USDA 

 

 

1

THERMAL PROCESSING 

TRAINING 

Module 6. Principles of Thermal 

Processing 

Thermal Processing for Meat and Poultry 

Products Training 

1

1
 

 

 

 

THERMAL PROCESSING 

TRAINING 

Purpose and Objectives 

 Purpose of Module 7 

• Provide concepts used to establish thermal 

processes 

 Performance Objective 

• Identify the techniques involved in the 

establishment of a thermal process 

• Identify the major factors affecting thermal 

processes 

2 
3

THERMAL PROCESSING 

TRAINING 

Key Factor Affecting the Sterilization 

of Canned Products: Temperature 

 Temperature is easily regulated 

 Effects are dependent on magnitude and 

exposure time 

13 
 

 

 

4

THERMAL PROCESSING 

TRAINING 

Question that Must be Answered for 

Process Schedule Development 

 What time and temperature (heat treatment) is 

needed to destroy the pathogens and 

spoilage organisms of concern? 

• Note that spoilage organisms are normally 

more resistant 

14 
 

 

 

5

THERMAL PROCESSING 

TRAINING 

Basis for Developing Process 

Schedules 

 Processing authority has extensive knowledge of 

• Food microbiology-heat resistance of contaminating 

and/or target microorganisms, 

• The characteristics of the product and how it heats, 

 Heat penetration for retorted product 

 Flow characteristics for aseptic processed product 

• The container in which the product is packed, and 

• The thermal processing systems used to heat the 

food containers 

15 
 

 

 

6

Basis for Developing Process 

Schedules 

THERMAL PROCESSING 

TRAINING 

 The processing authority must have the ability 

to communicate with the processor to gather 

as much information about the overall process 

and product preparation as possible. 

16 
 

 

 

 

7

THERMAL PROCESSING 

TRAINING 

Basis for Developing Process 

Schedules 

 The processing authority must have the ability 

to recognize the limitations of the processor 

and/or the processing system. 

• e.g., can the processor properly measure and 

control critical factors 

• A critical factor is a characteristic, condition or 

aspect of the product, container, preparation 

procedure or processing system that affects the 

process schedule 

17 
 

 

8

THERMAL PROCESSING 

TRAINING 

What is a Process Schedule? 

 The thermal (heat) process selected by the 

processor required under the conditions of a 

manufacturer for a given product to achieve 

commercial sterility 

18 
 

 

 

 

9

THERMAL PROCESSING 

TRAINING 

Process Schedule Components 

 Thermal processing parameters such as 

• Initial temperature (IT) of product 

• Process time 

• Process temperature 

 Critical factors (as needed) 

• e.g., minimum headspace and maximum thickness 

(consistency) for agitating processes 

• Maximum pH for acidified products 

19 
 

 

THERMAL PROCESSING 

TRAINING 

Process Schedule Components (2) 

 The product type and style 

• e.g., chili with beans, chili without beans 

 The container type and size, and 

• e.g., 300 X 407 can, or 145mm X 200mm X 19mm 

pouch 

 The thermal processing system 

• e.g., aseptic, continuous rotary retort , or water 

spray retort 

10 
 

 

 

THERMAL PROCESSING 

TRAINING 

Importance of Process Schedule 

 An established process schedule is specific to 

that product, preparation, thermal processing 

system, and container 

 Process schedules and MUST NOT BE 

ALTERED without consulting a processing 

authority 

11 
THERMAL PROCESSING 

TRAINING 

PROCESS SCHEDULE 

DEVELOPMENT 

12 
I 

l 

1, 

Process Schedule Development: 

Heat Resistance of Microorganisms 

THERMAL PROCESSING 

TRAINING 

HEAT RESISTANCE OF PRODUCT HEATING DATA MICROORGANISMS 

CALCULATED PROCESS SCHEDULE 

CONFIRMATION BY INOCULATED TEST PACK 

Source: FDA STATE TRAINING BRANCH COURSE MANUAL FOR LOW ACID CANNED FOODS, 1988 

13 
Target Microorganisms 

THERMAL PROCESSING 

TRAINING 

 LACF 

• Clostridium botulinum 

• C. sporogenes (PA 3679) 

 Acidified LACF 

• Vegetative cells of 

pathogens and acid tolerant 

non-pathogenic spores 

• Acidity (pH) controls any 

surviving spore germination 

14 
 

 

 

THERMAL PROCESSING 

TRAINING 

Heat Resistance of Microorganisms 

 Factors affecting heat resistance of the target 

microorganisms: 

• Growth characteristics of the target organism 

• The media (food product) in which the 

organism grows 

• The conditions under which the organism 

grows, and 

• The age of the organism 

15 
 

 

 

 

THERMAL PROCESSING 

TRAINING 

Determining the Heat Resistance of 

Microorganisms 

 Thermal Death Time (TDT) studies 

• Inoculate small amounts of substrate (phosphate 

buffer or food product) with a known number of 

bacteria 

• Heat buffer or food in containers at the same 

temperature for several time periods 

• Containers are incubated and observed for spoilage 

or opened and subcultured for direct survivor count 

• Repeat using different temperatures 

16 
THERMAL PROCESSING 

TRAINING 

TDT Study Instruments and Equipment 

 Three-neck flask 

 Thermal death time (TDT) tube 

 Mini Retorts 

17 
TDT Study Instruments and Equipment 

THERMAL PROCESSING 

TRAINING 

Thermal death 

Three-neck flask time (TDT) tube 

Mini Retorts 

TDT can 

06/28/081 
 

 

 

 

 

 

 

THERMAL PROCESSING 

TRAINING 

Microbiological Parameters 

Determined from the TDT Study 

 3 microbiological parameters are obtained 

from the TDT study: 

• D value 

• z value, and 

• F value 

The D, z and F values are used to define the heat 

resistance of a microorganism and indicate how much 

effect a thermal process will have on a population of 

that microorganism 

19 
 

 

 

 

 

20

THERMAL PROCESSING 

TRAINING 

D-value 

(Decimal Reduction Value) 

 D value refers to the time, at a constant 

temperature, required to kill 90% of the 

organisms present 

 This is the same as a one log reduction in the 

organism’s population 

 Expressed as D240°F = 4.5 minutes (when it 

takes 4.5 minutes to reduce the population 1 

log10 at 240°F) 

120 
lJ t 

lJ t 

lJ t 

lJ t 

21

THERMAL PROCESSING 

TRAINING 

Example of Log10 - Decimal 

Reduction 

Known # of Organisms = 10,000 104 

1 min 

-90%: 10,000-9,000 = 1,000 103 

2 min 

-90%: 1,000-900 = 100 102 

3 min 

-90%: 100-90 = 10 101 

4 min 

121 -90%: 10-9 = 1 100 
 

 

 

22

THERMAL PROCESSING 

TRAINING 

“Minimum Health” Thermal 

Processes for LACF 

 Based on the destruction of C. botulinum 

spores 

 A 12D (12 log reductions or 10-12) destruction 

for spores of C. botulinum is the industry 

standard 

122 
 

 

 

 

23

THERMAL PROCESSING 

TRAINING 

“Minimum Health” (12D) Process 

Example 

 The typical D250°F for C. botulinum spore 

destruction in most foods is ~0.23 minutes 

 Therefore, a 12D destruction would be ~2.76 

(12 x 0.23) minutes at 250°F 

 To protect public health, a thermal process 

must provide a lethality (lethal rate) equivalent 

to 3 minutes (2.76 rounded up) at 250°F 

123 
 

 

 

24

THERMAL PROCESSING 

TRAINING 

“Commercial Sterility” Thermal 

Processes for LACF 

 Based on the destruction of C. sporogenes or 

PA 3679 spores 

 A 5D (5 log reductions or 10-5) destruction for 

spores of PA3679 is the industry standard 

124 
 

 

 

 

25

THERMAL PROCESSING 

TRAINING 

“Commercial Sterility” (5D) Process 

Example 

 A typical D250°F for PA 3679 spore destruction 

in most foods is ~1.2 minutes 

 Therefore, a 5D destruction would be ~6.0 (5 

x 1.2) minutes at 250°F 

 To achieve commercial sterility in most foods, 

a thermal process must provide a lethality 

(lethal rate) equivalent to 6 minutes at 250°F 

125 
 

 

 

26

THERMAL PROCESSING 

TRAINING 

Comparison of D Values 

 Since PA 3679 spores are 5 times more heat 

resistance than C. botulinum spores (D250°F = 

1.2 min. vs 0.23 min.), a 5D process for PA 

3679 applied to most foods typically destroys 

26 logs of C. botulinum spores 

• 6 minute required lethality at 250°F ÷ .23 minute D 

value at 250°F = 26 logs 

126 
 

 

 

 

 

27

THERMAL PROCESSING 

TRAINING 

Z value 

 The change in temperature that changes the 

D value by a factor of 10 or organism’s heat 

resistance by a factor of 10 

 It measures the effect of temperature on the 

D value, i.e., the change in the death rate 

based on temperature 

127 
 

 

 

 

 

28

THERMAL PROCESSING 

TRAINING 

F Value 

 The number of minutes at a given temperature 

necessary to destroy a given number of 

microorganisms 

 The F value is the D value times the number of 

required log reductions of the target 

microorganism, e.g., C. sporogenes 

• D250°F = 1.2 minutes x 5 (5D process or 5 log 

reductions) = 6 minutes 

128 
29

Process Establishment: Product Heating Data 

THERMAL PROCESSING 

TRAINING 

HEAT RESISTANCE OF 

MICROORGANISMS PRODUCT HEATING DATA 

CALCULATED PROCESS SCHEDULE 

CONFIRMATION BY INOCULATED TEST PACK 

Source: FDA STATE TRAINING BRANCH COURSE MANUAL FOR LOW ACID CANNED FOODS, 1988 

129 


 

 

 

 

 

 

 

30

THERMAL PROCESSING 

TRAINING 

Product Heating Data 

HEAT PENETRATION TESTS 

 Monitor the rate of change in temperature of 

the food inside the container as it is being 

heated in a specific retort system 

 Temperature sensor or thermocouple located 

in the product at the slowest heating region 

(cold spot) of the container 

 Use heat penetration data to “mathematically 

define” the heating rate 

130 
 

 

 

31

THERMAL PROCESSING 

TRAINING 

Heat Penetration Tests (2) 

 Slowest heating region or container cold spot 

depends on the: 

• Type of product, 

• Container type and size, 

• Thermal processing method/system, and 

• Heat transfer mechanism 

131 
 

 

 

 

 

32

THERMAL PROCESSING 

TRAINING 

Heat Penetration Tests (3) 

 The number of containers per test run and the 

number of test runs necessary to ensure the 

data is adequate depends on the variability of 

the product and the retorting system 

 The more variable the product and/or system, 

the more test runs and containers per test run 

are required 

132 
 

 

 

 

33

THERMAL PROCESSING 

TRAINING 

Heat Penetration Tests (4) 

 Important to simulate the worst case scenario 

likely to occur when producing the product 

 Need to account for the affect of production 

variations which are usually critical factors 

• Changing the type and amount starch or protein in 

the formulation 

• Filling the product differently 

• Improperly soaking/rehydrating ingredients 

133 
 

 

34

THERMAL PROCESSING 

TRAINING 

Heat Penetration Tests (5) 

Potential Critical Factors 

 Raw or cooked meat 

 Moisture content 

 Clumping of product 

 Particle size and style 

 Solids to liquid ratio 

 Fill weight 

 Consistency/viscosity 

134 

 Can orientation 

 Product orientation 

 Fresh or frozen 

ingredients 

 Formulation ingredients

and preparation 

procedures 

 Hold time prior to 

conduction heat 

penetration testing 
 

35

THERMAL PROCESSING 

TRAINING 

Heat Penetration Tests (6) 

Container Fill Weight 

Beans in Brine 

300 X 407 Can 

Fill Weight (oz) Process Time (min) 

7.8 41 

9.2 66 

135 
 

 

36

Heat Penetration Tests (7) 

THERMAL PROCESSING 

TRAINING 

 Heat penetration tests should be conducted on both 

product orientations and use the data from the 

slowest heating orientation 

136 
 

 

37

Heat Penetration Tests (8) 

THERMAL PROCESSING 

TRAINING 

 Heat penetration tests should determine if the nesting

of the containers affects how the container heats 

137 
 

38

Heat Penetration Tests (9) 

THERMAL PROCESSING 

TRAINING 

 Heat penetration tests should be conducted on 

different can orientations and use the data from the 

slowest heating orientation 

138 
39

Heat Transfer Mechanisms 

THERMAL PROCESSING 

TRAINING 

 Convection 

 Conduction 

 Convection/conduction 

 Induced convection 

139 
 

 

 

 

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THERMAL PROCESSING 

TRAINING 

Conduction Heating 

 Particle to particle heat transfer with no particle 

movement 

 Product is typically viscous with little free liquid 

 Container’s geometric center is slowest heating 

region 

 Examples- refried beans, pumpkin, stews, 

corned beef hash, etc 

 Simple heating or straight line 

140 
41 

THERMAL PROCESSING 

TRAINING 

Conduction Heating (2) 

Cold spot would be COLD 

1 41 in center of container SPOT
 

 

 

 

 

 

 

42

THERMAL PROCESSING 

TRAINING 

Convection Heating 

 Particle to particle heat transfer with particle 

movement 

 Product typically less viscous with free liquid 

 Slowest heating region is usually 1/4 container 

height from bottom but can vary 

 Examples- broths, brine packed products, 

(olives, green beans, carrots, etc) 

 Simple heating or straight line 

142 
COLD SPOT 

WOULD BE

EXPECTED IN

BOTTOM ONE

THIRD OF

CONTAINER

,_;;,·. 

f'f.o/ 

r.!l 

.ii i"M"" 

---;;*1 ,Y 

* 

~-~ ;f.,;.,,i;,=·,~,-;:;..;.. 

 

Convection Heating (2) 

431 

COLD 

SPOT 

THERMAL PROCESSING 

TRAINING 
+ 

I 

 44

Convection Heating (3) 

THERMAL PROCESSING 

TRAINING Semilog Plot of Time Temperature Data for Convection Heating 

Product in 300x407 can 

0.00 

1.00 

2.00 

3.00 

0 3 6 9 12 

Time 

log(RT-can temperature) 

144 

Source: Center for Food and Pharmaceutical Process Safety 
 

 

 

45

THERMAL PROCESSING 

TRAINING 

Convection/Conduction Heating 

 Brine pack product with large particles and 

liquid 

• Liquid by convection 

• Particles by conduction 

 Products where thickening occurs 

• Starts as convection heating and goes to conduction 

heating due to thickening of product 

145 
.

 

 

 

 

 

46

THERMAL PROCESSING 

TRAINING 

Convection/Conduction Heating (2) 

 Slowest heating region-is usually 1/4 container 

height from the bottom and at particle center 

but can be variable 

 Examples: meatballs in sauce, hot dogs in 

brine, whole chicken in a can, stews with 

starch, etc 

 Broken line heating or 2 straight lines 

146 
THERMAL PROCESSING 

TRAINING 

Induced Convection Heating 

 Mechanical agitation 

which creates 

product movement to 

enhance convection 

heating of the 

product 

 Container’s 

geometric center is 

slowest heating 

region 

147 

AGITATION 

ROTATION-REEL 

5 RPM 

0 

 

 

 

 

 

47
48

Molded Thermocouple 

THERMAL PROCESSING 

TRAINING 

148 
 

49

Flexible Thermocouple: Can be 

Inserted into the Product 

THERMAL PROCESSING 

TRAINING 

149 
50

Thermocouples Installed in Cans 

THERMAL PROCESSING 

TRAINING 

150 
51

Thermocouples Installed in Jar Caps 

THERMAL PROCESSING 

TRAINING 

151 
Side 

View 

Top 

View 

Spring Insertion Technique 

!:-1- >>""" ___ _..._ _ _._._ __________ ~--Plates 

Spacer Drilled 

for Various 

TC Positions 

Spacers 

 

 

 

 

52

Thermocouple Location and Mounting 

THERMAL PROCESSING 

TRAINING 

 Must be located in 

the slowest heating 

region (cold spot) 

of the product 

 Mounting must 

place and maintain 

thermocouple at 

the desired location 

152 
 

 

53

Thermocouple Location and Mounting (2) 

THERMAL PROCESSING 

TRAINING 

 May need to impale 

particle with thermocouple 

• Formulated particles 

• Non-Formulated particles 

• Vegetable particle 

 Use needle or thin wire 

sensor 

153 
 

 

 

 

 

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THERMAL PROCESSING 

TRAINING 

Food Particle Impalement 

 Formulated particle – 1⁄2-inch or larger 

meatball, ravioli, etc., in the geometric center 

 Meat particle – 1⁄2-inch or larger chicken or beef 

cube in the geometric center 

 Vegetable particle – 1⁄2-inch or larger potato 

chunk, beet dice, whole carrot, etc., a 1⁄4-inch 

below surface 

154 
Ready for the Heat Penetration Test 

THERMAL PROCESSING 

TRAINING 

551 
 

56

A Production or Laboratory Retort Can be Used 

THERMAL PROCESSING 

TRAINING 

156 
 

 

57

Heat Penetration Data Collection 

THERMAL PROCESSING 

TRAINING 

 Heat penetration thermocouples are 

connected to a data logging system or 

multipoint recorder 

157 
weights, etc.)

 

 

58

THERMAL PROCESSING 

TRAINING 

Heat Penetration Test Recordkeeping 

 Product preparation and formulation sheets for 

product formula tested 

 Filled and sealed test product information, e.g., 

fill weights, gross weights, fill temperature, 

particle size 

 Data logger information, e.g., thermocouple 

time and temperature printouts 

 Post heat penetration test information, e.g., 

gross weights, drain weights 

158 
59

Process Establishment: Calculated Process 

THERMAL PROCESSING 

TRAINING 

HEAT RESISTANCE OF 

MICROORGANISMS PRODUCT HEATING DATA 

CALCULATED PROCESS SCHEDULE 

CONFIRMATION BY INOCULATED TEST PACK 

Source: FDA STATE TRAINING BRANCH COURSE MANUAL FOR LOW ACID CANNED FOODS, 1988 

159 
 

 

 

 

60

THERMAL PROCESSING 

TRAINING 

Keys to Calculating a Process Schedule 

 Use the thermal resistance data for the target 

microorganism 

 Use the heat penetration data for the product 

 Use of a scientific method to calculate the 

process schedule for the product 

160 
 

 

 

61

THERMAL PROCESSING 

TRAINING 

Purpose of Process Schedule Calculation 

 The purpose of a process schedule 

calculation is to: 

• Demonstrate (document) that the thermal process is 

capable of delivering the required lethality 

(destruction of the microorganism or Fo) 

• Determine how changes in the product formula, 

preparation parameters, or filling affects the lethal 

treatment 

• Measure the effect of a processing deviation 

161 
 

 

 

 

62

THERMAL PROCESSING 

TRAINING 

Determining Process Schedules 

 There are two scientific methods for 

determining process schedules (thermal 

processes) that will achieve the sterilization 

(Fo) value for a given product 

• The general or graphical method, and 

• The formula method 

162 
 

 

 

 

 

63

THERMAL PROCESSING 

TRAINING 

General Method 

 Lethality (Fo ) is calculated directly from the HP 

time and temperature data using a z value of 

18°F and the reference temperature of 250°F 

 Lethality (Fo ) = lethal rate X time 

 Lethality (Fo ) is determined at small time 

increments and added up over the duration of 

thermal process and if desired during the 

cooling period 

163 
64

THERMAL PROCESSING 

TRAINING 

General Method (3) 

Temperature °F Lethal Rate 

212 .008 

221 .024 

230 .077 

232 .100 

239 .246 

248 .774 

250 1.00 

257 2.45 

260 3.60 

268 10.00 164 
 

 

65

THERMAL PROCESSING 

TRAINING 

General Method (4) 

 Advantages 

• Measures the exact sterilizing value for the process 

• A simple equation is used 

 Disadvantages 

• Specific for process conditions-minimal room for 

error and the process schedule is established for the 

tested conditions (i.e., RT and IT are set) 

• Cannot easy evaluate process schedule deviations 

 Processing deviations may have to be recreated to 

evaluate the thermal process 

165 
 

 

 

 

THERMAL PROCESSING 

TRAINING 

Mathematical Formula Models 

 Numerous mathematical models have been 

developed over the years 

 The model that has received the most use is 

the Ball formula method (1923) 

 With the use of computers, numerical 

methods have also become popular today 

66 
I 

I 

THERMAL PROCESSING 

TRAINING 

Ball Formula Method Steps 

Perform Heat Penetration Test 

Determine Heating Factors 

Perform Calculations 

Verify Fo or 

Determine Process Time 

to Achieve Required Fo 67 
 

 

THERMAL PROCESSING 

TRAINING 

Heating Factors 

 j value 

• a number representing the time lag before the 

heating curve assumes a straight line 

 fhvalue 

• the slope of first straight line 

 length of time the straight line takes to pass 

through one log cycle 

68 
curve.

 

 

THERMAL PROCESSING 

TRAINING 

Heating Factors (2) 

 f2 value 

• the slope of second straight line 

 length of time the straight line takes to pass 

through one log cycle 

 xbh value 

• time at which the break in a broken heating curve 

occurs 

 fc value 

• the slope of cooling curve (rate of product cooling) 

69 
 

70

THERMAL PROCESSING 

TRAINING 

Ball Formula Calculation Requirements 

 Initial temperature (IT) 

 Retort temperature (RT) 

 Heating factors (fh, jh, xbh, f2, fC) 

 Cooling water temperature 

 Required sterilization (Fo) value for the 

product or process time (Bb) 

170 
 

 

71

THERMAL PROCESSING 

TRAINING 

Formula Methods 

 Advantages 

• Can use different initial temperatures and retort 

temperature to calculate new process times and 

alternate process schedules 

• Can be used to evaluate process time, retort 

temperature and initial temperature deviations 

 Disadvantages 

• Thermal processes are more conservative than 

general method 

171 
72

Process Establishment: Confirmation by 

Inoculated Test Pack 

THERMAL PROCESSING 

TRAINING 

HEAT RESISTANCE OF 

MICROORGANISMS PRODUCT HEATING DATA 

CALCULATED PROCESS SCHEDULE 

CONFIRMATION BY INOCULATED TEST PACK 

Source: FDA STATE TRAINING BRANCH COURSE MANUAL FOR LOW ACID CANNED FOODS, 1988 

172 
 

 

73

THERMAL PROCESSING 

TRAINING 

Inoculated Pack Study 

 Rarely necessary 

 Used to confirm thermal processes 

 Used when other methods cannot be used 

 Inoculate product with microorganisms 

 Determine and quantify microorganism 

survival 

173 


 

74

THERMAL PROCESSING 

TRAINING 

Heat/Temperature Distribution 

HEAT/TEMPERATURE 

DISTRIBUTION TESTS 

For Retort Systems 

174 
 

 

 

 

 

 

75

THERMAL PROCESSING 

TRAINING 

Purpose of Heat/Temperature Distribution Tests 

 HD/TD tests determine temperatures around 

containers in retort systems 

 PAs/equipment manufacturers use HD/TD 

tests to develop retort operating procedures 

• Steam Retorts: HD tests determine the “Venting 

Schedule” 

• Other Systems: HD tests determine a “Defined 

Come Up Profile” 

175 
 

 

76

THERMAL PROCESSING 

TRAINING 

Heat/Temperature Distribution Test Data 

 HD/TD data must be kept on file at the 

establishment and available to IPP 

 Designed to provide uniform HD/TD within the 

retort 

 Accomplished during retort come-up time (CUT) 

176 
 

 

 

77

THERMAL PROCESSING 

TRAINING 

Retort Come Up Time (CUT) 

 Come-up-time is the elapsed time between 

the introduction of the heating medium into a 

closed retort and the start of process timing. 

 For pure steam retorts this will include the 

“venting time” from the venting schedule 

177 
 

78

Retort Come Up Time (CUT) 

THERMAL PROCESSING 

TRAINING 

 Batch operations: 

CUT occurs every 

time a batch is 

processed 

 Continuous 

operations: CUT 

occurs before 

containers enter 

the retort 

178 
 

 

 

79

THERMAL PROCESSING 

TRAINING 

Process Timing 

 Must not start until the retort temperature in 

the process schedule is achieved and 

required retort operating procedures are 

completed 

179 
 

 

 

 

 

80

THERMAL PROCESSING 

TRAINING 

Heat/Temperature Distribution Tests 

 For all retort systems, a large number 

thermocouples or self-contained data loggers 

are located throughout the retort baskets or 

racks filled with containers and the 

temperature is monitored as the retort is 

operated 

180 
 

 

 

81

Heat/Temperature Distribution Tests (2) 

THERMAL PROCESSING 

TRAINING 

 Use copper-constantan thermocouples with 

welded tip protected in some way (e.g. shrink 

wrap) so it does not contact containers or 

stacking equipment surfaces 

Thermoco 

uple of Tip

is

Protected 

181 
 

82

Heat/Temperature Distribution Tests (4) 

THERMAL PROCESSING 

TRAINING 

Thermocouple 

wires (leads) are 

fed into retort 

through steam 

tight gasket. 

182 
 

Heat/Temperature Distribution Tests (5) 

THERMAL PROCESSING 

TRAINING 

Thermocouple 

leads must be 

placed so they are 

not damaged 

during the test 

83 
Heat/Temperature Distribution Tests (6) 

Leads are 

held in 

place to 

ensure 

they do 

not 

contact 

metal. 

THERMAL PROCESSING 

TRAINING 

84 
85

Heat/Temperature Distribution Tests (2) 

THERMAL PROCESSING 

TRAINING 

 HD/TD thermocouples 

are connected to a data 

logging system 

185 
= \ 

l 

I I I 

 

 86

0 2 4 6 8 10 12 14 16 18 

THERMAL PROCESSING 

TRAINING 

Retort Temperature Distribution Data 

270

250 

Temperature 230

210

190

170

150

130 

Vents

Closed Steam Up Process 

Starts 

A

1

2

3

4 

Time in minutes after steam-on 

The time the process starts, 3 leads are at temperatures below 190°. 

It takes several minutes for them to reach operating temperature. 

186 
 

 

 

 

 

87

THERMAL PROCESSING 

TRAINING 

Guidelines for Conducting HD/TD Tests 

 The Institute for Thermal Processing 

Specialists (IFTPS) guidelines for still steam, 

water retorts, etc., are in your reference 

manual 

 National Food Processors Association Bulletin 

26 L 

187 
 

 

 

88

THERMAL PROCESSING 

TRAINING 

Key Points 

 Process establishment considerations: 

• Heat resistance of organism in the product 

• Product heating data in the container being 

used 

 Who establishes the process 

 Definition of commercial sterility 

 What is a scheduled process 

188 
 

 

 

 

89

THERMAL PROCESSING 

TRAINING 

Key Points (2) 

 Critical factors 

 Definition of D-value 

 Definition of Z-value 

 Methods of heat penetration 

• Conduction 

• Convection 

• Combination 

 Definition of F-value 

189 
 

 

 

90

THERMAL PROCESSING 

TRAINING 

Key Points (3) 

 GENERAL METHOD: 

• Lethality of the thermal process is derived 

by summing small increments of time and 

temperature 

• Very accurate 

• Difficult to determine effect of deviations in the 

process 

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THERMAL PROCESSING 

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Key Points (4) 

 FORMULA METHODS: 

• Require heating factors 

• Can be used to calculate deviations in 

processes 

• Can be used to calculate new processes 

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THERMAL PROCESSING 

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Key Points (5) 

 INOCULATED PACKS: 

• Used to confirm calculated processes 

• Can be used to establish process when 

other methods cannot be used 

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Key Points (6) 

 OPERATING PROCEDURES: 

• Need uniform heating medium to deliver the 

thermal process 

• Determined by heat distribution studies 

• Performed in heating medium on exterior of the 

container 

• Used to determine operating procedures for 

thermal processing system (retort) 

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Process Schedules 

 The students should read: 

 9 CFR 431.3 – Thermal Processing 

 9 CFR 431.4 – Critical factors and the application 

of the process schedule 

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Questions? 

THERMAL PROCESSING 

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Questions?