Canning

Canningis a method offood preservationin which food is processed and sealed in an airtight container (jarslikeMason jars, andsteel and tin cans). Canning provides ashelf lifethat typically ranges from one to five years,although under specific circumstances, it can be much longer.A freeze-dried canned product, such as canned driedlentils, could last as long as 30 years in an edible state.
In 1974, samples of canned food from the wreck of theBertrand, a steamboat that sank in the Missouri River in 1865, were tested by theNational Food Processors Association. Although appearance, smell, and vitamin content had deteriorated, there was no trace of microbial growth and the 109-year-old food was determined to be still safe to eat.
Shortly before theNapoleonic Wars, the French government offered a hefty cash award of 12,000 francs to any inventor who could devise a cheap and effective method of preserving large amounts of food to create well-preservedmilitary rationsfor theGrande Armée. The larger armies of the period required increased and regular supplies of quality food. Limited food availability was among the factors limiting military campaigns to the summer and autumn months. In 1809,Nicolas Appert, a French confectioner and brewer, observed that food cooked inside a jar did not spoil unless the seals leaked, and developed a method of sealing food in glass jars.Appert was awarded the prize in 1810 by Count Montelivert, a French minister of the interior.The reason for lack of spoilage was unknown at the time, since it would be another 50 years beforeLouis Pasteurdemonstrated the role of microbes in food spoilage and developedpasteurization.
The Grande Armée began experimenting with issuing canned foods to its soldiers, but the slow process of canning and the even slower development and transport stages prevented the army from shipping large amounts across theFrench Empire, and the wars ended before the process was perfected.
Following the end of the Napoleonic Wars, the canning process was gradually employed in other European countries and the United States.
Based on Appert's methods of food preservation, thetin canprocess was allegedly developed by FrenchmanPhilippe de Girard, who came to London and used British merchantPeter Durandas an agent to patent his own idea in 1810.Durand did not pursue food canning himself, selling his patent in 1811 toBryan DonkinandJohn Hall, who were in business as Donkin Hall and Gamble, ofBermondsey.Bryan Donkin developed the process of packaging food in sealed airtight cans, made of tinned wrought iron. Initially, the canning process was slow and labour-intensive, as each large can had to be hand-made, and took up to six hours to cook, making canned food too expensive for ordinary people.
The main market for the food at this stage was theBritish ArmyandRoyal Navy. By 1817, Donkin recorded that he had sold £3000 (equal to £277,470 today) worth of canned meat in six months. In 1824, SirWilliam Edward Parrytook canned beef and pea soup with him on his voyage to the Arctic inHMSFury, during his search for a northwestern passage to India. In 1829, Admiral SirJames Rossalso took canned food to the Arctic, as did SirJohn Franklinin 1845.Some of his stores were found by the search expedition led by Captain (later Admiral Sir)Leopold McClintockin 1857. One of these cans was opened in 1939 and was edible and nutritious, though it was not analysed for contamination by the lead solder used in its manufacture.
During the mid-19th century, canned food became astatus symbolamong middle-class households inEurope, being something of a frivolousnovelty. Early methods of manufacture employed poisonousleadsolderfor sealing the cans. Studies in the 1980s attributed the lead from the cans as a factor in the disastrous outcome of the 1845Franklin expeditionto chart and navigate theNorthwest Passage.However, studies in 2013 and 2016 suggested that lead poisoning was likely not a factor, and that the crew's ill health may, in fact, have been due to malnutrition—specifically zinc deficiency—possibly due to a lack of meat in their diet.
Increasing mechanization of the canning process, coupled with a huge increase in urban populations across Europe, resulted in a rising demand for canned food. A number of inventions and improvements followed, and by the 1860s smaller machine-made steel cans were possible, and the time to cook food in sealed cans had been reduced from around six hours to thirty minutes.
Canned food also began to spread beyond Europe—Robert Ayars established the first American canning factory inNew York Cityin 1812, using improved tin-plated wrought-iron cans for preservingoysters,meats,fruits, andvegetables. Demand for canned food greatly increased during wars. Large-scale wars in the nineteenth century, such as theCrimean War,American Civil War, andFranco-Prussian War, introduced increasing numbers of working-class men to canned food, and allowed canning companies to expand their businesses to meet military demands for non-perishable food, enabling companies to manufacture in bulk and sell to wider civilian markets after wars ended. Urban populations inVictorianBritaindemanded ever-increasing quantities of cheap, varied, quality food that they could keep at home without having to go shopping daily. In response, companies such asUnderwood,Nestlé,Heinz, and others provided quality canned food for sale toworking classcity-dwellers. The late 19th century saw the range of canned food available to urban populations greatly increase, as canners competed with each other using novel foodstuffs, highly decorated printed labels, and lower prices.
Demand for canned food skyrocketed duringWorld War I, as military commanders sought vast quantities of cheap, high-caloriefoodto feed their millions of soldiers, which could be transported safely, survivetrenchconditions, and not spoil in transport. Throughout the war, British soldiers generally subsisted on low-quality canned food, such as the Britishbully beef,pork and beans, canned sausages, andMaconochie's stew, but by 1916, widespread dissatisfaction and increasing complaints about the poor quality canned food among soldiers resulted in militaries seeking better-quality food to improve morale, and complete meals-in-a-can began to appear. In 1917, theFrench Armybegan issuing cannedFrench cuisinesuch ascoq au vin,beef bourguignon,french onion soup, andVichyssoise, while theItalian Armyexperimented with cannedravioli,spaghetti bolognese,minestrone, andpasta e fagioli. After the war, companies that had supplied military canned food began to improve the quality of their goods for civilian sale.
The original fragile and heavy glass containers presented challenges for transportation, and glass jars were largely replaced in commercial canneries with cylindricaltin canor wrought-iron canisters (later shortened to "cans") following the work ofPeter Durand(1810). Cans are cheaper and quicker to make, and much less fragile than glass jars.
Can openerswere not invented for another thirty years. At first, soldiers would cut the cans open withbayonetsor smash them open with rocks.Today, tin-coatedsteelis the material most commonly used.Aseptically processedretort pouchesare also used for canning.
Glass jars have remained popular for some high-value products and inhome canning.
To prevent the food from being spoiled before and during containment, a number of methods are used: pasteurisation, boiling (and other applications of high temperature over a period of time), refrigeration, freezing, drying, vacuum treatment, antimicrobial agents that are natural to the recipe of the foods being preserved, a sufficient dose of ionizing radiation, submersion in a strong saline solution, acid, base, osmotically extreme (for example very sugary) or other microbially-challenging environments.
Other thansterilization, no method is perfectly dependable as a preservative. Sterilization is done after the can is sealed, so that both the container and the food are secured.
The spores of the microorganismClostridium botulinum(which causesbotulism) can be eliminated only at temperatures above the boiling point of water. As a result, from a public safety point of view, foods with lowacidity(apHmore than 4.6) need sterilization under high temperature (116–130 °C). To achieve temperatures above the boiling point requires the use of apressure canner. Foods that must be pressure canned include mostvegetables,meat,seafood,poultry, anddairyproducts. The only foods that may be safely canned in an ordinary boiling water bath are highlyacidicones with a pH below 4.6, such asfruits,pickledvegetables, or other foods to which acidic additives have been added. Although an ordinary boiling temperature does not kill botulism spores, the acidity is enough to stop them from growing.
Invented in 1888 by Max Ams,moderndouble seamsprovide an airtightsealto a can. This airtight nature is crucial to keeping micro-organisms out of the can and keeping the can's contents sealed inside. Thus, double seamed cans are also known as Sanitary Cans. Developed in 1900 in Europe, this sort of can was made of the traditional cylindrical body made withtin plate. The two ends (lids) were attached using what is now called a double seam. A can thus sealed is impervious to contamination by creating two tight continuous folds between the can's cylindrical body and the lids. This eliminated the need forsolderand allowed improvements in manufacturing speed, reducing cost.
Double seaming uses rollers to shape the can, lid and the final double seam. To make a sanitary can and lid suitable for double seaming, manufacture begins with a sheet of coated tin plate. To create the can body, rectangles are cut and curled around a die, and welded together creating a cylinder with a side seam.
Rollers are then used to flare out one or both ends of the cylinder to create a quarter circle flange around the circumference. Precision is required to ensure that the welded sides are perfectly aligned, as any misalignment will cause inconsistent flange shape, compromising its integrity.
A circle is then cut from the sheet using a die cutter. The circle is shaped in a stamping press to create a downward countersink to fit snugly into the can body. The result can be compared to an upside down and very flattop hat. The outer edge is then curled down and around about 140 degrees using rollers to create the end curl.
The result is a steel tube with a flanged edge, and a countersunk steel disc with a curled edge. Arubbercompound is put inside the curl.
The body and end are brought together in a seamer and held in place by the base plate and chuck, respectively. The base plate provides a sure footing for the can body during the seaming operation and the chuck fits snugly into the end (lid). The result is the countersink of the end sits inside the top of the can body just below the flange. The end curl protrudes slightly beyond the flange.
Once brought together in the seamer, the seaming head presses a first operation roller against the end curl. The end curl is pressed against the flange curling it in toward the body and under the flange. The flange is also bent downward, and the end and body are now loosely joined. The first operation roller is then retracted. At this point five thicknesses of steel exist in the seam. From the outside in they are:
The seaming head then engages the second operation roller against the partly formed seam. The second operation presses all five steel components together tightly to form the final seal. The five layers in the final seam are then called; a) End, b) Body Hook, c) Cover Hook, d) Body, e) Countersink. All sanitary cans require a filling medium within the seam because otherwise the metal-to-metal contact will not maintain a hermetic seal. In most cases, a rubberized compound is placed inside the end curl radius, forming the critical seal between the end and the body.
Probably the most important innovation since the introduction of double seams is the welded side seam. Prior to the welded side seam, the can body was folded and/or soldered together, leaving a relatively thick side seam. The thick side seam required that the side seam end juncture at the end curl to have more metal to curl around before closing in behind the Body Hook or flange, with a greater opportunity for error.
Many different parts during the seaming process are critical in ensuring that a can is airtight and vacuum sealed. The dangers of a can that is not hermetically sealed are contamination by foreign objects (bacteria or fungicide sprays), or that the can could leak or spoil.
One important part is the seamer setup. This process is usually performed by an experienced technician. among the parts that need setup are seamer rolls and chucks which have to be set in their exact position (using a feeler gauge or aclearance gauge). The lifter pressure and position, roll and chuck designs, tooling wear, and bearing wear all contribute to a gooddouble seam.
Incorrect setups can be non-intuitive. For example, due to thespringbackeffect, a seam can appear loose, when in reality it was closed too tight and has opened up like a spring. For this reason, experienced operators and good seamer setup are critical to ensure that double seams are properly closed.
Quality control usually involves taking full cans from the line – one per seamer head, at least once or twice per shift, and performing a teardown operation (wrinkle/tightness), mechanical tests (external thickness, seamer length/height and countersink) as well as cutting the seam open with a twin blade saw and measuring with a double seam inspection system. The combination of these measurements will determine the seam's quality.
Use of astatistical process control(SPC) software in conjunction with a manual double-seam monitor, computerized double seam scanner, or even a fully automatic double seam inspection system makes the laborious process of double seam inspection faster and much more accurate. Statistically tracking the performance of each head or seaming station of thecan seamerallows for better prediction of can seamer issues, and may be used to plan maintenance when convenient, rather than to simply react after bad or unsafe cans have been produced.
Canning is a way of processing food to extend itsshelf life. The idea is to make food available and edible long after the processing time. A 1997 study found that canned fruits and vegetables are as rich withdietary fiberandvitaminsas the same corresponding fresh or frozen foods, and in some cases the canned products are richer than their fresh or frozen counterparts.The heating process during canning appears to make dietary fiber more soluble, and therefore more readily fermented in the colon into gases and physiologically active byproducts. Canned tomatoes have a higher availablelycopenecontent. Consequently, canned meat and vegetables are often among the list of food items that are stocked during emergencies.
In the beginning of the 19th century the process of canning foods was mainly done by small canneries. These canneries were full of overlooked sanitation problems, such as poor hygiene and unsanitary work environments. Since the refrigerator did not exist and industrial canning standards were not set in place it was very common for contaminated cans to slip onto the grocery store shelves.
According toThe Fruits of Empire: Art, Food and the Politics of Race in the Age of American Expansionby Shana Klein, "Workers also suffered injuries, specifically bruised knuckles and open sores, from trimming and packaging pineapples. Gloves were one preventative measure to protect a canner's hands from the acidity of the pineapple, but gloves did not always help."
In canning toxicology,migrationis the movement of substances from the can itself into the contents.Potential toxic substances that can migrate are lead, causinglead poisoning, orbisphenol A(BPA), a potentialendocrine disruptorthat is an ingredient in the epoxy commonly used to coat the inner surface of cans. Some cans are manufactured with a BPA-free enamel lining produced from plant oils and resins.In February 2018, the Can Manufacturers Institute, a  trade association in the United States, surveyed the industry and reported that at least 90% of food cans no longer contained BPA.
Salt(sodium chloride), dissolved in water, is used in the canning process, which helps prevent spoilage and can improve sensory characteristics.As a result, canned food can be a major source of dietary salt.Too much salt increases the risk of health problems, includinghigh blood pressure. Therefore, health authorities have recommended limitations of dietary sodium.Many canned products are available in low-salt and no-salt alternatives.
Rinsing thoroughly after opening may reduce the amount of salt in canned vegetables, since much of the salt content is thought to be in the liquid, rather than the food itself.
Foodbornebotulismresults from contaminated foodstuffs in whichC. botulinumspores have been allowed to germinate and produce botulism toxin,and this typically occurs in canned non-acidic food substances that have not received a strong enough thermal heat treatment.C. botulinumprefers low oxygen environments and is a poor competitor to other bacteria, but its spores are resistant to thermal treatments. When a canned food is sterilized insufficiently, most other bacteria besides theC. botulinumspores are killed, and the spores can germinate and produce botulism toxin.Botulism is a rare but seriousparalyticillness, leading to paralysis that typically starts with the muscles of the face and then spreads towards the limbs.The botulinum toxin is extremely dangerous because it cannot be detected by sight or smell, and ingestion of even a small amount of the toxin can be deadly.In severe forms, it leads to paralysis of the breathing muscles and causesrespiratory failure. In view of this life-threatening complication, all suspected cases of botulism are treated asmedical emergencies, andpublic healthofficials are usually involved to prevent further cases from the same source.
Canned goods and canning supplies sell particularly well in times of recession due to the tendency of financially stressed individuals to engage incocooning, a term used by retail analysts to describe the phenomenon in which people choose to stay at home instead of adding expenditures to their budget by dining out and socializing outside the home.. Also, some people may becomepreppersand proceed to stockpile canned food.Adoomerwould also be interested in stockpiling canned food upon learning about a recession.
In February 2009 during a recession, the United States saw an 11.5% rise in sales of canning-related items.
Some communities in the US have county canning centers which are available for teaching canning, or shared community kitchens which can be rented for canning one's own foods.