loading configuration and design expected in

production may need to be tested to determine which yields the worst‐case

situation.  The smallest anticipated partial load and location of the partial load
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should be compared to full load conditions noting the uniformity and temperature

control and stability throughout the retort.

4.19.Conducting the Test

Data Collection/Monitoring Points – Depending upon the retort system, the following should

be monitored and recorded during temperature distribution studies.

All Retorts

4.19.1.Temperature and Pressure Controller set point(s), including if there is an overshoot set

point for come‐up and a lower set point for processing

4.19.2.Product or Ballast Initial Temperature

4.19.3.Time process cycle starts, Time = 0 (time zero)

4.19.4.Times when the end of come‐up, start of thermal processing/cook step has been

achieved, as indicated by either the step change in a control program or the achievement

of process set‐point temperature at both the reference TID and the recorder/controller

4.19.5.Reference TID readings at sufficient intervals during the entire cycle, including the point

in time it reaches the process temperature set point.

4.19.6.Monitor rotation or agitation rate at sufficient intervals using an accurate calibrated

stopwatch or calibrated device including any points where rotation rate changes during

processing or on a continuous chart where rotation or agitation is used.

4.19.7.Time at the end of thermal process, and start of cool.

4.19.8.Actual basket/crate/rack orientation in the retort.

4.19.9.Operating activity of other retorts including the number of retorts entering come‐up

during the study.

4.19.10.Numbers and descriptions of other equipment using steam (e.g., blanchers) at the time

of the study and before, during, and after come‐up.

In addition to the above, these items should be monitored and recorded based on the retort

being studied:

Steam/Air

4.19.11.Temperature of air supply entering the retort.

4.19.12.Water level in relation to spreaders and lowest level of containers in the retort, if

applicable.

4.19.13.Time when the pressure set‐point(s) is achieved.

4.19.14.Time and temperature when the drain is closed, if it is open during a portion of the vent

if applicable.

4.19.15.Time and temperature taken from the reference TID when the vent closes.

4.19.16.Air flow in scfm or liters per minute, if applicable and available.

4.19.17.Line steam pressure at the time of the test and before, during, and after come‐up, if

possible.

4.19.18.Retort pressure, throughout the test cycle at sufficient intervals or on continuous chart.
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Issue Date: March 13, 2014

Supersedes Date:  New     4‐6

Saturated Steam

4.19.19.Water level in relation to spreaders and lowest level of containers in the retort.

4.19.20.Time and temperature when the drain is closed, if it is open during a portion of the

vent.

4.19.21.Time and temperature taken from the reference TID when the vent closes.

4.19.22.Line steam pressure at the time of the test and before, during, and after come‐up, if

possible.

4.19.23.Time steam bypass valve closes.

Water Spray and Water Cascade

4.19.24.Temperature of initial process water.

4.19.25.Water level in relation to spreaders and lowest level of containers in the retort.

4.19.26.Flow or recirculation rate of water as determined by flow meter or other acceptable

means.

4.19.27.Time when the pressure set‐point(s) is achieved.

4.19.28.Retort pressure, throughout the test cycle at sufficient intervals or on continuous chart.

Water Immersion

4.19.29.Temperature of initial process water.

4.19.30.Fill time (displacement) in those systems dropping water from a storage drum or tank

into the working processing vessel.

4.19.31.Water level in process vessel in relation to the top surface of containers, stated as a

minimum or an actual level throughout the process.

4.19.32.Flow or recirculation rate of water as determined by flow meter or other acceptable

means.

4.19.33.Time when the pressure set‐point(s) is achieved.

4.19.34.Air flow in scfm or liters per minute, if applicable and available.

4.19.35.Line air pressure at the time of the test and before, during, and after come‐up, if

possible.

4.19.36.Retort pressure, throughout the test cycle at sufficient intervals or on continuous chart.

4.20.Data‐logger

4.20.1.The data‐logger should record the temperature of each TMD at sufficient sampling

frequencies, typically 10‐30seconds, throughout the length of the study.  

4.20.2.The data‐logger should record the temperature from cycle start through completion of

cooling.

4.21.Other critical data collection point frequencies

4.21.1.Assumed or potential process‐related critical factors should be recorded at intervals of

sufficient frequency to describe and verify retort operating parameters during the test.  

Recordings are part of the permanent test records and should include the temperature

recording chart, the pressure readings/chart, flow rate records, reference TID readings,

and other data gathered that were identified as critical data collection points.
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Supersedes Date:  New     4‐7

4.22.Study time duration

4.22.1.The test should extend for at least as long as needed for the retort control system to

stabilize, establish a definite temperature profile, and all monitoring and TMDs have

reached a steady‐state condition.

4.22.2.If desired, retort cooling phase temperatures may be recorded through the entire cooling

cycle.  This is particularly important if product cooling lethality will be based on actual

retort cooling profiles in developing scheduled processes.

4.23.Retort Test Conditions

Operating Procedures – Normal commercial operating procedures testing the extremes of

allowable ranges to examine the effects of loading, overpressure, and agitation should be

followed.

4.23.1.Temperature distribution studies should be run at the maximum retort temperature to

be used for commercial processing.  For example, one should not run temperature

distribution studies at 250°F (121°C) if the product is processed at 266°F (130°C).  

Generally, temperature distribution studies should not be run any higher or lower than 5F°

(~2.5C°) from the temperature at which product will be processed.  

4.23.2.Minimum vent temperature and time is a critical factor for steam retorts.  The

temperature and time at which the vent is closed become the minimum vent schedule for

the process.

4.23.3.Partial loading conditions should be studied in addition to the full load where permitted.

4.23.4.Basket rotation should be studied at or below the expected Scheduled Process value.

Where applicable, the following additional conditions may be tested at the standard retort

processing temperature used for commercial production:

Steam/Air

4.23.5.High steam to air ratio (Low Overpressure).

4.23.6.Low steam to air ratio (High Overpressure).

Water Spray, Water Cascade, and Water Immersion Retorts

4.23.7.Low flow of the heat transfer medium.

4.24.Replication – To demonstrate reproducibility, at a minimum duplicate temperature

distribution studies should be performed for each situation (e.g., container size, container type,

operating temperature, basket/crate/rack system) with uniform and comparable results

obtained from each test.

4.25.Post‐test inspection

4.25.1.The condition of the measuring sensors, the test containers, and other attributes of the

retort load should be examined after the completion of the entire set of studies to

determine if the test results may have been affected by movement or other changes to the

desired test setup.
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Supersedes Date:  New     4‐8

DATA ANALYSES

4.26.Plot or tabulate the minimum and maximum measured temperatures for all TMDs within the

retort load at each scan/time interval.  The TID, Controller, and Chart temperatures at specific

time points should be evaluated relative to the TMD’s temperature.

4.27.Evaluate the difference between the minimum measured temperature and the programmed or

set‐point minimum process temperature at specific time points to establish or confirm

temperature off‐sets and to establish come‐up time.

4.28.Identify the location of the TMD that was the slowest to achieve come‐up criteria.  Identify the

time this TMD achieved come‐up criteria.

4.29.Identify the minimum Initial Temperature.

SUCCESS CRITERIA

4.30.Come‐Up –  

4.30.1.The TID should be at or above minimum process temperature at the end of come‐up.  

4.30.2.All TMDs should be within 1F° (0.5C°) of minimum process temperature at the end of

come‐up.  

4.30.3.All TMDs should be at or above the minimum process temperature within 1 minute of

starting the hold time.   

4.31.Cook/Hold –  

4.31.1.After the start of Hold, the TID should not fall below the minimum process temperature.

4.31.2.After the first minute of the Hold phase, the uniformity and stability of temperatures is

confirmed by having no TMD temperature fall below minimum process temperature once

that TMD has reached the minimum process temperature.

4.32.Cooling – If specific cooling profiles are critical to the process delivery, the temperature

distribution during cooling must support those profiles.

4.33.Other –  

4.33.1.The location of all TMDs must be confirmed at the end of all studies.  Any TMD that

shifted during data collection should be evaluated for impact on study outcomes.

4.33.2.The integrity of test packages/ballast should be confirmed to be acceptable.

4.33.3.All critical retort operating parameters (e.g., Temperature, Rotation, Pressure, Flow,

Water Level, and Fan Speed) were achieved as planned and/or programmed.

4.33.4.Situations or conditions that do not meet these criteria should be critically evaluated.

4.33.5.Identify the minimum Initial Temperature for which the temperature distribution is valid.

4.33.6.Identify all other aspects of the product, package, ballast, loading pattern, and so forth

for which the temperature distribution is valid.
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Issue Date: March 13, 2014

Supersedes Date:  New     4‐9

DOCUMENTATION

Temperature distribution findings should be summarized in a report.  Supporting items that should be

included are:

4.34.Reason(s) for retort selection.

4.35.Results from the retort survey and test retort documentation.

4.36.Schematic showing placement of all measuring devices in the retort.

4.37.Reason(s) for product selection.

4.38.Retort charts, operator logs, retort control program, and control system reports.

4.39.Critical point observations to include Initial Temperature.

4.40.Calibration information for all sensors/devices used.

4.41.Data‐logger data for both retort and product.

4.42.Graphical depictions of minimum/maximum data.

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date:  New     5‐1

5 CONDUCTING HEAT TRANSFER DISTRIBUTION TESTS

This Guideline covers the scientific basis and fundamentals for conducting Heat Transfer Distribution

Studies with emphasis on critical elements to be considered.  This Guideline provides rationale for

considerations to be used by an end user in deciding when Heat Transfer Distribution Studies are

needed in addition to Temperature Distribution Studies.

SCOPE

5.1. The guidelines in this chapter are applicable to conducting Heat Transfer Distribution Studies in

steam/air retorts and may be applied to water spray, water cascade, and water immersion

retorts where air overpressure in excess of the saturated steam pressure (corrected for

altitude) at process temperature is used. These guidelines are applicable to retorting systems

operating in both still and agitated modes.

OBJECTIVES

The objectives of Heat Transfer Distribution Studies include:

5.2. Identification of the slowest to heat location in a retort to the extent that it impacts process

delivery within the retort load when using the same process, product, package, and load

conditions.  Load Conditions include: Partial loading of baskets (e.g., less than a full basket of

trays), less than a full retort load (e.g., 4 baskets in a 5‐basket retort), tray/racks loading (e.g.,

not all package locations filled with a package), and density and/or percentage of open

volume/void volume.

5.3. Identification of the repeatability of those relatively slower to heat locations across retorts and

studies using the same process, product, package, and load conditions.

5.4. Identification of recommended locations to place Heat Penetration containers for Process

Establishment.

5.5. Verification of the adequate delivery of the thermal process over time for a given

product/package combination and loading condition(s).

INTRODUCTION and BACKGROUND

5.6. Temperature Distribution testing usually focuses on come‐up and cook portions of the retort

cycle.  Temperature uniformity in these portions of the retort cycle may not always correlate to

adequate heat transfer into packages throughout the retort, hence the need for Heat Transfer

Distribution studies. Acceptable Temperature Distribution is recommended prior to conducting

Heat Transfer Distribution Studies.

5.7. Heat Transfer Distribution testing may be recommended when:
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Issue Date: March 13, 2014

Supersedes Date:  New     5‐2

5.7.1.A non‐condensable gas such as nitrogen or air is introduced into the heat transfer medium

to provide overpressure in excess of the saturated steam pressure (corrected for altitude)

at the Cook Temperature.

5.7.2.For heating medium delivery systems (including type, flow, rack, package, etc.) whenever

it is possible that in certain areas of the retort load the rate of heat energy supplied to the

package is not in excess of the rate at which the package can absorb the heat energy.

5.7.3.For new retorts, new retort programs/controls, new product/package/closure

combinations including trays/racks/load configurations requiring overpressure air in

excess of the saturated steam pressure at Cook Temperature.

5.7.4.As part of an overall Change Control Program.

5.7.5.When partial loads may be processed during manufacturing.

5.7.6.Any time there are concerns that heat transfer delivery may be impacted by the retort’s

heating medium mixing and distribution system such as the presence of a fan, nozzles,

shrouds/plenum, racking/tray design, and so forth.

5.8. Heat Transfer Distribution data may assist in conducting deviation analyses provided data are

collected using actual product and package.

5.9. Heat Transfer Distribution data can be used as part of an overall ongoing program to verify

retort operations over time.

5.10.The effects of package location along the radius of rotating loads are often not considered in

Temperature Distribution testing, nor are effects of fastest to heat packages compared to those

that are fastest to cool.  Heat Transfer Distribution Studies may provide insight into potential

effect of location along the radius of rotating loads as well as effects of faster to heat and cool

packages within the retort load.   In addition, insight may be gained on retort fan position,

heating medium/air inlet design and shroud design, and their influence on the flow and mixing

of the heating medium.

5.11.If desired, lethality data collected using actual packaged product (vs. non‐product based HIUs)

may be separated into that achieved during come‐up and cook versus that achieved in cool.  

This information may be valuable in assessing the effects on nutrients and the product’s

physical stability throughout the retort load.  Modifications to the retort, package, loading

configurations, trays/racks, processing cycle, etc. to reduce or minimize the lethality differential

throughout the load may be then possible.  Note that Heat Transfer Distribution data are not

used for Process Establishment.

5.12.As part of an overall Change Control program, Heat Transfer Distribution data collection should

be considered whenever:

5.12.1. Changes are made to packaged product loading such as new or modified trays, baskets,

etc. are introduced.

5.12.2.Changes are made to load density, flow rate of heat transfer medium, and shroud design.

5.12.3.Changes are made to the primary package (e.g., heavier bottle), change to package fill

volume and/or headspace volume, etc.

5.12.4.New formulations are introduced.
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Supersedes Date:  New     5‐3

5.12.5.Changes are made to utilities or the retort such as those done as part of upgrades to

equipment or significant repairs.

5.12.6.The amount of air overpressure in excess of saturated steam pressure (when corrected

for altitude) at Cook Temperature is modified.

5.12.7.Partial loads are to be processed.

5.13.Heat Transfer Distribution studies, in contrast to Heat Penetration studies, must always be

conducted in the production retort(s).  Pilot Plant Retorts or Research Simulators should not be

used for studying or extrapolating Heat Transfer Distribution performance.

5.14.Microbiological techniques are not recommended for Heat Transfer Distribution studies.

5.15.Temperature and pressure must be independently controlled and recorded.

MATERIALS, TOOLS, EQUIPMENT

5.16.See IFTPS Guidelines for Conducting Thermal Processing Studies, Chapter 2 – Test Equipment

and Calibration of Test Equipment.

5.17.Heat Transfer Distribution measurements may be obtained from instrumented/probed:‐  

5.17.1.Product‐filled packages; or

5.17.2.Non‐product based HIUs made from polymer‐based materials such as Teflon, clays such

as bentonite suspensions, and oils.  Please refer to, Section 2.14.11 for criteria regarding

use of non‐product based HIUs.

5.18.A sufficient number of instrumented/probed samples to ensure that all areas of the retort load

are being studied and to support statistically valid analyses must be included in each study.

METHODS

Test Retort Selection

5.19.In general, all of the information taken in the processing equipment survey should be used to

select the retort(s) that will be used for Heat Transfer Distribution Studies.  The reasons for

retort selection should be documented in testing records or all retorts should be studied.  

5.20.The retort(s) selected should represent the one(s) identified as having the greatest potential

for diminished mixing and delivery of the heat transfer medium.

5.21.Heat Transfer Distribution Studies must be conducted using production retorts under expected

production and operating conditions.

Test Retort Documentation

5.22.Information based on data from the processing equipment survey and from Temperature

Distribution Studies should be included in study documentation.

5.23.The specific process, product, package, and load conditions being studied must be

documented.

Ballast Retort Load

5.24.The ballast used may be product‐filled packages of the type and size being evaluated.  

Alternatively, other materials may be used provided their heating characteristics are consistent

with the product being studied.
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Supersedes Date:  New     5‐4

5.25.Ballast packages should retain their heating and physical characteristics if they are to be re‐

used.  Re‐use of ballast packages should be documented in a Test Report.   

5.26.Note that water‐filled packages generally should not be used as ballast for Heat Transfer

Distribution Studies to allow the retort controls to perform representatively for heating media,

delivery and its replenishment within the load.

Baskets/Trays and Loading Considerations

5.27.The loading conditions used or expected to be permitted during manufacture of packaged

product must be studied.  This includes using the baskets, trays/racks, dividers, cassettes, etc.

that will hold/carry product‐filled packages.

5.28.Load density may have a dramatic impact on Heat Transfer Distribution.  This is due to

inhibition or retardation of distributing the heat transfer medium throughout the retort load.  

Therefore, optimization with respect to the specific retort’s heat transfer medium mixing and

distribution should be considered wherever possible.  Optimization factors to consider include

the design of:

5.28.1.Trays/racks/baskets,

5.28.2.Package,

5.28.3.Number of packages per layer/rack/basket, and

5.28.4.Retort operating parameters such as temperature and pressure values and ramps, timing

of air introduction, any venting at the start of the retort cycle, or pre‐heating of the

overpressure air.

Locations of Probed Packaged Product/HIU in the retort

5.29.Heat Transfer Distribution test units are placed in suspected or known slower to heat locations

within the retort load.  Multiple studies may be required to confidently identify the slower to

heat locations within the retort load.  

5.29.1.TMDs to measure temperatures surrounding the test packages should be located in

proximity to those test packages.  These TMDs are to be used to accurately calculate fh

values of adjacent test packages.

5.30.TMDs to measure product/HIU temperatures to be used for data analyses should be securely

fastened inside the test package so that the measuring junction/tip is held in the test package

cold spot.

5.31.At a minimum, five (5) probed product packages/HIUs should be located in separate suspected

or known slower to heat areas of each basket.  Symmetry and rotation effects should also be

considered when determining locations for Heat Transfer Distribution test units.

5.32.All baskets in the retort should contain test units.

Location of pressure sensor(s)

5.33.Independent verification of total retort pressure during Heat Transfer Distribution Studies is

recommended when possible and practical.

Location of flow meter(s)

5.34.Independent verification of flow rates of the heating medium is recommended when possible

and practical.

Record of Monitored Locations (Loading Pattern/Map)
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Supersedes Date:  New     5‐5

5.35.A schematic drawing to show the placement of all monitoring devices within the retort should

become part of the documentation for Heat Transfer Distribution Studies.

Retort Control and Process Conditions

5.36.Heat Transfer Distribution Studies should be conducted using the process parameter conditions

such as temperature, pressure, mixing and distributing the heat transfer medium, and rotation

set‐points used during normal production or manufacture of the packaged food being studied.

5.36.1.Since fh and the associated %CV are used as the primary measures to assess adequacy of

Heat Transfer Distribution, data do not necessarily need to be collected at the highest

allowed overpressure permitted for the product/package being evaluated.  This is in

contrast to Heat Penetration studies where all “worst case” retort conditions and

parameters must be used.It is important that the amount of overpressure used during

Heat Transfer Distribution Studies be representative of the expected production condition

for the product/package being studied.

Conducting the Test

5.37.Data Collection/Monitoring Points – Heat Transfer Distribution test units must be located in

suspected or known slower to heat locations within the retort load.  Independent verification of

parameters such as controlling temperature, pressure, heat transfer medium flow rates, etc. is

recommended.  Location of independent sensors is at the discretion of the persons responsible

for the study design.

5.38.Scan Frequency for Measurement Devices

5.38.1.Where possible, measurement devices should be set to a scan frequency sufficient to

accurately determine heating parameters (i.e., fh).

5.39.Study time duration

5.39.1.Cook durations should be of sufficient length to adequately determine fh values and to

confirm that Temperature Distribution success criteria were satisfied (See Temperature

Distribution success criteria).

5.40.Replication

5.40.1.At a minimum, duplicate Heat Transfer Distribution Studies should be performed for each

situation (e.g., package size, package type, operating temperature, basket/tray/rack

system, etc.) with uniform and comparable results obtained from each test.  Success

Criteria must be met in all replicate studies.

5.40.2.Replicates should be true replicates in all respects, including Initial Temperature, Retort

Temperature, Pressure, rpm, and so forth.

5.41.Pre‐ and Post‐test inspections

5.41.1.See Chapter 2 –Test Equipment and Calibration of Test Equipment.

5.41.2.The fabrication, accuracy, condition of the HIUs, the product‐filled test packages, and

other attributes of the retort load should be examined before Heat Transfer Distribution

are initiated to determine if they are acceptable for use and Heat Transfer Distribution

results using them will not be adversely affected by the testing sub‐systems.

5.41.3.The condition of the measuring sensors, the HIU/product‐filled test packages, and other

attributes of the retort load should be examined after the completion of the test to
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determine if the test results may have been affected by movement of these sensors or

other changes to the desired test setup.

5.41.4.Comparison of pre‐ and post‐test fill weights to ensure test packages have not leaked

during testing.  Consideration should be given to discarding data from leaking packages.

DATA ANALYSES

5.42.Calculate fh values and the associated % CV

5.43.Identify the slower to heat locations within the retort load, e.g., fh distribution within the

retort.

5.44.Confirm adequate Temperature Distribution including come‐up time.

5.45.Confirm that retort control and process conditions were achieved as designed.

5.46.If HIUs/product‐filled test packages have also been placed in faster to heat locations, the fh

differential between slow and fast to heat locations may also be compared.

5.47.Determine product slower and faster to heat locations for the HIUs/product‐filled test package

combination.  The slowest to heat location is determined based on the largest fh value.

5.48.All subsequent process determination studies, i.e. Heat Penetration, should be conducted

placing test packages in the known slowest to heat locations determined from Heat Transfer

Distribution studies.

5.49.If desired, determine product slowest and fastest to cool locations.

SUCCESS CRITERIA

Heat Transfer Distribution may be considered acceptable when:  

5.50.Temperature Distribution success criteria have been met during each Heat Transfer

Distribution Study.

5.50.1.Note that demonstration of adequate Temperature Distribution is recommended prior to

conducting Heat Transfer Distribution Studies.

5.51.Retort control and process conditions achieved/met as designed.

5.52.fh % CV ≤ 5% within and across replicate studies.  When this condition is met, uniform heat

transfer conditions have been confirmed and Heat Penetration probes may be located

anywhere in the retort.

5.52.1.In the event the fh CV is found to be>5%, it should first be confirmed that the sensors

used were consistent with accuracy stipulations (see Chapter 2 – HIU).  Additional Heat

Transfer Distribution studies need to be conducted to ascertain that the slowest to heat

locations have been reliably and consistently determined, with appropriate confidence and

rigor.  Thereafter, all Process Establishment Heat Penetration Studies for the test (i.e.

product, package, process, retort and load) combination need to be conducted at the

identified slowest to heat locations.

5.52.2.Alternatively, when the %CV is >5%, iterative changes could be made to the retort, retort

control, load density, rack design, etc. in an attempt to achieve an fh % CV ≤ 5%.  Once
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changes have been completed, replicate Heat Transfer Distribution studies should be

conducted.  Note that temperature distribution studies are a pre‐requisite to conducting

heat transfer distribution studies.  The need to collect temperature distribution data after

making changes should be evaluated prior to conducting additional heat transfer

distribution studies.

5.53.Verified that the retort is uniform in terms of heat transfer media distribution and delivery

and/or the slowest to heat location(s) within the retort load that may be used for Heat

Penetration studies for Process Establishment have been identified.

5.54.If product‐filled packages are used, product functionality and seal integrity are within accepted

parameters.

RISKS, ISSUES, AND OTHER CONSIDERATIONS

5.55.HIU geometry should not interfere with the normal flow pattern and mixing of the heat

transfer medium within the retort load.

5.56.Heat Transfer Distribution data are not used for Process Establishment.

5.57.fh values determined from HIU other than actual the product/package may not be used for

deviation evaluations.

5.58.Sufficient quantity of probed packages/HIU to conduct a valid statistical evaluation of the fh

variability within a test is required.  Typically this will require that more than 6 values are used

to calculate a mean fh and the associated standard deviation and %CV.  In general, a larger

number of values will provide more robust values.

5.59.Replicate studies are recommended.  The number of replicate studies will depend upon the

number of retorts being evaluated and whether you are studying a new

retort/process/package/formulation or if this is part of a periodic (e.g., annual) re‐verification

program.  When replicate studies fail to meet Success Criteria for Heat Transfer Distribution,

additional studies are needed.

5.60.Since fh and the associated % CV are used as the primary measures to assess adequacy of Heat

Transfer Distribution, data do not necessarily need to be collected at the highest allowed

overpressure for the product/package being studied.  This is in contrast to Heat Penetration

studies where the “worst case” retort conditions as defined by the Scheduled Process must be

used.   It is important that the amount of overpressure used during Heat Transfer Distribution

Studies be representative of the expected production condition for the product/package being

studied.

5.61.Non‐product based HIUs may be a preferred option to product‐filled packages when the food

being studied heats primarily by conduction.

DOCUMENTATION

Documentation of heat transfer distribution studies should include:

5.62.Reason(s) for retort selection.
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5.63.Results from the retort survey and test retort documentation including digital photos showing

the heating media delivery system including fans, pumps, nozzles, spreaders, shrouds, and so

forth.

5.64.Schematics and/or digital photos showing placement of all monitoring devices in the retort.

5.65.Reason(s) for use of the specific HIU selected, i.e., packaged product vs. non‐product based

HIU.

5.66.Reason(s) for use of the specific Ballast selected, i.e., packaged product, packaged water or

HIU.

5.67.Schematics and digital photos or packages, HIUs, Racks, Trays and Loads used for testing.

5.68.Retort charts, operator logs, retort control program, and control system reports

5.69.Critical factor records.

5.70.Calibration information for all sensors/devices used.

5.71.Raw data for both Temperature and Heat Transfer Distribution probes and that for any other

monitoring devices such as pressure sensors that were used during the study.

5.72.Data and statistical analyses, re‐tests, results and discussion as part of a Heat Transfer

Distribution Testing Report, documenting testing deviations, findings, success criteria and

recommendations for additional/subsequent work.

   
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Supersedes Date:  New     6‐1

6 CONDUCTING HEAT PENETRATION STUDIES

SCOPE

The guidelines in this chapter apply to conducting heat penetration studies in any retort system

including saturated steam, steam/air, water spray, water cascade, water immersion, and crateless.  

Batch retorts may be operated in either the still or agitating mode.  Considerations for collecting

heat penetration data in continuous rotary/reel and spiral and hydrostatic retorts are included.  The

intent of this document is to provide guidance in regards to the preparation and execution of heat

penetration studies.  Suggestions regarding data analysis of heat penetration data are also provided.

OBJECTIVES

6.1. The purpose of a heat penetration study is to determine the heating and cooling behavior of a

product/package combination in a specific retort system for the establishment of safe thermal

processes to deliver commercially sterile products and to assist in evaluating process

deviations.

6.2. The study must be designed to adequately and accurately examine all critical factors associated

with the product, package and process which affect heating rates.

6.3. Before commencing a heat penetration study, where applicable, an evaluation of retort

temperature distribution and heat transfer distribution should have been completed.

6.4. A goal in conducting these studies is to identify the worst case temperature response expected

to occur in commercial production as influenced by the product, package and process.

INTRODUCTION and BACKGROUND

Several product, process, package and measurement related factors can contribute to

variations in the time‐temperature data gathered during a heat penetration test. Establishment

of a process requires expert judgment and sound experimental data for determining which

factors are critical and the effect of changing those factors both within and beyond established

critical limits. The list of items addressed in this section is extensive, but should not be assumed

to cover all possible factors. Quantitative data on variability should be recorded where

appropriate and all pertinent data should be documented to better understand and account for

possible variations in heat penetration behavior.

6.5. Product

6.5.1.Product formulation and weight variation of ingredients should be consistent with worst

case production values.  Changes in formulation may necessitate a new heat penetration

study.

6.5.2.Fill weight used for heat penetration studies should not be less than the maximum

declared on the process schedule. Excess product may be expressed as percent overfill.
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6.5.3.Solids content should be measured for nonhomogeneous products both before and after

processing. Solids content deposited in a sieve should be weighed and expressed as a

percentage of total weight. Note: Addition of compressed or dehydrated ingredients may

result in increased drained weight.

6.5.4.Note that solids content may be considered a critical factor for homogeneous products

and should be measured before processing.

6.5.5.Consistency or viscosity of semi‐liquid or liquid components should be measured before

and after processing. Flow behavior will change with type and concentration of thickening

agents (e.g., starch, gums, etc.), temperature and shear rate. Changes may be reversible

or irreversible which may be important when reprocessing product.

6.5.6.Size, shape and weight of solid components should be measured before and after

processing, when appropriate.  For example, measuring size and shape of cooked rice in

product may not be possible or useful.

6.5.7.Integrity and size of solid component clusters may change during processing and affect

temperature sensor placement in the product and cold spot location.

6.5.8.Methods of product preparation prior to filling should simulate commercial practice. For

example, blanching may cause swelling, matting or shrinkage which could influence heat

penetration characteristics.

6.5.9.Product matting or clumping may change heat penetration characteristics and influence

cold spot location. Also, caution should be exercised with sliced products which may stack

together during processing.

6.5.10.Rehydration of dried components, either before or during processing, is a critical factor

which may influence heat penetration behavior, as well as process efficacy with respect

to spore inactivation. Details of rehydration procedures should be recorded during the

heat penetration study.

6.5.11.Product may heat by convection, conduction or mixed convection/conduction

depending on its physical properties. Heating properties may also be influenced by

presence/absence of agitation during processing, headspace volume, etc.  

6.5.12.Some foods exhibit complex (broken) heating behavior. Product may initially heat by

convection, then due to a physical change in the product, change to conduction heating

behavior. For example, for products such as soups which contain starch, a change in

heating behavior may be due to starch gelatinization at a particular temperature. Small

variations in product formulation or ingredients may cause the transition from convection

to conduction heating to occur at a different temperature and related time. Special care

should be taken to identify and control specific product and process variables related to

the heating rates of these products.

6.5.13.Additional product characteristics such as salt content, water activity, pH, specific

gravity, concentration of preservatives, and methods of acidification may influence heat

transfer or microbiological resistance and should be recorded.
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6.6. Container

6.6.1.Manufacturer and brand name information for the container should be recorded in case

information related to filling, sealing or processing is required.

6.6.2.Container type (metal cans, glass jars, retort pouches, semi‐rigid containers); size and

dimensions should be recorded.

6.6.3.Nesting of low profile packages can influence heating behavior. Heat penetration studies

where nesting can occur, including jumbled loads, should include tests conducted on

stacks of packages as well as non‐nested packages.  

6.6.4.Container vacuum and headspace should be recorded for rigid containers. For flexible and

semi‐rigid containers, the volume of residual gases in the container should be determined.

Entrapped and dissolved gases may create an insulating layer in the container causing a

shift in the cold spot location and a decrease in the heating rate. Controlled overpressure

during processing has been found to reduce these effects.

6.6.5.Maximum thickness of flexible packages (pouches) has a direct relationship to the cold

spot temperature history with thicker packages heating more slowly. Heat penetration

studies should be carried out at the maximum specified and permitted package thickness.

6.6.6.Container orientation (vertical, horizontal, and specific location of top/bottom of the

package) within the retort may be a critical factor for some product/package combinations

and should be studied, where appropriate. Changes in container orientation may also

influence vent schedules and come‐up time as well.

6.6.7.Post‐processing examination of test containers for abnormalities should be conducted

with special emphasis on the slowest and fastest heating containers. It is strongly

recommended that flexible packages be carefully examined following processing to

identify the thermocouple junction location. If the intended sensing location has shifted, it

is likely that heat penetration data collected are not reliable.

6.7. Method of Fill

6.7.1.Fill temperature of the product should be controlled. It will affect the initial temperature

which may influence some heat penetration parameters (lag factor, retort come‐up

period). This may constitute a critical factor for a process, particularly for products which

exhibit broken heating behavior.

6.7.2.Fill and net weights may influence heating rates both in still and rotary cooks. Information

on variability may be found in statistical process control and product quality control

records.

6.7.3.In most cases, controlling headspace by determining net weight is not sufficient due to

possible variations in the specific gravity of the food product. Care should be taken to

avoid incorporation of air which would affect the headspace vacuum. In rotary processes,

container headspace is a critical factor since the headspace bubble helps mix the product

during agitation.
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6.8. Closing or Sealing

6.8.1.Closing or sealing equipment should provide a strong, hermetic seal which is maintained

during the thermal process.

6.8.2.Vacuum is affected by variables such as: headspace, product temperature, entrapped air,

and vacuum efficiency of the closing equipment.

6.8.3.Some products such as vegetables vacuum‐packed in cans may have a minimum vacuum

as a critical factor. For others packed in flexible or semi‐rigid containers, vacuum setting

will influence the residual air content in the package, also constituting a critical factor.

6.9. Retort  System ‐ The type of retort system used may have a significant influence on the heating

rates of products processed in the retort. Results from a heat penetration test should be

reported with reference to the retort type, heat transfer medium, agitation, and other pre‐

defined conditions existing at the time of testing.

6.9.1.When testing convection and conduction heating products, retort come‐up time should be

as short as possible consistent with obtaining satisfactory temperature distribution.  

Results will be conservative when using laboratory size retorts or simulators as these tend

to have shorter come‐up times and cool more quickly than production retorts.  However,

caution should be exercised when processing broken heating products where the length of

the come‐up period may affect the time at which the product heating characteristics

change from convection to conduction.  This may also be of concern where come‐up times

are longer in production than defined by the designed process.

6.9.2.Laboratory size retorts or simulators may be used for development work on heat

penetration behavior. After development, the thermal process should, if physically

possible, be verified in an appropriate production retort.

6.9.3.Heat transfer distribution studies should be conducted prior to conducting heat

penetration studies for overpressure retort systems.

6.9.4.Racking systems may be used to separate layers of cans or jars; constrain the expansion of

semi‐rigid and flexible containers; provide support and circulation channels for thin profile

containers; and ensure maximum pouch thickness is not exceeded. Care should be taken

to understand the influence of a specific rack design on retort performance and heat

transfer to containers.

6.9.5.Still batch retort systems vary in operation based on: type of heating medium(e.g., steam,

steam/air, water); orientation of the retort (vertical, horizontal); method of heating

medium agitation (fans, pumps, air injection); and other factors which may influence the

heating behavior.

6.9.6.Rotational batch retort systems (e.g., axial, end‐over‐end) are designed to rotate (or

oscillate) entire baskets of product during processing. Container agitation may provide

faster rates of heat penetration to the container cold spot as compared to still cooks.

6.9.7.It is recommended that data be collected at small time increments (e.g., 15‐seconds or

less) particularly for low viscosity fluids where the cold spot may move in relationship to a

fixed TMD during rotation, producing erroneous results. Short time intervals are important
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with low viscosity liquids and broken heating products that change from convection to

conduction.   Slightly longer time intervals (e.g., 30‐seconds) may be acceptable for

conduction heating products.  1 minute is adequate for most conduction heating products,

and 3 minutes may be adequate for large containers of conduction heating products

where the process time is longer.  In general, 50 to 100 data points collected over the

collection time may be sufficient for many conduction heating products.  

6.9.8.Slip‐ring connectors should be cleaned and TMD calibration verified at regular intervals.

Critical factors for rotational batch retorts may include: headspace, product consistency,

solids to liquid ratio, initial temperature, container size, rotational speed and radius of

rotation.

6.9.9.Continuous retort systems move containers through the processing vessel along a spiral

track located at the outside circumference of a horizontal retort shell or may be carried

through a hydrostatic retort in chain driven flights. Regardless of the configuration, it

becomes difficult or impossible to use thermocouples to collect heat penetration data in

these systems. Data may be obtained using simulators and then confirmed using wireless

data‐loggers in the commercial vessel.

6.9.10.Heat penetration data, in some cases can be collected using process simulators.  An

understanding of scaling or other differences between commercial vessels and the process

simulator and the impact on heat penetration is needed and should be documented.

MATERIALS, TOOLS, EQUIPMENT

6.10.See Chapter 2 – Test Equipment and Calibration of Test Equipment

METHODS

6.11.Positioning of Temperature Measuring Devices (TMDs) in the Container

6.11.1. The method of inserting a TMD into a container should result in an airtight, watertight

seal which should be verified after testing.  Verification may be accomplished through

comparison of container weights recorded pre‐and post‐testing.

6.11.2.TMD sensing junctions should be positioned in the cold‐spot of the package.  

6.11.3.During insertion of the TMD, caution must be taken to avoid physical changes to the

product components such as creating a conduction pathway to the particulate center. Care

should also be taken to address potential agitation created by the probe, which can occur

in rotation processes if the probe acts as a stirrer.

6.11.4.The method employed for mounting the TMD into the container should not affect the

container geometry which could influence heat penetration characteristics.

6.11.5.Flexible or rigid TMDs may be inserted into rigid, flexible or semi‐rigid containers using

compression fittings or packing glands. For flexible containers, NFPA (4) provides

illustrations of thermocouple positioning into a solid particulate and several thermocouple
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positioning devices to ensure the thermocouple remains in a fixed position within the

container.

6.11.6.The most appropriate TMD device for a particular application will depend upon the

product, racking system, container type and sealing equipment.

6.11.7.Leakage may be detected by weighing the container before and after processing to

determine changes in gross weight. If there is leakage caused by improperly mounted

TMDs or the failure of a hermetic seal, data collected for that container should be

discarded.

6.12.Type and Placement of Containers

6.12.1.The type and size of container used in the heat penetration study should be the same as

that used for the commercial product.

6.12.2.The racking and loading of rigid (e.g., cans), semi‐rigid (e.g., plastic bottles, trays and

cups) and flexible (e.g., pouches) containers should simulate commercial practice.

6.12.3.Test containers should be placed at the slowest heating location(s) in the retort, as

determined by temperature and heat transfer distribution studies.

6.13.Temperature of the Heating Medium

6.13.1.TMDs to measure the heating medium should be positioned so as to prevent direct

contact with racks or containers and identified according to their specific locations in the

retort.

6.13.2.A minimum of two TMDs are recommended for retort temperature measurement: one

situated close to the sensing bulb of the retort reference TID, the other located near the

test containers.

6.13.3.In addition, at least one TMD should be placed near the sensor for the temperature

controller when that location is remote from the location of the reference TID.

6.14.Retort Pressure ‐ Worse case overpressure conditions should be used when collecting heat

penetration data.

6.14.1.Overpressure conditions during processing will influence package expansion by

constraining the expansion of headspace gases. This may be beneficial by improving heat

transfer to food in flexible and semi‐rigid containers or detrimental by restricting the size

of the headspace bubble in rotary processes.

6.14.2.Cooling without overpressure may result in depressurization within a container at the

end of a process, leading to accelerated decreases in temperature for fluid foods.  Glass

packages may also break if overpressure is not properly maintained during cooling.

6.15.Cold Spot Determination

6.15.1. The location of the slowest heating or cold spot in a container is critical to establishing a

process and should be determined experimentally. A cold spot location study should be

completed to determine the slowest heating location for a specific

product/package/process combination. Usually, the cold spot location will be determined

from a series of heat penetration tests employing several containers with TMDs inserted at

different locations. Alternatively, more than one TMD per container may be used;

however, multiple TMDs may influence heating behavior, especially for products in smaller
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containers (6).  Care and judgement based on a number of preliminary experiments, must

be exercised to ensure the cold spot location has been identified.

6.16.Initial Product Temperature

6.16.1.Measurement of initial product temperature should be taken immediately prior to

testing.

6.17.Number of Containers per Test Run

6.17.1.A heat penetration test should evaluate at least 10 working TMDs for each test run (6). If

the retort cannot accommodate this quantity, the number of replicate test runs should be

increased.

6.18.Number of Test Runs

6.18.1.Replication of heat penetration test runs is important in order to obtain results which

account for run‐to‐run, product, container and process variability.

6.18.2.After initial cold spot determination tests are completed and all critical factors have been

determined, at least two full replications of each test are recommended. Should results

from these tests show variation, a minimum of a third test is recommended.

6.18.3.Variation in the results is expected and quite common, especially for products which are

non‐homogeneous or exhibit complex heating behavior. Variability is generally evaluated

based on plots of the heating and cooling curves and/or lethality calculations and should

be considered when identifying or predicting the slowest heating behavior of a process.

DATA ANALYSES

6.19.Various methods are available for analyzing heat penetration data (4, 6, 7, and 8).  Regardless

of the method used, awareness of the potential pros/cons for each method should be

understood and addressed.

RISKS, ISSUES AND OTHER CONSIDERATIONS

6.20.Use of self‐contained (i.e., wireless data‐loggers) TMDs should be evaluated for accuracy,

reliability, and applicability prior to use as the product temperature measuring devices for heat

penetration studies.  In some cases these devices may provide benefits over using wired

thermocouples, e.g., in agitating retorts such as continuous rotary sterilizers, batch retorts

operated in an agitating mode, and hydrostatic retorts.  

6.21.Ecklund (5) reported correction factors for heat penetration data to compensate for errors

associated with the use of non‐projecting, stainless steel receptacles. While not reported in the

literature, this may also be a concern with other fittings.

6.22.Type of Connectors and Associated Errors: Connectors used in a thermocouple circuit are

fittings attached to a thermocouple within which electrical connections are made. Several types

of connectors are available for specific applications and thermocouple type. Caution must be

exercised to avoid certain sources of error which may be associated with the use of connectors

and extension wires. These include: disparity between thermocouples, connectors and
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extension wires; temperature differences between two wire junctions; and reversed polarity at

the thermocouple‐extension wire junction. Thermocouple connectors should be cleaned

frequently to remove oxidation from contacts to assure good electrical contact and prevent

errors in thermocouple readings. Similar concerns should be addressed when using RTDs and

thermistors.

DOCUMENTATION

The following provides a summary of details which may be incorporated in a checklist and

documented in their entirety or partially as deemed appropriate for a specific study.  Other

factors not listed in this section may also be relevant.

6.23.Pre‐test Documentation

6.23.1.Product characteristics

6.23.2.Product name, form or style and packing medium

6.23.3.Net weight and volume

6.23.4.Consistency of viscosity of the liquid component

6.23.5.Size, shape and weight of solid components

6.23.6.Size of solid component clusters

6.23.7.pH of solid and liquid components

6.23.8.Methods of preparation prior to filling (ingredient mixing methods, special equipment,

etc.)

6.23.9.Matting tendency

6.23.10.Rehydration of components

6.23.11.Acidification procedures

6.23.12.Other characteristics (e.g., % solids, density, etc.)

6.24.Container Description

6.24.1.Container material (brand name and manufacturer)

6.24.2.Type, size and inside dimensions

6.24.3.Container test identification code

6.24.4.Maximum thickness (flexible container)

6.24.5.Gross weight of container

6.24.6.Container nesting characteristics

6.24.7.Slowest heating or cold spot location in container

6.25.Data Acquisition Equipment and Methodology

6.25.1.Identification of data logging system

6.25.2.TMDs and connector plug maintenance

6.25.3.TMDs and connectors numbered

6.25.4.Electrical ground checked (using thermocouples)

6.25.5.Calibration of TMDs placed in heating medium

6.25.6.Type, length, manufacturer and identification code of TMDs and connectors
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6.25.7.TMD location in container

6.25.8.Positioning technique for TMDs

6.26.Fill Method

6.26.1.Fill temperature of product

6.26.2.Fill weight of product

6.26.3.Headspace

6.26.4.Filling method (comparison to commercial process)

6.26.5.Sealing operations

6.26.6.Type of sealing equipment

6.26.7.Time, temperature, pressure and vacuum settings (if applicable0

6.26.8.Gas evacuation method

6.26.9.Can vacuum

6.26.10.Volume of residual gases (i.e., flexible containers)

6.27.Retort System

6.27.1.Retort system – still or rotary, type of agitation (end‐over‐end, axial, oscillatory, none)

6.27.2.Retort identification number

6.27.3.Reel diameter (number of container positions) and rotational speed

6.27.4.Heating medium (steam, steam/air, water immersion, water spray/cascade) and flow

rate

6.27.5.Circulation method for water or overpressure media

6.27.6.Temperature distribution records

6.27.7.Where applicable, heat transfer distribution records

6.27.8.Retort venting schedule

6.27.9.Package position study data for batch rotary retorts

6.28.Loading of Retort

6.28.1.Loading or racking system details

6.28.2.Container orientation

6.28.3.Location of thermocouples for retort temperature

6.28.4.Use of ballast containers to ensure fully loaded retort (applicable to some retort systems)

6.28.5.Selected time interval for data logging system

6.28.6.Location of test containers in retort (slowest heating zone)

6.29.Additional Information

6.29.1.Date

6.29.2.Test identification

6.29.3.Processor and location

6.29.4.Individual(s) performing heat penetration test

6.30.Test‐Phase Documentation

6.30.1.Test run identification

6.30.2.Initial temperature of product at the start of heating

6.30.3.Rotation speed (if applicable)
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6.30.4.Time heating starts

6.30.5.Time vent closed and temperature, if applicable

6.30.6.Time retort reaches set point temperature (tc)

6.30.7.Temperature indicated on reference TID and when cook starts

6.30.8.Pressure from a calibrated pressure gauge or transducer

6.30.9.Time process begins

6.30.10.Time cooling begins (pressure cooling, if applicable)

6.30.11.Cooling water temperature

6.30.12.Time cooling ends

6.30.13.Any process irregularities or inconsistencies

6.31.Post‐Test Documentation

6.31.1.Container location and orientation

6.31.2.Container net and gross weight check for leakage

6.31.3.Thickness of container (flexible pouches)

6.31.4.Measurement of container vacuum or residual air content (if applicable)

6.31.5.Location of the TMD and whether or not it is impaled in a food particle

6.31.6.Post‐processing product characteristics (e.g., syrup strength, appearance, viscosity,

headspace, drained weight, pH, consistency, shrinkage, matting, clumping, etc.)

   
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Supersedes Date:  New    Appendix  A‐1

APPENDIX A – SELECTED BIBIOGRAPHY

The following references represent a selection of publications that may provide more insight and

information regarding thermal processing studies.

   

1. Pflug, I. J and Berry M. R. 1987. Using Thermocouples to Measure Temperature during Retort or

Autoclave Validation. J. Food Protection. Vol 50 (11): 975‐981.  

2. Tung, M. A and Britt, I. J. 1995. Food Material Science and Food Process Engineering: Keys to

Product Quality and Safety.  Food Research International. Vol 28 (1): 101 – 108.

3. Tung, M. A. Britt, I. J. and Ramaswamy, H. S. 1990. Food Sterilization in Steam/Air Retorts. Food

Technology. 44(12) 105 ‐109.

4. NFPA 1985.  Guidelines for Thermal Process Development for Foods Packaged in Flexible

Containers.  National Food Processors Association, Washington, DC.

5. Ecklund, O.F. 1956.  Correction factors for heat penetration thermocouples.  Food Technol.  

10(1): 43‐44.

6. Pflug, I.J. 1975.  Procedures for Carrying Out a Heat Penetration Test and Analysis of the

Resulting Data.  University of Minnesota, Minneapolis, MN.

7. CFPRA 1977.  Guidelines for the Establishment of Scheduled Heat Processes for Low‐Acid Foods.  

Technical Manual No. 3.  Campden Food Preservation Research Association, Chipping Campden,

Gloucestershire, UK.

8. ASTM. 1988.  Standard Guide for Use in the Establishment of Thermal Processes for Foods

Packaged in Flexible Containers.  F 1168‐88.  American Society for Testing and Materials,

Philadelphia, PA.

9. Bee, G.R. and Park, D.K.  1978.  Heat penetration measurement for thermal process design.  

Food Technol.  32(6): 56‐58.

10. Ball, C.O. 1923. Thermal Process Time for Canned Food, Bulletin of the National Research

Council, Washington, DC. Vol. 7, Part 1, Number 37.

11. Ball, C.O. 1927. Theory and practice in processing. The Canner, 64 (5), 27.

12. Ball C.O. and Olsen F.C.W. 1957. Sterilization in Food Technology. Theory, Practice and

Calculation. New York, McGraw‐Hill Book Co.

13. Jackson, J.M. and Olson, F.C.W.  1940.  Thermal processing of canned foods in tin containers. IV.

Studies of the mechanisms of heat transfer within the container.  Food Research. 5(4): 409‐420.

14. Niekamp, A., Unklesbay, K., Unklesbay, N., and Ellersieck, M.  1984. Thermal properties of

bentonite‐water dispersions used for modelling foods. J. Food Science. 49(1): 28‐31.

   
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date: New Appe

APPENDIX B ‐ Documenting Processing Equipment and Test Conditions Worksheet

Where possible, drawings, schematics, pictures of the retort and associated equipment could be beneficial to include whe

retorts and test retort conditions. The following table is an example of a worksheet that may be used to document proces

test conditions. This example may be modified as needed.

Survey InformationDate

________________

Location

_________________

Done by _____________________

Altitude

___________________ Height above sea level _____________________

TYPE OF RETORT

’ Continuous Reel ’ Hydrostat – Saturated Steam ’ Batch – Steam/Air ’ Batch – Water Spray ’ Batch – Water C

’ Batch – Water Immersion ’ Batch – Crateless ’ Other (Describe) ___________________________

PRODUCT INFORMATION (optional)

Product Name

__________________________

Product Heating ’ Simple, Convection ’ Simple, Conduction ’ Broken ’ Other (describe) _______________

Container – Material

________

Dimensions

_________

Orientation for processing ’ Vertical ’ Horizontal ’ Jumbled

Fill/Net/Drained Weight _____________________

List product critical factors, targets, and limits _____________________________________________

PACKAGE INFORMATION (optional)

Type of package ‐ ’ Rigid ’ Semi‐Rigid ’ Flexible ’ Paperboard ’ Other, describe ____________________________

Material of construction (describe) ‐ ______________________________________________________________For metal cans ‐ ’ 2pc ’ 3pc Side seam construction ___________________________________

Loading Patterns ‐ ’ Jumble Pack ’ Arrayed ’ Other (describe) _____________________________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Package Information, continued

Seal/Closure – Type _______________

Container Vacuum ‐ ’ Yes ’ No If yes, allowed limits ___________________________________

RETORT OPERATION

Throughput (CPM) ___________________________________ Containers/load _______________________

Cook Temperature Set‐point ________________ Pressure Set‐point during Cook ______________________

Rotation Set‐point _____________________________Partial Loads ’ Yes ’ No If yes, describe allowed conditions ________________________________________________

___________________________________________________________________________________________________Where applicable, include retort control program.

For Water Immersion ‐ ’ Full Immersion ’ Partial Immersion Water recirculation rate

_________________

For Water Spray – Number and type of nozzles _______________________________ Flow Rate ___________________

For Water Cascade – Number and type of spreader/manifold _________________________ Flow Rate _______________

For Steam/Air – Fan location ___________________ Fan RPM _________________ Shroud ‐ ’ Yes ’ No

Pre‐heating of overpressure air/nitrogen ‐ ’ Yes ’ No If yes, describe how heated, how controlled, and to what tempera

___________________________________________________________________________________________________Steam/Air Ratio ___________________ Is venting part of the process ‐ ’ Yes ’ No If yes, when is vent closed _________

LOADING CONSIDERATIONS (where possible secure drawings, schematics, pictures)

Loading Configuration ‐ ’ Layered ’ Nested ’ Compartmented ’ Offset ’ Other (describe) _______________________
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Loading considerations, continued

Water displacement requirements (ballast) ________________________________________________________________

Cassette, Basket, or Rack ‐ Dimensions _____________________ Distance between (if applicable) ___________________

Orientation in retort during processing _________________________ Percent open area ________________

Separator/Divider Trays – Material of construction ___________________________ Hole Size (if applicable) __________

Percent open area ______________________________

Hole Open Area, Spacing and Pattern – Base plate ________________ Sides of cassettes/baskets/rack _______________

Separator/divider Sheets _________________________

RETORT SPECIFICS (where possible secure factory blueprints/schematics of the retort and all attendant piping as well as a

retort was installed)

Manufacturer

________________________

Date Installed

_______________ Physical Dimensions of shell _________

Capacity – Continuous Reel: Zone 1 _________ Zone 2 __________ Zone 3 _________ Zone 4 ________ Cooker _____

Cooler

_________

Pressure Cooler

__________

Total

_________

Capacity – Hydrostatic: Preheat ______________ Sterilization ______________ Cooling _____________ Total ________

Number of flights ________________________

Capacity – Batch: No. of Baskets/Crates per Retort ____________ No. of packages per load ________________

Capacity – Crateless: Maximum number of containers per load __________________________________

Heat Transfer Medium: ’ Saturated Steam ’ Steam/Air ’ Water ’ Other _________________

Method of Heating Heat Transfer Medium (describe) ‐ _____________________________________________________
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Retort specifics, continued

Cooling Medium : ’ Ambient well water ’ Chilled water ’ Other (describe) ____________________________________

Method of process water microbial control _______________________________________________

Method of distributing/mixing heat transfer medium: ’ Fan ’ Pump(s) ’ Air plenum/shroud ’ Nozzles ’ Not Applicable

’ Other (describe) _______________________________

Controls (e.g., PLC, Computer Control, etc.) ‐ (Describe):

_________________________________________________________________________________________Note any differences between retorts in the test group.

List of all controlling/sensing devices (note that ideally a schematic/drawing should be available): ____________________

___________________________________________________________________________________________________Rotation: ’ Yes ’ No Continuous Reel – RPM

___________________________ Hydrostatic – CPM ________________

Batch – RPM

_______________________________

Batch – Oscillatory _________________________

Vents – Type _________________________ Size ________________________ Location ___________________________

Pipe size and connection to drain headers or channels ____________________________________

Vent manifold/manifold header – Location __________________ Pipe size(s) including connecting pipes _____________

Bleeders/Mufflers – Number __________ Size(s) _______________________ Location(s)__________________________

Construction

_______________________________________________________________

Drains – Valve Type __________________ Valve Size ________________ Pipe size ___________ Pipe Length _________

Connections to drain headers or channels

____________________________________ Location(s) ___________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Retort specifics, continued

Condensate Removal System(s) – Type ________________________ Size _______________________ Location _______

Check Valves ’ Yes ’ No If yes, Size ______________________ Type _____________________ Location(s) __________

Safety Valves – Size __________________ Type __________________________ Location(s) _______________________

Centering guides or baffles present ’ Yes ’ No If yes, indicate location ________________________________________

Water re‐circulation system (if applicable) – Pump type _____________ Pump Size ___________ Pump Capacity ______

Inlet/outlet port – Locations __________________ Size _______________ Filters _____________________ Recirculatio

Flow meter (if applicable) – type __________________ Capacity ______________

Horsepower _________ Pipe diameter for pump inlet ___________ and for pump outlet ____________

UTILITIES TO/FROM RETORT

Steam Supply

Boiler Capacity ____________ Method of Firing ____________________ Pressure _______________

Steam header pressure (peak usage) _____________________ Pipe Size ______________ Length __________________

Steam header pressure (off‐load hour usage) _____________________

Steam injection chamber (if applicable) ________________________________

Valve Type ___________ Valve Size ________________

Pipe fittings including steam by‐pass pipes from main line to retort (presence, type, size) ___________________________

Size of all connecting steam pipes to the main line __________________________________________________________

Note all equipment using steam from same supply line ______________________________________________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Utilities to/from retort, continued

Pressure Reducing Valve/Regulator ’ Yes ’ No If yes, type and pressure into retort _____________________________

Size and Type of Valve for Steam entry into Retort __________________________________________________________

Steam distribution system in retort – Number, location and size of steam spreaders/distributors _____________________

Steam injection points – Size ___________ Type _______________________ Location(s) __________________________

Steam spreader or nozzle – Shape ________________ Size ______________ Location(s) __________________________

Configuration ___________________________ Number of _________________ Size and location in pipe ____________

Size of “T”

_____________________

Size of other pipe fittings __________________________________________

Water Supply (where possible, attach a P&ID)

Water pressure to retort _______________________________________ Water temperature to retort _____________

Water distribution system in retort – Number, size and location of water spreaders/manifolds ______________________

___________________________________________________________________________________________________Process Water Supply – Source __________________ Quality ____________ Temperature _______ Controls (if any) ___

Cooling water supply – Source _____________ Quality ______________ Temperature _______ Controls (if any) _______

Method of heating processing water (describe) ____________________________________________________________Heat exchanger – Size ______________ Type __________________

Pump – Size ________ Type __________ Location ____________________

Air/Nitrogen Supply

Compressor Type ______________________________ Capacity __________________ Operating Pressure ___________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Utilities to/from retort, continued

Filter Type ________________________ Filter Size ____________________ Dryer Type ___________________ Dryer Si

Tank Type ______________________ Tank Size _______________________________

Line – Size

____________

Pressure

___________

Filters and dryers for instrument air ____________________________

Process air header – Line size

_____________

Pressure

_______________ Regulation (if applicable) ________________

Entry – Location ______________________ Inlet Size _________________

Control Valve – Size

____________________ Type ______________________ Pressure setting ____________ Flow rate 

Indicate availability to supply instruments _________________________________________________________________

Air heated ’ Yes ’ No Indicate if air lines are in close proximity to steam or water lines ___________________________

For Overpressure – Pipe location(s) _______________ Pipe size ________________ Valve type ______________ Valve s

Method of control (describe) ____________________________________________

SENSORSTemperature

Type of Reference TID ____________________________ Model of TID _______________________ Location(s) _______

Range ______________________________ Response time __________________ Length of insertion _______________

Length of scale (MIG) _______________________________ Increments (MIG) __________________________________

Calibration status – Date last calibrated

_________________

Next calibration date

______________________

Size, shape, location of wells ___________________________________________________________________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Sensors, continued

Temperature Control Sensing Device – Type __________________ Location _________________ Relationship to TID ___

For Water Spray and Water Cascade – Is this device in the water spray/cascade ’ Yes ’ No

For Steam/Air – Is this device in the retort or in the air (return) plenum ‐ ’ Retort ’ Air return/plenum

Pressure

Type of PID _________________________________ Model of PID ___________________________ Location(s) _______

Range ___________________________________ Calibration status – Date last calibrated _____________

Next calibration date

____________________

Water

Water level indicator type (if applicable) ____________________________________ Location(s) ____________________

Other

Rotation sensor Type __________________________ Location ____________________________ Drive system _______

Throughput/speed sensor Type ____________________________ Location ________________________

Type and size of flow meter _________________________________ Location(s) ______________________________

RECORDING DEVICES

Recorder/Recorder Controller – Type _______________________ Resolution __________________________

Parameters recorded

_________________________________________

Calibration status

_________________________

List Process critical factors and their associated limits ‐ 

______________________________________________________

___________________________________________________________________________________________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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WATER SPRAY AND WATER CASCADE RETORT – These are items that may not be covered in other areas of the survey.

Water Spreader(s) – Type _____________ Size ________________ Location _________________________

Water recirculation system – Pump Type ______________ Pump Capacity ________________ Pump Impeller Size _____

Pump Motor size ___________________Inlet/Outlet port Location ___________________ Size ______________________

Water flow rate ‐ 

______________________________

Process water retention channel or trough in bottom of retort ’ Yes ’ No If yes, Length ________ Width ______ Wate

Process water retained for cooling ‐  ’ Yes ’ No

Process water retained for re‐use ‐  ’ Yes ’ No

Amount of process water at start of process ‐   ____________ Controlled by ____________________ Measured by ____

Steam distributors (if applicable) – Location in relation to channel or trough _____________________________________

Water Distribution Plate(s) – Water Cascade only – Inlet pipe to manifold location : ’ Top/center of retort shell ’ Top/re

Dimensions of manifold

__________________________

Material of Construction

________________________________

Number of holes

____________

Size of holes

__________

Location (hole pattern) _______________________________

Percent open area ________________________________

Water distribution pipes (Water Spray only) – Location of water inlet pipe to retort shell ___________________________

Location of water distribution pipes in relation to circumference of interior of retort ______________________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Water spray/cascade retorts, continued

Length of pipes (do they extend length of shell) _______________________________________

Number of holes

_____________

Size of holes

__________________

Location of holes

___________________________

Nozzles – Type (if applicable) ___________________________ ’ Fixed ’ Oscillatory ’ Other (describe) ______________

Restrict hole opening ’ Yes ’ No If yes, how much ______________________________________________________

STEAM/AIR RETORTS –Air plenum and fan shroud – Distance (length) from retort shell to plenum if designed as a “shell in shell” ____________

If not designed as “shell in shell”, describe: ________________________________________________________________

Fan shroud details (describe) _____________________________
IFTPS Guidelines for Conducting Thermal Processing Studies

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Supersedes Date:  New                                                                                                                 Appendix C 1

APPENDIX C – Temperature Distribution Data Collection/Monitoring Points

The following table is a compilation of suggested data collection/monitoring points when

collecting temperature distribution data in different types of retorts.

Data Collection/Monitoring Points

Retort Type

ST SA WS WC WI

Temperature and Pressure Controller set point(s), including if there is an

overshoot set point for come‐up and a lower set point for processing ( ( ( ( (

Product or Ballast Initial Temperature. ( ( ( ( (

Time process cycle starts, Time 0. ( ( ( ( (

Time when the end of come‐up, start of thermal processing/cook step has been

achieved, as indicated by either the step change in a control program or the

achievement of process set‐point temperature at both the reference TID and the

recorder/controller.

( ( ( ( (

Reference TID readings at sufficient intervals during the entire cycle, including the

point in time it reaches the process temperature set point. ( ( ( ( (

Monitor rotation or agitation rate at sufficient intervals using an accurate

calibrated stopwatch or calibrated device including any points where rotation rate

changes during processing or on a continuous chart where rotation or agitation is

used.

( ( ( ( (

Time at the end of thermal process and start of cool. ( ( ( ( (

Actual basket/crate/rack orientation in the retort. ( ( ( ( (

Operating activity of other retorts including the number of retorts entering come‐

up during the study. ( ( ( ( (

Numbers and descriptions of other equipment using steam (e.g., blanchers) at the

time of the study and before, during, and after come‐up.

( ( ( ( (

Temperature of air supply entering the retort. (

Water level in relation to spreaders and lowest level of containers in the retort. ( ( (

Time when the pressure set‐point(s) is achieved. ( ( ( (

Time and temperature when the drain is closed, if it is open during a portion of the

vent. ( (    

Time and temperature, if or when the vent closes, taken from the reference TID. ( (

Air flow in scfm or liters per minute, if applicable and available. ( (

Line steam pressure at the time of the test and before, during, and after come‐up,

if possible. ( (    

Retort pressure, throughout the test cycle at sufficient intervals or on continuous

chart. ( ( ( (

Time steam bypass valve closes. (    

Temperature of initial process water. ( ( (

Flow or recirculation rate of water as determined by flow meter or other

acceptable means.

( ( (

Fill time (displacement) in those systems dropping water from a storage drum or

tank into the working processing vessel.     (

Water level in process vessel in relation to the top surface of containers, stated as

a minimum or an actual level throughout the process.     (

Line air pressure at the time of the test and before, during, and after come‐up, if

possible.     (

ST – Saturated Steam   SA – Steam/Air   WS – Water Spray   WC – Water Cascade   

WI – Water Immersion
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

Supersedes Date: New Appe

APPENDIX D – Heat Penetration Documentation Checklist

The following table is an example of a checklist that may be used for Heat Penetration Studies. This example may 

needed.

Pre‐Test Documentation

Item/Parameter Data 

Product characteristicsProduct name, form, style, packing mediumNet weight and volumeConsistency or viscosity of the liquid componentSize, shape, and weight of solid componentsSize of solid component clusterspH of solid and liquid componentsMethods of preparation prior to filling (e.g., ingredient

mixing methods, special equipment, etc.)

Matting tendencyRehydration of componentsAcidification proceduresOther characteristics (e.g., % solids, density, etc.)

Container Description

Container material (brand name and

manufacturer)

Type, Size, and Inside dimensionsContainer test identification codeMaximum thickness (flexible

container)

Gross weight of containerContainer nesting characteristicsSlowest heating or cold spot location

in container
IFTPS Guidelines for Conducting Thermal Processing Studies

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Data Acquisition Equipment and Methodology

Identification of data logging systemTMD type and where applicable,

connector plug maintenance

Type, length, manufacturer and

identification code of TMDs and

connectors

Electrical ground checked (using

thermocouples)

Calibration of TMDs placed in

heating medium

TMD location in containerPositioning technique for TMDs

Fill Method

Fill temperature of productFill weight of productHeadspaceFilling method (comparison to

commercial process)

Sealing operationsType of sealing equipmentTime, temperature, pressure, andvacuum setting (if applicable)Gas evacuation methodCan vacuumVolume of residual gases (i.e.,

flexible container)
IFTPS Guidelines for Conducting Thermal Processing Studies

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Retort System

Retort system – still or rotary, type

of agitation (end‐over‐end, axial,

oscillatory, none)

Retort identification numberReel diameter (number of containerpositions) and rotational speedHeating medium (steam, steam/air,

water immersion, water

spray/cascade, hydrostatic) and flow

rate

Circulation method for water or

overpressure media

Temperature distribution recordsHeat transfer distribution records (if

applicable)

Retort venting schedulePackage study position for batch

retorts

Loading of Retort

Loading or racking system detailsContainer orientationLocation of TMDs for retort

temperature

Use of ballast containers to ensure

fully loaded retort (applicable for

some retort systems)

Selected time interval for data

logging system

Location of test containers in retort
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

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Additional Information

DateTest identificationProcessor and locationIndividuals performing test

Test Phase Documentation

Test run identificationInitial temperature of product at the

start of heating

Rotation speed (if applicable)Time heating startsTime vent closed and temperature, if

applicable

Time retort reaches set point

temperature (tc)

Temperature indicated on referenceTID when cook startsPressure from a calibrated pressure

gauge or transducer

Time process beginsCooling water temperatureTime cooling begins (pressure

cooling, if applicable)

Time cooling endsAny process irregularities or

inconsistencies
IFTPS Guidelines for Conducting Thermal Processing Studies

Issue Date: March 13, 2014

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Post‐Test Documentation

Container location and orientationContainer net and gross weight

check for leakage

Thickness of container (i.e., flexible

pouches)

Measurement of container vacuum

or residual air content (if applicable)

Location of the TMD and whether or

not it is impaled in a food particle (if

applicable)

Post‐processing product

characteristics (e.g., syrup strength,appearance, viscosity, etc.)
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

1

GUIDE1 TO INSPECTIONS OF

LOW ACID CANNED FOOD MANUFACTURERS

Part 3-Containers/Closures

1 Note: This document is reference material for investigators and other FDA personnel. The document does not bind FDA and does not 

confer any rights, privileges, benefits or immunities for or on any person(s).

TABLE OF CONTENTS

Introduction.....................................................pg.1

Coding of Containers.....................................pg. 2

Empty Container Handling............................pg. 2

Container Closing...........................................pg. 2

Metal Cans

 Container Structure.....................................pg. 2

 Double Seam Structure..............................pg. 3

 Double Seam Formation............................pg. 3

 Seam Guidelines (Specifications).............pg. 4

 Seamer Maintenance and Adjustment..... pg. 4

 Container Defects........................................pg. 5

 Double Seam Evaluation Requirements

Visual Seam Examination ......................pg. 6

Double Seam Examination ....................pg. 7

Visual and Double Seam Examination

Records .................................................... pg. 7

Post Process Container Handling.................pg. 8

Glass Jars

 Container Structure

Glass Container .......................................pg. 8

Metal Closure...........................................pg. 8

 Vacuum Formation .....................................pg. 9

 Vacuum Closures ........................................pg. 10

 Closure Evaluation Requirements

Visual Examination .................................pg. 10

Physical Examination..............................pg. 11

Visual and Physical Examination Records

...................................................................pg. 12

 Other Quality Control Equipment ............pg. 12

Retortable Pouch

 Container Structure and Sealing Method. Pg. 12

 Critical Factors in Sealing...........................Pg. 13

Semirigid Trays and Bowls

 Sealing Method ...........................................pg. 13

 Critical Factors in Sealing...........................pg. 13

 Container DefectsPouches/Semirigid Containers/Heat Sealed 

Packages.........................................................pg. 13

 Seam Evaluation Requirements................pg. 14

Visual Seam Examination .....................pg. 14

Physical Examination ............................. pg. 15

Visual and Physical Examination Records 

 ................................................................. pg. 16

References ...................................................... pg. 16

Attachments.................................................... pg. 18

INTRODUCTION

The Guide to Inspection of Low-Acid 

Canned Foods consists of three separate 

documents; Part 1 covers Administrative 

Procedures\Scheduled Processes; Part 2 covers 

Manufacturing Procedures/Processes and Part 3 

covers Container/Closures. In addition to providing 

guidance for inspections of low acid canned foods 

(LACF) manufacturers, the guide(s) also contains 

background and general information on LACF 

regulations and procedures. 

In addition to the information and 

instructions provided in IOM Subchapter 530, 

21CFR 108 and 113, and applicable compliance 

programs, direct attention to areas covered in this 

Guide when covering LACF manufacturers. 

Another good reference is the Food Processors 

Institute 'Canned Foods' manual, which should be 

available from anyone in your district who has 

attended a Better Process Control School.

At the current time DEIO has available, for 

loan only, the following NFPA manuals:

1. Thermal Processes For Low-Acid Foods in 

Metal Containers (NFPA Bulletin 26-L, 13th 

Edition)

2. Thermal Processes For Low-Acid Foods in 

Glass Containers (Bulletin 30-L)

3. Flexible Package Integrity Bulletin (Bulletin 

41-L)

4. Guidelines for Thermal Process 

Development for Foods Packaged in 

Flexible Containers

5. Continuous Rotary Sterilizers-Design and 

Operation (Bulletin 44-L)
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

2

6. Automatic Control Guidelines For Aseptic 

System Manufacturers and Companies 

Using Aseptic Processing and Packaging 

for Preserving Foods (Bulletin 43L) 

DEIO also has a supply of Institute for 

Thermal Processing Specialists (IFTPS), 'Protocol 

for Carrying Out Heat Penetration Studies'.

The AOAC Chart "Classification of Visible 

Can Defects (Exterior)" is helpful when performing 

field exams. Districts should have this chart 

available (usually the labs have them).

The sampling schedule for canned and 

acidified foods is in the Investigations Operations 

Manual and the Guide to Inspections of Low Acid 

Canned Food Manufacturers , Part 2

CODING OF CONTAINERS 

See Guide to Inspections of Low Acid 

Canned Food Manufacturers Part 2, pg. 46.

EMPTY CONTAINER HANDLING:

Empty containers for low acid canned food 

processing are typically received in bulk quantities, 

packaged to avoid container damage in transit, by 

the food manufacturer. For example, metal cans 

are typically received on pallets with a cardboard 

divider between each can layer or nested in paper 

sleeves on pallets; glass jars are received in boxes 

with separate compartments for each jar; plastic 

bowls and cups are received nested in cardboard 

boxes; and empty pouches are received securely 

packed in cardboard boxes. 

It is important that empty containers are 

handled during receipt and processing in a manner 

that precludes container damage. For example, if 

the flange of a metal can is damaged during 

shipment, receipt, or filling, it can result in a can 

seam defect. Therefore, it is important that the 

LACF manufacturer has a program for inspecting 

incoming containers for defects prior to the filling 

operation. This inspection program should include 

a visual examination and when appropriate, a tear 

down examination for defects that could affect 

product and/or package integrity. Incoming 

container inspection programs range from a small 

manufacturer checking every container before 

filling, to large manufacturers that may follow a 

statistically valid sampling plan (e.g., mil-standard 

105E) to inspect their incoming containers for 

defects. 

During the inspection determine if the firm 

has a program and/or procedure for handling and 

inspecting incoming containers and if the program 

is followed. Also, inspect empty containers prior to 

filling for damage that may result in container 

defects. Any damage should be noted, and followup visual examination of finished containers should 

be performed to determine if the damage caused 

defects in the containers. Evidence of container 

damage causing defects in the finished containers 

should be reported on the FDA-483 if no corrective 

actions had been taken by the firm on the affected 

lots. (Reference individual container type sections 

of this guide for definitions and discussion of 

container defects.)

Empty containers (except pouches) should 

be inverted and cleaned prior to fill. Typically 

containers are cleaned using vacuum, air, or a 

water spray to remove possible foreign material 

prior to filling.

CONTAINER CLOSING:

After filling the container, a can cover (end 

or lid) is placed onto the container and seamed. 

The closing operation is what produces a hermetic 

seal; i.e., a seal designed to be secure against the 

entry of microorganisms. For cans, to secure the 

hermetic seal an appropriate sealing compound is 

applied to the inside of metal can ends at the curl; 

and for glass jars the sealing compound is applied 

to the metal closures during container lid 

manufacturing. It is very important that the seam 

is adequate to prevent entry of microorganisms. A 

brief description of the different container types 

and closing operations for these container types is 

as follows:

METAL CANS

Container Structure:

The container structures that help form and 

become a part of the finished double seam are the 

body flange and the end curl (refer to Attachment 

1). Attachment 1 also illustrates and defines double 

seam terminology:

Flange: The flange is the edge of the body 

cylinder that is flared outward resulting in a rim or 

ledge. The flange is formed into the body hook 

during double seaming and becomes interlocked 

with the cover hook. The width and radius of the 

flange are determined by the container 

manufacturer and are designed to form a proper 

body hook when using the container 
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

3

manufacturer's specifications for the double 

seaming operations. 

End Curl: The end curl is the extreme edge 

of the can end (cover) that is turned inward after 

the end is formed. It is the structure used to form 

the cover hook and is designed to provide sufficient 

metal and proper contour for a good cover hook, 

and easy feeding of end units into the closing 

machine.

Double Seam Structure:

The double seam structure is judged by 

measurement and evaluation of specific 

components comprising the seam. These 

measurements are based on guidelines provided 

by the container manufacturer to the low-acid 

canned food manufacturer to assist in maintaining 

acceptable seams during production. The final 

evaluation of the double seam can only be made 

by a visual inspection of the torn down seam in 

conjunction with the measurements. The seam 

measurements that can be performed to evaluate 

the double seam are as follows (refer to 

Attachment 2):

Countersink: The countersink is the 

distance measured from the top of the double 

seam to the end panel adjacent to the inside wall of 

the double seam.

Seam thickness: Seam thickness is the 

maximum dimension measured across or 

perpendicular to the layers of material in the seam. 

This measurement is one, but not the only 

indication of the tightness of the double seam. 

Seam width (length or height): Seam width 

(also referred to as seam length or seam height) is 

the dimension measured from the top to the 

bottom of the double seam (parallel to the hooks of 

the seam). 

Body and cover hook: These are internal 

measurements. As previously referenced the body 

hook is formed from the body flange, and the cover 

hook is formed from the end curl during the double 

seaming operation. These structures, observed in 

a cross section, have an interlocking relationship to 

each other. 

Overlap: The degree or length of interlock 

between the body hook and cover hook is known 

as overlap. 

Tightness: Seam tightness is judged by the 

degree of wrinkling at the end of the cover hook. 

During double seam formation, the cover curl is 

guided around and up under the body flange. This 

crowds the cut edge of the curl into a smaller 

circumference, resulting in a wavy cut edge with 

accompanying wrinkles around the seam. The 

second operation in the formation of the double 

seam presses the body and cover hooks together 

to such a degree that the wrinkles should be ironed 

out sufficiently to ensure a hermetic seal. 

In a completed double seam, any 

remaining wrinkles help to indicate double seam 

tightness. Tightness rating is a numerical 

designation which indicates the relative freedom 

from wrinkles or % smoothness of the cover hook. 

Refer to Attachment 3.

After the coverhook is removed, the can 

body should be examined for body wall impression 

or what is commonly referred to as pressure ridge. 

This impression is caused by the seaming roll 

pressure during the seaming operation. Visual 

inspection of the pressure ridge provides additional 

assurance of the tightness of the can seal. The 

body wall impression or pressure ridge should be 

visible and complete around the inside periphery of 

the can body where the coverhook was removed. 

Refer to Attachment 4.

Double Seam Formation:

The seal for the metal can is made in two 

operations, hence the term "double seam". The 

can seamer (or closing machine) has four basic 

parts that are directly involved in forming the 

double seam. These parts are: 

1. Seaming Chuck: A flat round plate which 

fits inside the can cover and supports the can 

against the seaming rolls.

2. Can Lifter or Base Plate: a round plate 

which lifts the can and can end to the seaming 

chuck and applies upward pressure during the 

seaming cycle.

3. First Operation Seaming Roll: A roller 

adjacent to the seaming chuck that has a deep, 

narrow groove (forming tool).

4. Second Operation Seaming Roll: A roller 

adjacent to the seaming chuck with a wide and 

shallow groove (tightening, flattening tool).

These four basic parts of the can seamer 

are adjustable, and precise adjustment is critical in 

obtaining a well formed double seam. 

The double seaming operation is a form of 

metal spinning. The sequence of steps in the twoseaming-roll operation is as follows: 

1. Either the can is placed on the can lifter 

(base plate) and the cover is automatically placed 

on the can; the can cover is placed on the can as it 

moves onto the can lifter; or if the cover is placed 
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

4

on the can during the clinching operation, the can 

with the cover is placed on the can lifter.

2. The base plate raises the can and cover 

onto the seaming chuck tightly clamping the cover 

onto the can. 

3. The first operation seaming roll(s) is 

brought into contact with the can and cover, and 

the metal spinning groove forms the first operation 

seam. The first operation seam can be defined as 

curling the cover (end) hook around the inside of 

the body hook to form a loose interlock of the can 

end and can body.

4. The second operation seaming roll(s) is 

brought into contact with the can and cover, and 

the metal spinning groove forms the second 

operation seam. The second operation seaming 

roll flattens the seam and seals the can.

Attachment 5 illustrates the sequence of 

operation in seaming a can end onto a can body. 

Attachment 1 illustrates a completed double seam 

and details double seam terminology.

Can double seamers are generally of two 

types:

The can spin type: The seaming rolls are 

stationary and the can spins as it is held between 

the base plate and the seaming chuck. In this type 

of seamer the base plate and chuck both spin at a 

high rate of speed while the stationary rolls swing 

in to make contact with the can and cover and then 

swing back out after the seaming operations are 

complete.

The can stationary type: The can, base 

plate and chuck are all stationary and one or two 

first and second operation seaming rolls roll 

around the stationary can forming the double 

seam.

With either type of double seamer, a can 

may be placed by hand onto the base plate, or fed 

mechanically onto the base plate in the seamer.

First Operation Seaming

The first roll seaming operation is the most 

critical part in the formation of a good seam. The 

second roll seaming operation simply flattens the 

closure fold made during the first roll seaming 

operation; so deficiencies in the first seaming roll 

operation cannot be corrected during the second 

roll seaming operation.

The first operation roll has a narrow and 

deep groove profile. The body hook and cover 

hook are determined by the first operation roll and 

the base plate pressure. Upward pressure on the 

base plate should be sufficient to force the cover 

right onto the chuck and hold the can firmly in 

contact. The first operation seaming roll then 

engages the cover and curls the cover curl (which 

becomes the cover hook) into the flange of the 

body which then becomes the body hook in the 

finished seam. In a good or normal first operation 

roll, the cover hook is rounded at the bottom and is 

in contact with the body of the can. The ends of 

the cover hook and body hook are essentially 

parallel. There should be no curvature in the 

extremities of the cover and body hooks. Refer to 

Attachment 11.

Second Operation Seaming:

The second operation roll has a shallow 

and flat profile in comparison to the narrow and 

deep groove profile of the first operation roll. The 

second operation roll flattens the fold resulting 

from the first operation and presses the folds 

together tightly enough to compress and force the 

sealing to flow into the seam voids. Refer to 

Attachment 6.

Seam Guidelines (Specifications)::

Can seam guidelines (specifications) are 

provided to the low acid canned food manufacturer 

by the supplier of the container and end being 

used. The guidelines detail the measurements, in 

thousands of an inch, of each attribute of the 

double seam for both the first and second seaming 

operations. They also provide a set-up aim or ideal 

starting dimensions for the set up of the seamer. 

The operating limits set the range for good 

practice. Attachment 7 provides an example of a 

seam guideline.

It is extremely important to understand that 

seam guidelines by themselves cannot be used for 

determining the quality of a double seam. The 

seam guidelines are to be used in setting up the 

double seams initially and maintaining seam 

integrity during production. Final acceptability of 

the double seam should be based on total 

evaluation of the seam by a qualified person and 

not on dimensions alone. Good seaming practice 

requires constant visual examination, frequently 

scheduled tear-down evaluation, machine 

maintenance, and immediate correction of 

unacceptable conditions.

Since seam guidelines will vary depending 

on the source of the container (i.e., Crown Cork & 

Seal, Ball, Siligan, etc.), the guidelines should 

always be provided by the container manufacturer. 

If the LACF manufacturer cannot provide a copy of 
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

5

the appropriate seam guidelines, they have nothing 

on which to evaluate the double seam. This can be 

listed as an objectionable condition on the FDA483.

Seamer Maintenance and Adjustment :

It is important that the LACF manufacturer 

has in place a preventative maintenance program 

for the seamer. Under normal use conditions, the 

seaming rolls, bearings, base plate, chuck etc. can 

become worn resulting in the possibility of 

defective double seams. Seaming rolls are 

evaluated and changed routinely because they 

wear during production, thus altering the groove 

profiles. For example, a badly worn first operation 

roll can result in a loose first operation seam and 

when a normal second operation roll pressure is 

applied, can cause droops (see Attachment # 8) in 

the finished double seam.

Adjustment of Closing Machine to Correct Out-OfGuideline Measurements and/or Defective Seams:

Whenever the set-up aim or operating limit 

checks indicate that seams are not meeting the 

guidelines or when an obvious seam defect is 

found on visual inspection, the manufacturer must 

know what steps to take to correct the condition. 

The FDA investigator must also be aware of 

seaming conditions that could result in container 

defects in order to evaluate whether the firm took 

the appropriate corrective action. Evaluation of the 

firm's actions are made through review of their 

container records. Container records will be 

discussed later in this section.

If an obvious and recurring can seam defect 

is found on visual inspection and in a second 

sample, it usually signifies that some mechanical 

fault has developed and the production line should 

be stopped in order to take corrective action. 

Product from previous production that may have 

been affected should also be isolated.

The most critical attributes to consider in 

judging the quality of the double seam are overlap 

and tightness (wrinkle). If one of the can seam 

measurements (i.e. body hook) is slightly beyond 

the specified guidelines but the rest of the seam is 

evaluated and the overlap and tightness (wrinkle) 

are within specified guidelines, then adjustments to 

the seamer can be made at the next scheduled 

shut-down. In this instance, the manufacturer 

should identify the out-of-guideline measurement 

and document they have evaluated the rest of the 

double seam, but did not find immediate corrective 

action necessary. However, if overlap 

measurement or tightness rating evaluation are 

below the minimum guidelines a resample from 

the questionable seaming station should be made. 

If the resample continues to show out-of-guideline 

measurements in overlap and/or wrinkle the 

machine should be stopped and adjusted.

A LACF manufacturer should have 

experienced, competent personnel to adjust the 

seamer and evaluate double seams.

Container Defects - Metal Cans:

Container defects are seam abnormalities 

that are generally serious and may result in the loss 

of the hermetic seal. Following is a description of 

some of the more common container defects:

Droop (Refer to Attachment 8): A droop is a 

smooth projection of a double seam below the 

bottom of a normal seam. The droop may occur at 

any point of the double seam. If the container has 

a side seam it is common to have a slight droop 

where the double seam crosses over the lap of the 

side seam. This area of cross over is referred to as 

the "juncture". A slight droop at the juncture may 

be considered normal, however, if the droop is 

excessive the overlap may be too short or nonexistent. Some possible causes of droops are 

listed in Attachment 8.

Vee or Lip (Refer to Attachment 8): "Vees" 

or "lips" are projections of the double seam below 

the bottom of a normal seam that resemble a "V" 

shape. There is usually no overlap of the cover 

hook with the body hook and these defects usually 

occur in small areas of the seam. The probable 

causes for "vees" or "lips" is the same as for 

"droop".

Sharp seam (Refer to Attachment 9): A 

"sharp seam" refers to a sharp edge at the top 

inside portion of the seam. Usually a sharp seam is 

noticeable at the side seam juncture in a three 

piece container, however, a sharp seam can be felt 

at any point along the inside top of the seam. The 

sharp seam is caused by a portion of the end 

(cover) being forced over the top of the seaming 

chuck during double seaming. A sharp seam can 

usually be felt more easily than seen. A sharp 

seam can be the first indication of a more serious 

defect known as a cut-over.

Cut-over (Refer to Attachment 9): A "cutover" is a seam defect where the top of the inside 

portion of the seam has become sharp enough to 

fracture the metal. As in the definition of "sharp 

seam", this condition usually occurs at the side 

seam juncture of a three piece container. Some 
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

6

possible causes of both sharp seams and cut-overs 

are listed on Attachment 9.

Jumped seam or Jump over (Refer to 

Attachment 10): A jumped seam or jump-over is a 

portion of the double seam which is not rolled tight 

enough. This defect occurs adjacent to the side 

seam or juncture area in a three piece container 

and is caused by the seaming rolls jumping at the 

juncture. Wrinkles will be left in the coverhook at 

the point where the rolls jumped. During 

examination of the seams the area immediately 

adjacent to either side of the juncture should be 

carefully inspected for excessive wrinkle. Possible 

causes of a jumped seam are listed on Attachment 

10.

Deadhead or spinner (Refer to Attachment 

11): A deadhead or spinner (also referred to as slips 

or skids) is an incomplete seam caused by the 

chuck spinning in the countersink during the 

seaming operation. Some causes of deadheads 

are listed on Attachment 11.

Mis-assembly: A "mis-assembly" is the 

result of the can body and the can end having been 

improperly aligned in the closing machine. 

Therefore, the seam is completely disconnected 

partway around the can. The most common cause 

of a mis-assembly is incorrect closing machine 

timing or settings.

False seam (Refer to Attachment 12): A 

"false seam" is a seam or portion of the seam 

which is completely unhooked, and in which the 

folded cover hook is compressed against the folded 

body hook. A false seam is not always detectable 

in an external examination. Some causes of false 

seams are listed on Attachment 12.

There are other terms that more specifically 

describe a false seam condition. They are:

Knocked down flange: which is usually 

caused by a bent can flange before double 

seaming.

Damaged end curl: is a defect resulting 

when the end curl is flattened in one or more spots, 

causing the curl to fold back on itself. This is 

usually caused by handling damage to ends or 

improper cover feed.

Can body buckling: The can body directly 

under the double seam is buckled or twisted.

Possible causes are:

1. Excessive baseplate pressure

2. Improper pin-gauge height (distance 

between base plate and chuck)

Cocked body (Refer to Attachment 12): A 

"cocked body" is a can manufacturing defect. It 

occurs when the can body blank is manufactured 

out of square causing an unevenness at the lap or 

juncture in three piece cans. 

Cut seam (Refer to Attachment 13): A "cut 

seam" is a fractured double seam where the outer 

layer (cover hook) of the double seam is fractured. 

Possible causes are listed on attachment 13.

Fractured embossed codes: "Fractured 

embossed codes" are fractures through the metal 

end of the can at the code mark. Possible causes 

for the fractured metal are:

1. Mis-alignment of male and female 

coding dies.

2. Intermixing of new and old type code 

characters.

3. Improper matching of male and female 

type code characters.

4. Too deep a code mark.

Broken chuck: A "broken chuck" defect 

occurs when a portion of the seaming chuck lip has 

broken and results in an excessively loose seam at 

the broken part due to a lack of backup support for 

the seaming roll. Possible causes are:

1. Severe jam in the closing machine.

2. Seaming rolls binding on chuck.

3. Metal fatigue in chuck lip.

4. Prying against the seaming chuck to 

clear a jam.

FDA, in cooperation with the Association of 

Official Analytical Chemists, published a brochure 

titled "Classification of Visible Can Defects". The 

brochure defines metal can defects in three 

categories. They are:

1. Critical: Defects which provide evidence that the 

container has lost its hermetic seal (e.g., holes, 

fracture, puncture etc.)

2. Major: Defects that result in cans which do not 

show visible signs of having lost their hermetic 

seal, but are of such magnitude that they may have 

lost their hermetic seal.

3. Minor: Defects which have had no adverse effect 

on the hermetic seal.

The brochure also provides a pictorial of 

can seam defects and rates the defects as critical, 

major and minor. If you cannot locate a copy of 

this brochure in your district, contact your servicing 

lab.

Double Seam Evaluation Requirements:

Visual Seam Examination (Non-Destructive Test):

21 CFR Part 113.60(a) requires a visual 

examination of at least 1 can per seaming head by 
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

7

a qualified container closure inspector at intervals 

of sufficient frequency. The regulation requires 

that double seamed containers be visually 

inspected for gross closure defects such as sharp 

seams, cut-overs, deadheads, false seams, droops 

and broken chuck. The frequency of the visual 

examination should be made at intervals not to 

exceed 30 minutes (of operational time); and 

additional visual examinations must be performed 

immediately following a jam in a closing machine, 

after closing machine adjustment, or after startup 

of a machine following a prolonged shut-down. An 

example of a prolonged shut down may be when 

the plant ceases production at 6:00 PM and restarts 

production at 8:00 AM the next day.

Double Seam Teardown Examination 

Requirements (Destructive Test):

The double seam teardown examination is 

a destructive test. Tools that are used to perform 

this test include a seam micrometer, countersink 

gauge, can opener and nippers. Optional 

equipment for seam teardown examinations 

include a seam saw, seam projector and seam 

scope. Although it is not imperative the 

investigator carry this equipment to each LACF 

inspection, it is very important that they know how 

to operate this equipment and read measurements 

from the micrometer, seam projector or seam 

scope. It is also important that the investigator 

know how to determine the tightness or wrinkle 

rating of the cover hook. Knowledge of the 

procedures used to perform double seam teardown 

examination are essential to evaluating the firm's 

knowledge and ability to do this examination. 

Attachment 14 explains the procedure for using a 

seam projector for examining a cross section of the 

seam. Attachment 15 explains the can seam 

micrometer and procedure for use, and Attachment 

16 explains the use of a seamscope for the same 

exam. 

The requirements for double seam 

examinations are specified in 21 CFR Part 

113.60(a)(1). The regulation states that teardown 

examinations shall be performed by a trained 

closure technician at intervals of sufficient 

frequency to ensure proper closure. The teardown 

examinations shall be made on the packer's end 

double seams on at least 1 can from each seaming 

head to ensure maintenance of seam integrity. 

Sufficient frequency is defined in the regulation as 

intervals not to exceed 4 hours (operational time).

The regulation allows for 2 different 

methods of double seam examination; the 

"micrometer" method or the "optical" method.

If the processor is using the micrometer 

method the regulation requires that 3 

measurements are taken at points approximately 

1200 apart around the double seam. On 3 piece 

cans the first measurement can be taken directly 

across from the side seam and the next two 

measurements are then taken 1200 to either side of 

the first measurement. On 3 piece cans the 

measurements must be taken at least one-half inch 

from the side seam juncture as the juncture may 

interfere with a true seam measurement. 

Micrometer measurements are made and 

recorded in thousandths of an inch. The high and 

low measurements are recorded on the double 

seam teardown examination record. If the 

manufacturer is using the micrometer method the 

required 

measurements are:

Cover hook length

Body hook length

Width (also referred to as length or height)

Tightness (by observation for wrinkle)

Thickness

Optional measurements are:

Overlap (by calculation)

Countersink

The regulation specifies the formula used to 

calculate overlap when micrometer measurements 

are used: 

CH + BH + T (.010in)* - W, where

CH = cover hook

BH = body hook

T = cover thickness *(general 

practice use .010 inches for tin plate 

thickness)

W = width

Measurements used to calculate the 

overlap should not be averaged. In fact, the lowest 

values should be used to determine the worst case 

scenario. For example, to calculate the worst case 

scenario you should use the lowest measurements 

for CH and BH and the highest measurements for 

W.

If a seam scope or seam projector is used 

(optical method) to make the seam measurements, 

the required measurements are:

Body hook length

Overlap
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

8

Tightness (observation for wrinkle)

Thickness (determined by 

micrometer measurement if the 

optical instrument cannot read this 

value)

Optional measurements are:

Width (also referred to as length or 

height)

Cover hook

countersink

Visual Seam and Double Seam Teardown 

Examination Record Requirements:

The regulations require that the 

results of visual seam and double seam teardown 

examinations along with any corrective action 

taken shall be recorded. 21CFR Part 113.100(c) 

details 

the minimum requirements for visual and double 

seam examination records as follows: "Written 

records of all container closure examinations shall 

specify the product code, the date and time of 

container closure inspection, the measurements 

obtained, and all corrective actions taken." Records 

must be signed or initialed by the container closure 

inspector and reviewed by management with 

sufficient frequency to ensure that the containers 

are hermetically sealed. 

Sufficient frequency can be defined as, at 

least prior to shipment of the product. However, 

FDA investigators should encourage LACF 

processors to review the container records at the 

same time as the thermal processing records; or 

not later than 1 working day after the process, and 

prior to shipment of the product. 

Attachment 17 and 18 respectively, are 

examples of a visual examination record and 

double seam teardown examination records.

When reviewing visual and double seam 

examination records it is important the investigator 

knows how to interpret the information provided 

on the records. For example, if a visual or 

teardown examination found a defective container 

or measurements outside of guidelines, the 

processor should have taken a repeat sample from 

the questionable seaming station to evaluate 

before any machine adjustments are attempted. If 

the repeat sample shows the same defect or out of 

guideline measurement then the processor will 

have to determine whether the nature of the defect 

is of sufficient magnitude to warrant immediate 

shut down of the production line to make 

adjustments, or to continue processing until the 

next scheduled break in the production period.

Some examples under which processing 

could continue with little risk to the product are:

1 . If visual inspection indicates a slight sharpness, 

especially in the junction area.

2. If the container guidelines require body hook 

measurements in the range of .072" - .088" and 1 

measurement was taken and recorded as .071 for a 

low and .076 for a high. All other measurements 

are within guidelines including overlap, wrinkle, 

and pressure ridge.

3. When the thickness guidelines require a range 

of .046" to .052" and measurements show thickness 

up to .053", but the cover hook displays a 100% 

wrinkle (tightness) rating. Refer to Attachment 3.

Some examples under which processing 

should be shut down and corrective action taken 

are:

1. During visual seam examination a cut-over is 

found around the periphery of the inside of the 

seam.

2. During visual seam examination and on a repeat 

sample, vees or lips are found protruding below 

the bottom of the double seam.

3. Evidence of skidding or deadheading.

4. During both initial and repeat teardown 

examination on one seaming head, calculated 

overlap is below the minimum guideline 

requirement.

Good seam formation cannot be judged 

solely by mechanical means or measurements. 

The evaluation of good double seams requires 

experience and skill. This is why it's important for 

a firm to have experienced and well trained can 

seam mechanics. If observations indicate the 

individual(s) performing can seam examinations 

lack adequate training or skills this should be 

discussed with plant management.

Post Process Container Handling

See Guide to Inspections of Low Acid 

Canned Food Manufacturers, Part 2, pg. 44. 

Glass Jars:

Container Structure:

Glass container:

There are 3 basic parts to a glass container 

(Refer to Attachment 19):

1 . Finish: The finish is the very top part of the jar 
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

9

that contains threads or lugs that contact and hold 

the cap or closure. Specific areas identified in the 

"finish" are sealing surface, glass lug, continuous 

thread, transfer bead, vertical neck ring seam and 

the neck ring parting line.

2. Body: The body of the container is that portion 

which is made in the "body mold". It is the largest 

part of the container and lies between the finish 

and the bottom. The characteristic parts of the 

"body" are the shoulder, heel, side wall, and mold 

seam.

3. Bottom: The bottom of the container is made in 

the "bottom plate" part of the glass-container mold. 

The designated parts of the bottom area are 

normally the bottom plate parting line and the 

bearing surface.

Metal closure:

Among the terms commonly used for 

describing parts of metal vacuum closures are the 

following (Refer to Attachment 19):

Face: The outside of the cap

Reverse: The inside of the cap

Panel: The flat center area in the top of the 

cap.

Radius/Shoulder: The rounded area at the

outer edge of the panel connecting the panel and 

skirt.

Skirt: The flat side of the cap. The skirt 

may be smooth, knurled, or fluted and serves as 

the gripping surface.

Curl: The rounded portion at the bottom of 

the skirt that adds rigidity to the cap and serves to 

protect the cut edge of the metal.

Lug: A horizontal inward protrusion from 

the curl that seat under the thread or lug on the 

finish of the glass container and holds the cap in 

position.

Coatings: Coatings and inks used on the 

inner and outer surfaces of the cap to protect the 

metal from attack, adhere gasket materials, and 

decorate the closure.

Gasket: The actual sealing member of the 

cap which must make intimate contact with the 

glass finish at the proper point to form an effective 

seal. Gaskets are made of either rubber or 

plastisols.

Safety Button or Flip Panel: A raised, 

circular area in the center of the panel which is 

used only for vacuum packed products and serves 

two principle purposes which are detection of low 

or no vacuum packages and an indicator to the 

consumer of a properly sealed package.

Vacuum Formation:

Almost all low-acid foods packaged in glass 

containers are sealed with vacuum-type closures. 

The vacuum within the package and the 

overpressure in the retort on the outside of the cap 

play an important role in forming and maintaining 

a good seal. There are two basic types of cappers 

which apply caps while forming a vacuum in the 

container:

1. Mechanical Vacuum Capper: applies the cap to 

the jar in an evacuated chamber (usually used on 

dry products and rarely on low-acid processed 

foods).

2. Steam Flow Capper: the container is subjected 

to a controlled steam flow that displaces the 

headspace gases from the jar by a flushing action. 

The steam is trapped in the headspace as the cap is 

applied, then condenses to form a vacuum which 

helps hold the closure in place.

There are four primary factors that affect 

vacuum formation (however, 1-3 are considered 

critical factors only if designated critical by the 

process authority):

1. Headspace: There must be sufficient void or 

headspace at the top of the container to allow 

adequate steam to be trapped in the container for 

forming a vacuum, and to accommodate product 

expansion during retorting. The correct amount of 

headspace varies with products, processes, and 

package design, but a rule-of-thumb in the industry 

is that it should be not less than 6% of the 

container volume. Inadequate headspace can 

result in displacement or deformation of the 

closure during retorting.

2. Product fill/sealing temperature: Product filling 

temperature affects the final vacuum in the 

container (due to product contraction upon 

cooling). The higher the product temperature at 

the time of sealing, the higher the final package 

vacuum. Higher filling temperatures also result in 

less air being entrapped in the product.

3. Residual air in the product: Air can have a direct 

effect on the final package vacuum and should be 

kept at a minimum for good sealing. The more air 

that is trapped in the product, the lower the 

vacuum. Expansion of residual air in the container 

during processing can exert pressure against the 

closure and adversely affect seal integrity. Air in 

the container can also impede heat penetration into 
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

10

the container during retorting.

4. Capper vacuum efficiency: Capper vacuum 

efficiency refers to the ability of a steam flow 

capper to produce a vacuum in sealed glass 

containers. The most convenient, routine check on 

the vacuum efficiency of a steam-flow capper is the 

"cold-water vacuum check." This measurement is 

required by 21CFR 113.60(a)(2), and must be 

performed before actual filling operations, and 

results must be recorded. 

The method of cold-water vacuum check 

requires a series of jars to be filled with cold tap 

water to the approximate headspace that will be 

maintained with the product to be run. A series 

means 4 to 6 containers for a straight-line capper, 

and 1 container for each capping head on a rotary 

capper. The capper is allowed to warm up to 

operating temperature and normal steam setting 

and these jars are then sealed in the capper. The 

jars are then opened and re-run through the capper 

and then checked for vacuum. By running the jars 

through the capper the first time the water is deaerated, and thus a truer vacuum reading is 

obtained after the second run. Vacuum is 

measured using a standard vacuum gage. The 

range of vacuum is recommended by the container 

manufacturer, but typically should be 22 inches or 

more.

Vacuum Closures:

Currently, two primary types of vacuum 

closures are used on low-acid food products (refer 

to Attachment 20):

1. Lug type closure: This closure is the 

predominate vacuum-cap type. It is a convenient 

closure because it can be removed without a tool 

and forms a good reseal for storage.

Structurally, the lug cap consists of a steel 

shell and can have four, six, or eight metal lugs 

depending on its diameter. Normally it contains a 

flowed-in plastisol gasket. 

During closure application the headspace is 

swept by steam and lug caps are secured to the 

glass finish by turning or twisting the cap onto the 

finish to seat the lugs of the cap under the threads 

on the glass finish. 

With this lug type of closure the top of the 

glass finish makes contact with the gasket on the 

inside of the lid. In most instances the lids are 

heated with steam to soften the compound and 

facilitate sealing. Both the lugs and vacuum hold 

the cap in place on the glass finish, but vacuum is 

the most important.

2. Press on-Twist off (PT) closures: This closure is 

in widespread use on baby foods as well as other 

products. Structurally, the PT cap consists of a 

steel shell with no lugs. The gasket is molded 

plastisol on the inside vertical wall and covers a 

sealing area extending from the outer edge of the 

top panel to the curl of the cap. These closures 

typically have a safety button or flip panel. 

The cap is first heated to soften the 

plastisol. It is then pushed directly down on the 

glass finish after air is swept from the headspace 

with steam. The glass threads form impressions in 

the skirt of the cap gasket and allow the cap to be 

cammed-off and on. The PT closure is held in place 

on the finish primarily by vacuum, with some 

assistance from the thread impressions in the 

gasket wall when the cap is cooled.

3. Plastisol-Lined Continuous Thread (PLCT) Cap: 

The PLCT cap consists of a metal shell with a 

threaded skirt curled at the end. It contains a 

flowed-in plastisol gasket on the inside that makes 

intimate contact with the top of the finish when the 

cap is screwed onto the jar finish. The PLCT cap 

may be used in both steam and non-steam 

applications. Security measurements on this type 

of container closure can be performed. However, 

pull-up cannot be determined.

Closure Evaluation Requirements:

Generally closure application inspections 

are performed either visually (non-destructive), or 

by cap removal (destructive). It is important to 

know the tests and observations on the different 

types of closures as well as the defects that can 

occur (refer to Attachment 21).

Visual Examinations (Non-Destructive):

As with metal cans, requirements for visual 

examination of closures for glass containers 

include regular observations for gross closure 

defects of at least one container from each capper 

head by a qualified container closure inspection 

person. 

Required frequency of the visual 

examination is as often as necessary to ensure 

proper closure and should not exceed 30 minutes 

of operational time. Additional visual examination 

must be performed immediately following a 

container jam, machine adjustments or a 

prolonged shut down. An example of a prolonged 

shutdown may be when the plant ceases 

production at 6:00 PM and restarts production at 

8:00 AM the next day.
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

11

Gross closure defects for glass jars include:

Loose or cocked caps: "Cocked cap" is a 

condition of the lug-type cap and is caused by a lug 

failing to seat under the glass thread. It is apparent 

during a visual examination as it usually results in 

an unlevel or tilted cap.

Cap tilt: On PT and lug caps, the cap 

should be approximately level, not cocked or tilted, 

and seated well down on the finish. This is judged 

in relation to the transfer bead located at the 

bottom of the container finish . The distance 

between the bottom of the closure and the transfer 

bead should not exceed 3/32"

Crushed lug: A crushed lug on a lug-type 

cap may or may not be visible during a visual 

examination as it does not necessarily result in a 

tilted cap. It is caused by a lug being forced down 

over the glass thread during the closure process. 

The lugs appear bent inward.

Stripped cap: On a lug-type cap, a stripped 

cap refers to a lug cap that has been over-applied 

to the extent that the lugs have been stripped 

through the glass threads on the finish. On visual 

examination the lugs appear scrapped or 

scratched.

Low vacuum by visual examination

Physical Examination (Destructive):

The regulation requires that physical or 

destructive testing be performed by a trained 

closure technician at intervals of sufficient 

frequency to ensure proper closure. Sufficient 

frequency is defined as intervals not to exceed 4 

hours of continuous closing machine operation. 21 

CFR Part 113.60(a)(2) also requires that for glass 

containers with vacuum closures, capper efficiency 

be checked by measurement of the cold water 

vacuum (See Vacuum Formation section). The 

regulation requires that the cold water vacuum 

check be performed before actual filling operations, 

and the results recorded.

Physical examinations can include:

Vacuum: Generally there will be vacuum in 

the package when it comes out of the capper and 

the panel of the cap will be concave. For a PT cap, 

there must be at least 3" vacuum after capping to 

avoid loose caps. Determining vacuum is a 

destructive test and a standard vacuum gauge is 

used.

Temperature: The temperature of the 

product should be within the normal range for the 

product being run or as specified by the process 

authority. The product temperature should be 

recorded in conjunction with the vacuum.

Headspace: Generally, headspace should 

not be less than 6% of the container volume at the 

sealing temperature.

Gasket: After the cap is removed there 

should be a visible, continuous, and even 

impression in the plastisol gasket on the underside 

of the lid. The impression is made by tight contact 

with the glass finish.

Cut-thru: "Cut-thru" is a term used to 

describe when the top of the glass finish has 

pushed completely through the gasket compound 

to the metal coating. A cut-thru can result in a 

leaking seam and requires immediate corrective 

action.

Removal torque: Removal torque is the 

force required to remove the cap. It is typically 

measured using a torque meter. Removal torque is 

considered a valuable quality control check but is 

not recommended as a control for cap application.

Pull-up (Refer to Attachment 22): Pull-up is 

a non-destructive test for measuring the position of 

the closure lug on the threads of the glass finish. It 

is the distance between the leading edge of the cap 

lug and the vertical neck ring seam on the glass 

finish in 1/16 inch increments. When measuring 

this position, first find the vertical neck ring seam 

on the glass finish remembering the vertical neck 

ring does not always correlate with the two vertical 

seams on the glass finish. Then measure the 

distance from the vertical neck ring seam to the 

leading edge of the nearest cap lug. A lug 

positioned to the right of the vertical line is referred 

to as positive (+) and to the left of the vertical line 

as negative (-). A positive measurement means the 

cap has been properly applied. A negative lug 

position can indicate an over-application of the cap 

and may result in a stripped cap. Generally, a cap 

lug will be about 1/4 inch to the right of the vertical 

line, however, the distance can vary and 

measurements between 0" to 8/16" can still result 

in a good security value. It is not recommended 

that pull-up measurements replace the "security" 

measurements described below, but are useful 

once the relationship between pull-up and security 

has been established.

Security (Refer to Attachment 22): Security 

values (lug tension of an applied closure) are the 

most reliable measurement of proper lug cap 

application. Security value ranges are supplied by 

the closure manufacturer to the processor. 

Generally, if measured values are always higher 

that the range specified, it indicates a secure 

package with some degree of over-application. If 

measured values are always lower than the range 

specified usually indicate under-application. Some 

factors that may affect the measured values are, 
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

12

type of plate, compound, and glass surface 

treatment applied by the container manufacturer.

Security measurement is a destructive test. 

There is no requirement as to the number of 

containers that should be tested; however, being a 

destructive test there are practical limits to the 

number of containers that one would test. A 

security test is performed as follows:

-Mark a vertical line on the cap and a 

corresponding line on the container.

-Turn cap counter-clockwise until the 

vacuum is broken.

-Reapply the cap until the closure is fingertight.

-Measure the distance between the marked 

vertical lines in 1/16 inch increments.

Security is considered positive if the line on 

the cap is to the right of the line on the container 

and negative if the line on the cap is to the left of 

the line on the container. A high positive security 

can indicate under application; a negative security 

value can indicate over application. The cause of 

negative security should be determined and 

corrective action taken immediately.

Security can be measured at the capper 

and after processing and cooling. The range of 

measurement, however, should be lower after 

processing due to compound sink that occurs with 

heat and high pressure.

Visual and Physical Examination Record 

Requirements:

21 CFR Part 113.60(a) requires that 

observations made during visual seam 

examinations be recorded. Any defects found 

during the examinations shall also be recorded as 

well as steps taken for corrective action.

 21 CFR Part 113.100(c) outlines the minimum 

required information for the visual and physical 

examination record by stating "Written records of 

all container closure examination shall specify the 

product code, the date and time of container 

closure inspection, the measurements obtained, 

and all corrective actions taken." The regulation 

requires that the records be signed or initialed by 

the container closure inspector and reviewed by 

management with sufficient frequency to ensure 

that the containers are hermetically sealed.

Sufficient frequency can be defined as prior 

to shipment of the product. However, FDA 

investigators should encourage LACF processors to 

review the container records at the same time as 

the thermal processing records or not later than 

one working day after the actual process, and prior 

to shipment or release of the product. 

Refer to Attachment 23 which is an 

example of glass examination records.

Other Quality Control Equipment:

Other equipment including mechanical 

headspacers (which control headspace limits in the 

container) cocked-cap detectors and ejectors, and 

dud detectors (which detect low vacuums) are 

commonly found on glass-container closing lines 

and can affect sealing of the container. For 

example, if a headspacer is incorporated in the 

processing line, it is imperative that it is set 

properly. A headspacer can contribute to product 

overhanging the finish by dripping liquid and 

product on the glass finish, which may affect good 

sealing. Cocked-cap detectors/ejectors and dud 

detectors, if used, maintained, and set properly, 

can serve as useful tools in the evaluation of 

defective seals and sealing problems.

Retortable Pouch

Container Structure and Sealing Method:

Preformed pouches are received by the 

food processor from the pouch manufacturerer, 

who has sealed 3 sides under ideal conditions at 

the pouch manufacturing plant. The pouches are 

filled by hand, in a straight line fashion or on a 

rotary carousel. After filling the packer's end seam 

is fusion sealed by the food manufacturer. Prior to 

sealing, the two sides of the pouch are pulled taut 

by mechanical grippers to assure that the two 

sealing surfaces are smooth and parallel to avoid 

wrinkle in the seal area. It is very important to 

prevent food, grease, moisture and other 

containants from becoming entrapped in the seal 

area; such contaminants can prevent or weaken a 

fusion seal.

Two common types of heat sealers are hot 

bar (also called bar or conductance) and impulse 

sealers: 

1. Hot bar: (jaw type sealing with one or two 

heated opposed bars) is the most widely used 

method for heat sealing. Each heated bar contains 

a heater element that heats up and remains hot 

during production. A thermocouple is implanted in 

each bar near the surface which is connected by 

wire to the instrument control panel where the 

temperature near the sealing surface is digitally 

displayed. The steel bars are usually covered with 

teflon to prevent plastic contamination of the bars. 

Often there is a second cold bar station where the 

sealed pouch is pressurized by a set of cold bars to 

set the seal.
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

13

2. Impulse bar: Heating and cooling dwell times 

are achieved with one set of sealing bars at one 

station. Impulse sealers have 2 bars covered with a 

resilient surface such as silicone rubber. A taut 

Nichrome ribbon (wire) covered with an electrically 

insulating layer of thin heat resistant material ,such 

as Teflon coated fiberglass, is laid over one or both 

of the resilient bars. The bars press the two sealing 

surfaces through the Nichrome ribbon for a few 

seconds which heats the wire to the desired 

temperature for heat sealing. After the specified 

heating dwell time, the voltage (heat) is turned off 

and the resilient bars and pouch seal cools (cooling 

dwell time). The bars are then opened and the 

sealed pouch removed. 

Retort pouches can also be produced on 

site. This is typically called a "form/fill/seal" 

operation, where a multi-layered laminated web of 

polyester/polypropylene/aluminum foil is run along 

a horizontal plane and molded into concave (bowl) 

shapes. The pouches are then filled and a 

continuous web of multi-layer plastic is fed from an 

overhead roller on top of the filled pouches. The 

top web is then heat sealed onto the pouches by 

heat sealing bars that descend from above. A 

vacuum is pulled on each pouch just prior to 

sealing the two material webs. After sealing, the 

individual pouches are cut from the web by a cutter 

wheel as the web exits the vacuum heat sealer.

Critical Factors in Sealing:

Critical factors in heat sealing the retort 

pouch include:

1. Seal bar temperature

2. Pressure exerted on the seal by the sealing bars

3. Dwell time (time seal bar pressure is exerted on 

seal)

These critical factors are interdependent. 

For example, increased production line speeds and 

shorter dwell time can be compensated for by 

increased seal bar temperature.

It is also very important to ensure that the 

seal area is not contaminated with food, grease, 

moisture or some other contaminant which may 

contribute to a weak or defective seal. The sealing 

surface should be smooth, parallel, wrinkle and 

contaminant free.

During inspections, investigators should 

determine if the food processor has validated the 

heat sealing equipment being used to assure that 

the seal bar temperature, pressure and dwell time 

parameters are adequate to create a well fused 

seal. Validation can be accomplished by burst 

testing a number of filled and sealed pouches using 

different heat sealing parameters and choosing the 

most ideal parameters (seal bar temperature, 

pressure and dwell time) for production runs.

SEMI-RIGID RETORTABLE TRAYS 

AND BOWLS:

Sealing Method:

Semi-rigid trays and bowls are filled and 

sealed in a manner similar to the form/filled/sealed 

web system previously described under pouches. 

The trays are filled and vacuum heat sealed using 

hot seal bars. Some of these fill/seal machines 

include a nitrogen gas flush just before fusion heat 

sealing a plastic or plastic/foil closure onto the 

container body.

Critical Factors in Sealing:

Critical factors in attaining a good heat seal 

with semi-rigid trays are similar as those for retort 

pouches. They are:

1. Seal bar temperature

2. Seal bar pressure

3. Seal bar dwell time

4. Smooth, continuous, non-contaminated sealing 

material surfaces

CONTAINER DEFECTS - POUCHES AND 

SEMI-RIGID RETORTABLE TRAYS / 

BOWLS AND PAPERBOARD HEAT SEALED 

PACKAGES:

National Food Processors Association 

(NFPA) has developed a Flexible Package Integrity 

Bulletin (BUL 41-L) that defines three classes of 

defects for flexible packages. These are:

Class I Defects:

Class I defects are defined as critical. They 

are gross closure or package defects that result in a 

hole or leak through the package including a leaky 

seal. Some of the more common Class I defects for 

pouches and semi-rigid containers are:

Channel leaker: A patch or pathway of nonbonding across the width of the seal, creating a 

leak.

Cut: A mechanical slash or slicing that goes 

into the package with a loss of hermetic seal.

Fracture: A break through the packaging 

material.

Leaker: A container that is unsealed or 

exhibiting evidence of lost integrity.
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

14

Non-bonding: Failure of two sealant films 

to combine during the sealing process.

Notch leaker: A leak at a manufactured 

notch used for easy opening.

Puncture: A mechanical piercing that goes 

into the package with a loss of hermetic integrity.

Swollen package: A package the shape of 

which has been altered due to gas formation within 

the package.

Class I defects for paperboard heat sealed 

packages are similar to those for pouches and 

semi-rigid containers and include channel leaker, 

cut, puncture, and swollen packages. Additional 

Class I defects for paperboard heat sealed packages 

are:

Corner leaker: A leak occurring in one of 

the corners of the package.

Perforation leaker: Leakage through or 

around a perforated area.

Pull tab leaker: Leakage through or around 

pull tab.

Seal leaker: Product leaking along the seal.

Class II Defects:

Class II defects are defined as major. These 

defects show no sign of visible leakage but are of 

such magnitude that the container may have lost 

its hermetic seal. Class II defects for pouches and 

semi-rigid containers are:

Abrasion: A scratch partially through the 

surface layer(s) of the package caused by 

mechanically rubbing or scuffing.

Blister: A void within the bonded seal 

caused by entrapped grease or moisture vaporizing 

during seal formation and then condensing.

Compressed seal: A seal formed by 

excessive pressure and/or heat and evidenced by 

cracking and delamination.

Contaminated seal: Foreign matter in the 

seal areas, such as water, grease, or food.

Delamination: A separation of the laminate 

materials forming the package.

Misaligned seal: Improper seal position.

Seal creep:. Partial opening of the inner 

border of seal compromising seal width.

Wrinkle: A fold of material in the seal area.

Crushed package: Alteration of the 

packages' original dimensions caused by force.

Uneven impression: Impression from seal 

bar is uneven around the periphery of container. 

This could be due to uneven thickness of container 

flange resulting in uneven pressure during heat 

sealing.

Seal width variation: Seal width varies 

from specification around the periphery of 

container.

Class II defects for paperboard heat sealed

packages are as defined above: abrasion; crushed; 

and misaligned seal.

Class III Defects:

A Class III defect is defined as a defect that 

has no adverse effect on the hermetic seal. 

NFPA in cooperation with FDA and the 

Association of Official Analytical Chemists 

published a pictorial brochure titled "Classification 

of Visible Exterior Flexible Package Defects. The 

brochure along with NFPA BUL 41-L provide 

valuable information concerning flexible package 

defects. The FDA investigator should be familiar 

with the information contained in these 

documents.

Seam Evaluation Requirements:

21 CFR Part 113.60(a)(3) specifies that for 

closures other than double seamed and glass 

containers, appropriate detailed inspections and 

tests shall be conducted by qualified personnel at 

intervals of sufficient frequency to ensure proper 

closing machine performance and consistently 

reliable hermetic seal production. The regulation 

also states that records of such tests shall be 

recorded.

Part 113 does not specify what tests are 

required. The following guidelines are used by the 

LACF industry for performing both visual and 

destructive tests for flexible and semi-rigid 

containers.

1. FDA Bacteriological Analytical Manual (BAM), 

7th Edition/1992.

2. NFPA Flexible Package Integrity Bulletin, BUL 41-

L with an accompanying Flexible package Defect 

Pictorial Guide, 1989. (As previously mentioned.)

3. Military Specification "Packaging and Thermal 

Pocessing of Foods in Flexible Pouches".

4. USDA Regulations 9, CFR Parts 431 "Canning of 

Meat and Poultry Products".

5. 1982 USDA bulletins "Test Cycles for Small Size 

Semirigid Containers", "Test Cycles for Small Size 

Flexible Retortable Pouches" and "Test Cycles for 

Large Size Flexible and Semirigid Containers".

Visual Seam Examination (Non-Destructive Test):
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

15

As with metal cans and glass jars, 21 CFR 

Part 113.60(a) requires that regular observations 

shall be made during production runs for gross 

closure defects. The top seal of 1 container from 

each seaming head or lane (for pouches) shall be 

visually examined at intervals of sufficient 

frequency and the results recorded. The frequency 

of the visual examination should not exceed 30 

minutes of operational time and additional visual 

examination must be performed immediately 

following a jam in the closing machine, after 

closing machine adjustment, or after startup of a 

machine following a prolonged shut down. A 

prolonged shut down can be when the plant ceases 

production at 6:00pm and restarts production at 

8:00 am the next day.

Visual and destructive testing methods and 

frequencies for flexible and semi-rigid containers 

are outlined in the guidelines referenced above. 

For example, NFPA BUL 41-L recommends the 

following examinations:

Retort pouch: Visual on-line examination of 

the retort pouch container and seals at a rate of 1 

pouch from each filling station at start-up and 

every 30 minutes thereafter. The visual 

examination includes a "squeeze test" whereby 1 

pouch is manually kneaded 10 times in succession. 

After kneading, the seal areas are examined for 

evidence of product leakage or delamination.

Plastic containers with heat sealed lids: 

BUL 41-L recommends a visual examination for 

defects every 15 minutes; and at intervals of 30 

minutes recommends the sides of each plastic test 

container be manually squeezed to cause the lid to 

bulge 1/8 inch. The seal area is then visually 

examined for defects such as contamination and 

non-bonding. 

Paperboard cartons: BUL 41-L recommends 

that for web fed systems, the material web be 

checked at 15 to 30 minute intervals for correct 

alignment of the longitudinal seal. After sealing 

the cartons should be checked for proper 

alignment of transverse seals and for evidence of 

container defects.

Physical examination (destructive and nondestructive testing):

As stated previously, 21 CFR Part 

113.60(a)(2) states that for closures other than 

double seams and glass containers, appropriate 

detailed inspections and tests shall be conducted at 

intervals of sufficient frequency to ensure proper 

closing machine performance and consistently 

reliable hermetic seal production. For physical 

testing of the reliability of the hermetic seal the 

regulation does not specify test methods or 

frequency of testing. Again, we rely on the 

guidelines, previously referenced, that have been 

published for these containers. Some of the 

common destructive and non-destructive testing 

methods for flexible and semi-rigid containers that 

are described in the guidelines are as follows:

Destructive testing:

Burst testing (Refer to Attachment 24): The 

burst test is a good overall test for seal integrity 

(especially for retortable containers). The test 

stresses a package uniformly in all directions and 

identifies the location of the weakest point and the 

pressure at which it fails. The burst test can be 

used for retort pouches to test the seal strength 

along the two sides and one end as well as all four 

sides.

Vacuum or bubble test (Refer to 

Attachment 24): The vacuum or bubble test (also 

referred to as air pressure testing), is performed 

inside a transparent vacuum chamber such as a 

bell jar connected to a vacuum source. A vacuum 

is pulled on the inside of the chamber for a period 

of time and a container or seal leak is indicated if 

the container fails to swell to normal dimensions. 

This can also be done with the container 

submerged under water in the bell jar (bubbles 

emanating from the container would indicate a 

leak). This test is most commonly used for 

aseptically filled containers with fusion or peelable 

lidstock.

Tensile (seal strength) testing (Refer to 

Attachment 24): The tensile test is used to measure 

seal strength of the retort pouch. The test involves 

taking 3 strips (1"x3") from the seal area of the 

pouch and attaching the two ends of each strip to a 

tensile testing device. The device slowly pulls 

apart the seam and the force required to separate 

the seam is measured. The disadvantage of tensile 

testing is it tests only sampled portions of the seam 

area. For this reason, it is used only for 

surveillance of material sealability and to spot 

check equipment operations and sealing 

conditions.

Drop testing (Refer to Attachment 25): The 

drop test (also referred to as an immediate 

container abuse test) is commonly used to test the 

package and seal integrity of flexible containers, 

and semirigid trays and bowls. This test was 

designed to simulate the dropping of individual 

containers under a controlled and reproducible 

basis. After drop testing, each container is visually 

inspected for evidence of leakage. After the visual 
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

16

inspection, the container is then "peel tested". Peel 

testing is described below.

Peel testing (Refer to Attachment 26): The 

peel test is intended to measure the pounds of 

force necessary to peel a fused or sealed lid off a 

plastic container body. For the form/filled/sealed 

plastic containers, the peel test is conducted by 

peeling back the lid on each container held at a 45 

degree angle and observing the area for a general 

frosty appearance on both the lid and sealed 

surfaces. This frosty material is polypropylene 

residue from the lid sealing layer. The presence of 

this material on the flange, around the periphery of 

the container, indicates a well fused seam. Peel 

testing can be performed by hand or with the use 

of a tensile testing device. This test is often 

performed after drop testing as previously 

described.

Residual Gas testing (Refer to Attachment 

27): The quantity of residual gas in retortable 

flexible pouches and semirigid plastic containers is 

normally measured prior to retorting. Too much 

residual air can exert excessive pressure on the 

inner seal area during retorting, which results in 

weakened seals and reduced heat penetration to 

the product cold spot. To much air in the product 

can also shorted the product shelf life.

Electroconductivity testing (Refer to 

Attachment 27): Electroconductivity testing tests a 

container's ability to prevent the flow of electric 

current through the package. A tight inner layer of 

plastic material will not allow the flow through of 

electric current unless there is a hole or crack in the 

plastic material. Electroconductivity tests are 

commonly run to confirm leaks in packages 

detected by other non-destructive tests such as 

incubation.

Dye testing: Dye tests are usually 

conducted to identify the location of micro size 

holes in food packages that have tested positive for 

leaks by electroconductivity, incubation or biotest 

methods.

Non-destructive testing:

Incubation testing : Incubation testing 

involves the storage of finished product samples 

for a week or more at temperatures within the 

range required for growth of spoilage 

microorganisms. The growth of microorganisms 

indicates either insufficient processing or a loss of 

hermetic seal.

Biotesting: Biotesting is a means of 

challenging a containers's ability to prevent 

leakage under the worst case conditions of 

processing and/or storage. Biotesting involves 

filling containers with a broth or other food 

conducive to growth of gas producing 

microorganisms and then subjecting the container 

to processing or abuse, followed by immersion in 

a solution heavily contaminated with the target 

spoilage organism. The containers are then 

incubated. After incubation, a leak would be 

evidenced by a swollen container.

On-Line non-destructive tests: There are a 

number of on-line non-destructive tests designed 

to detect leaks in semi-rigid and flexible packages 

after filling and sealing. Most of these tests involve 

the measurement of pressure differential between 

the pressure inside the container and the external 

pressure. After establishing a set differential 

pressure, any change in pressure would indicate a 

leak.

These test methods although not required 

by regulation, are presented in detail in various 

guidelines, as previously referenced. 

Visual and Physical Seam Examination Record 

Requirements:

The regulation requires that observations 

made during visual and physical examinations be 

recorded. Any defects found during the visual 

examination shall also be recorded, as well as 

steps taken for corrective action. 

Although the regulation does not specify 

what test methods or frequency of examination is 

required, it does say that tests will be performed 

and "Records of such tests shall be maintained. 21 

CFR Part 113.100(c) requires the written container 

closure records must specify the product code, date 

and time of container closure inspection, any 

measurements obtained, and all corrective actions 

taken. These records must also be signed or 

initialed by the container closure inspector and 

reviewed by management with sufficient frequency 

to ensure adequate hermetic seal production.

REFERENCES

"Canned Foods, Principles of Thermal Process 

Control, Acidification and Container Closure 

Evaluation", 1988 and 1995, The Food Processors 

Institute, Washington, DC.

Flexible Packaging Used in the Thermal Processing 

and Aseptic Filling of Low Acid Foods, Brian 

Hendrickson, 1989.

Food and Drug Administration State Training 
Guide to Inspections of Low Acid Canned Food Manufacturers -Part 3 November 1998

17

Branch Course Manuals, "Low Acid Canned Foods", 

U. S. Department of Health and Human Services, 

Food and Drug Administration, 1996.

Food Packaging Principles and Practice, Gordon L. 

Robertson, Marcel Dekker, Inc., New York 1993

NFPA Bulletin 41-L, "Flexible Package Integrity 

Bulletin" The Flexible Package Integrity Committee, 

National Food Processor's Association, 1989, 

Washington, D.C.

Pictorial Poster "Classification of Visible Exterior 

Can Defects", Published by AOAC, 1984

Pictorial poster of flexible package defects, The 

NFPA Flexible Package Integrity Committee, 1989

Report by Meal Ready-To Eat (MRE) Task Force, 

Office of the Deputy Chief of Staff for Logistics 

Headquarters, Dept. of the Army, The Pentagon, 

Washington, D.C., July 1986.

Test Cycles for Large Size Flexible and Semi-rigid 

Containers, USDA, Washington, D.C., 1982.

Test Cycles for Small Size Flexible Retortable 

Pouches, USDA, Washington, D.C., 1982.

Test Cycles for Small Size Semi-rigid Containers, 

USDA, Washington, D.C., 1982.

The FDA Bacteriological Analytical Manual (BAM), 

7th Edition, 1992, Published by AOAC International.

The Wiley Encyclopedia of Packaging Technology, 

Second Edition, Aron L. Brody and Kenneth S. 

Marsh; John Wiley & Sons, Inc., New York, 1997.

Title 21 Code of Federal Regulations Part 113-

Thermally Processed Low-Acid Foods Packaged in 

Hermetically Sealed Containers.

Title 9 Code of Federal Regulations Part 431-

Canning of Meat and Poultry Products.

"Top Double Seaming Manual", Department of 

Food Science and Technology of Oregon State 

University, 1977. 

U.S. Military Specification, MIL-PRF47073E, 

Packaging and Thermal Processing of Foods in 

Flexible Pouches, 30 November, 1995.
November 1998 Guide to Inspections of Low Acid Canned Food Manufacturers - Part 3

18

ATTACHMENTS:

1. Metal Can Flange/ Metal Can End Curl/ Double Seam Structure and Terminology

2. Double Seam - Countersink/Thickness/ Width/Body Hook and Cover Hook/Overlap/Cover Hook Wrinkles

3. Seam Tightness Evaluation

4. Body Wall Impression

5. Formation of the Double Seam

6. Stages in the Formation of the Double Seam-1st and 2nd Operation Roll

7. Example- Double Seam Guidelines

8. Can Seam Defects - Droop, Lips, Vees

9. Can Seam Defects - Sharp Seams, Cut-Overs

10.Can Seam Defect - Jumpover

11. Can Seam Defects - Deadheads, Spinner, Slips and Skids

12. Can Seam Defects - False Seam/ Knocked Down Flange/Body Buckle/Cocked Body

13. Can Seam Defect - Cut Seam

14. Can Seam Projector

15. Can Seam Micrometer

16. Seamscope

17. Example-Visual Seam Examination Record-Cans

18. Double Seam Examination Records - Cans

19. Glass Container Structure and Terminology/ Metal Vacuum Closure Structure and Terminology

20. Metal Vacuum Closures

21. Glass Container Defects

22. Security Test/Pull-Up Test

23. Example-Glass Closure Evaluation Records

24. Sealed Pouches and Semi-Rigid Containers-Burst Test/Bubble Test

25. Sealed Pouches and Semi-Rigid Containers-USDA Drop Test

26. Sealed Pouches and Semi-Rigid Containers-Peel Test

27. Sealed Pouches and Semi-Rigid Containers- Residual Gas Test/Electroconductivity Test
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Chapter 21A 

Examination of Canned Foods 

Authors 

(Return to Table of Contents)

The incidence of spoilage in canned foods is low, but when it occurs it must be investigated properly. 

Swollen cans often indicate a spoiled product. During spoilage, cans may progress from normal to 

flipper, to springer, to soft swell, to hard swell. However, spoilage is not the only cause of abnormal 

cans. Overfilling, buckling, denting, or closing while cool may also be responsible. Microbial spoilage 

and hydrogen, produced by the interaction of acids in the food product with the metals of the can, are the 

principal causes of swelling. High summer temperatures and high altitudes may also increase the degree 

of swelling. Some microorganisms that grow in canned foods, however, do not produce gas and 

therefore cause no abnormal appearance of the can; nevertheless, they cause spoilage of the product. 

Spoilage is usually caused by growth of microorganisms following leakage or underprocessing. Leakage 

occurs from can defects, punctures, or rough handling. Contaminated cooling water sometimes leaks to 

the interior through pinholes or poor seams and introduces bacteria that cause spoilage. A viable mixed 

microflora of bacterial rods and cocci is indicative of leakage, which may usually be confirmed by can 

examination. Underprocessing may be caused by undercooking; retort operations that are faulty because 

of inaccurate or improperly functioning thermometers, gauges, or controls; excessive contamination of 

the product for which normally adequate processes are insufficient; changes in formulation or handling 

of the product that result in a more viscous product or tighter packing in the container, with consequent 

lengthening of the heat penetration time; or, sometimes, accidental bypassing of the retort operation 

altogether. When the can contains a spoiled product and no viable microorganisms, spoilage may have 

occurred before processing or the microorganisms causing the spoilage may have died during storage. 

Underprocessed and leaking cans are of major concern and both pose potential health hazards. However, 

before a decision can be made regarding the potential health hazard of a low-acid canned food, certain 

basic information is necessary. Naturally, if Clostridium botulinum (spores, toxin, or both) is found, the 

hazard is obvious. Intact cans that contain only mesophilic, Gram-positive, sporeforming rods should be 

considered underprocessed, unless proved otherwise. It must be determined that the can is intact 

(commercially acceptable seams and no microleaks) and that other factors that may lead to 

underprocessing, such as drained weight and product formulation, have been evaluated. 

The preferred type of tool for can content examination is a bacteriological can opener consisting of a 

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

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puncturing device at the end of a metal rod mounted with a sliding triangular blade that is held in place 

by a set screw. The advantage over other types of openers is that it does no damage to the double seam 

and therefore will not interfere with subsequent seam examination of the can. 

Table 1. Useful descriptive terms for canned food analysis. 

The number of cans examined bacteriologically should be large enough to give reliable results. When 

the cause of spoilage is clear-cut, culturing 4-6 cans may be adequate, but in some cases it may be 

Exterior can condition 

leaker 

dented 

rusted 

buckled 

paneled 

bulge 

Internal can condition

normal 

peeling 

slight, moderate or severe etching 

slight, moderate or severe 

blackening 

slight, moderate or severe rusting 

mechanical damage 

Micro-leak test 

packer seam 

side panel 

side seam 

cut code 

pinhole 

Product odor

putrid 

acidic 

butyric 

metallic 

sour 

cheesy 

fermented 

musty 

sweet 

fecal 

sulfur 

off-odor 

Product liquor 

cloudy 

clear 

foreign 

frothy 

Solid product 

digested 

softened 

curdled 

uncooked 

overcooked 

Liquid product 

cloudy 

clear 

foreign 

frothy 

Pigment

darkened 

light 

changed 

Consistency

slimy 

fluid 

viscous 

ropy 

Flat - a can with both ends concave; it remains in this condition even when the can 

is brought down sharply on its end on a solid, flat surface. 

Flipper - a can that normally appears flat; when brought down sharply on its end 

on a flat surface, one end flips out. When pressure is applied to this end, it flips in 

again and the can appears flat. 

Springer - a can with one end permanently bulged. When sufficient pressure is 

applied to this end, it will flip in, but the other end will flip out. 

Soft swell - a can bulged at both ends, but not so tightly that the ends cannot be 

pushed in somewhat with thumb pressure. 

Hard swell - a can bulged at both ends, and so tightly that no indentation can be 

made with thumb pressure. A hard swell will generally "buckle" before the can 

bursts. Bursting usually occurs at the double seam over the side seam lap, or in the 

middle of the side seam. 

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necessary to culture 10-50 cans before the cause of spoilage can be determined. On special occasions 

these procedures may not yield all the required information, and additional tests must be devised to 

collect the necessary data. Unspoiled cans may be examined bacteriologically to determine the presence 

of viable but dormant organisms. The procedure is the same as that used for spoiled foods except that 

the number of cans examined and the quantity of material subcultured must be increased. 

A. Equipment and materials 

1. Incubators, thermostatically controlled at 30, 35, and 55°C 

2. pH meter, potentiometer 

3. Microscope, slides, and coverslips 

4. Can opener, bacteriological can opener, and can punch, all sterile 

5. Petri dishes, sterile 

6. Test tubes, sterile 

7. Serological pipets, cotton-plugged, sterile 

8. Nontapered pipets, cotton-plugged (8 mm tubing), sterile 

9. Soap, water, brush, and towels, sterile and nonsterile 

10. Indelible ink marking pen 

11. Diamond point pen for marking cans 

12. Examination pans (Pyrex or enamel baking pans) 

B. Media and reagents

1. Bromcresol purple (BCP) dextrose broth (M27) 

2. Chopped liver broth (M38) or cooked meat medium (CMM) (M42) 

3. Malt extract broth (M94) 

4. Liver-veal agar (without egg yolk) (LVA) (M83) 

5. Acid broth (M4) 

6. Nutrient agar (NA) (M112) 

7. Methylene blue stain (R45), crystal violet (R16), or Gram stain (R32) 

8. Sabouraud's dextrose agar (SAB) (M133) 

9. 4% Iodine in 70% ethanol (R18) 

C. Can preparation 

Remove labels. With marking pen, transfer subnumbers to side of can to aid in correlating 

findings with code. Mark labels so that they may be replaced in their original position on the can 

to help locate defects indicated by stains on label. Separate all cans by code numbers and record 

size of container, code, product, condition, evidence of leakage, pinholes or rusting, dents, 

buckling or other abnormality, and all identifying marks on label. Classify each can according to 

the descriptive terms in Table 1. Before observing cans for classification, make sure cans are at 

room temperature. 

D. Examination of can and contents 

Classification of cans. NOTE: Cans must be at room temperature for classification. 

1. Sampling can contents

a. Swollen cans. Immediately analyze springers, swells, and a representative number (at 

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least 6, if available) of flat and flipper cans. Retain examples of each, if available, 

when reserve portion must be held. Place remaining flat and flipper cans (excluding 

those held in reserve) in incubator at 35°C. Examine at frequent intervals for 14 days. 

When abnormal can or one becoming increasingly swollen is found, make note of it. 

When can becomes a hard swell or when swelling no longer progresses, culture 

sampled contents, examine for preformed toxin of C. botulinum if microscopic 

examination shows typical C. botulinum organisms or Gram-positive rods, and 

perform remaining steps of canned food examination. 

b. Flat and flipper cans. Place cans (excluding those held in reserve) in incubator at 

35°C. Observe cans for progressive swelling at frequent intervals for 14 days. When 

swelling occurs, follow directions in l-a, above. After 14 days remove flat and flipper 

cans from incubator and test at least 6, if available. (It is not necessary to analyze all 

normal cans.) Do not incubate cans at temperatures above 35°C. After incubation, 

bring cans back to room temperature before classifying them. 

2. Opening the can. Open can in an environment that is as aseptic as possible. Use of vertical 

laminar flow hood is recommended. 

a. Hard swells, soft swells, and springers. Chill hard swells in refrigerator before 

opening. Scrub entire uncoded end and adjacent sides of can using abrasive cleanser, 

cold water, and a brush, steel wool, or abrasive pad. Rinse and dry with clean sterile 

towel. Sanitize can end to be opened with 4% iodine in 70% ethanol for 30 min and 

wipe off with sterile towel. DO NOT FLAME. Badly swollen cans may spray out a 

portion of the contents, which may be toxic. Take some precaution to guard against 

this hazard, e.g., cover can with sterile towel or invert sterile funnel over can. 

Sterilize can opener by flaming until it is almost red, or use separate presterilized can 

openers, one for each can. At the time a swollen can is punctured, test for headspace 

gas, using a qualitative test or the gas-liquid chromatography method described 

below. For a qualitative test, hold mouth of sterile test tube at puncture site to capture 

some escaping gas, or use can-puncturing press to capture some escaping gas in a 

syringe. Flip mouth of tube to flame of Bunsen burner. A slight explosion indicates 

presence of hydrogen. Immediately turn tube upright and pour in a small amount of 

lime water. A white precipitate indicates presence of CO2. Make opening in sterilized 

end of can large enough to permit removal of sample. 

b. Flipper and flat cans. Scrub entire uncoded end and adjacent sides of can using 

abrasive cleanser, warm water, and a brush, steel wool, or abrasive pad. Rinse and dry 

with clean sterile towel. Gently shake cans to mix contents before sanitizing. Flood 

end of can with iodine-ethanol solution and let stand at least 15 min. Wipe off iodine 

mixture with clean sterile towel. Ensure sterility of can end by flaming with burner in 

a hood until iodine-ethanol solution is burned off, end of can becomes discolored 

from flame, and heat causes metal to expand. Be careful not to inhale iodine fumes 

while burning off can end. Sterilize can opener by flaming until it is almost red, or 

use separate presterilized can openers for each can. Make opening in sterilized end of 

can large enough to permit removal of sample. 

3. Removal of material for testing. Remove large enough portions from center of can to 

inoculate required culture media. Use sterile pipets, either regular or wide-mouthed. 

Transfer solid pieces with sterile spatulas or other sterile devices. Always use safety devices 

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for pipetting. After removal of inocula, aseptically transfer at least 30 ml or, if less is 

available, all remaining contents of cans to sterile closed containers, and refrigerate at about 

4°C. Use this material for repeat examination if needed and for possible toxicity tests. This 

is the reserve sample. Unless circumstances dictate otherwise, analyze normal cans 

submitted with sample organoleptically and physically (see 5-b, below), including pH 

determination and seam teardown and evaluation. Simply and completely describe product 

appearance, consistency, and odor on worksheet. If analyst is not familiar with 

decomposition odors of canned food, another analyst, preferably one familiar with 

decomposition odors, should confirm this organoleptic evaluation. In describing the product 

in the can, include such things as low liquid level (state how low), evidence of compaction, 

if apparent, and any other characteristics that do not appear normal. Describe internal and 

external condition of can, including evidence of leakage, etching, corrosion, etc. 

4. Physical examination. Perform net weight determinations on a representative number of 

cans examined (normal and abnormal). Determine drained weight, vacuum, and headspace 

on a representative number of normal-appearing and abnormal cans (1). Examine metal 

container integrity of a representative number of normal cans and all abnormal cans that are 

not too badly buckled for this purpose (see Chapter 22). CAUTION: Always use care when 

handling the product, even apparently normal cans, because botulinal toxin may be present. 

5. Cultural examination of low-acid food (pH greater than 4.6). If there is any question as 

to product pH range, determine pH of a representative number of normal cans before 

proceeding. From each container, inoculate 4 tubes of chopped liver broth or cooked meat 

medium previously heated to 100°C (boiling) and rapidly cooled to room temperature; also 

inoculate 4 tubes of bromcresol purple dextrose broth. Inoculate each tube with 1-2 ml of 

product liquid or product-water mixture, or 1-2 g of solid material. Incubate as in Table 2. 

After culturing and removing reserve sample, test material from cans (other than those 

classified as flat) for preformed toxins of C. botulinum when appropriate, as described in 

Chapter 17. 

a. Microscopic examination. Prepare direct smears from contents of each can after 

culturing. Dry, fix, and stain with methylene blue, crystal violet, or Gram stain. If 

product is oily, add xylene to a warm, fixed film, using a dropper; rinse and stain. If 

product washes off slide during preparation, examine contents as wet mount or 

hanging drop, or prepare suspension of test material in drop of chopped liver broth 

before drying. Check liver broth before use to be sure no bacteria are present to 

contribute to the smear. Examine under microscope; record types of bacteria seen and 

estimate total number per field. 

Table 2. Incubation times for various media for examination of low acid foods (pH > 4.6).

Medium No. of tubes Temp. (°C) Time of incubation (h)

Chopped liver (cooked meat) 2 35 96-120

Chopped liver (cooked meat) 2 55 24-72

Bromcresol purple dextrose broth 2 55 24-48

Bromcresol purple dextrose broth 2 35 96-120

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b. Physical and organoleptic examination of can contents. After removing reserve 

sample from can, determine pH of remainder, using pH meter. DO NOT USE pH 

PAPER. Pour contents of cans into examination pans. Examine for odor, color, 

consistency, texture, and overall quality. DO NOT TASTE THE PRODUCT. 

Examine can lining for blackening, detinning, and pitting. 

Table 3.Schematic diagram of culture procedure for low-acid canned foods 

a

 LVA, liver-veal agar; NA, nutrient agar; CMM, cooked meat medium; BCP, bromcresol purple 

dextrose broth. 

Table 4. Incubation of acid broth and malt extract broth used for acid foods (pH 4.6) 

Table 5. Pure culture scheme for acid foods (pH 4.6).

Medium No. of tubes Temp. (°C) Time of incubation (h)

Acid broth 2 55 48

Acid broth 2 30 96

Malt extract broth 2 30 96

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a

 NA, nutrient agar; SAB, Sabouraud's dextrose agar.

E. Cultural findings in cooked meat medium (CMM) and bromcresol purple dextrose broth (BCP) 

Check incubated medium for growth at frequent intervals up to maximum time of incubation 

(Table 2). If there is no growth in either medium, report and discard. At time growth is noted 

streak 2 plates of liver-veal agar (without egg yolk) or nutrient agar from each positive tube. 

Incubate one plate aerobically and one anaerobically, as in schematic diagram (Table 3). 

Reincubate CMM at 35°C for maximum of 5 days for use in future toxin studies. Pick 

representatives of all morphologically different types of colonies into CMM and incubate for 

appropriate time, i.e., when growth is sufficient for subculture. Dispel oxygen from CMM broths 

to be used for anaerobes but not from those to be used for aerobes. After obtaining pure isolates, 

store cultures to maintain viability. 

1. If mixed microflora is found only in BCP, report morphological types. If rods are 

included among mixed microflora in CMM, test CMM for toxin, as described in Chapter 

17. If Gram-positive or Gram-variable rods typical of either Bacillus or Clostridium

organisms are found in the absence of other morphological types, search to determine 

whether spores are present. In some cases, old vegetative cells may appear to be Gramnegative and should be treated as if they are Gram-positive. Test culture for toxin according 

to Chapter 17. 

Table 6. Classification of food products according to acidity

Low acid--pH greater than 4.6 Acid pH 4.6 and below

Meats Tomatoes

Seafoods Pears

Milk Pineapple

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Meat and vegetable Mixtures and "specialties" 

Spaghetti 

Soups 

Other fruit

Sauerkraut

Vegetables 

Asparagus 

Beets 

Pumpkin 

Green beans 

Corn 

Lima beans 

Pickles

Berries

Citrus

Rhubarb

Table 7. Spoilage microorganisms that cause high and low acidity in various 

vegetables and fruits

Spoilage type pH groups Examples

Thermophilic

Flat-sour >5.3 Corn, peas

Thermophilic(a) >4.8 Spinach, corn

Sulfide spoilage(a) >5.3 Corn, peas

Mesophilic

Putrefactive anaerobes(a) >4.8 Corn, asparagus

Butyric anaerobes >4.0 Tomatoes, peas

Aciduric flat-sour(a) >4.2 Tomato juice

Lactobacilli 4.5-3.7 Fruits

Yeasts <3.7 Fruits

Molds <3.7 Fruits

a

 The responsible organisms are bacterial sporeformers.

Table 8. Spoilage manifestations in low-acid products 

Group of 

organisms

Classification Manifestations

Flat-sour Can flat Possible loss of vacuum on storage

Product Appearance not usually altered; pH markedly 

lowered, sour; may have slightly abnormal 

odor; sometimes cloudy liquor

Thermophilic 

anaerobe

Can swells May burst

Product Fermented, sour, cheesy or butyric odor

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Sulfide spoilage Can flat H2S gas absorbed by product 

Product Usually blackened; rotten egg odor

Putrefactive 

anaerobe

Can swells May burst

Product May be partially digested; pH slightly above 

normal; typical putrid odor

Aerobic 

sporeformers

Can flat or 

swollen

Usually no swelling, except in cured meats 

when nitrate and sugar present; coagulated 

evaporated milk, black beets

Table 9. Spoilage manifestations in acid products

Type of organism Classification Manifestation

Bacillus thermoacidurans (flat, 

sour tomato juice)

Can flat Little change in vacuum

Product Slight pH change; off-odor

Butyric anaerobes (tomatoes and 

tomato juice)

Can swells May burst

Product Fermented, butyric odor

Nonsporeformers (mostly lactic 

types)

Can swells Usually burst, but swelling 

may be arrested

Product Acid odor

Table 10. Laboratory diagnosis of bacterial spoilage

Underprocessed Leakage

Can Flat or swelled; seams generally normal Swelled; may show 

normal defects(a)

Product 

appearance

Sloppy or fermented Frothy fermentation; 

viscous

odor Normal, sour or putrid, but generally 

consistent from can to can

Sour, fecal; generally 

varying from can to can

pH Usually fairly constant Wide variation

Microscopic 

and cultural

Cultures show sporeforming rods only Mixed cultures, 

generally rods and cocci; 

only at usual 

temperatures 

Growth at 35 and/or 55°C. May be 

characteristic on special growth media, 

e.g., acid agar for tomato juice. 

If product misses retort completely, 

rods, cocci,yeast or molds, or any 

combination of these may be present. 

History Spoilage usually confined to certain Spoilage scattered

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portions of pack

In acid products, diagnosis may be less 

clearly defined; similar organisms may 

be involved in understerilization and 

leakage.

a

 Leakage may be due not to can defects but to other factors, such as 

contamination of cooling water or rough handling, e.g., can unscramblers, rough 

conveyor system.

Table 11. pH range of a few selected commercially canned foods

Food pH range Food pH range

Apples, juice 3.3 - 3.5 Jam, fruit 3.5 - 4.0

Apples, whole 3.4 - 3.5 Jellies, fruit 3.0 - 3.5

Asparagus, green 5.0 - 5.8 Lemon juice 2.2 - 2.6

Beans Lemons 2.2 - 2.4

 Baked 4.8 - 5.5 Lime juice 2.2 - 2.4

 Green 4.9 - 5.5 Loganberries 2.7 - 3.5

 Lima 5.4 - 6.3 Mackerel 5.9 - 6.2

 Soy 6.0 - 6.6 Milk

Beans with pork 5.1 - 5.8 Cow, whole 6.4 - 6.8

Beef, corned, hash 5.5 - 6.0 Evaporated 5.9 - 6.3

Beets, whole 4.9 - 5.8 Molasses 5.0 - 5.4

Blackberries 3.0 - 4.2 Mushroom 6.0 - 6.5

Blueberries 3.2 - 3.6 Olives, ripe 5.9 - 7.3 

Boysenberries 3.0 - 3.3 Orange juice 3.0 - 4.0 

Bread Oysters 6.3 - 6.7

 White 5.0 - 6.0 Peaches 3.4 - 4.2

 Date and nut 5.1 - 5.6 Pears (Bartlett) 3.8 - 4.6

Broccoli 5.2 - 6.0 Peas 5.6 - 6.5

Carrot juice 5.2 - 5.8 Pickles

Carrots, chopped 5.3 - 5.6 Dill 2.6 - 3.8

Cheese Sour 3.0 - 3.5

 Parmesan 5.2 - 5.3 Sweet 2.5 - 3.0

 Roquefort 4.7 - 4.8 Pimento 4.3 - 4.9

Cherry juice 3.4 - 3.6 Pineapple

Chicken 6.2 - 6.4 Crushed 3.2 - 4.0

Chicken with noodles 6.2 - 6.7 Juice 3.4 - 3.7

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Chop suey 5.4 - 5.6 Sliced 3.5 - 4.1

Cider 2.9 - 3.3 Plums 2.8 - 3.0

Clams 5.9 - 7.1 Potato salad 3.9 - 4.6

Cod fish 6.0 - 6.1 Potatoes

Corn Mashed 5.1

 Cream style 5.9 - 6.5 White, whole 5.4 - 5.9

 On-the-cob 6.1 - 6.8 Prune juice 3.7 - 4.3

 Whole grain Pumpkin 5.2 - 5.5

 Brine-packed Raspberries 2.9 - 3.7

 Vacuum-packed 6.0 - 6.4 Rhubarb 2.9 - 3.3

Crab apples, spiced 3.3 - 3.7 Salmon 6.1 - 6.5

Cranberry Sardines 5.7 - 6.6

 Juice 2.5 - 2.7 Sauerkraut 3.1 - 3.7

 Sauce 2.3 Juice 3.3 - 3.4

Currant juice 3.0 Shrimp 6.8 - 7.0

Dates 6.2 - 6.4 Soups

Duck 6.0 - 6.1 Bean 5.7 - 5.8

Figs 4.9 - 5.0 Beef broth 6.0 - 6.2

Frankfurters 6.2 - 6.2 Chicken noodle 5.5 - 6.5

Fruit cocktail 3.6 - 4.0 Clam chowder 5.6 - 5.9

Gooseberries 2.8 - 3.1 Duck 5.0 - 5.7

Grapefruit Mushroom 6.3 - 6.7

 Juice 2.9 - 3.4 Noodle 5.6 - 5.8

 Pulp 3.4 Oyster 6.5 - 6.9

 Sections 3.0 - 3.5 Pea 5.7 - 6.2

Grapes 3.5 - 4.5 Spinach 4.8 - 5.8

Ham, spiced 6.0 - 6.3 Squash 5.0 - 5.8

Hominy, lye 6.9 - 7.9 Tomato 4.2 - 5.2

Huckleberries 2.8 - 2.9 Turtle 5.2 - 5.3

 Vegetable 4.7 - 5.6

Strawberries 3.0 - 3.9 Miscellaneous products

Sweet potatoes 5.3 - 5.6 Beers 4.0 - 5.0

Tomato juice 3.9 - 4.4 Ginger ale 2.0 - 4.0

Tomatoes 4.1 - 4.4 Human

Tuna 5.9 - 6.1 Blood plasma 7.3 - 7.5

Turnip greens 5.4 - 5.6 Duodenal contents 4.8 - 8.2

Vegetable juice 3.9 - 4.3 Feces 4.6 - 8.4

Vegetables, mixed 5.4 - 5.6 Gastric contents 1.0 - 3.0

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2. If no toxin is present, send pure cultures for evaluation of heat resistance to Cincinnati 

District Office, FDA, 1141 Central Parkway, Cincinnati, OH 45202, if cultures meet the 

following criteria: 

 Cultures come from intact cans that are free of leaks and have commercially 

acceptable seams. (Can seams of both ends of can must be measured; visual 

examination alone is not sufficient.) 

 Two or more tubes are positive and contain similar morphological types. 

3. Examination of acid foods (pH 4.6 and below) by cultivation. From each can, inoculate 4 

tubes of acid broth and 2 tubes of malt extract broth with 1-2 ml or 1-2 g of product, using 

the same procedures as for low-acid foods, and incubate as in Table 4. Record presence or 

absence of growth in each tube, and from those that show evidence of growth, make smears 

and stain. Report types of organisms seen. Pure cultures may be isolated as shown in Table 

5. 

F. Interpretation of results (see Tables 6-11) 

1. The presence of only sporeforming bacteria, which grow at 35°C, in cans with satisfactory 

seams and no microleaks indicates underprocessing if their heat resistance is equal to or less 

than that of C. botulinum. Spoilage by thermophilic anaerobes such as C. thermobutylicum

may be indicated by gas in cooked meat at 55°C and a cheesy odor. Spoilage by C. 

botulinum, C. sporogenes, or C. perfringens may be indicated in cooked meat at 35°C by 

gas and a putrid odor; rods, spores, and clostridial forms may be seen on microscopic 

examination. Always test supernatants of such cultures for botulinal toxin even if no toxin 

was found in the product itself, since viable botulinal spores in canned foods indicate a 

potential public health hazard, requiring recall of all cans bearing the same code. Spoilage 

by mesophilic organisms such as Bacillus thermoacidurans or B. coagulans and/or 

thermophilic organisms such as B. stearothermophilus, which are flat-sour types, may be 

indicated by acid production in BCP tubes at 35 and/or 55°C in high-acid or low-acid 

canned foods. No definitive conclusions may be drawn from inspection of cultures in broth 

if the food produced an initial turbidity on inoculation. Presence or absence of growth in 

this case must be determined by subculturing. 

Vinegar 2.4 - 3.4 Milk 6.6 - 7.6

Youngberries 3.0 - 3.7 Saliva 6.0 - 7.6

 Spinal fluid 7.3 - 7.5

 Urine 4.8 - 8.4

Magnesia, milk of 10.0 -10.5

Water

Distilled, CO2 6.8 - 7.0

 Mineral 6.2 - 9.4

 Sea 8.0 - 8.4

Wine 2.3 - 3.8

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2. Spoilage in acid products is usually caused by nonsporeforming lactobacilli and yeasts. 

Cans of spoiled tomatoes and tomato juice remain flat but the products have an off-odor, 

with or without lowered pH, due to aerobic, mesophilic, and thermophilic sporeformers. 

Spoilage of this type is an exception to the general rule that products below pH 4.6 are 

immune to spoilage by sporeformers. Many canned foods contain thermophiles which do 

not grow under normal storage conditions, but which grow and cause spoilage when the 

product is subjected to elevated temperatures (50-55°C). B. thermoacidurans and B. 

stearothermophilus are thermophiles responsible for flat-sour decomposition in acid and 

low-acid foods, respectively. Incubation at 55°C will not cause a change in the appearance 

of the can, but the product has an off-odor with or without a lowered pH. Spoilage 

encountered in products such as tomatoes, pears, figs, and pineapples is occasionally caused 

by C. pasteurianum, a sporeforming anaerobe which produces gas and a butyric acid odor. 

C. thermosaccolyticum is a thermophilic anaerobe which causes swelling of the can and a 

cheesy odor of the product. Cans which bypass the retort without heat processing usually 

are contaminated with nonsporeformers as well as sporeformers, a spoilage characteristic 

similar to that resulting from leakage. 

3. A mixed microflora of viable bacterial rods and cocci usually indicates leakage. Can 

examination may not substantiate the bacteriological findings, but leakage at some time in 

the past must be presumed. Alternatively, the cans may have missed the retort altogether, in 

which case a high rate of swells would also be expected. 

4. A mixed microflora in the product, as shown by direct smear, in which there are large 

numbers of bacteria visible but no growth in the cultures, may indicate precanning spoilage. 

This results from bacterial growth in the product before canning. The product may be 

abnormal in pH, odor, and appearance. 

5. If no evidence of microbial growth can be found in swelled cans, the swelling may be due to 

development of hydrogen by chemical action of contents on container interiors. The 

proportion of hydrogen varies with the length and condition of storage. Thermophilic 

anaerobes produce gas, and since cells disintegrate rapidly after growth, it is possible to 

confuse thermophilic spoilage with hydrogen swells. Chemical breakdown of the product 

may result in evolution of carbon dioxide. This is particularly true of concentrated products 

containing sugar and some acid, such as tomato paste, molasses, mincemeats, and highly 

sugared fruits. The reaction is accelerated at elevated temperatures. 

6. Any organisms isolated from normal cans that have obvious vacuum and normal product 

but no organisms in the direct smear should be suspected as being a laboratory contaminant. 

To confirm, aseptically inoculate growing organism into another normal can, solder the hole 

closed, and incubate 14 days at 35°C. If any swelling of container or product changes occur, 

the organism was probably not in the original sample. If can remains flat, open it aseptically 

and subculture as previously described. If a culture of the same organism is recovered and 

the product is normal, consider the product commercially sterile since the organism does not 

grow under normal conditions of storage and distribution. 

Headspace Gas Determination by Gas-Liquid Chromatography

Nitrogen, the principal gas normally present in canned foods during storage, is associated with lesser 

quantities of carbon dioxide and hydrogen. Oxygen included in the container at the time of closure is 

initially dissipated by container corrosion and/or product oxidation. Departure from this normal pattern 

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can serve as an important indication of changes within the container, since the composition of headspace 

gases may distinguish whether bacterial spoilage, container corrosion, or product deterioration is the 

cause of swollen cans (2). Use of the gas chromatograph for analyzing headspace gases of abnormal 

canned foods has eliminated the possibility of false-negative tests for different gases. It has also allowed 

the analyst to determine the percentage of each gas present, no matter what the mixture is. By knowing 

these percentages, the analyst can be alerted to possible can deterioration problems or bacterial spoilage. 

A rapid gas-liquid chromatographic procedure is presented here for the determination of carbon dioxide, 

hydrogen, oxygen, nitrogen, and hydrogen sulfide from the headspace of abnormal canned foods. 

The analysis of 2352 abnormal canned foods, composed of 288 different products by a gas-liquid 

chromatography showed viable microorganisms in 256 cans (3). Analysis of this data showed that 

greater than 10 percent carbon dioxide in the headspace gas was indicative of microbial growth. 

Although greater than 10 percent carbon dioxide is found in a container, long periods of storage at 

normal temperatures can result in autosterilization and absence of viable microorganisms. Carbon 

dioxide my be produced in sufficient quantities to swell the container. Storage at elevated temperatures 

accelerates this action. Hydrogen can be produced in cans when the food contents react chemically with 

the metal of the seam (3). 

A. Equipment and materials 

1. Fisher Model 1200 Gas Partitioner, with dual thermal conductivity cells and dual in-line 

columns. Column No. 1 is 6-1/2 ft x 1/8 inch, aluminum packed, with 80-100 mesh 

ColumpakTM PQ. Column No. 2 is 11 ft x 3/16 inch, aluminum packed, with 60-80 mesh 

molecular sieve 13X (Fig. 1). 

NOTE: Other gas chromatograph instruments equipped with the appropriate columns, 

carrier gas, detector and recorder or integrator may also be suitable for this analysis. 

Operating conditions: column temperature, 75°C; attenuation, 64/256; carrier gas, argon, 

with in-let pressure of 40 psig; flow rate, 26 ml/min through gas partitioner and 5 ml/min 

through flush line; bridge current, 125 mA; column mode, 1 & 2; temperature mode, 

column; injector temperature, off. 

NOTE: Installation of flush system. Injection of gas samples through either sample out 

port or septum injection port may lead to damaged filaments in detector and excessive 

accumulation of moisture on columns due to bypassing the sample drying tube. To avoid 

this, make all injections in the sample in port. To avoid cross-contamination, install a flush 

line off the main argon line (Fig. 2), and flush sample loop between injections. 

2. Strip chart recorder, with full scale deflection and speed set at 1 cm/min, 1 mv 

3. Can puncturing press (Fig. 3) 

4. Sterile stainless steel gas piercers (Fig. 4) 

5. Miniature inert valve, with 3-way stopcock and female luer on left side (Popper & Sons, 

Inc., 300 Denton Ave., New Hyde Park, NY 11040), or equivalent (Fig. 5) 

6. Plastic disposable 10-50 ml syringes, with restraining attachment for maximum volume 

control (Fig. 6). Syringes may be reused. 

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7. Gas chromatograph and caps, for capping syringes (Alltech Associates, Inc., 202 Campus 

Drive, Arlington Heights, IL 60004), or equivalent (Fig. 6) 

8. Beaker, 1 liter, glass or metal 

9. Plastic gas tubing, 3 ft x 1/8 inch id, for exhaust tubing 

10. Soap solution, for detecting gas leaks ("SNOOP" Nuclear Products Co., 15635 Saranac 

Road, Cleveland, OH 44110), or equivalent 

11. Small pinch clamp, to weigh down exhaust tubing in beaker 

12. Nupro Valve, flow-regulating valve for flush line, 1/8 inch, Angle Pattern Brass (Alltech), 

or equivalent (Fig. 2) 

13. Silicone rubber tubing, seamless, red, autoclavable, 1/8 inch bore x 3/16 inch wall thickness 

(Arthur H. Thomas Co., Vine St. at 3rd, Philadelphia, PA), or equivalent 

B. Calibration of gas chromatograph 

Calibration gases of known proportions are commercially available. Construct calibration curves 

from analysis of pure gases and at least 2-3 different percentage mixtures of gases. Plot linear 

graph of various known concentrations of each gas as peak height (mm) vs percent gas (Fig. 7). 

C. Preparation of materials 

Prepare gas collection apparatus as illustrated in Figs. 8 and 9. Adjust height of gas collection 

apparatus to height of can to be examined. Attach male terminal of miniature valve to female 

Luer-Lok terminal mounted on top of brass block on can-puncturing press. Attach one end of gas 

exhaust tubing to female terminal of miniature valve. Attach small pinch clamp to other end of gas 

exhaust tubing and place in beaker partially filled with water. Attach disposable syringe to other 

female Luer-Lok terminal on miniature valve. Turn 2-way plug so that gas entering from piercer 

will flow toward disposable syringe. Place sterile gas piercer in position on male terminal 

mounted on bottom of brass block on can-puncturing press. 

D. Collection of headspace gas 

Place can under gas press (cans to be cultured should first be cleaned and sterilized). Lower 

handle until gas piercer punctures can and seals. Hold in position until adequate volume of gas has 

been collected (minimum of 5 ml); then turn 2-way plug to release excess gas through exhaust 

tubing. Release handle, remove syringe, and cap immediately. Identify syringe appropriately. 

E. Injection of gas into gas chromatograph 

Turn on gas chromatograph and recorder. Let stabilize for about 2 h. Make sure flush line is 

attached and gas sampling valve is open to allow flushing of sample loop. Turn on chart drive on 

recorder. Remove flush line, uncap, and immediately attach syringe to Sample-In Injection Port. 

Inject 5-10 ml of gas and immediately close gas sampling valve. Remove syringe and cap. 

Reattach flush line onto Sample-In Port and open gas sample valve to allow flushing of system 

before next injection. Observe chromatogram and switch attenuation from 64 to 256 after carbon 

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dioxide peak has been recorded and returned back to base line. This allows hydrogen peak to be 

retained on scale. After hydrogen peak returns to base line, switch attenuation back to 64. After 

instrument has separated gases (about 6 min), determine retention time and peak height for each 

gas recovered from unknown sample and percent determined from standard graph by comparing 

retention times and peak heights with known gases, usually associated with headspace gases from 

abnormal canned food products. Mount chromatogram on mounting paper and identify properly as 

in Fig. 10. For each sample examined, inject control gases for each type of headspace gas 

recovered. 

Figure 1. Fisher Model 1200 gas partitioner. 

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Figure 2. Flush System. 

 

Figure 3. Can puncturing press. 

Figure 4. Stainless steel gas piercer. 

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Figure 5. Miniature inert valve. 

Figure 6. Plastic disposable syringe with restraining attachment. 

Figure 7. Calibration graph for gas chromatography of headspace gas, using pure and unknown 

mixtures. 

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Figure 8. Gas collection apparatus. 

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Figure 9. Gas collection apparatus (detail). 

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Figure 10. Gas chromatograph of headspace gas. 

References

1. Association of Official Analytical Chemists. 1990. Official Methods of Analysis, 15th ed. AOAC, 

Arlington, VA. 

2. Vosti, D.C., H.H. Hernandez, and J.G. Strand. 1961. Analysis of headspace gases in canned foods by 

gas chromatography. Food Technol. 15:29-31. 

3. Landry, W.I., J.E. Gilchrist, S. McLaughlin, and J.T. Peeler 1988. Analysis of abnormal canned 

foods. AOAC Abstracts. 

Hypertext Source: Examination of Canned Foods, Bacteriological Analytical Manual, 8th Edition, 

Revision A, 1998. Chapter 21A. 

Authors: Warren L. Landry, Albert H. Schwab, and Gayle A. Lancette 

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FDA/CFSAN BAM - Examination of Glass Containers for Integrity http://www.cfsan.fda.gov/~ebam/bam-22b.html

1 of 3 3/28/08 10:26 AM

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 22B

Examination of Containers for Integrity

II. Examination of Glass Containers for Integrity

Authors

(Return to Table of Contents)

Almost all low-acid foods packaged in glass containers are sealed with vacuum-type closures. Currently

4 types of vacuum closures are widely used on low-acid food products: LT (lug-type twist) cap, PT

(press-on twist-off) cap, pyr-off (side seal) cap, and CT (continuous thread) screw cap (Fig. 25).

Packers' tests and examinations to ensure a reliable hermetic seal of containers are required by 21 CFR

113.60 (a) (2) and (3).

Vacuum Twist Lug Finish Vacuum Pry Off Finish

Press On Twist Off Finish Continuous Thread Finish

Figure 25. Types of vacuum closures and glass finishes.
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Visual examination for closure and glass defects (for definition of terms, see the glossary section

of this chapter)

cap tilt

crushed lug

chipped glass finish

cut-through

cocked cap

stripped cap

cracked glass finish

A.

Seal integrity examination

Vacuum. Use standard open-closed type of vacuum gauge or USG No. 12118 gauge with

both vacuum and pressure scales (Fig. 26). Wet rubber gasket on piercing device with

water. Shake off excess water. Puncture closure, using piercing needle attached to vacuum

gauge. Read and record vacuum in inches (0-30 inches), or pressure (0-15 psi).

Figure 26. Vacuum gauge for seal integrity examination.

1.

Removal torque (cam-off) for PT or LT type closures (Fig. 27). Properly secure jar on

torque meter. Ease closures off in smooth, continuous motion rather than rapid, jerking

motion. Use one hand to twist cap counterclockwise to open cap from sealed jar while

avoiding any downward pressure on cap. Record maximum torque in inch-pounds required

to open cap.

Figure 27. Torque meter.

2.

Security values (lug tension) on lug-type twist cap (Fig. 28). Make vertical line on cap

and corresponding line on container wall with marking pen. Turn closure counterclockwise

just until vacuum is broken. Reapply closure to container just until gasket compound

3.

B.
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touches glass finish and closure lug touches glass thread (or until closure is at 2 inch-pound

reapplication torque to achieve uniformity for application). Measure and record, in 1/16

inch increments, distance in front of vertical lines that were made before opening. Security

is considered positive if line on cap is to right of line on container, and negative if line on

cap is to left of line on container.

Figure 28. Security measurement for lug type twist closure.

Pull-up (lug position) for lug-type twist cap (Fig. 29). Mark vertical neck ring seam on

glass finish. Measure distance from this vertical line, in 1/16 inch increments, to leading

edge of cap lug position nearest it. Record lug position measurements made on right side of

vertical neck ring seam (as analyst looks at package) as positive (+) and those to left side of

parting line as negative (-).

Figure 29. Pull-up lug position of LTD measurement. 

4.

Hypertext Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. Chapter 22.

*Authors: Rong C. Lin, Paul H. King, and Melvin R. Johnston

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1 of 28 3/28/08 10:27 AM

U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 22C

Examination of Containers for Integrity

III. Examination of Flexible and Semirigid Food Containers for Integrity 

George W. Arndt, Jr. (NFPA)

Author

(Return to Table of Contents)

Flexible and semirigid food packages are composed mainly or in part of plastic materials. Closure is

achieved by heat sealing or double seaming. The 4 main groups of packages that cause similar integrity

concerns and that are examined by common methods are paperboard packages, flexible pouches, plastic

cups and trays with flexible lids, and plastic cans with double-seamed metal ends.

The purpose of a hermetic closure is to provide a barrier to microorganisms and to prevent oxygen from

degrading the food. Closure integrity is significant because sealing surfaces may contain food particles

and moisture that contribute to heat-seal and double-seam defects. Critical control must be exercised in

this operation. Visual examination will reveal most defects. For many flexible packages, seal strength

may be ascertained by squeezing.

Package examination

Note condition of package (exterior and interior) and quality of seals or seams; observe and feel

for gross abnormalities, mechanical defects, perforations, malformations, crushing, flex cracks,

delamination, and swelling. Measure dimensions as recommended by manufacturer of closing

equipment or packaging material. Perform teardown procedure as described. Note condition of

package and closure. If there is evidence that a package may lose or has lost its hermetic seal, or

that microbial growth has occurred in the package contents, further investigation is required.

Visual examination

Use hand as well as eye. A magnifying glass with proper illumination is helpful. Rub

thumb and forefinger around seal area, feeling for folds and ridges. Rub fingers over flat

surfaces to feel for delamination, roughness, or unevenness. By sight and touch, determine

presence of defects. Mark location of defects with indelible ink. See Fig. 30 for visual 

inspection criteria for closure seal.

1.

A.
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Figure 30. Visual inspection criteria for closure seal.

(Courtesy of Brik Pak, Inc.)

2. Examination of packages (see Tables 1 and 2)

Table 1. Test methods for plastic packages containing food (5)

Package type

Test methods Paper 

board

Flexible 

pouch

Plastic, 

heat-sealed lid

Plastic, double-seam 

metal end

Air leak testing O O O O

Biotesting O O O O

Burst testing O R R O

Chemical etching O O O NA

Compression, squeeze 

testing R O O O

Distribution (abuse) 

test O O O O

Dye penetration R O R O

Electester O NA NA NA

Electrolytic R O R NA

Gas leak detection O O O O

Incubation R R R R

Light NA O O O

Machine vision O O O O

Proximity tester O O O R

Seam scope projection NA NA NA R

Sound R NA R R

Tensile (peel) testing NA R R NA

Vacuum testing NA O R O

Visual inspection R R R R

Abbreviations: R, test method is recommended by NFPA Bulletin 41-L, 

Flexible Package Integrity Bulletin; O, other commercially accepted test method applications;

NA, test method is inappropriate for this style package.

Table 2. List of visible package defects provided by National Food Processors Association (5)
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Package type(a)

Defect Paper 

board

Flexible 

pouch

Plastic, 

heat-sealed lid

Plastic, double-seam 

metal end

Abrasion + + + +

Blister - + - -

Burnt seal - - + -

Channel leak(er) - + + -

Clouded seal - + - -

Compressed seal - + - -

Contaminated seal - + + -

Convolution - + - -

Corner dent + - - -

Corner leaker + - - -

Crooked seal - + - -

Crushed + - + +

Defective seal - - + -

Deformed + - - -

Deformed seal + - - -

Delamination + + + +

Embossing - + - -

Flexcracks - + + +

Foreign matter 

(inclusion) - - + +

Fracture - + + +

Gels - - + +

Hotfold - + - -

Incomplete seal - - + -

Label foldover - - + -

Leaker - + - -

Loose flaps + - - -

Malformed - - + +

Misaligned seal - - + +

Nonbonding - + - -

Notch leaker - + - -

Puncture + + + +

Seal creep - + - -

Seal leaker + - - -

Seal width variation - - + -

Shrinkage wrinkle - - + -
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Stringy seal - + - -

Swell (swollen 

package) + + + +

Uneven impression - - + -

Uneven seal junction - + - -

Waffling - + - -

Weak seal + - - -

Wrinkle - + + -

a +, Definition is applicable to that package type; -, definition is not applicable.

Paperboard packages (20)

Teardown procedures. Unfold all flaps (except gable top packages); check integrity

and tightness of transverse (top and bottom) and side (vertical or longitudinal) seals

by firmly squeezing package. If package has longitudinal sealing (LS) strip, pull off

overlapping paper layer at side (longitudinal) seal. Check air gap of longitudinal

sealing strip application (about 1 mm). Squeeze package and check that there are no

leaks or holes in the LS strip.

Next, on side opposite side seal, puncture container with sharp scissors and empty

contents. Saving side seal portion, cut near fold at each end of package and down

length of package to remove a large rectangular body portion. Observe this large

rectangular body portion for holes, scratches, or tears anywhere on the surface. Pay

close attention to corners of package, particularly directly under end seals and near

the straw hole or pull tab, if present. Now cut remaining package in half through the

center of the side seam. Wash both halves of remaining package and dry them with a

paper towel. Mark to identify the package.

Evaluation procedures for seal quality differ between package designs, constructions,

and sealing methods. Obtain specific procedures for a given package from the

manufacturer. For example, seal evaluation may consist of starting at one end of the

seal, and very slowly and carefully pulling the seal apart. In some packages the seal

is good if the polymer stretches the entire length of the seal (that is, stretching of

polymer film continues to a point beyond which paper and laminates have separated).

In other packages, fiber tear can be seen the entire length of the seal (that is, raw

paperboard is visible on both sides of the separated seal areas). This is known as

100% fiber tear and indicates a good seal. Test all 3 seals of each package half.

Problems to look for are absence of (or narrow) fiber tear, lack of polymer stretch,

"cold spots" (no polymer bond in seal area), and "tacking" (polymer melt but no

stretch or fiber tear). For longitudinal sealing strip-type packages, additional tests

(such as centering examination, heat mark examination, and appearance of aluminum

foil examination when stripped) should be made according to manufacturer's

directions.

Electrolytic and dye testing. These tests differ according to each system

manufacturer's filed procedure. Contact the individual manufacturer, obtain

recommendations, and follow them.

a.

Flexible pouches (20)

1. Teardown procedures. Check tightness of both head and side seals by

b.
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squeezing each package from each fill tube or sealing lane. Important points

are corners and crossing of head and side seals. This is a rapid determination

of obvious defects. Each seal must be accurately torn apart and evaluated for

correct integrity. Carefully inspect edges of each head and side seal for

evidence of product in seal areas. No product should be visible.

Observe width of each seal area. Width must comply with machine-type

specifications: for example, 1/16 inch minimum on all head and side seals for

fill tube or sealing lane machines. Look for presence of smooth seal junction

along inside edge of seal. Open each package to check side seals and head

seals. Visually inspect for such defects as misaligned seal, flex cracking,

nonbonding, and seal creep. If applicable, tear the seals by doing a seal tensile

strength test or a burst test. Then observe appearance of tear at each seal. Seals

should tear evenly so that foil and part of laminated layer from one side of

package tears off, adhering to seal on other side of package. The seal should

appear rough and marbleized. The seal is also adequate if the foil is laid bare

across entire length of seal. Retain records of test results as required.

Other test procedures

Squeeze test. Apply manual kneading action that forces product against

interior seal surface. The sealing surface must be smooth, parallel, and free of

wrinkles. Examine all seal areas for evidence of product leakage or

delamination. Packages that exhibit delamination of the outer ply on seal area

but not at product edge should be tested further by manually flexing the

suspect area 10 times and examining all seal areas for leakage or reduction in

the width of the seal area to less than 1/16 inch.

Seal tensile strength. Results to be expressed in pounds per linear inch,

average of sample (that is, 3 adjacent specimens cut from that seal) should not

be less than specified for the material and application.

Burst strength test. With internal pressure resistance as the measurement to

check all seals, apply uniform pressure, under designated test conditions, to a

level of not less than specified for a material or application, for 30 s. Then

evaluate seals to ensure that proper closure seal is still in effect.

2.

Plastic package with heat-sealed lid (20)

Container integrity testing. Peel test procedures of form fill and seal containers.

Squeeze container side walls of entire set from a mold. Squeeze each cup to cause 1/8

inch bulge of lid area. Lid should not separate from package when package is

squeezed. Observe sealing area for fold-over wrinkles in sealant layer of lidstock.

From a first set of containers, visually observe embossed ring in sealed area for

completeness. (Embossed ring should be at least 90% complete if present.) Remove a

second set of containers (1 cup per mold) and gently peel back each lid at

approximately a 45 angle. Observe the peeled area for a generally frosty appearance

on both the lid and cup sealed surfaces. Observe entire package for holes, scratches,

even flange widths, smooth inside surfaces, and any deformities caused by dirty

mold or sealing die.

Leak test procedures (optional). These tests differ according to each system

manufacturer's filed procedure. Contact the individual manufacturer, obtain

recommendations, and follow them.

c.
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Electrolytic test. Plastic packages generally do not conduct a flow of low-voltage

electricity unless a hole is present. Use a volt meter or amp meter to determine the

presence of a closed circuit. If a voltage flow can be measured, use a dye solution to

identify the presence of a hole.

Dye penetration test. Use a dye to locate leaks in packages or to demonstrate that

no leaks exist.

Air pressure or vacuum test. Apply pressure or vacuum to a closed package to test

for holes and to observe any loss of pressure or vacuum. Underwater vacuum testing

may reveal a steady stream of small bubbles emitting from a hole in a package.

Plastic cans with double-seamed metal ends (20)

Procedures for examining metal cans with double seams are described in Chapter 21

and in 21 CFR, Part 113. Use these methods to examine plastic cans with

double-seamed metal ends. Make the following changes to 21 CFR 113.60 (a,1,i,a

and b).

d.

Micrometer measurement system

Metal cans. Required: cover hook, body hook, width (length, height), tightness (observation for

wrinkle), and thickness. Optional: overlap (by calculation) and countersink.

Plastic cans with double-seamed metal ends. Required in addition to seam scope examination:

thickness and tightness. Compare seam thickness to that calculated from individual thicknesses of

plastic flange and neck and metal end, excluding compound. Optional: cover hook, countersink,

and width (length, height).

Seam scope of projector

Metal cans. Required: body hook, overlap, tightness (observation for wrinkle), and thickness by

micrometer. Optional: width (length, height), cover hook, and countersink.

Plastic cans with double-seamed metal ends. Required: overlap, body hook, countersink,

width (length, height). Optional: cover hook.

Visual examination for plastic cans with double-seamed metal ends. Required: tightness.

Note compression of pressure ridge or flange during overlap measurement. Remove entire cover

and examine pressure ridge for continuity. Under 21 CFR 113.60 (a,1,i,c) add the following:

pressure ridge for plastic cans with double-seamed ends; impression around complete inside

periphery of can body in double seam area.

B.

Microleak detection

Microleak testing methods are not listed in order of sensitivity, nor is it necessary to use them all.

Each test has advantages and disadvantages, depending on the package, equipment, and set of

conditions. Optional methods are appropriate when additional information will clarify the nature

of various package defects. Some test methods are not appropriate for some package materials,

closures, or package styles. Refer to the manufacturer of the package or closure system for

recommended test methods or see Table 1. Common methods are presented to provide the analyst

with procedures and options. Visible defects of the 4 flexible package groups are summarized in

Fig. 30.

Measure packages before testing for microleaks. Mark visually detected defects to aid location

C.
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during or after microleak testing (non-water soluble markers are recommended). Record all

results, methods used, and environmental conditions (temperature, relative humidity) and retain

these records. Conduct all tests in the standard laboratory atmosphere of 23 + 2°C and 50 + 5% 

relative humidity. When this is not possible, report temperature and relative humidity along with

test results (14).

Figure 31. Air leak testing of packages.

Airleak testing (5) (Fig. 31)

Dry method

Materials

Compressed air with regulator

Needle, valve, hoses

Pressure gauge or flow meter

1.

Procedure

Puncture container wall with needle. Inject air while increasing at 1 psi/s until a

standard pressure is reached. Standard pressure used for testing should be less

than the normal unrestrained burst pressure for the package. Observe pressure

gauge for loss of internal pressure over a 60 s period. If a flow meter is used,

observe for airflow, which indicates presence of openings in the test package.

Dye testing may be used to locate air leaks that are not visible with the dry

method. Inject air to create internal pressure within the package without

causing it to burst. Observe all surfaces and seals for air leaks. Observe flow

meter for indication of air loss from the package.

2.

a.

b. Wet method

Materials

Compressed air with regulator

Needle, valve, hoses

Water

Transparent container to observe bubbles

1.

2. Procedure

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Inject air to create internal pressure within the package without causing it to

burst. Immerse package in water and inspect visually for a stream of bubbles

emitting from a common source.

Results

Positive. - A steady stream of bubbles comes from the package at one or more

locations.

Negative. - No bubbles are emitted from the package.

False positive. - Bubbles are emitted from point at which needle entered package; or

bubbles cling to surface of the package after package is submerged in water.

False negative. - Food particles block holes through which air might escape from

defective package; or air pressure used is insufficient to force air through minute

holes in package.

c.

Figure 32. Biotesting of packages.

Biotesting (5,21) (Fig. 32)

The objective of biotesting is to detect the presence of holes in hermetic packages by

placing them in an agitated solution of fermentation bacteria in water for an extended period

of time.

Obtain representative packages and submerged them in an agitated solution of active

bacteria. The bacterial concentration should be >107/cm3. The temperature of the solution 

that surrounds the packages should be maintained at a temperature that permits rapid

growth of the bacteria within any packages they may enter. However, growth of the

bacteria in the liquid surrounding the submerged packages is not desirable. The bacteria

must cause fermentation of the product within the package if they penetrate and must not be

pathogenic. Packages should be flexed during immersion to expose cracks and holes to

incursion. The solution that surrounds the packages should be maintained at a temperature

that permits rapid growth of bacteria within defective packages. After biotesting, packages

are incubated for 3 weeks at 95-100F. This test should be used only to evaluate new

package designs or to validate packaging systems. It should not be used as routine quality

control procedure. Other methods are cheaper, simpler, and just as reliable.

Materials

Water bath with temperature control and agitation solution of

 Enterobacter aerogenes for foods, pH >5.0. Solution of

 Lactobacillus cellobiosis for foods, pH <5.0 

Sample packages

Apparatus to flex packages 

a.

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Incubator

Procedure

Obtain representative samples. Mix active bacteria in water at about 1.0 x 107/ml. 

Immerse samples in mixture. Agitate water bath and flex sample for 30 min. Remove

packages and rinse with chlorinated water. Incubate samples for 2 weeks at 95-100F.

Observe packages for swelling for 3 weeks. Open each package by cutting in half

across the middle, leaving a hinge and observe contents for spoilage. Thoroughly

wash insides of both halves from each spoiled package. Subject each half to a dye

test to locate leaks.

b.

c. Results. Report location of leaks.

Figure 33. Burst tester.

Figure 34. Pouch air burst tester.

Burst testing (5) (Figs. 33 and 34)

The objective of burst testing is to provide a means for determining the ability of a

hermetically sealed package to withstand internal pressure (psig). The entire package is 

subjected to uniform stress and failure generally reveals the weakest point. Both restrained

and unrestrained burst testing may be used. Restraint limits expansion by minimizing the

angle of the package seal, which becomes greater as a package is inflated. With restraint,

packages with strong seals fail at greater internal pressure than do packages with weak

seals. Thus, use of a restraining device during burst testing permits noticeable separation

between packages having strong or weak seals.

Fused seals are stronger than the walls of a flexible package. Burst failure generally occurs

adjacent to fused seals. Peelable seals are weaker than the walls of a flexible package, and

less pressure is needed to induce pressure failure. Lower pressure and a longer time

increment are required to burst test peelable seals.

Dynamic burst testing involves a steady increase of internal pressure until failure occurs.

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Static burst testing involves a steady increase in internal pressure to a pressure less than

failure, followed by a 30-s hold. Both methods are used for packages with fused seals.

Peelable seals are burst-tested by inflating at a steady rate to a point less than failure

pressure and held for 30 s, followed by a 0.5 psig pressure increase and another 30-s hold.

Pressure and time indexing is continued with observation of the seal area for seal separation

(peeling) until failure occurs.

Materials

Compressed air or water

Regulation valve

Needle with gasket and pressure tubing

Solenoid with timer(s)

Pressure indicator(s), digital or gauge with sweep hand

Restraining device (optional)

a.

Procedure

Use empty sealed package, or cut and remove contents of a filled package. Place

package in restraining fixture (if used). Pierce package with gasketted needle(s) and

inject air or water. Inflate at 1 psig/s.

Dynamic method. Continue inflation at 1 psig/s until failure occurs. Record internal

pressure at failure.

Static method. Inflate at 1 psig/s to specified internal pressure, and hold at specified

pressure for 30 s. Record as pass or fail.

Indexed method. Inflate to 5 psig and hold for 30 s, inflate additional 0.5 psig and

hold for 30 s. Continue increase and hold sequence until failure occurs. Observe

peelable seal separation. Report internal pressure at failure.

b.

Results

Positive. Pressure failure occurs below specified level of performance, indicating a

hole in the package.

Negative. No pressure failure occurs below specified level of performance.

False positive. A leak is present at point where air or water is injected into package

and pressure cannot be maintained.

False negative. A small leak occurs, but is not sufficient to reduce pressure

noticeably.

c.

Chemical etching (5)

Multilaminate and composite packaging materials may be etched to remove overlying

layers, revealing the hermetic seal of packages that have polyolefin heat seals. This allows

comparison of visually detected package defects on the external surface before etching and

within the seal area after all external layers have been removed.

Composite paperboard packages. The outer layers of a package are removed by tearing,

abrasion, and chemical action to expose the sealant layer intact. By photographing or

photocopying the package before etching, the etched seal can be compared with the

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photograph to determine the significance of visually discernible defects.

Materials

Water bath and heater with thermostat

Three l-L Pyrex glass beakers

Running tap water

Graduated cylinder

Automatic stirring device (heated is preferred)

Drying oven equilibrated to 65°C (150F)

Paper towels

Rubber gloves, protective goggles, apron, tongs

Fume hood with chemical-resistant surface

Chemicals for etching of paperboard aseptic packages:

 hydrochloric acid (HCl) solution, 3.7 N

 acidified solution of copper chloride (CuC12)

 saturated solution of bisodium carbonate (Na2CO3) in water

a.

Preparation of solutions. CAUTION: Always pour acid into water; never pour

water into acid.

Pour 0.5 L of concentrated HCl into 1 L of cold distilled water. Pour slowly, as heat

will be produced when acid and water mix. Stir until mixed completely. Cover to

prevent evaporation. Solution will be 3.7 N HCl.

Pour 0.5 L of concentrated HCl into 1.5 L of cold distilled water. Add 10 g of

CuC12. Stir until completely mixed. Cover beaker and let warm to room temperature

before using.

Pour enough Na2CO3 into a container to make a saturated solution at room

temperature. Some undissolved Na2CO3 should remain on bottom of beaker after

stirring.

b.

Procedure

Cut transversal seal from package approximately 1 inch from end. Identify multiple

samples by notching cut edge with scissors. Manually strip paper from sample to be

etched. Place sample in hot HCl solution (65°C) for 5 min. Remove sample with

tongs and immerse it in Na2CO3 solution to neutralize the acid. Remove sample from

the Na2CO3 solution with tongs and rinse it in running tap water. Pull off

polyethylene layer that lies between paperboard layer and aluminum foil.

Using a glass stirring rod to manipulate the sample, drop it into the CuC12 solution 

so that it is completely immersed. Observe closely while stirring to ensure that the

heat of the reaction does not damage the polyethylene sealant layer as the foil is

dissolved. Remove from solution.

Dip sample in Na2CO3 solution to neutralize it, and then rinse it with water. Press

sample gently between soft absorbent paper towels and place in oven at 65°C (150F)

until dry. Apply alcohol-based dye solution to inner and outer seal edges. (See

fluorescein dye solution formula, described above).

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Observe pattern of ink dispersion and check for leaks and channels within fused seal

area. Use overhead projector to enlarge seal samples and provide a more accurate

visual inspection.

Figure 35. Chemical etching of package seal.

Retortable pouches (Fig. 35)

Materials

Two l-L Pyrex beakers

Running tap water

Paper towels

Rubber gloves, apron

Protective goggles, tongs

Fume hood with chemical-resistant surface

Chemicals for etching retortable pouches

6 N HCl solution, commercial grade

Tetrahydrofurant (THF), commercial grade, stabilized

1.

Procedure

Cut off end of pouch and remove contents. Wash inside of pouch. Dry the pouch.

Cut all but suspected area away from area of interest, leaving about 1 inch adjacent to

seal. Soak sample in tetrahydrofurant (THF) to remove outer polyester layer by

softening adhesive and/or inks. Do this in a fume hood; wear protective gloves

resistant to THF. (If separation cannot be obtained, proceed to next step.) Remove

most of the ink and adhesive from aluminum foil with THF and paper towels. Soak

remaining structure in 6 N HCl in a fume hood to remove aluminum foil by etching.

Rinse sealant layers with water and dry with paper towels.

2.

Figure 36. Compression testing of packages.
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Compression test (5) (Fig. 36)

Place a filled and sealed food package on flat surface and apply pressure while observing

for leaks.

Materials

Flat surface or conveyor belt

Sealed package

Heavy flat object or mechanical press

Timer

a.

Procedure

Static method. Place sealed package on flat surface and lay a flat-surfaced weight on

it. Observe effect of weight on integrity of package seals over time. A similar test

may be performed by applying a constant weight to a package moving on a conveyor

belt. The speed of the moving belt determines the time of compression.

Dynamic method. Use a press to continually increase the force applied to a package

at a constant rate. Observe the maximum force required to cause failure of the

package.

Squeeze test. Apply a manual kneading action that forces product against the interior

seal surface area. Examine all seal areas for evidence of product leakage or

delamination. Packages that exhibit delamination of the outer ply on the seal area but

not at product edge should be tested further by again manually flexing the suspect

area 10 times and examining all seal areas for leakage or short-width.

b.

Results

Positive. Holes form in package or its seals or seams, with measurable movement of

top plate or deflection on a force gauge.

Negative. No loss of hermetic integrity, and no measurable movement of top plate or

deflection on a force gauge.

False positive. Underfilled or weak packages deflect in a manner that simulates

failure without loss of hermetic integrity.

False negative. Holes form in package but food product closes off the holes,

permitting pressure to increase within package.

c.

5.

Distribution (abuse) test (5)

Packages are subjected to vibration, compression, and impact at levels typical of the

distribution system for which they are designed. After the test, which is a conditioning

regimen, the packages are examined. Defects are quantified and described in relation to

package failures observed in normal distribution. Fragility is eliminated by design changes

in the package system. Whenever possible all samples should be incubated for 2 weeks at

100F before abuse-testing (Fig. 37).

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Figure 37. Distribution abuse testing.

Materials

Packages to be tested

Drop tester

Vibration table

Compression tester

Standard laboratory conditions 23 + 2°C, 50 + 5% relative humidity

Incubator at 100F to contain all test packages

a.

Procedure. See ASTM D-4169 Standard Practice for Performance Testing of

Shipping Containers and Systems (15).

Select distribution cycle 6 for flexible packages in shipping cases transported by

motor freight. Before testing, incubate all packages for 14 days at 100F and inspect

visually for defects.

Perform the following 10 steps (see Section 9 of ASTM D-4169) (15).

1. Define shipping unit - Shipping unit to be tested is a typical pallet load.

Establish assurance level - Assurance level II will be used, based on value and

volume of shipment.

2.

Determine acceptance criteria at assurance level II: Criterion 1 - no product 

damage; criterion 2 - all packages in good condition.

3.

4. Select distribution cycle (DC) - DC-6 will be used for pallet shipments.

Write test plan (values for X must be determined before conducting the test).

Select representative samples for test. Condition samples to 23 + 1°C, 50 +

2% relative humidity, in accordance with Practice D 4332 (14).

5.

Perform tests in accordance with test plan in step 5, as directed in the

referenced ASTM standards and in the special instructions for each shipment.

6.

Evaluate results - Examine products and packages to determine if acceptance

criteria have been met.

7.

8. Document test results (16) - Write a report to cover all steps in detail.

Report fully all the steps taken. At a minimum, the report should include all the

criteria in step 10.

9.

10. Description of product and shipping unit DC and test plan Assurance levels

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and rationale

Number of samples tested

Conditioning used

Acceptance criteria

Variation from recommended procedures

Condition of specimens after test

After testing, examine all failed (positive) packages to determine location and

cause of damage. Incubate all containers that do not fail (negative) during

testing for 14 days at 100F and inspect visually for defects before destructive

testing by other methods listed in this chapter.

Results

Positive. A package loses hermetic integrity during any one phase of the testing

protocol or during the incubation period that follows.

c.

Type test ASTM

Method

Level

Handling (12) D-1083 One impact on 2 opposite base edges from X inches

Stacking (10) D-642 Compression to X lb (individual container) *

Vibration (13) D-999

Method C

Search 3-100 Hz at 0.5 g peak. Dwell 10 min at 0.5 g peak

Handling (11) D-959 One impact on 2 opposite base edges from X inches

(12) D-1083

(17) D-997

(18) D-775

Stacking (10) D-642 Compression to X lb (individual container) *

*Alternative full pallet load compression test, X lb per bottom tier container.

Negative. A package retains hermetic integrity through the test, and contents do not

show evidence of microbial growth after incubation.

False positive. A package appears to be defective, yet confirmational testing by

incubation or dye penetration reveals that no loss of the hermetic barrier occurred

during the abuse test.

False negative. A package appears to pass testing but later exhibits failure when

incubated.

7. Dye testing (5)
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Dye or ink is applied to inside surface of a cleaned package at the seal or suspected location

of failure and observed to determine whether it can pass through to the outside (Figs. 24,

38, 39).

Figure 24. Can piercer and gas collection apparatus.

Figure 38. Dye testing.

Figure 39. Dye testing results.

(Courtesy of Brik Pak, Inc.)

Materials

Disposable plastic gloves

Dye solution: 1 L of isopropanol (solvent) and 5 g of rhodamine (powder) mixed (or 

other appropriate dye solution)

Sink

Scissors or knife

Oven to dry sample packages

Paper towels

Magnifying glass or low-power microscope

a.

Procedure

Open and empty a package; wash, and dry by wiping or by oven drying (180F, 15

min). Apply low surface-tension solution containing dye along the closure or on side

of package at suspected location of hole. The solution moves by capillary action

through the hole and appears on opposite side of package wall. After dye is

completely dry, cut package with scissors and examine the hole closely.

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Cut open cans, tubs, or bowls through bottom (leaving seal areas or double seams

untouched) and remove product. Cut pouches and paperboard containers along

equator, leaving a hinge (so that both ends can be tested), and remove product. Wash

package with water containing mild detergent, rinse thoroughly with tap water, and

wipe dry. Holding package upside down and at slight angle, place 1 drop of dye

solution at inside edge of seal surface. Rotate to allow dye to wet entire inside seal

circumference.

CAUTION: A number of dyes are known or suspected to cause cancer. Rhodamine

B is a possible carcinogen. Wear disposable plastic gloves and avoid skin contact

with dyes.

Let dye solution dry completely. Very slowly peel the seal completely and observe

the frosty, white, sealed surfaces for evidence of dye. In some packages the

innermost laminates must be carefully observed for stretching as the seal is peeled.

Results

Positive. Dye penetrates hole in package, indicating loss of hermetic barrier.

Negative. Dye does not pass through the package (wall or seal).

False positive. Solution dissolves packaging material, creating hole in package, or

dye is accidentally splattered on outside of package, indicating hole or leakage where

none exists.

False negative (for paperboard only). Solution penetrates holes in hermetic barrier

layers but fails to reach outside of package where it would be visible.

c.

Electester (5)

The objective is to determine changes in viscosity of liquid foods after incubation of filled

packages (Fig. 40).

Figure 40. Electester

Microbial fermentation can cause changes in the viscosity of still liquids. If all factors are

constant, shock waves will dampen at different rates in liquids with different viscosities.

Incubation of shelf-stable liquid foods and nondestructive testing of each package may

identify containers that have been subjected to microbial activity.

Materials

Packages filled with still, liquid food, incubated

Electesting device

Fixture to restrain test packages

a.

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Procedure

Remove representative samples from production line and incubate at 95°F for 4 days.

Place packages containing still liquids in restraining device with largest flat surface of

package facing downward. Rotate package 90 horizontally and back to its original

position very rapidly; do this only one time. The motion creates a shock wave.

Fixture holding the package is precisely balanced to minimize outside interference

and minimize dampening as shock wave moves back and forth within package.

Motion is sensed and displayed on an oscilloscope with alarms alerting operator to

vibrations that dampen more quickly or more slowly than normal for a specific liquid

food product. Examine contents with a microscope and determine pH to confirm

spoilage if there is any doubt.

b.

Results

Positive. Wave dampens more quickly or slowly than normal, indicating change in

product viscosity.

Negative. Rate of wave dampening is within range established by testing "normal"

liquid product that did not display microbial spoilage during incubation.

False positive. Range of acceptance is too narrow, and normal product is incorrectly

identified as spoiled.

False negative. Range of acceptance is too broad, and spoiled product is incorrectly

identified as normal.

c.

Electroconductivity (5)

The objective is to detect holes in hermetic packages by sensing the flow of electrical

current. Plastics are generally poor conductors of electricity. Consequently, plastic food

packages without holes will form an effective barrier to mild electrical current; therefore,

this method may be used to detect minute breaks in plastic food packages. A detectable

flow of low-voltage electrical current generally indicates that the hermetic barrier has been

lost.

Materials

1% NaCl in water (brine solution)

Scissors

Battery 9V, three 12-inch lengths of wire, 9V light bulb, or a conductivity meter

(VOM). Remove insulation from each end of wires. One wire from positive pole

goes to light bulb that has a wire as probe. The second wire from the negative pole is

the other probe (Fig. 41).

Plastic bowl large enough to submerge package

Figure 41. An electrolytic cell for leak examination.

a.

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Procedure

Obtain sample food package and cut off one end with scissors. Aseptic paperboard

packages and flexible pouches may be cut on all but one edge along package equator

and folded 180 on uncut side to form 2 equal halves. Wash samples to remove all

food contents and any dried plugs that may occlude holes. Oven drying at 180F is

recommended but not required before immersion. Wipe the cut edges with a paper

towel if necessary, as wet edges may result in false-positive test results. Place

samples in bowl containing brine solution and partially fill sample with brine so that

it stands upright and is almost completely submerged. Place conductivity meter or

light bulb with one probe inside the package and the other outside the package.

Submerge both probes into their respective brine solutions. Test the other half of

package similarly for current flow.

b.

Results

Positive. Current flow indicates break in hermetic barrier.

Negative. No current flow indicates hermetic barrier exists.

False positive. Aluminum foil conducts electricity. A pinhole or partial break

through inner layers of a package may expose the foil layer, resulting in

false-positive test result. Dye testing will confirm presence or absence of holes.

Moisture may form a bridge over cut edge of a package, creating a false

positive.False negative. Dried product may occlude minute holes in a package. If

plugs do not rehydrate quickly, they will not conduct electricity when packages are

immersed.

c.

Gas detection (5)

The objective is to detect microleaks in hermetically sealed packages with sensors tuned to

detect only gas leaking from within package. The package must be a barrier to the test gas

so that the rate of gas permeation through the package wall will not raise the normal

background concentration in atmosphere of testing area. Gas concentrations may be

detected by impact to a sensor. The sensor may be a heated element in which electrical

resistance varies in relation to gas molecules removing heat as they impact. Examples of test

gases suitable for package include oxygen, nitrogen, hydrogen, carbon dioxide, and helium.

Procedure for detecting helium leak

Gas obtained from storage tanks or air fractioning may be used to displace headspace

gases within food packages before closure. Concentration of gas within package

must be greater than the concentration of that gas in the atmosphere where packages

are tested. There are three modes for detection: ASTM E493, inside-out tracer mode

(6); ASTM E498, tracer probe testing mode (7); and ASTM E499, detector probe

testing mode (8). Slight compression of a package may assist the movement of gas

molecules through microleaks.

a.

Results

Positive. Detection of gas concentrations greater than the normal atmospheric

concentration indicates break in hermetic barrier of sample package. Confirm with

dye testing to locate hole in sample package.

Negative. No detection of test gas concentration greater than the normal atmospheric

b.

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concentration indicates hermetically sealed container.

False positive. Detection of gas concentrations in excess of the normal background

level may result from increase in test gas concentration in the testing area. Test

background concentration before and after testing sample. Packages with high

permeability may lose gas.

False negative. Internal gas concentration may be reduced through absorption by the

product, reaction with a component inside the package, or permeability if over an

extended storage period.

Incubation (5)

The objective is to determine whether a package has lost hermetic barrier by holding

containers at an ideal temperature for sufficient time to ensure microbial growth. Hermetic

integrity is the condition that bars entry of microorganisms into a package. Growth of

microorganisms indicates either insufficient processing or loss of hermetic barrier. Growth

may be observed as gas formation, change in pH, growth of viable organisms, or changes

in the appearance of food.

Materials

Insulated box or room to serve as an incubator

Heater with thermostat

Storage racks

Recording thermometer

Temperature recording charts

Knife, scissors

pH meter

Inoculating loop and flame

Sterile culture dishes and tubes, and culture media

a.

Procedure

Obtain representative sample packages containing processed product. Inspect all

samples visually for defects. Place packages in incubator for recommended period of

time at recommended temperature.

Products stored in incubator at 95°F (35°C)

 FDA products - 14 days 

 USDA products - 10 days

Products stored in warehouse

 85-95°F (29-35°C) 30 days

 70-85°F (21-29°C) 60 days

 60-70F (16-21°C) 90 days

Visually inspect packages for evidence of spoilage. Open and inspect all (or some)

packages for visible signs of microbial growth, aroma, and change in pH. Never taste

incubated product if spoilage may have occurred. Aseptically obtain product samples

to culture microbiologically and confirm cause of spoilage. Conduct appropriate

integrity test on package to identify presence or absence of microleaks. Dispose of

product safely. Autoclave any product or packages showing spoilage before

disposal.

b.

c. Results

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Positive. Spoilage has occurred and is evident as swelling, putrefactive odor, change

in product pH from normal, or change in appearance.

Negative. Spoilage has not occurred.

False positive. Chemical reaction or enzymatic activities alter product characteristics

without microbial activity.

False negative. Should not occur because this would be commercial sterility.

Light (5)

Infrared light. The objective is to observe differences in the absorbance and

transmittance of heat energy (infrared light) in a package or seal. Infrared light may

be absorbed, transmitted, and emitted by a package or a seal. Differences between

these parameters provide a means for visual interpretation when sensed automatically

and enhanced for visibility.

Materials

Infrared light or oven (180F)

Visual infrared light detector

1.

2. Procedure: Expose samples to infrared radiation before examining.

a.

Laser light. The objective is to measure small changes in the relative position of

similar surfaces on separate packages as they are subjected to changes in external

pressure. Flexible packages possessing some headspace gas may be flexed by

altering the external pressure in a closed chamber. Packages are held by fixtures so

that a split laser beam may be directed to the same position on both packages. The

reflected beams are recombined with mirrors and prisms. Laser light has a

well-defined wave length that does not change by reflection. However, if packages

move differently when flexed, one beam segment will travel a greater distance than

the other. When beam segments are recombined, differences in position of reflecting

surfaces will cause the recombined laser beam to be out of phase. This condition can

be sensed and used to segregate packages that do not flex in the normal manner from

those that do.

1. Materials: Laser set up with chamber and means to read the differences.

Procedure: Flex packages in chamber by applying and releasing vacuum.

Observe any difference in the 2 packages and determine by controls which

package leaks.

2.

b.

Polarized light. The objective is to observe differences in the transmittance of visible

light through translucent and transparent heat seals (Fig. 42). Polarized light filters

are composed of minute parallel lines on a glass surface or plastic film. When 2

polarized filters are rotated to be 90 different, no light will pass through. At 0, both

sets of lines are parallel and a light bulb set in line with the 2 polarized filters will be

visible.

c.

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Figure 42. Visual inspection of transparent seals with polarized light.

During heat sealing of transparent and translucent plastic materials, energy is added,

providing free movement of polymer chains. Close packing and increased hydrogen

bonding occurs, resulting in alignment of carbon chains and increased crystalline

structure. Differences between random, oriented, and crystalline configuration affect

both light absorption and transmission in these materials. A seal sample placed

between 2 polarizing filters is first illuminated by polarized light. To enhance color

changes resulting from differences in crystalline structure, rotate the other filter to

block most of the transmitted light. Inspect visually to determine degree of

crystalinity within fused seals. Uniform crystalinity, seen as uniform color tone along

the inner edge of the primary seal, is one indicator of fusion. Areas that are not fused

appear as a different color. Colors differ with materials and thickness.

Materials

Light bulb, white, 40, 75, 100 W 

Polarized camera filters, 2 each 

Frame to hold filters and permit free rotation of both

filters in line with light bulb and sample

1.

Procedure

Obtain a clean transparent seal sample. Turn on light. Place seal sample

between polarized filters. Rotate one filter to obtain maximum difference in

color between fused seal and nonseal area. Examine fused seal area for

uniformity.

2.

Visible light. The objective is to detect holes in packages by sensing transmitted and

reflected visible light. Package is placed over low-wattage light bulb in darkened

room to enhance visual inspection. Aluminum foil will block all light transmission

except where holes and flexcracks in foil are present. Close inspection is required to

determine whether other lamina overlay holes in foil layer. Dye testing is required to

establish presence or absence of minute holes. Chemical etching may be used to

remove materials external to polyolefin seals. Magnification of etched seals with

backlighting aids inspection.

Materials

Light bulb

Scissors

Sink with running water

Paper towels

Darkened room

Indelible marking pen

Dye (optional)

1.

2. Procedure

d.
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Remove contents, wash, and dry container. Inspect package for light leaks.

Mark location of light leaks with a marking pen; draw a circle around the

defect location. Closely examine defects for presence of holes through all

layers. Use dye test to verify presence or absence of holes.

Results

Positive. A hole through all layers is detected in a package.

Negative. No light leaks are detected.

False positive. A hole in the foil layers permits light to pass, but no holes exist

in overlying layers and hermetic barrier is maintained.

False negative. A hole through all layers is not aligned so that light can be

transmitted.

3.

Machine vision (5)

The objective is to detect holes in hermetic packages by computer evaluation of images with

previously defined patterns of acceptance. This system is designed to eliminate visual

inspection of packages. Packages are positioned before a camera to present a consistent

pattern. The video image obtained is digitized. Both grayscale and color density may be

evaluated. The computer compares coded patterns with acceptable patterns stored in

memory. Some systems evaluate one image at a time. Others use parallel computers to

evaluate different segments of the video image in less time. Patterns that do not match the

acceptance criteria are rejected and the package is automatically rejected from the production

line.

Materials

Video imaging system

Computer with stored images for acceptance criteria

Strobe light (optional)

Packages

a.

Results

Positive. Image does not match acceptance criteria.

Negative. Image matches acceptance criteria.

False positive. Image was not presented to camera correctly and does not match

acceptance criteria.

False negative. Acceptance criteria include defects.

b.

13.

Proximity devices (5)

The objective is to detect holes by measuring changes in the shape of hermetically sealed

packages as a function of time. The position of a package containing metal may be

established by the strength of a magnetic field, detected with a galvanometer. By comparing

2 readings as a function of time, a determination can be made as to whether the shape of a

package has changed.

14.
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Materials

Proximity detection system

Computer with stored acceptance criteria

Packages

a.

Procedure

Compare multiple packages to a standard value. Fix limits of acceptance or alter

automatically by computing a running average and standard deviation. Packages

displaying stronger or weaker disturbances to a magnetic field sensed by a

galvanometer may fall outside of the limits of acceptance. Mark these packages for

removal from packaging line.

Read magnetic fields of single packages at one location and, after a period of time,

make a second reading at a downstream location. If shape of container changes, mark

package for removal from packaging line. Confirm with dye testing to locate holes in

packages.

b.

Results

Positive. Disturbance of magnetic field exceeding limits of acceptance.

Negative. Disturbance of magnetic field within limits of acceptance.

False positive. External disturbance of magnetic field or imprecise positioning of

package resulted in values that exceeded limits of acceptance.

False negative. Distortion of package sufficient to cause disturbance of magnetic

field outside normal range of acceptance.

c.

Seam scope projection (5)

The objective is to measure critical dimensions in the closure profile of plastic packages.

Packages are cut in cross-section to reveal all components in their proper thickness and

relative position. The cut edge is magnified with a projector to aid measurement and visual

inspection.

Materials

Knife, saw, or scissors

Microprojector

Micrometer, calipers, ruler, or measurescope

a.

Procedure

Cut directly across seal or closure with knife, saw, or scissors and remove section

containing adjacent material. Magnify cross section. Compare observed dimensions

with criteria for acceptance or rejection provided by manufacturer of package or

closure machine. Accept or reject sample.

b.

Results

Positive. Dimensions of sample exceed limits of criteria for acceptance.

c.

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Negative. Dimensions within limits of criteria for acceptance.

False positive. Magnification with incorrect scale or measuring error results in

rejection of acceptable sample.

False negative. Measuring error results in acceptance of defective sample.

Sound (5)

Ultrasonic. The objective is to passively sense air moving through small orifices in

packages possessing internal vacuum or pressure by monitoring the presence or absence of

high-frequency sound waves.

Materials

Microphone

Audiofilters

Oscilloscope with alarm system

Packages

a.

Procedure

Place packages in a chamber to eliminate external disturbances and subject to changes

in external pressure. Air movement through small holes in package wall generates

ultrasonic sound waves. A microphone senses the vibration. Audiofilters eliminate

all frequencies except those of interest.

b.

Results

Positive. Package exhibits ultrasonic whistling sound, indicating a leak is present,

permitting air to enter or exit package.

Negative. No sound is emitted by package within range of frequencies monitored.

False positive. Background noise occurred within range monitored.

False negative. Hole does not emit a noise within the range monitored, or hole was

occluded by moisture or food.

c.

Echo. The objective is to actively sense the frequency of echoes in hermetically sealed

containers. When a package possessing a vacuum is tapped, the tightness of the package

creates a sound that is audibly different from that of the same package without a vacuum.

Two changes can be monitored: frequency and amplitude. Changes in frequency (vibrations

per second) are recognized as differences in tone (pitch). Changes in amplitude are

recognized as 2 relative difference in volume. Loss of hermetic integrity will result in

microbial growth within the contents of a food package during incubation. Changes in

sound accompany changes in viscosity. Consequently, this method may be used as a

nondestructive test for a number of product/package combinations.

Materials

Control sample

Samples to be evaluated

Tapping device (electronic device or unsharpened pencil to be used like a drumstick)

Incubator

a.

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Procedure

Obtain sample packages, either newly packed or incubated, and a control package

(known to be properly sealed) containing the same product as sample packages. Tap

the section of the package covering that is taut. Listen to the echo for differences

between packages. Commercial devices are available that electronically monitor the

echos, allowing for a less subjective determination.

b.

Results

Positive. Package displays audibly different sound, indicating loss of hermetic

integrity.

Negative. Package resonates at same frequency as control package.

False positive. Differences in vacuum level or fill volume create different sounds in

test packages.

False negative. Audible difference between control package and test package cannot

be differentiated.

c.

Tensile strength (5)

The objective is to measure the tensile strength required to cause separation of peelable or

fused seals. A section of a seal is obtained by cutting a 1/2 or 1 inch strip perpendicular to

the seal edge. The strip is then clamped by opposing grippers and pulled at constant speed

and defined angle until failure is obtained. The peak force required to fully separate the 2

halves is recorded as the strength of the seal.

Materials

Sample packages

Sample cutting apparatus

Scissors (sample dimensions are critical to precision)

Tensile strength testing device

a.

Procedure. See ASTM D-882 - Standard test methods for tensile properties of thin

plastic sheeting (9).

Remove representative sample from production line. Cut open sample and remove

contents. Do not disturb seal to be tested. Cut a segment of the seal to produce a test

strip. Test strip must be cut perpendicular to the seal to be tested. Secure both ends of

test strip in separate clamps. With screwdriver, move one screw clamp away from the

other, creating a 180° separation of the seal. Observe force required to fully separate

seal. Fixtures are required to hold samples at angles different from 180°.

b.

Results

Positive. Sample separates at peak tensile strength less than established standard.

Negative. Sample separates uniformly at peak tensile strength greater than or equal to

established standard.

False positive. Sample separates at peak tensile strength less than established

standard because of equipment miscalibration or greater separation speed of jaws.

c.

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False negative. Sample separates at tensile strength greater than or equal to

established standard. However, a different portion of the same sample failed at a

tensile strength less than the standard.

Vacuum testing (5)

The objective is to cause the movement of air out of a sealed container through leaks by

using external vacuum within a testing chamber. Closed packages are placed inside a sealed

testing chamber and vacuum is created to cause movement of air through leaks in the

packages. Deflection of the package may be measured as a function of time to determine

whether leakage has occurred. If vacuum chamber contains water, bubbles from holes in

packages may be observed.

Materials

Bell jar (glass or plastic) with tight-fitting lid

Water to cover package within bell jar

Weighted fixture to keep package below water level during test

Vacuum pump

Vacuum gauge

Valve

Grease for tight gasketing of lid on chamber

a.

Procedure

Obtain representative sample from production line. Place one sample inside vacuum

chamber. Evacuate chamber. Observe package swelling and any movement of air

(bubbles) or product through holes that may be present or may have developed.

When vacuum is released, observe packages to determine if original shape is retained

or if atmospheric pressure causes sample to appear slightly crushed.

b.

Results

Positive. Leak in test package causes air or product to escape through holes in

container. Container ruptures or lid separates because of weak closure. When

vacuum is released, package appears distorted or crushed by atmospheric pressure.

Negative. Package distorts under vacuum but no loss of product or air is observed.

When vacuum is released, package assumes its original configuration.

False positive. Air clinging to surface of package or within paper laminates is

mistaken for bubbles emitting from a defect.

False negative. Food particles prevent movement of air out of a hole in container

while under vacuum.

c.

18.

Visual inspection (5)

The objective is to visually observe defects in food packages. Representative samples are

obtained from production line. External surfaces are examined for holes, abrasions,

delamination, and correct design. Critical dimensions are measured and observations

recorded.

a. Materials

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Strong light without glare, for visual inspection of packages

Measuring devices, such as ruler, calipers, micrometer

Scissors or knife

Procedure

Refer to examination procedures for paperboard packages, flexible pouches, plastic

packages with heat-sealed lids, and plastic cans with double-seamed metal ends.

b.

Results

Positive. Visually detected defect.

Negative. No visually detected defects.

False positive. Visual identification of defect not actually present.

False negative. Defect is present, but not visually detected.

c.

Acknowledgments

We thank the American Can Co. for permission to include various useful items of information. We are

grateful to Donald E. Lake, George A. Clark, and Arnold A. Kopetz of American Can Co. for assisting

our development of this project in their laboratories.

We also thank the following individuals for reviewing the manuscript and contributing many valuable

suggestions: Keith A. Ito, National Food Processors Association; Raymond C. Schick and Robert A.

Drake, Glass Packaging Institute; Irvin J. Pflug, University of Minnesota; Fred J. Kraus, Continental

Can Co.; Robert M. Nelson, W.R. Grace & Co.; Don A. Corlett, Jr., Del Monte Corp.; Harold H. Hale

and J. W. Bayer, Owens-Illinois; Charles S. Ochs, Anchor Hocking; Rachel A. Rosa, Maine Sardine

Council; Melvin R. Wadsworth, Consultant; Tedio Ciavarini, U.S. Army Natick R&D Laboratories;

Robert A. Miller, U.S. Department of Agriculture; Helen L. Reynolds (retired), Lois A. Tomlinson,

Patricia L. Moe, and Dorothy H. Hughley, Technical Editing Branch, FDA; and Thomas R. Mulvaney,

Division of Food Chemistry and Technology, FDA.

We acknowledge the following individuals for their valuable comments specific to flexible and semirigid

containers: Pete Adams, International Paper Co.; Kent Garrett, Continental Can Co.; Donald A. Lake,

Roger Genske, and Stan Hotchner, American National Can Co.; Charles Sizer, Tetra Pak International,

Sava Stefanovic, Ex-Cell-O; and Clevel Denny, Jean Anderson, Nina Parkinson, and Jenny Scott,

National Food Processors Association.

Hypertext Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. Chapter 22.

*Author: George W. Arndt, Jr. (NFPA)

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U.S. Food & Drug Administration

Center for Food Safety & Applied Nutrition

Bacteriological Analytical Manual Online

January 2001

Chapter 22D

Examination of Containers for Integrity

Glossary and References

Authors

(Return to Table of Contents)

Glossary

BASE PLATE PRESSURE. Force of the base plate that holds the can body and end against the chuck

during the double seaming operation. In general, it has the following effect on the seam formation: low

pressure, short body hook; high pressure, long body hook.

BODY - The principal part of a container, usually the largest part in one piece comprising the sides. The

body may be cylindrical, rectangular, or another shape.

BODY HOOK - The flange of the can body that is turned down in the formation of the double seam.

BOTTOM SEAM - Double seam of the can end put on by the can manufacturer, also known as factory

end seam.

CABLE CUTS - Cuts or grooves worn into can ends and bodies by cables of the runway conveyor

system.

CAN, SANITARY - Full open-top 2-piece drawn can and 3-piece can with double seamed bottom.

Cover or top end is attached with a double seam by the packer after filling. Ends are compound-lined.

Also known as packer's can or open-top can.

CANNER'S END - See packer's end.

CAP TILT - Cap should be essentially level with transfer bead or shoulder.

CHIPPED GLASS FINISH - Defect in which a piece of glass has broken away (chipped) from the

finish surface.

CHUCK - Part of a closing machine that fits inside the end countersink and acts as an anvil to support

the cover and body against the pressure of the seaming rolls.
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CHUCK WALL - Part of the can end that comes in contact with the seaming chuck (Fig. 2).

COCKED CAP - Cap not level because cap lug is not properly seated under glass lug.

CODE CUT - Fracture in the metal of a can end caused by improper code embossing.

COLD WELD - Weld appears narrower and lighter than normal and may be scalloped. Fails the pull

test, possibly exhibiting a zipper or sawtooth type of failure.

CONTAMINATION IN WELD AREA - Any visible burn at one or more points along side seam.

COMPOUND - Sealing material consisting of a water or solvent dispersion or solution of rubber and

placed in the curl of the can end. The compound aids in producing a hermetic seal by filling spaces or

voids in the double seam

COUNTERSINK DEPTH - Measurement from top edge of double seam to end panel adjacent to chuck

wall.

COVER - See packer's end.

COVER HOOK - The part of the double seam formed from the curl of the can end. Wrinkling and other

visual defects can be observed by stripping off the cover hook.

CRACKED GLASS FINISH - Actual break in the glass over the sealing surface of the finish. Also

known as split finish.

CRAWLED LAPS - Occurs when two layers of metal are bent and the outer layer looks shorter

because it has a greater radius to traverse than the inner layer, which has a smaller radius, perhaps being

bent almost double. Also known as creep.

CROSS-OVER - The portion of a double seam at the juncture with the side seam of the body.

CROSS-SECTION - A section cut through the double seam for the purpose of evaluating the seam.

CRUSHED LUG - Lug on cap forced over glass lug, causing the cap lug not to seat under glass lug.

CURL - Extreme edge of the cover that is turned inward after the end is formed. In metal can double

seaming, the curl forms the cover hook of the double seam. For the closure for glass containers, the curl

is the rolled portion of metal at the bottom of the closure skirt (may be inward or outward).

CUTOVER - A break in the metal at top of inside portion of double seam caused by a portion of the

cover being forced over the top of the seaming chuck. This condition usually occurs at the cross-over.

Also known as a cut through by some can manufacturers. These manufacturers refer to a cutover as the

same condition without the break.

CUT THROUGH - Gasket damage caused by excessive vertical pressure.

DEADHEAD - An incomplete double seam resulting from the seaming chuck spinning in the end's

countersink during the double seaming operation. Also known as a spinner, skidder, or slip.

DELAMINATION - Any separation of plies (laminate materials) that results in questionable pouch

integrity.

DOUBLE SEAM - Closure formed by interlocking and compressing the curl of the end and the flange

of the can body. It is commonly produced in 2 operations. The first operation roll preforms the metal to
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produce the 5 thicknesses or folds; the second presses and flattens them together to produce double

seam tightness.

DROOP - Smooth projection of the double seam outside and below the bottom of the normal seam.

Usually occurs at the side seam lap area.

FACTORY END - See manufacturer's end.

FALSE SEAM - Double seam where a portion of the cover hook and body hook are not interlocked,

i.e., no hooking of body and cover hooks.

FINISH - That part of the glass container for holding the cap or closures.

FLANGE - Outward flared edge of the can body cylinder that becomes the body hook in the double

seaming operation. For weld cans, any flange crack at or immediately adjacent to the weld is a major

defect.

FLEXIBLE CONTAINER - A container, the shape or contour of which, when filled and sealed, is

affected by the enclosed product.

HEAVY LAP - A lap containing excess solder. Also called a thick lap.

HOOK, BODY - See body hook.

HOOK, COVER - See cover hook.

IMPROPER POUCH SEAL - A defect (e.g., entrapped food, grease, moisture, voids, or fold-over

wrinkles) in that area of the closure seal that extends 1/8 inch vertically from edge of seal on food

product side and along full length of seal.

IRREGULAR WELD WIDTH - Any obvious irregularity in weld width along length of side seam.

JUMPED SEAM - See jumpover.

JUMPOVER - Double seam that is not rolled tight enough adjacent to the cross-over; caused by

jumping of the seaming rolls at the lap.

JUNCTURE - The junction of the body side seam and the end double seam, or that point where the 2

seams come together. Also known as the cross-over.

KNOCKED-DOWN FLANGE - Common term for a false seam where the bottom of the flange is

visible below the double seam. A portion of the body flange is bent back against the body without being

engaged with the cover hook.

LAP - The section at the end of the side seam consisting of 2 layers of metal bonded together. As the

term implies, the 2 portions of the side seam are lapped together to allow for the double seam, rather

than hooked, as in the center of the side seam.

LID - See packer's end.

LIP - Projection where the cover hook metal protrudes below the double seam in one or more "V"

shapes. Also known as a vee.

LUG CAP - Closure with raised internal impressions that intermesh with identical threads on the finish

of the glass container. It is a closure with horizontal protrusions that seat under angled threads on the
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glass container finish.

MANUFACTURER'S END - End of the can that is attached by the can manufacturer.

NOTCH - Small cut-out section in the lap designed to facilitate the formation or the body hook at

cross-over.

OPEN LAP - A lap that is not properly soldered or has failed by separating or opening because of

various strains in the solder.

OVERLAP - Distance the cover hook laps over the body hook. Any observable loss of overlap along

the side seam is a critical defect.

PACKER'S END - End of the can attached and coded by the food packer. Also known as the canner's

end.

PLATE - General term for tinplate, aluminum, and the steel sheets from which cans are made. It is

usually tin plate, which is black plate with tin applied to it.

PRESSURE RIDGE - Impression (chuck impression) around the inside of the can body directly

opposite the double seam.

PULL-UP - Term applied to distance measured from the leading edge of the closure lug to the vertical

neck ring seam.

SAWTOOTH - Partial separation of the weld side seam overlap at one or more points along the seam. If

observed after performing the pull test, it is considered a critical defect.

SEAM NARROWING - A steadily visible narrowing of the weld at either end of the weld side seam is

a critical defect.

SEAM THICKNESS - Maximum dimension of double seam measured across or perpendicular to

layers of seam.

SEAM WIDTH (LENGTH OR HEIGHT) - Maximum dimension of double seam measured parallel to

folds of seam.

SECURITY - Residual clamping force remaining in the closure application when gasket has properly

seated after processing and cooling.

SEMIRIGID CONTAINER - A container, the shape or contour of which, when filled and sealed, is not

affected by the enclosed product under normal atmospheric temperature and pressure, but which may be

deformed by external mechanical pressure of less than 10 psi (0.7 kg/cm2) (i.e., normal firm finger 

pressure).

SIDE SEAM - The seam joining the 2 edges of the body blank to form a can body.

SKIDDER - Can with incompletely finished double seam because the can slipped in the seaming chuck.

In this defect, part of the seam will be incompletely rolled out. The term has the same meaning as

deadhead when referring to seamers that revolve the can. Also known as a spinner.

SOFT CRAB - Colloquial term used to describe a breakdown in the packer's can resulting in a hole

between end and body.
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SPINNER - See deadhead and skidder.

STRIPPED CAP - Lug closure applied with too much torque, which causes lugs to pass over glass

lugs. May have vacuum but has no security value.

TIGHTNESS - Degree to which the double seam is compressed by the second operation roll. Tightness

is determined primarily by the degree of freedom from wrinkles in the cover hook. Tightness rating is a

percentage that ranges from 100 to 0, depending on the depth of the wrinkle: 100% indicates no wrinkle

and 0% indicates a wrinkle extending completely down the face of the cover hook. A well-defined

continuous impression around the circumference of the can in the double seam area indicates a tight

seam. This impression is known as a pressure ridge.

TOP SEAM - Top of packer's end seam.

UNEVEN HOOK - Body or cover hook that is not uniform in length.

WELD CRACK - Class I corrosion products plus any observable seam crack, and any cracks that

extend 25% or more across the width of the weld at any point along the weld seam are considered

critical defects.

WELD PROTRUSION - Protrusion of the weld in excess of 1/16 inch beyond the leading or trailing

edge of the can body.

WRINKLE (COVER HOOK) - A waviness occurring in the cover hook from which the degree of

double seam tightness is determined.

ZIPPER - Gross separation of the side seam overlap along all or any part of the side seam. If observed

during pull test, it is a critical defect.

References

1. American Can Company. 1975. Test Procedures Manual (Internal Publication). Barrington Technical

Center, Barrington, IL.

2. American Can Company. 1978. Top Double Seam Inspections and Evaluation: Round Sanitary Style

Steel Cans. Book No. 4800-S. Barrington Technical Center, Barrington, IL.

3. APHA. 1966. Recommended Methods for the Microbiological Examination of Foods, 2nd ed. J.M.

Sharf (ed). American Public Health Association, New York.

4. APHA. 1984. Chapter 55. Canned foods--tests for cause of spoilage. In: Compendium of Methods

for the Microbiological Examination of Foods, 2nd ed. Marvin L. Speck (ed). American Public Health

Association, Washington, DC.

5. Arndt, G.W. 1990. Burst Testing for Paperboard Aseptic Packages with Fusion Seals. Michigan

State University, School of Packaging, East Lansing, MI.

6. ASTM. 1980. Test for leaks using the mass spectrometer leak detector in the inside out mode. E-493.

Annual Book of ASTM Standards. ASTM, Philadelphia.

7. ASTM. 1980. Test for residual gas using the mass spectrometer in the tracer mode. ASTM E-498.

Annual Book of ASTM Standards. ASTM, Philadelphia.
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

6 of 7 3/28/08 10:34 AM

8. ASTM. 1980. Method for testing for residual gas using the mass spectrometer in the detector probe

mode. ASTM E-499. Annual Book of ASTM Standards. ASTM, Philadelphia.

9. ASTM. 1985. Tensile properties of thin plastic sheeting. ASTM D-882 A or B. Annual Book of

ASTM Standards. ASTM, Philadelphia.

10. ASTM. 1992. Method of compression testing for shipping containers D-642-90. Annual Book of

ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging

Products. ASTM, Philadelphia.

11. ASTM. 1992. Method of drop test for filled bags D-959-80-86. Annual Book of ASTM Standards,

Vol. 15.09. Paper; Packaging; Flexible Barrier Materials: Business Copy Products. ASTM,

Philadelphia.

12. ASTM. 1992. Methods for mechanical handling of unitized loads and large shipping cases and

crates D-1083-91. Annual Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier

Materials; Business Imaging Products. ASTM, Philadelphia.

13. ASTM. 1992. Methods for vibration testing of shipping containers D-999-91. Annual Book of

ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging

Products. ASTM, Philadelphia.

14. ASTM. 1992. Practice for conditioning containers, packages, or package components for testing

D-4332-89. Annual Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier

Materials; Business Imaging Products. ASTM, Philadelphia.

15. ASTM. 1992. Standard practice for performance testing of shipping containers and systems

D-4169-91a. Annual Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier

Materials; Business Imaging Products. ASTM, Philadelphia.

16. ASTM. 1992. Terminology of packaging and distribution environments D-996-91. Annual Book of

ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging

Products. ASTM, Philadelphia.

17. ASTM. 1992. Test method for drop test of cylindrical shipping containers D-997-80-86. Annual

Book of ASTM Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging

Products. ASTM, Philadelphia.

18. ASTM. 1992. Test method for drop test of loaded boxes D-775-80-86. Annual Book of ASTM

Standards, Vol. 15.09. Paper; Packaging; Flexible Barrier Materials; Business Imaging Products.

ASTM, Philadelphia.

19. Bee, G.R., R.A. DeCamp, and C.B. Denny. 1972. Construction and use of a vacuum microleak

detector for metal and glass containers. National Canners Association, Washington, DC.

20. National Food Processors Association. 1989. Flexible Package Integrity Bulletin by the Flexible

Package Integrity Committee of NFPA. Bulletin 41-L. NFPA, Washington, DC.

21. Wagner, J.W., et al. 1981. Unpublished data. Bureau of Medical Devices, Food and Drug

Administration, Washington, DC.

General Reading

Bernard, Dane T. 1984. Evaluating container integrity through biotesting. In: Packaging Alternatives for 

Food Processors. Proceedings of National Food Processors Association. NFPA, Washington, DC.
FDA/CFSAN BAM - Examination of Containers for Integrity: Glos... http://www.cfsan.fda.gov/~ebam/bam-22d.html

7 of 7 3/28/08 10:34 AM

Carnation Company, Can Division. No date. Double seam standards and procedures. Oconomowoc, 

WI.

Code of Federal Regulations. 1991. Title 21, part 113. Thermally processed low-acid foods packaged in 

hermetically sealed containers. U.S. Government Printing Office, Washington, DC.

Continental Can Company. 1976. Top double seaming manual. New York. (Revisions by H.P. 

Milleville, Oregon State University, Corvallis, OR).

Corlett, D.A., Jr. 1976. Canned food-tests for cause of spoilage, pp. 632-673. In: Compendium of 

Methods for the Microbiological Examination of Foods. M.L. Speck (ed). American Public Health 

Association, Washington, DC.

Food Processors Institute. 1982. Canned Foods, 4th ed. FPI, Washington, DC.

Grace, W.R. & Co., Dewey and Almy. 1971. Evaluating a double seam. Chemical Division, Lexington, 

MA.

Lampi, R.A., G.L. Schulz, T. Ciavarini, and P.T. Burke. 1976. Performance and integrity of retort

pouch seals. Food Technol. 30(2):38-46

National Canners Association. 1968. Laboratory Manual for Food Canners and Processors, Vol. 2. 

AVI Publishing, Westport, CT.

Put, H.M.C., H. Van Doren, W.R. Warner, and J.T. Kruiswijk. 1972. The mechanisms of

microbiological leaker spoilage of canned foods: A review. J. Appl. Bacteriol. 35:7-27.

Hypertext Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. Chapter 22.

*Authors:Rong C. Lin, Paul H. King, and Melvin R. Johnston

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USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-1

CHAPTER 10. EXAMINATION OF HEAT PROCESSED, HERMETICALLY SEALED

 (CANNED) MEAT AND POULTRY PRODUCTS

George W. Krumm, Charles P. Lattuada,

Ralph W. Johnston, James G. Eye, and John Green

10.1 Introduction

Thermally processed meat and poultry products in hermetically

sealed containers include both shelf stable products as well as

those that must be kept refrigerated (i.e. perishable product).

There are a wide variety of packages designed to totally exclude

air. These include traditional rigid containers, such as metal

cans and glass jars; semi-rigid containers such as plastic cans,

bowls and trays; and flexible containers such as retortable

pouches and bags. The microbiological examination of these food

products requires knowledge and a thorough understanding of food

microbiology, food science, and packaging technology and

engineering. Many books and scientific articles are available on

the processing and the laboratory testing of these products.

Individuals who perform these analyses should be familiar with the

current procedures and methods. Some of these references are

listed in section 10.6.

10.2 Important Terms and Concepts

a. Shelf Stability (commercial sterility):

The term "shelf stability" traditionally has been used

by the Agency and is synonymous with the terms

"commercial sterility" or commercially sterile". Shelf

stability is defined in CFR title 9, part 318, Subpart

G, 318.300 (u) of the Food Safety and Inspection Service

(meat and poultry) USDA regulations. Shelf stability

(commercial sterility) means "the condition achieved by

application of heat, sufficient, alone or in combination

with other ingredients and/or treatments, to render the

product free of microorganisms capable of growing in the

product at non-refrigerated conditions (over 50°F, 10°C)

at which the product is intended to be held during

distribution and storage". Such a product may contain

viable thermophilic spores, but no mesophilic spores or

vegetative cells. These products usually are stable for

years unless stored at temperatures of 115-130°F (46-

55°C) which may allow swelling or flat sour spoilage to
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-2

occur because of germination and growth of the

thermophilic spores. Many low acid canned meat/poultry

products contain low numbers of thermophilic spores.

For this reason, samples of canned foods are not

routinely incubated at 55°C because the results usually

will be confusing and provide no sound information.

Canned food lots that are to be held in hot vending

machines or are destined for tropical countries are

exceptions to this rule.

b. Hermetically Sealed Container:

A container that is totally sealed to prevent the entry

or escape of air and therefore secure the product

against the entry of microorganisms.

c. Adventitious contamination:

Adventitious contamination may be defined as the

accidental addition of environmental microorganisms to

the contents of a container during analysis. This can

occur if the microbiologist has not sterilized the

puncture site on the container surface or the opening

device adequately, or is careless in manipulating

equipment or cultures. Strict attention to proper

procedures is required to avoid this type of

contamination.

d. Cured Meat/Poultry Products:

Many canned meat/poultry products contain curing salts

such as mixtures of sodium chloride and sodium nitrite.

When included in a canned meat/poultry product

formulation, sodium chloride and sodium nitrite inhibit

the outgrowth of bacterial spores, particularly

clostridial spores. Lowering the pH and increasing the

sodium chloride concentration enhance the inhibitory

action of sodium nitrite. Thus, most canned, cured

meat/poultry products are minimally heat processed and

are rendered shelf stable by the interrelationship of

heat, pH, sodium chloride, sodium nitrite and a low

level of indigenous spores. Spoilage in canned cured

meat/poultry products attributed to underprocessing is

rare. When it occurs, it is usually the result of

improper curing rather than inadequate heating. The

heat processes used for canned, cured, shelf stable

meat/poultry products are unique in that they usually
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-3

are not designed to destroy mesophilic bacterial spores

but merely to inhibit their outgrowth.

e. Uncured Meat/Poultry Products:

Canned uncured meat/poultry products are given a much

more severe heat treatment than canned cured products.

The treatment given to canned uncured meat/poultry

products is commonly referred to as a "full retort

cook".

10.21 Classification of Containers

a. Metal and plastic cans with metal double sealed end(s):

Cans must be at room temperature for classification.

Cans are classified as NORMAL if both ends are flat or

slightly concave; FLIPPER when one end of a normalappearing can is struck sharply on a flat surface, the

opposite end "flips out" (bulges) but returns to its

original appearance with mild thumb pressure; SPRINGER

if one end is slightly convex and when pressed in will

cause the opposite end to become slightly convex; SOFT

SWELL if both ends are slightly convex but can be

pressed inward with moderate thumb pressure only to

return to the convex state when thumb pressure is

released; HARD SWELL if both ends are convex, rigid and

do not respond to medium hard thumb pressure. A can with

a hard swell will usually "buckle" before it bursts.

Hard swollen cans must be handled carefully because they

can explode. They should be chilled before opening

except when aerobic thermophiles are suspected. Never

flame a can with a hard swell, use only chemical

sanitization.

b. Glass jars:

Classify glass jars by the condition of the lid

(closure) only. Do not strike a glass jar against a

surface as you would a can. Instead shake the jar

abruptly to cause the contents to exert force against

the lid; doing so occasionally reveals a flipper.

Scrutinize the contents through the glass prior to

opening. Compare the contents of the

abnormal/questionable jar with the contents of a normal

jar (e.g., color, turbidity, and presence of gas

bubbles), and record observations.
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c. Flexible containers (pouches):

Pouches usually are fabricated from laminates consisting

of two or more layers (plies) of material. Retortable

pouches are the most common type of flexible container

used for canned, shelf-stable products. Most pouches

are 3-ply: an outer ply of polyester film, a middle ply

of aluminum foil, and an inner ply of polypropylene.

The polyester functions as the heat resistant, tough

protective layer; the aluminum foil as a moisture, gas

and light barrier; and the polypropylene functions as

the food contact surface and the film for heat sealing.

The polypropylene also provides added strength, and

protects the aluminum film against corrosion by the food

product. Not all retortable pouches contain an aluminum

foil ply. Pouches and paperboard containers used for

non-retorted, shelf stable products (e.g. pH-controlled

and hot-filled product) or aseptically filled containers

may be quite different from retortable pouches in

construction. Pouches and other flexible containers are

either factory-formed and supplied ready for filling, or

are formed by the processor from roll stock.

10.22 Container Abnormalities

To determine the cause of product abnormalities, both normal and

abnormal containers from the same production lot should be

examined. All observed microbiological results should be

correlated with any existing product abnormalities (Section 10.46

a) such as atypical pH, odor, color, gross appearance, direct

microscopic examination, etc. as well as the container evaluation

findings (Section 10.46, b,c). Non-microbial swells (such as

hydrogen swells) are usually diagnosed by considering all product

attributes because culture results are negative or insignificant.

a. Metal cans, plastic containers and glass jars:

Conditions such as "swells" are defined in Section 10.21

(a). The defects and abnormalities associated with

these containers have been extensively detailed by

others. Rather than include extensive descriptions for

each of them in this section, the analyst is referred to

several excellent references presented in Section 10.6.

These references provide detailed information on the

numerous defects and abnormalities that can occur with

these containers. The analyst should be familiar with

these conditions before beginning any analysis of a
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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defective or abnormal container. The effect of

processing failures, such as overfilling, closure at low

temperature or high altitude; container damage; and

storage temperature changes, must be taken into

consideration as the analyst evaluates possible causes

for the defect or abnormality. For quick reference, a

Glossary of Terms is provided in Appendices I and II.

b. Pouches:

A Glossary of Terms for these containers can be found in

Appendix III. It is imperative to follow uniform

procedures (Section 10.46,c) when examining defective or

abnormal pouches. The APHA, 1966 reference (Section

10.6) provides detailed information on the analysis of

pouch defects.

10.3 Analysis of Containers

The number of containers available for analysis will vary.

However, it is important that the number be large enough to

provide valid results. Unless the cause of spoilage is clear cut,

at least 12 containers should be examined. With a clear cut

cause, one half this number may be adequate. If abnormal

containers have been reported, but are not available for analysis,

incubation of like-coded containers may reproduce the abnormality.

The "normal" cans should be incubated at 35°C for 10 days prior to

examination. Incubation temperatures in excess of 35°C should not

be used unless thermophilic spoilage is suspected. This

incubation may reproduce the abnormality, and thereby document

progressive microbiological changes in the product. Examine the

incubated cans daily. Remove any swells from the incubator as

they develop and culture them along with a normal control. After

the 10 day incubation period, cool the cans to room temperature

and reclassify. Swollen, buckled and blown containers should NOT

be incubated but analyzed immediately along with a normal control.

All steps in the analysis should be conducted in sequence

according to protocol.

10.31 Physical Examination of Metal and Plastic Containers

a. Before opening, visually examine the double end seam(s)

and side seam (if present) for structural defects, flaws

and physical damage; record pertinent observations.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-6

b. Run thumb and forefinger around the inside and outside

of the double seams for evidence of roughness,

unevenness, or sharpness.

c. Using a felt marker, make three slash marks at irregular

intervals across the label and the code-end seam.

Remove the label and copy any label code-numbers to the

side of the container along with a mark indicating the

code end of the can. Correlate any stains on the label

with suspicious areas on the side panel (can body) by

returning the label to its exact position relative to

the slash marks.

d. Examine all non-seam areas of the can and ends for any

evidence of physical damage. If the code is embossed,

carefully examine it for any evidence of puncturing.

Circle any suspect and/or defective areas with an

indelible pen and record this information on the work

sheet. For an illustration of these defects see the

APHA, 1966 reference (Section 10.6).

10.32 Physical Examination of Glass Jars

a. Before opening, remove the label and, using a good light

source such as a microscope light, examine the container

for apparent or suspected defects. Microorganisms may

enter jars through small cracks in the glass. Make note

of any residue observed on the outer surface and the

location.

b. Test the closure gently to determine its tightness.

After sampling has been completed, examine the lid

(closure) and the glass rim (sealing surface) of the

jar. Look for flaws in the sealing ring or compound

inside the closure; for food particles lodged between

the glass and the lid; and for chips or uneven areas in

the glass rim.

10.33 Physical Examination of Pouches

a. Pouches should be examined using an illuminated 5X

magnifier.

b. Hold the pouch in one hand, examine it for

abnormalities, such as swelling, leakage, overfilling,

and defects such as delamination and severe distortion.

Record any pertinent observations.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-7

c. Hold the pouch at both ends and examine both sides for

noticeable cuts, cracks, scratches, food residues,

punctures, missing labels, foreign materials or other

abnormalities.

d. Carefully examine all seal areas for incomplete fusion.

Pay attention to such defects as entrapped product,

wrinkles, moisture and foreign material in the seal.

Particular attention should be given to the final or

closing seal.

e. All actual and suspected defects should be circled with

an indelible marking pen for more detailed examination

after all sampling is complete.

10.4 Analysis of the Contents

Processing errors occur infrequently with canned products, but may

result in the improper processing of large quantities of product.

Swollen cans, for instance, may signal a microbial spoilage

problem. Each abnormality in a "canned" product must be

investigated thoroughly and correctly. The following procedures

should be followed carefully.

10.41 Equipment and Material

a. Incubators 20°, 35° & 55 ± 1°C

b. Vertical laminar flow hood

c. Microscope, microscope slides & cover slips

d. pH meter equipped with a flat electrode

e. Felt-tip indelible marker

f. Illuminated 5X magnifier

g. Sterile Bacti-disc cutter or other suitable opening

device

h. Large, sterile plastic or metal funnel

i. Large autoclavable holding pans

j. Sterile towels

k. Clean laboratory coat and hair covering(s)

l. Sterile wide bore pipettes or 8 mm glass tubing with

cotton plugs

m. Sterile serological pipettes with cotton plugs

n. Safety aspiration device for pipetting (e.g. propipette)

o. Sterile petri dishes, beakers, and large test tubes

p. Sterile triers, cork borers, scissors, knives and 8"

forceps. Triers can be made from the tail piece of
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-8

chrome finish sink drain pipe, 1 1/2" in diameter,

flanged on one end and sharpened on the other end.

q. Sterile cotton swabs with wooden handles in glass test

tubes, one per tube, or commercially sterilized swabs in

paper sleeves

r. Sterile gloves

s. Small wire basket to hold pouches in an upright position

t. Seam analysis tools (micrometer, calipers, saw,

countersink meter, metal plate scissors, nippers).

u. Vacuum gauge

v. Light source such as a microscope light

w. Sonic cleaning apparatus

x. Transparent acrylic plate with a hole and tubing to a

vacuum source

y. Bituminous compound in strips (tar type strips usually

available in hardware stores) stored in the 35°C

incubator

z. Seamtest Type U (Concentrate), Winston Products Co., Inc

Box 3332, Charlotte, N.C., Dilute 1:300 with distilled

water for use.

aa. Wooden dowels, 1/2" diameter

bb. Gas cylinder clamp

cc. Abrasive chlorinated cleaner or a scouring pad

10.42 Media and Reagents

a. Modified Cooked Meat Medium (MCMM) STEAM JUST BEFORE USE

b. Brom Cresol Purple Broth (BCPB) or Dextrose Tryptone

Broth

c. Plate Count Agar

d. APT Agar

e. KF Broth

f. Strong's Sporulation Medium

g. Gram stain reagents

h. Spore stain

i. Dishwashing detergent

j. Chlorine solution, (Commercial Bleach with approximately

5% available chlorine diluted 1:100 with 0.5 M phosphate

buffer, pH 6.2)

10.43 Preparation

a. The Analyst

i. The analyst must wear a clean full length

laboratory coat.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-9

ii. Hair must be completely covered with a clean,

disposable operating room type hair cover. A

surgical face mask should be worn; if the analyst

has facial hair such as beards and sideburns, the

mask must completely cover it.

iii. Hands, forearms and face should be washed with

germicidal soap and water.

iv. The analyst should wear safety glasses or goggles,

preferably in combination with some type of face

shield when opening swollen cans or cans suspected

of being contaminated with Clostridium spp.

b. Preparing the Environment

i. If possible, the analysis should be done in a

vertical laminar flow hood. If a hood is not

available, the area used must be clean and

draft-free.

ii. Flat cans should be opened in the laminar flow

hood.

iii. Swells may explode or spew, therefore they should

be opened outside the hood and the container

transferred to the hood only after it is opened and

all gas released.

iv. Disinfect the work surface before beginning any

work.

c. Preparing Metal Cans Prior to Opening

i. Scrub the non-coded end of the metal can with

abrasive cleaner or a scouring pad. This removes

bacteria-laden oil and protein residues. Rinse

well with tap water. Cans with an "easy open" end

usually are coded on the bottom. Record the code

exactly and prepare the code end as described

above.

ii. Sanitize the cleaned end with chlorine solution

(Section 10.42 j) either by placing clean tissues

over the end and saturating it with chlorine

solution or by immersing the end in a shallow pan

containing the solution. Allow a 15-minute contact
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-10

time; wipe dry with sterile towels or tissue. (An

alternative sanitization procedure which can be

used on Normal-appearing cans ONLY is to heat the

entire can surface using a laboratory burner or a

propane torch until the metal becomes slightly

discolored from the heat.) Proceed as outlined in

Section 10.44.

d. Preparing Jars Prior to Opening

i. Scrub the surface of the jar closure with abrasive

cleaner or scouring pads. Rinse well with tap

water.

ii. Sanitize the jar closure with chlorine (Section

10.42 j) either by placing clean tissues over the

closure and saturating it with chlorine solution or

immersing the closure in a shallow pan containing

the solution. Allow a 15-minute contact time; wipe

dry with sterile towels or tissue.

e. Preparing Plastic Containers Prior to Opening

i. Scrub the bottom surface of the container with

abrasive cleaner or scouring pads. Rinse well with

tap water.

ii. Sanitize the bottom with chlorine solution (Section

10.42 j) by placing clean tissues over the bottom

and saturating it with chlorine or immersing the

bottom of the container in a shallow pan containing

the solution. Allow a 15-minute contact time; then

wipe dry with sterile towels or tissue.

f. Preparing Normal and Abnormal-Appearing Flexible

Retortable Pouches Prior to Opening

i. Clean the outside of the pouch with a sanitizer and

rinse well.

ii. Sanitize the entire pouch in a suitably sized pan

with chlorine solution (Section 10.42 j). Allow a

15-minute contact time; then wipe dry with sterile

towels or tissue.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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g. Preparing Swollen Cans Prior to Opening

i. Scrub the non-coded end of the chilled metal can

with an abrasive cleaner or a scouring pad. This

removes bacteria-laden oil and protein residues.

Rinse well with tap water.

ii. Sanitize the cleaned end with chlorine solution

(Section 10.42 j) either by placing clean tissues

over the end and saturating it with chlorine

solution or immersing the end in a shallow pan

containing the solution. Allow a 15-minute contact

time; then wipe dry with sterile towels or tissue.

h. Opening Devices

i. The preferred type of opening device is the

adjustable Bacti-disc cutter (available from the

Wilkens-Anderson Company, 4525 W. Division Street,

Chicago, IL.; a similar device is available from

the American National Can Co., 1301 Dugdale Rd.,

Waukegan, IL. Order Number WT2437). The opener

should be pre-sterilized or heated in a flame to

redness. If this type of device is not available,

individually packaged and heat sterilized regular,

all metal, kitchen-type can openers may be used.

The advantage of the Bacti-disc type opener is that

it causes no damage to the double seam (simplifying

later examination) and the size of the opening can

be adjusted.

ii. Sometimes a large can (e.g. a #10 size can) may be

difficult to open. The analyst could be exposed to

pathogens or their toxins if the can is not

properly secured. The container can be held

tightly with a gas cylinder clamp secured in an

inverted position in a shallow metal drawer or tray

lined with a large disposable poly bag or an

autoclavable tray to contain any overflow. Place

the #10 container against the clamp and secure the

strap. Rotate the can and continue cutting until

the opening is completed. The metal tray and liner

may be removed for cleaning and the clamp is

autoclavable.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-12

10.44 Sampling

a. Normal-Appearing Metal Cans and Jars with Metal Closures

i. Prepare the area and can or jar closure as

described in section 10.43.

ii. Shake the container to distribute the contents.

iii. Use a sterilized opening device to cut the desired

size entry hole. Transfer samples immediately to

the selected media with a sterile pipette or swab

and proceed as outlined in Section 10.45.

iv. Aseptically transfer a representative amount of the

product to a sterile test tube or other sterile

container as a working reserve. Use a pipet or

sterile spoon to accomplish this.

v. Caution: The contents from overfilled cans may

flow out of the hole onto the surrounding lid

surface at the time of opening. This material can

then drain back into the can when the opening

device is removed. Should this occur, terminate

the analysis.

b. Normal and Abnormal-Appearing Plastic Containers

i. Immediately after removing the container from the

chlorine solution and wiping the excess liquid, use

a very hot, sterilized opening device to cut the

desired size entry hole. Transfer samples

immediately to the selected media with a sterile

pipette or swab and proceed as outlined in Section

10.45.

ii. Aseptically transfer a representative amount of the

product to a sterile test tube or other sterile

container as a working reserve. Use a pipet or

sterile spoon to accomplish this.

c. Normal and Abnormal Appearing Flexible Retortable

Pouches

i. Place the disinfected pouch upright in a sterile

beaker and cut a two inch strip about one quarter
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-13

of an inch under the seam edge using a sterile

scissors. If possible, use a pipette to remove

some of the pouch contents, otherwise use a swab.

Transfer the samples immediately to the selected

media with a sterile pipet or swab, proceed as in

section 10.45.

ii. Aseptically transfer a representative amount of the

product to a sterile test tube or other sterile

container as a working reserve. Fold the edge of

the opened pouch over against itself several times

and secure with tape until the microbiological

analysis is complete.

d. Swollen Cans

i. Cans displaying a hard swell should be chilled

before opening. Most foods spoiled by Bacillus

stearothermophilus will not produce gas (flat sour

spoilage). However, if nitrate or nitrite is

present in the meat/poultry product, gas may be

produced by this microorganism. Cold usually will

kill B. stearothermophilus resulting in no growth

in Bromcresol Purple Broth. If possible, save one

or two cans and store without refrigeration.

ii. NEVER FLAME A SWOLLEN CONTAINER - IT MAY BURST.

Place the container to be opened in a large,

shallow, autoclavable pan. The side seam, if

present, should be facing away from the analyst. A

container with a hard swell may forcefully spray

out some its contents, posing a possible hazard to

the analyst if the contents are toxic. Therefore,

these cans should be considered a biohazard and

precautions must be taken to protect the analyst.

Protective gloves should be worn and the lab coat

should be tucked inside the cuffs of the gloves or

at least secured around the wrist. Some type of

facial shield is also recommended.

iii. Place the sanitized container into a biohazard bag

and cover with a sterile towel or invert a sterile

funnel with a cotton filter in the stem over the

can. Place the point of the sterile opening device

in the middle of the container closure. Make a

small hole in the center of the sterilized

end/closure. Try to maintain pressure over the
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-14

hole. Release the instrument slowly to allow gas

to escape into the towel or funnel.

iv. After the gas pressure has been released, enlarge

the opening to the desired size to permit sampling

and aseptically remove some of the container

contents. Sample as outlined in (a) above.

10.45 Culturing

a. Inoculation of Culture Media

i. The sampling and transfer processes must be

conducted aseptically; care must be taken to

prevent contamination during the various

manipulations.

ii. Transfer the sample at once to the selected media,

inoculating each tube at the bottom. Whenever

possible, use a pipet and pro-pipette to remove 1-2

ml of product for inoculating each tube of medium.

When the nature of the meat/poultry product makes

it impossible to use a pipet, use a sampling swab

(holding it by the very end of the shaft) to

transfer 1-2 g of the product to each tube. This

is accomplished by plunging the swab into the

product, then inserting the swab as far as possible

into the appropriate tube of medium and breaking

off the portion of the shaft that was handled. Use

one swab for each tube of medium. When inoculating

MCMM, force the broken swab to the bottom of the

tube by using the tip of another sterile swab.

iii. For each sample, inoculate 2 tubes of MCMM which

were steamed (or boiled) for 10 minutes and cooled

just before use and 2 tubes of Bromcresol Purple

Broth. If a tube of KF medium is inoculated at the

same time, the presence of enterococci can be

determined rapidly.

iv. As a process control, place uninoculated swabs into

each of two tubes of MCMM and BCP and one swab into

KF broth (if used). Additionally, label two

uninoculated tubes of each medium to serve as

controls. If multiple samples are cultured at the

same time, only one set of control tubes are needed

for each medium and each temperature.
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v. After all tubes have been inoculated with a sample,

aseptically transfer approximately 30 ml or a 30 g

portion of the container contents to a sterile

tube, Whirl-Pak® or jar for retention as a working

reserve sample. Appropriately label the container

and store it in a refrigerator at approximately

4°C.

vi. Finally, transfer a portion of the container

contents to a sterile Petri plate, clean jar or

beaker for pH, microscopic, organoleptic and other

relevant analyses (10.46).

vii. Cover the hole made in the container with several

layers of sterile aluminum foil, secure the foil

with tape and then store the container in a

refrigerator at approximately 4°C. This serves as

the primary reserve. Re-enter it only as a last

resort. If the sample is a regulatory sample,

chain of custody records must be maintained on it.

b. Incubation of Culture Media

i. Incubate one tube each of MCMM and BCP at 35°C and

one tube each at 55°C. If used, incubate the tube

of KF medium at 35°C. For the MCMM and BCP

controls, incubate one tube at 35° and one at 55°C.

ii. Observe all tubes at 24 and 48 h. Tubes incubated

at 35°C that show no growth should be incubated for

5 days before discarding. Tubes incubated at 55°C

should be incubated for 3 days before discarding.

Subculture any questionable tubes, especially if

the product under examination contributes

turbidity.

c. Identification of Organisms

i. Use conventional bacteriological procedures to

characterize the type(s) of microbial flora found

in the contents of the container.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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ii. Use descriptive terms such as: mixed culture or

pure culture, anaerobic or aerobic growth, spore

former or non-sporeformer, mesophile or

thermophile, cocci or rods.

iii. Cultures should be examined using a Gram stain.

Gram stains should be done only on 18-24 h

cultures. Record the morphological types observed

and their Gram reaction. If the container contents

are examined microscopically using a methylene blue

stain, record those observations as well. If

endospores are present, the spore stain can be used

for better definition of spore type and placement.

iv. Record all biochemical test results in addition to

any characteristic growth patterns on differential

and/or selective media.

v. MCMM tubes showing a bright yellow color with

visible gas bubbles, and containing gram positive

or gram variable rods should be suspected of

containing gas-forming anaerobes. If Clostridium

botulinum is suspected, sub-cultures should be made

and incubated for 4-5 days. The original tube

should be reincubated to check for spores. After 4

- 5 days incubation, test the cultures for toxin by

the mouse bioassay (see Chapter 14).

10.46 Supportive Determinations

a. Examination of Container Contents

i. Determine the pH of the sample (10.45, a, vii)

using a flat electrode. Disinfect the electrode

after taking this measurement.

ii. If applicable, determine the water activity of the

sample (Section 2.4).

iii. Examine the sample microscopically by making a

simple methylene blue or crystal violet stain. A

Gram stain is of no value since the age of the

cells is not known and Gram-stain reactions may not

be dependable in the case of old cells. Prepare a

spore stain if the contents of a swollen container

show signs of digestion and few bacterial cells.
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iv. Note abnormalities observed in the container

contents such as off-odors, off-color, changes in

consistency and texture when compared with normal

product. DO NOT TASTE!

b. Examination of Metal and Plastic Cans

NOTE: Whenever possible a "normal" companion can should

be examined along with the abnormal one.

i. After a reserve sample has been taken and all

examinations are complete, discard any remaining

product into an autoclavable bag and terminally

sterilize.

ii. Disinfect the inside of the container with a

phenolic disinfectant and carefully clean it with a

stiff brush or use an ultra sonic bath. Do not

autoclave the container since this may destroy any

defects.

iii. Examine the interior lining of metal containers for

blackening, detinning and pitting.

iv. The container code should have been recorded prior

to analysis; if it was not, do so now. Sometimes

embossed codes are poorly impressed and can be

revealed by rubbing a pencil on a paper held over

the code. If this does not work, place a thin

smooth piece of paper over the code, hold securely

and rub the paper with a clean finger in order to

impress the paper. Rerub the paper with a finger

coated with graphite. This is superior to using a

pencil to rub the code. If that fails, rub the

code with carbon paper. Place transparent adhesive

tape over the code and rub the tape with the back

of a fingernail. Lift the tape and transfer it to

any document requiring the can code. The latter

two techniques allow a record to be kept of any

partial numbers or symbols. It is also possible to

wait until the can is emptied, then view the

reverse of the code from the inside. If needed,

the code can be viewed in a mirror.

v. When leakage from double seams or side seams is

suspected, remove excess metal from the opened end,

leaving a 0.5 - 1 cm flange. Dry thoroughly,
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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preferably overnight, in the 55°C incubator. Add

leak detection liquid (10.41z) to the can to a

depth of 2-4 cm. Place a microleak detector on the

open end of the container. The leak detector

consists of a transparent acrylic plate with a

vacuum gauge and connector for a vacuum source.

Place a gasket (cut pieces of an automobile tire

inner tube will do) between the apparatus and the

can. If the fit is not tight (e.g., end seam is

bent), use modeling clay to fill in the gaps.

Large cans without beading or thin metal cans

having a wider diameter than height may collapse

when vacuum is applied. To prevent this from

happening, use 1/2" wooden dowels cut to the

appropriate length to support the can sides.

Bituminous compound on the dowel ends will hold

them in place. Generally, 4 dowels are sufficient

for a #10 can. Apply the gasket and any bituminous

compound, to the open can end and fit the leak

detector plate in place. Connect the vacuum and

apply 10 inches vacuum to the can. Swirl the

liquid to dissipate bubbles formed by gases

dissolved in the liquid. Examine seams by covering

them with the diluted Seamtest. Leaks are

identified by a steady stream of bubbles or a

steadily increasing bubble size. After carefully

examining all seams for leaks, increase the vacuum

to 20 inches vacuum and re-examine the seams.

Leave the can under vacuum until a leak appears or

for a maximum of 2 h, and examine at half-hour

intervals. Mark the location of leaks on the can's

exterior using a marking pen. When reporting, note

which seam, and the distance from the side seam or

some other appropriate reference point. If no

leaks were found, note test conditions (time and

amount of vacuum drawn).

vi. Perform a tear-down examination of the double

seams. The following references in Section 10.6

will guide you through this process: APHA, 1966;

Food Processors Institute, 1988; Double Seam

Manual; Evaluating a Double Seam, FDA

Bacteriological Analytical Manual, 1992.

vii. The tightness of double seams formed by plastic

cans and metal can ends may be evaluated by

comparing the actual seam thickness to the
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calculated thickness of the plastic flange, neck,

or metal end. This would include three thicknesses

of plastic and two of metal. Also, assess

tightness by inspecting the pressure ridge, since

it reflects the compression of the plastic body

wall. The pressure ridge should be visible and

continuous. Each packer may have different

specifications for the finished seams; if

necessary, the analyst must call the in-plant

inspector and ask for specifications for the

container of interest.

c. Examination of Pouches

i. The best way to determine if a pouch has leaked is

by the type of microorganisms recovered.

ii. The pouch should be examined microscopically

looking for points of light coming through the

film. These are potential leakage sites.

10.47 Interpretation of Results

Use Tables 2, 3 and 4 to arrive at possible causes of spoilage

based on all laboratory results. Caution: The tables are based

on a single cause of spoilage. If there are multiple causes, the

tables may not help.

10.5 Examination of Canned, Perishable Meat/Poultry Products

Perishable meat and poultry products, such as hams, luncheon

meats, and loaves are packaged in hermetically-sealed containers

and then heat-processed to internal temperatures of not less than

150°F (65.5oC) and usually not greater than 160°F (71oC).

"Perishable, Keep Refrigerated" must appear on the label of these

products. Although they are not shelf stable, good commercial

processing usually will destroy vegetative bacterial cells. The

combined effects of sodium nitrite, salt, refrigeration, and low

oxygen tension retard the outgrowth of the few vegetative cells

and/or spores that may survive the process. Such products can

retain their acceptable quality for 1 to 3 years when properly

processed and refrigerated.

10.51 Analysis of Containers

See Sections 10.3 - 10.33
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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10.52 Analysis of the Contents

a. Equipment and Material

See Section 10.41

b. Media and Reagents

See Section 10.42

c. Preparation

See Section 10.43

d. Sampling

i. Using procedures already described (Section 10.44)

remove approximately 50 g of sample with a

sterilized trier, large cork borers, scissors,

knife or forceps.

ii. Place the sample into a sterile blender jar or

Stomacher bag, add 450 ml of sterile Butterfield's

Phosphate Diluent and homogenize for 2 minutes.

This is a 1:10 dilution; make additional dilutions

through at least 10-4. Proceed with the culturing

steps given in Section 10.52 (e, f & g).

iii. After sampling, cover the container opening with

sterile aluminum foil several layers thick and

secure with tape. Place the opened sample unit in

the freezer until the analysis is complete.

e. Aerobic Plate Counts

i. Pipet 1 ml of each dilution prepared in 10.52 (d)

into each of two sets of duplicate pour plates

according to the instructions given in Section 3.4.

ii. Prepare one dilution set with Plate Count Agar.

Incubate this set at 35°C for 48 h.

iii. Substitute APT agar for the Plate Count Agar in the

other set of plates. Incubate this set at 20°C for

96 h.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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iv. Count and record the results from both sets as

described in Section 3.4.

f. Gas-Forming Anaerobes (GFAs)

i. Steam tubes of MCMM for 10 minutes and cool just

prior to use.

ii. Inoculate each tube with l ml of each dilution

prepared in 10.52 (d). Begin with the 1:10

dilution and continue with subsequent dilutions.

Use a separate pipet for each dilution. Dilutions

must be sufficiently high to yield a negative

endpoint. Be sure that the inoculum is deposited

near the bottom of the tube.

iii. Incubate these tubes for 48 h at 35°C, but read

daily.

iv. Consider any MCMM tubes showing a bright yellow

color, containing visible gas bubbles, and

containing gram positive or gram variable rods as

positive for GFAs.

v. Based upon the highest dilution showing these

organisms, report the approximate number of

gas-forming anaerobes per gram, calculated as the

reciprocal of the highest positive dilution. If

skips occur, disregard the final actual dilution

and calculate the end point at the dilution where

the skip occurred. This is only an approximation

of the gas forming anaerobe count. A minimum of

three tubes per dilution and an MPN table must be

used for a more accurate determination.

vi. If Clostridium botulinum is suspected,

representative tubes that have not been opened

should be reincubated for a total of 4 - 5 days and

then tested for botulinum toxin using the mouse

bioassay (Chapter 14).

g. Enterococci

i. Transfer 1 ml of each dilution prepared in 10.52(d)

to individual tubes of KF broth. Use a separate

pipette for each dilution. Begin with the 1:10

dilution and continue with each subsequent
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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dilution. Dilutions must be sufficiently high to

yield a negative end point.

ii. Incubate these tubes at 35°C for 48 h. Tubes

showing a yellow color, turbidity and buttoning of

growth are presumptive positives.

iii. Confirm all presumptive positives microscopically.

Either wet mounts examined under low light or gram

stained preparations are suitable for these

microscopic determinations. Microscopic

determinations yielding cells with ovoid

streptococcal morphology shall be considered

confirmed positive.

iv. Report the approximate number of enterococci per

gram, calculated as the reciprocal of the highest

positive confirmed dilution. If skips occur,

disregard the final actual dilution and calculate

the end point at the dilution where the skip

occurred. This is only an approximation of the

number of enterococci. A minimum of three tubes

per dilution and an MPN table must be used for a

more accurate determination of organisms as

described in 10.43-10.45 and Tables 2, 3 and 4.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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10.6 Selected References

APHA 1966. Recommended Methods for the Microbiological

Examination of Foods. 2nd Edition. American Public Health

Association, Inc., New York, New York.

Bee, G. R. and Denny, C. B., 1972, First Revision.

Construction and Use of a Vacuum Micro-Leak Detector for

Metal and Glass Containers. National Canners Association,

(now NFPA), Washington, D.C.

Crown Cork & Seal. Top Double Seaming Manual. Crown Cork

and Seal Co., Inc., 9300 Ashton Road, Philadelphia, PA 19136

Cunniff, P. (ed.). 1995. Official Methods of Analysis of

AOAC International, 16th Edition. Sections 17.6 - 17.8. AOAC

International, Inc., Gaithersburg, MD 20877.

Denny, C., Collaborative Study of a Method for the

Determination of Commercial Sterility of Low-Acid Canned

Foods, Journal of the Association of Official Analytical

Chemists 55 (3):613 (1972).

Double Seam Manual. Carnaud Metalbox Engineering, 79

Rockland Road, Norwalk, Connecticut 06854

Evaluating a Double Seam. W. R. Grace and Company, Grace

Container Products, 55 Hayden Ave., Cambridge, Massachusetts

02173

Food and Drug Administration, Bacteriological Analytical

Manual, Division of Microbiology, Center for Food Safety and

Applied Nutrition, 7th ed., 1992. Association of Official

Analytical Chemists, 1111 North 19th Street, Suite 210,

Arlington, VA 22209.

Food Processors Institute 1988. Canned Foods: Principles of

Thermal Process Control, Acidification and Container Closure

Evaluation. The Food Processors Institute, Washington, D.C.

20005.

Hersom, A. C. and Hulland, E. D., 1964. Canned Foods, An

Introduction to Their Microbiology. Chemical Publishing

Company, Inc. New York, New York.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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National Food Processors Association, 1979. Guidelines for

Evaluation and Disposition of Damaged Canned Food Containers

Bulletin 38-L, 2nd Edition. National Food Processors Assoc.,

Washinton, D.C.

National Food Processors Association, 1989. Flexible Package

Integrity Bulletin by the Flexible Package Integrity

Committee of NFPA. Bulletin 41-L. NFPA, Washington, D.C.

Schmitt, H. P. 1966. Commercial Sterility in Canned Foods,

Its Meaning and Determination. Assoc. Food and Drug

Officials of the U.S. 30:141.

Townsend, C. T., 1964. The Safe Processing of Canned Foods.

Assoc. Food and Drug Officials of the U.S. 28:206.

Townsend, C. T., 1966. Spoilage in Canned Foods. J. Milk

Food Tech. 20 (1):91-94.

United States Department of Agriculture, Food Safety

Inspection Service. Code of Federal Regulations, Title 9,

part 318.300, Subpart G (u).

Vanderzant, C., and D. F. Splittstoesser (ed.). 1992.

Compendium of Methods for the Microbiological Examination of

Foods, 3rd Edition. Amer. Publ. Hlth. Assoc., Washington,

D.C. 20005.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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Appendix I

Glossary of Metal/Plastic Can Seam Terminology

for Container Components and Defects

The same terms that are used to describe an all-metal seam apply

equally well to the metal end/plastic body seam.

Base Plate: Part of a closing machine which supports cans

during seaming operation.

Beaded Can: A can which is re-enforced by having ring

indentations around the body. The bead tends to keep the can

cylindrical and helps to eliminate paneling of the can body.

Body: Principal part of a container - usually the largest

part in one piece containing the sides (thus sidewall or body

wall).

Body Hook: Can body portion of double seam. Prior to

seaming, this portion was the flange of the can.

Bottom Seam: Factory end seam. The double seam of the can

end put on by the can manufacturer.

Buckling: A distortion in a can end.

Can Size: Two systems are commonly used to denote can size:

i. An Arbitrary system (1, 2, etc.) with no relation

to finished dimension.

ii. A system indicating the nominal finished dimensions

of a can; e.g. "307 x 512." In this example, the

first group of digits ("307") refers to the can's

diameter and the second set ("512"), the can's

height. The first digit in each set represents

inches, and the next two digits represent

sixteenths of an inch. Hence, the example can has

a diameter of 3-7/16 and a height of 5-12/16 (or 5-

3/4) inches.

Chuck: Part of a closing machine which fits inside the

countersink and in the chuck wall of the end during seaming.
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10-26

Closing Machine: Also known as a double seamer. Machine

which double seams the lid onto the can bodies.

Compound: Rubber or other material applied inside the end

curl to aid in forming a hermetic seal when the end is double

seamed on the can body.

Contamination in Weld Area: Any visible burn at one or more

points along the side seam of a welded can. This is a major

defect.

Countersink: On a seamed end, the perpendicular distance

from the outermost end panel to the top seam.

Cover: Can end placed on can by packer. Also known as top,

lid, packer's end, canner's end.

Cover Hook: That part of double seam formed from the curl of

the can end.

Cross Over: The portion of a double seam at the lap.

Cross Section: Referring to a double seam, a section through

the double seam.

Curl: The semi-circular edge of a finished end prior to

double seaming. The curl forms the cover hook of the double

seam.

Cut Code: A break in the metal of a can due to improper

embossing-marker equipment.

Cut-Over: During certain abnormal double seaming conditions,

the seaming panel becomes flattened and metal is forced over

the seaming chuck forming a sharp lip at the chuck wall. In

extreme cases the metal may split in a cut-over.

Dead-Head: An incompletely rolled finished seam. Also known

as a skip, skid or spinner.

Double Seam: The joint between the end and the can body

formed by rolling the curl under the flange (1st operation)

and then pressing the metal together (2nd operation).

Droop: A smooth projection of double seam below the bottom of

a normal seam. While droops may occur at any point of the

seam, they usually are evident at the side seam lap. A
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-27

slight droop at the lap may be considered normal because of

additional plate thickness incorporated into the seam

structure.

Excessive Slivers: One or more slivers which are 1/32" or

longer. This is a minor defect of welded cans.

Factory End: Bottom or can manufacturer's end.

False Seam: A seam fault where the end and body hook are not

over-lapped (engaged), although they give the appearance of a

properly formed seam. Also see Knockdown Flange.

Feather: Beginnings of a cut-over. See Sharp Edge.

First Operation: The first operation in double seaming. In

this operation, the curl of the end is tucked under the

flange of the can body which is bent down to form cover and

body hook, respectively.

Flange: The flared portion of the can body which facilitates

double seaming.

Flange Crack: Any crack at the flange or immediately adjacent

to the weld of welded cans. This is a major defect.

Headspace: The free space above the contents of a can and the

can lid.

Heavy Lap: A lap containing excess solder. Also called a

thick lap.

Hook: (i). The bent over edges of a body blank, which form

the side seam lock (ii). The body and cover hooks in a

double seam.

Internal Enamel: A coating applied to the inside of the can

to protect the can from chemical action by the contents or to

prevent discoloration. A lacquer is usually clear; an enamel

is pigmented and opaque.

Jumped Seam: A double seam which is not rolled tight enough

adjacent to the crossover caused by jumping of the seaming

rolls at the lap.

Knockdown Flange: A seam defect in which the flange is bent

against the body of the can. The cover hook is not tucked
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-28

inside the body hook, but lies outside of it. False seams,

knockdown flanges and soft crabs are degrees of the same

effect. In order to distinguish the degree of the defect,

the following terminology is suggested:

False Seam: The cover hook and body hook are not tucked

for a distance of less than an inch. Thus it may not be

possible to detect a false seam until the can is torn

down.

Knockdown Flange: As above, but more than an inch in

length. Body hook and cover hook in contact, but not

tucked.

Soft Crab: A defect in which the body of the can is

broken down and does not contact the double seam. Thus,

there is a wide open hole in the can below the double

seam where the body was not incorporated into the seam.

Lap: The soldered but not locked portions of a side seam at

the ends of the can body before seaming and removing the can

from the chuck at completion of the operation.

Lid: See Cover.

Lip, Spurs or Vees: Irregularities in the double seam due to

insufficient or sometimes absent overlap of the cover hook

with the body hook, usually in small areas of the seam. The

cover hook metal protrudes below the seam at the bottom of

the cover hook in one or more "V" shapes.

Loss of Overlap: Any observable loss of overlap along the

side seam of a welded can. This is a critical defect.

Loose Tin: A metal can which does not appear swollen, but

slight pressure reveals a looseness.

Mislock: A poor or partial side seam lock, due to improper

forming of the side seam hooks.

Neck: The thickness of the top of the sidewall (body wall) of

a plastic tub, one tenth of an inch below the junction of the

flange and the sidewall.

Notch: A small cut-away portion at the corners of the body

blank. This reduces droop when double seaming.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

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Oozier: An imperfect can which allows the escape of the

contents through the seam.

Open Lap: A lap failed due to various strains set up during

manufacturing operations. Also caused by improper cooling of

the solder (See Weak Lap). A lap which is not properly

soldered so the two halves are not properly joined.

Over Lap: The distance the cover hook laps over the body

hook.

Paneling: A flattening of the can side. Also used to define

concentric (expansion) rings in can ends.

Peaking: Permanent deformation of the expansion rings on the

can ends due to rapid reduction of steam pressure at the

conclusion of processing. Such cans have no positive

internal pressure and the ends can be forced back more or

less to their normal position.

Perforation: Holes in the metal of a can resulting from the

action of acid in food on metal. Perforation may come from

inside due to product in the can or from outside due to

material spilled on the cans.

Pleat: A fold in the cover hook which extends from the edge

downward toward the bottom of the cover hook and sometimes

results in a sharp droop, vee or spur.

Pressure Ridge: A ridge formed on the inside of the can body

directly opposite the double seam, as a result of the

pressure applied by the seaming rolls during seam formation.

Pucker: A condition which is intermediate between a wrinkle

and a pleat in which the cover hook is locally distorted

downward without actual folding. Puckers may be graded the

same way as wrinkles.

Sanitary Can: Can with one end attached, the other end put on

by the packer after the can is filled. Also known as

packer's can or open top can.

Sawtooth: Partial separation of the side seam overlap at one

or more points along the side seam after performing the pull

test on a welded side seam. This is a critical defect.
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Seam Arrowing: A readily visible narrowing of the weld at

either end of the can body. This is a major defect.

Seam Width: The maximum dimensions of a seam measured

parallel to folds of the seam. Also referred to as the seam

length or height.

Seam Thickness: The maximum dimension measured across or

perpendicular to the layers of the seam.

Second Operation: The finishing operation in double seaming.

The hooks formed in the first operation are rolled tight

against each other in the second operation.

Sharp Edge: A sharp edge at the top of the inside portion of

the double seam due to the end metal being forced over the

seaming chuck.

Side Seam: The seam joining the two edges of a blank to form

a body.

Skipper / Spinner: See Deadhead.

Uneven Hook: A body or cover hook which is not uniform in

length.

Vee: See Lip.

Weak Lap: The lap is soldered and both parts are together.

However, strain on this lap (e.g. by twisting with the

fingers) will cause the solderbond to break.

Weld Crack: Any observable crack in a welded side seam. This

is a critical defect.

Worm Holes: Voids in solder usually at the end of the side

seam. May extend completely through the width of the side

seam.

Wrinkle: The small ripples in the cover hook of a can. A

measure of tightness of a seam.
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Appendix II

Glossary of Glass Container Parts

From a manufacturing standpoint, there are three basic parts to a

glass container based on the three parts of glass container molds

in which they are made. These are the finish, the body and the

bottom.

Finish: The finish is that part of the jar that holds the cap

or closure. It is the glass surrounding the opening in the

container. In the manufacturing process, it is made in the

neck ring or the finish ring. It is so named since, in early

hand glass manufacturing, it was the last part of the glass

container to be fabricated, hence "the finish". The finish

of glass containers has several specific areas as follows:

Continuous Thread: A continuous spiral projecting glass ridge

on the finish of a container intended to mesh with the thread

of a screw-type closure.

Glass lug: One of several horizontal tapering protruding

ridges of glass around the periphery of the finish that

permit specially designed edges or lugs on the closure to

slide between these protrusions and fasten the number of

lugs on the closure and their precise configuration is

established by the closure manufacture.

Neck Ring Parting Line: A horizontal mark on the glass

surface at the bottom of the neck ring or finish ring

resulting from the matching of the neck ring parts with the

body mold parts.

Sealing Surface: That portion of the finish which makes

contact with the sealing gasket or liner. The sealing

surface may be on the top of the finish, or may be a

combination of both top and side seal.

Vertical Neck Ring Seam: A mark on the glass finish resulting

from the joint of matching the two parts of the neck ring.

NOTE: Some finishes are made in a one-piece ring and do not

have this seam.

Body: The body of the container is that portion which is made

in the "body-mold" in manufacturing. It is the largest part

of the container and lies between the finish and the bottom.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-32

The characteristic parts of the body of a glass container

are:

Heel: The heel is the curved portion between the bottom and

the beginning of the straight side wall.

Mold Seam: A vertical mark on the glass surface in the body

area resulting from matching the two parts of the body mold.

Shoulder: That portion of a glass container in which the

maximum cross-section or body area decreases to join the neck

or finish area. Most glass containers for processed foods

have very little neck. The neck would be a straight area

between the shoulder and the bottom of the bead or, with

beadless finishes, the neck ring parting line.

Side Wall: The remainder of the body area between the

shoulder and the heel.

Bottom: The bottom of the container is made in the "bottom

plate" part of the glass container mold. The designated parts

of the bottom normally are:

Bearing Surface: That portion of the container on which it

rests. The bearing surface may have a special configuration

known as the "stacking feature" which is designed to provide

some interlocking of the bottom of the jar with the closure

of another jar on which it might be stacked for display

purposes.

Bottom Plate Parting Line: A horizontal mark on the glass

surface resulting from the matching of the body mold parts

with the bottom plate.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-33

Appendix III

Glossary of terms - Flexible Retortable Pouches.

Adhesive: A substance applied to ply surfaces to cement the

layers together in a laminated film: (a). Polyurethane

adhesive for the outer layer (b). Maleic anhydride adduct of

polypropylene for the inner layer.

Blisters: Bubbles/gaseous inclusions/particulate material,

may be present between layers of laminate, usually are found

in the seal area.

Bottom of Closing Seal: Portion of closing (packer) seal

adjustment to the pouch contents.

Bottom Seal: A seal applied by heat and pressure to the

bottom of a flexible pouch.

Cosmetic Seal: Area above the primary seal designed to close

the edges of the pouch thus preventing the accumulation of

extraneous material.

Cuts, Punctures, Scratches: Mechanical defects that penetrate

one or more layers of the pouch.

Delamination: Any separation of plies through adhesive

failure. This may result in questionable integrity of the

package and safety of the product.

Dirty: Smeared with product or product trapped in top edges

(where there are no cosmetic seals).

Disintegrated Container: Evidence of delamination or

degradation after retorting.

Final Seal: A seal formed by heat and pressure by the packer

after pouch filling and prior to retorting.

Foil Flex Cracks/Foil Roll Holes: Visible cracks in the

aluminum foil layer caused by flexing of the pouch or pin

holes (roll holes) in the foil caused through manufacture of

the aluminum ply.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-34

Foreign Materials: Any material (solid food, condensate,

grease, voids, blemishes) that may be entrapped between the

plies but usually found in the seal area.

Fusion Seal: A seal formed by joining two opposing surfaces

by the application of heat and pressure.

Hard Swell or Blown: Distention or rupture due to internal

gas formation.

Inner Ply: Polypropylene coating bonded to the food surface

side of the aluminum foil.

Laminate: Two or more layers of material held together by

adhesive(s).

Leaker: Product leaking through any area of the pouch.

Outer Ply: The polyester film bonded to the exterior surface

of the aluminum foil.

Over Carton: A separate container (usually cardboard) in

which the flexible pouch is packaged for additional

protection.

Package Dimensions: The measurements of retortable flexible

pouches stated as length, the longest dimension (LGT), width

the second longest dimension (W), and thickness, the shortest

dimension (HGT). All are given as internal measurements.

Pin Holes, Roll Holes: Holes in the aluminum foil layer only,

originating during manufacturing; usually do not leak.

Preformed Seals: Seals formed by heat and pressure, by the

manufacturer of the pouches, along the sides and at the

bottom of the pouches.

Primary Seal: A fusion seal formed by the food processor by

applying heat and pressure immediately after filling.

Seal: A continuous joint of two surfaces made by fusion of

the laminated materials.

Seal Width: The maximum dimension of the seal measured from

the leading outside edge perpendicular to the inside edge of

the same seal.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-35

Severely Damaged: Punctures, cuts or ruptures which penetrate

all layers of the pouch and expose the product to

contamination.

Side Seals: Seals formed by applying heat and pressure to the

sides of the pouch's laminates to form the "preformed pouch".

Tear Nicks or Notch: Notches near the final seal to aid the

consumer in opening the pouch.

Wrinkle: A crease or pucker in the seal (Packer or Factory)

areas.
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-36

Appendix IV

Table 1. Normal pH Values for a Few Representative Canned

 Meat/Poultry Products.

__________________________________________________________________

 Kinds of Food pH 

 

Beans with Wieners 5.7

Beef Chili 5.6

Beef Paté 5.7

Beef Stew 5.4 - 5.9

Beef Taco Filling 5.8

Beef and Gravy 5.9 - 6.1

Chicken Noodle Soup 5.8 - 6.5

Chicken Soup with Rice 6.7 - 7.1

Chicken Broth 6.8 - 7.0

Chicken and Dumplings 6.4

Chicken Vegetable Soup 5.6

Chicken Stew 5.6

Chicken Vienna Sausage 6.1 - 7.0

Chorizos 5.2

Corned Beef 6.2

Corned Beef Hash 5.0 - 5.7

Egg Noodles & Chicken 6.5

Ham 6.0 - 6.5

Lamb, Strained Baby Food 6.4 - 6.5

Pork Cocktail Franks 6.2

Pork with Natural Juices 6.2 - 6.4

Pork Sausage 6.1 - 6.2

Roast Beef 5.9 - 6.0

Spaghetti and Meatballs 5.0

Spaghetti Sauce with Beef 4.2

Stuffed Cabbage 5.9

Sloppy Joe 4.4

Turkey, Boned in Bouillon 6.1 - 6.2

Turkey with Gravy 6.0 - 6.3

Vienna Sausage 6.2 - 6.5

Wieners, Franks 6.2

__________________________________________________________________
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-37

Appendix V

Table 2. KEY TO PROBABLE CAUSE OF SPOILAGE IN CANNED FOODS

Group 1.- Low-Acid Foods

pH Range 5.0 to 8.0

Condition of Characteristics of Material in Cans

 cans

Odor Appearance Gas

(CO2 &

H2)

pH Smear Cultures Diagnosis

Swells Normal to

"metallic"

Normal to frothy

(Cans usually etched

or corroded)

More than

20% H2

Normal Negative to

occasional

organisms

Negative Hydrogen swells

Sour Frothy; possibly ropy

brine

Mostly

CO2

Below

Normal

Pure or mixed

cultures of

rods, cocci,

yeasts or molds

Growth, aerobically

and/or anaerobically

at 35°C., and

possibly at 55°C.

Leakage

Sour Frothy; possibly ropy

brine, food particles

firm with uncooked

appearance

Mostly

CO2

Below

Normal

Pure or mixed

cultures of

rods, coccoids,

cocci and

yeasts

Growth, aerobically

and/or anaerobically

at 35°C., and

possibly at 55°C.

(If product received

high exhaust, only

spore formers may be

recovered)

No process given

Normal to

sourcheesy

Frothy H2 and

CO2

Slightly to

definitely

below

normal

Rods, med.

Short to med.

long, usually

granular;

spores seldom

seen

Gas, anaerobically

at 55°C., and

possibly slowly at

35°C.

Post-processing

temperature abuse

Thermophilic

anaerobes

Cheesy to

putrid

Usually frothy with

disintegration of

solid particles

Mostly

CO2;

possibly

some H2

Slightly to

definitely

below

normal

Rods; usually

spores present

Gas anaerobically at

35°C.

Underprocessing -

mesophilic anaerobes

(possibility of Cl.

botulinum)

Slightly

off –

possibly

ammoniacal

Normal to frothy Slightly to

definitely

below

normal

Rods; spores

occasionally

seen

Growth, aerobically

and/or anaerobically

with gas at 35°C and

possibly at 55°C.

Pellicle in aerobic

broth tubes. Spores

formed on agar and

in pellicle.

Underprocessing - B.

subtilis type
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-38

No

vacuum

and/or

Cans

buckled

Normal Normal No H2 Normal to

slightly

below

normal

Negative to

moderate number

of organisms

Negative Insufficient vacuum,

caused by: 1)

Incipient spoilage,

2) Insufficient

exhaust,

3) Insufficient

blanch,

4) Improper retort

cooling procedures,

5) Over fill

Flat

cans

(0 to

normal

vacuum)

Normal to

sour

Normal to cloudy

brine

Slightly to

definitely

below

normal

Rods, generally

granular in

appearance;

spores seldom

seen

Growth without gas

at 55°C. Spore

formation on

nutrient agar

Post-Processing

temperature abuse

Thermophilic flat

sours.

Normal to

sour

Normal to cloudy

brine; possibly moldy

Slightly to

definitely

below

normal

Pure or mixed

cultures of

rods, coccoids,

cocci or mold

Growth, aerobically

and/or anaerobically

at 35°C., and

possibly at 55°C.

Leakage
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-39

Appendix VI

Table 3. KEY TO PROBABLE CAUSE OF SPOILAGE IN CANNED FOODS

Group 3. Semi-Acid Foods

pH Range 4.6 to 5.0

Condition of Characteristics of Material in Cans

 cans

Odor Appearance Gas

(CO2 &

H2)

pH Smear Cultures Diagnosis

Swells Normal to

"metallic"

Normal to frothy

(Cans usually etched

or corroded)

More

than

20% H2

Normal Negative to

occasional

organisms

Negative Hydrogen swells

Sour Frothy; possibly

ropy brine

Mostly

CO2

Below Normal Pure or mixed

cultures of

rods, coccoids,

cocci, yeasts

or molds

Growth,

aerobically

and/or

anaerobically at

35°C., and

possibly at

55°C.

Leakage

Note:

Cans are

Sometimes

flat

Sour Frothy; possibly

ropy brine, food

particles firm with

uncooked appearance

Mostly

CO2

Below Normal Pure or mixed

cultures of

rods, coccoids,

cocci and

yeasts

Growth,

aerobically

and/or

anaerobically at

35°C., and

possibly at

55°C. (If

product received

high exhaust,

only spore

formers may be

recovered)

No process given

Normal to

sour-cheesy

Frothy H2 and

CO2

Slightly to

definitely

below normal

Rods - med.

Short to med.

long, usually

granular;

spores seldom

seen

Gas,

anaerobically at

55°C., and

possibly slowly

at 35°C.

Post-processing

temperature abuse

Thermophilic

anaerobes

Normal to

cheesy to

putrid

Normal to frothy

with disintegration

of solid particles

Mostly

CO2;

possibly

some H2

Normal to

slightly below

normal

Rods; possibly

spores present

Gas

anaerobically at

35°C. Putrid

odor

Underprocessing –

mesophilic

anaerobes

(possibility of

Cl. Botulinum)
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-40

Slightly off

- possibly

ammoniacal

Normal to frothy Slightly to

definitely

below normal

Rods;

occasionally

spores observed

Growth,

aerobically

and/or

anaerobically

with gas at 35°C

and possibly at

55°C. Pellicle

in aerobic broth

tubes. Spores

formed on agar

and in pellicle.

Underprocessing - B.

subtilis type

Butyric acid Frothy, large volume

gas

H2 and

CO2

Definitely

below normal

Rods - bipolar

staining;

possibly spores

Gas

anaerobically at

35°C. Butyric

acid odor

Under

processing -

butyric acid

anaerobe

No vacuum

and/or Cans

buckled

Normal Normal No H2 Normal to

slightly below

normal

Negative to

moderate number

of organisms

Negative Insufficient

vacuum, caused by:

1) Incipient

spoilage,

2) Insufficient

exhaust,

3) Insufficient

blanch,

4) Improper retort

cooling

procedures, 5)

Over fill

Flat cans

(0 to normal

vacuum)

Sour to

"medicinal"

Normal to cloudy

brine

Slightly to

definitely

below normal

Rods, possibly

granular in

appearance

Growth without

gas at 55°C. and

possibly at

35°C. Growth on

thermoacidurans

agar

Underprocessing B.

coagulans

Normal to

sour

Normal to cloudy

brine; possibly

moldy

Slightly to

definitely

below normal

Pure or mixed

cultures or

rods, coccoid,

cocci or mold

Growth,

aerobically

and/or

anaerobically at

35°C., and

possibly at

55°C.

Leakage
USDA/FSIS Microbiology Laboratory Guidebook 3rd Edition/1998

10-41

Appendix VII

Table 4. Characteristics of Normal and Abnormal Perishable Canned Meat/Poultry Products

Condition of

Cans

Odor Appearance pH Smear Cultures Probable

Cause

Flat Cans (0 to

Normal Vacuum)

Normal Normal Normal Negative to

occasional

organisms

0 to low # APC,

APT agar count

Normal product

0 to degrees of

swelling

Sour to off

odor

Normal to mushy,

possible gel

liquification

Slightly to

definitely

below normal

Mixed culture

of rods &

enterococci

Low # mesophiles,

high #

psychrophilic nonspore formers

(enterococci,

lactobacilli

1. Prolonged storage

at low temperatures

2. Abnormal high

levels in raw

materials 3.

Substandard process

Swell Sour or off

odor, possibly

putrid

Normal to mushy,

possible gel

liquification

Slightly to

definitely

below normal

Mixed culture

of rods, cocci

High # mesophilic

spore formers and

non-sporeformers

Product held without

refrigeration

Swell Normal to sour Normal Below normal Cocci, rods or

both

Enterococci, rods

or both

Leakage if shell

higher than core.

Underprocessing if

core higher than

shell

Swell Off odor Normal to off

color

Below normal Rods Psychrotrophic

clostridia (rarely

occurs in U.S.).

Low brine levels

Swell Normal to

putrid,

depending on

length of

storage.

Ranges from

uncooked

appearance to

digested

Normal to low,

depending on

length of

storage.

Vary Vary Missed processing

cycle.

Most of these are

detected soon after

distribution.