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THERMAL PROCESSING 

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Module 7. Thermal Processing System 

Components, Instrumentation, and 

Equipment, and Process Room 

Operation 

Thermal Processing for Meat and Poultry 

Products Training 

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Temperature Indicating Devices 

 Mercury-in-glass (MIG) thermometer serves 

as the reference instrument for LACF 

 Alternative devices such as thermocouples or 

resistance temperature devices (RTD) or 

digital temperature gauges (DTG) may be 

used 

 Each retort is required to have at least one 

MIG thermometer, DTG, RTD or equivalent 

thermometer or electronic device (PLC) 

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Mercury-In-Glass/Equivalent Thermometer 

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 Easily readable to 1°F 

 MIG range not to exceed 

17°F/inch graduation 

 Installed where easily read 

 Installation location varies 

depending on retort type 

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Temperature Indicating Devices 

 Tested for accuracy when installed and 

annually 

 Defective devices must be repaired or 

replaced 

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Example of Alternative Device (RTD) 

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Sensor of RTD installed on Retort and the Display 

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Temperature Indicating DevicesAcidified Low Acid Canned Foods 

 No specific regulation regarding temperature 

indicating devices 

 Calibration is necessary 

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Checking the Accuracy of Thermometers 

 Need an accurate reference device, e.g., a 

instrument of known accuracy. 

 Need a testing device that provides consistent 

temperature 

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Calibration Tree for MIG Thermometers 

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THERMAL PROCESSING 

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Temperature Indicating Devices 

 The accurate reference device must be 

traceable to a national or international 

standard 

 In the U.S., traceability is provided by the 

National Institute of Standards and 

Technology (NIST) 

 Records of the accuracy checks must be 

maintained 

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Temperature Indicating Devices 

 Records must specify the following 

information: 

• Identification of the device (MIG/DTG/RTD) 

• Manufacturer of the device 

• Identification of the reference device 

• Equipment and procedures used for check 

• Date and test results 

• Name of person or facility performing test 

• Date of next test (optional) 

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Temperature Indicating Devices 

 Each device must have a tag, seal, or other 

means to identify it and correlate it with the 

accuracy check record 

 A record is necessary for documenting the 

accuracy of the reference device 

 For acidified foods, no specific requirements 

on the type of device – should still test for 

accuracy 

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Temperature/Time Recording Devices 

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Low-acid foods: 

 Required for each retort 

 Can be combined with 

the steam controller to 

be a recorder controller 

 Provides a permanent 

record of temperature 

and time for the thermal 

process 

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THERMAL PROCESSING 

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Temperature/Time Recording Devices 

 The temperature/time recorder should agree 

as close as possible with MIG/RTD but never 

higher 

 Accuracy to 1°F 

 Pen arc adjusted properly 

 Time of day set properly 

 Prevent unauthorized changes with a lock or 

notice 

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Chart-Type Recorders 

THERMAL PROCESSING 

TRAINING  Use appropriate chart paper 

 Graduations not to exceed 2°F within a range of 

±10°F of the process temperature 

 Scale not to exceed 55°F/inch within ± 20°F of 

the process temperature 

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Temperature/Time Recording Devices 

 Continuous line or multipoint plotter 

 Installation location of recorder bulb or sensor 

will vary based on the type of thermal 

processing system 

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THERMAL PROCESSING 

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Temperature/Time Recording Devices 

Acidified Low Acid Canned Foods 

 Pasteurizers must be equipped with a 

temperature/time recording device 

 Must be operated to ensure uniform heat 

distribution throughout the processing system 

 Heat distribution data must be kept on file 

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Temperature Control System 

 Each retort must have an automatic steam 

controller 

 Air operated, electrically operated or selfactivated 

 Controller may be combined with recorder to 

form recorder-controller 

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1

PV - Pilot Valve 

D - Diaphragm 

F - Flapper Valve 

N - Nozzle 

R - Reducing Tube 

S - Valve Seats for Pilot 

Valve Plunger 

Pen Arm 

Temperature Bulb 

I 

I 

Fa F, 

Thermal Tube 

R 

l Air Inlet 

Air to 

Controller Valve 

Pneumatic Control System 

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AIR IN I DIAPHRAGM 

VALVE 

Pneumatic Control Valve 

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Electronic Automated Control Systems 

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 Can be programmed to control entire process 

 Consult with processing authority 

 Regulatory review may be necessary 

Momentum by FMC 

ICON by Stock 20 
 

 

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Instrument Air Supply 

Instrument Air Supply Requires: 

 Adequate filter system 

 Clean, dry air at the proper pressure 

 Independent air supply system 

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1

Cl 

Air 

Filter 

Recording 

Controller 

Reducing Valve 

Set for 20 psi 

Use 1/4" 0.0. Copper Tubing 

For Instrument Air Supply Line 

1/2" Minimum 

Main Air Supply 

75-100 

lb per sq in 

A ftercooler W ater 

Filter 

Drain Water 

out 

in 

Drain 

Intake 

filter 

Air Supply 

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Pressure Gauges 

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 Scale should not exceed 2 PSI 

 Useful when processing with overpressure, 

pressure cooling and as safety device 

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Timing Devices 

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 Wristwatches are not 

permitted 

 Use analog or digital 

clock 

 Located where easily 

and accurately read 

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Maintenance 

Instrument and plumbing maintenance is 

essential to proper operation 

The regulations require that each thermal 

processing system be examined at least once a 

year 

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Equipment 

Steam Supply: 

 Steam is the most common heating medium 

 Supply of steam to thermal processing area 

must be adequate to bring the retort up to 

process temperature 

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Glolte 

Gate (Rising stem) 

Valve Types and Uses 

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 Globe valve - better sealing 

 Gate valve - full flow 

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Valve Types and Uses 

 Gate or Ball: Used on vents for rapid 

discharge and are full flow 

 Air and water lines connected to the retort 

must be equipped with a globe valve or other 

suitable valve to prevent leaking into the retort 

 Double block and bleed configurations or 

three-way valves are often installed on water 

or air lines used for cooling 

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OPEN TO 

ATMOSPHERE 

DURING 

OPERATION 

• • 

WATER OR AIR 

' 

RETORT 

CLOSED DURING 

OPERATION 

• I 

CLOSED DURING 

OPERATION 

• • 

Set-up to protect against leaking 

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Bleeders 

Small openings on retorts used for: 

 Circulation of steam 

 Air removal that comes in with the steam 

 Condensate removal 

Required on external wells when the MIG/DTG 

and recorder probes are installed in an external 

well 

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Spreaders 

 Continuation of steam or water lines inside 

retort 

 Perforated pipe to provide uniform distribution 

of steam or water in the retort 

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Mufflers 

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 Used on vents and 

bleeders to reduce 

noise 

 Must not reduce air 

removal or interfere 

with heat distribution 

 Cartridges must be 

inspected and 

replaced as needed 

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THERMAL PROCESSING 

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Pasteurizers for Acidified Low Acid 

Canned Products 

 Use steam or water at atmospheric pressure 

 Generally heater/cooler combination 

 Continuous container handling 

 Need temperature distribution studies to show 

how uniform heat is maintained 

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Process Room Operation 

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Posting of Thermal Processes 

Operating processes 

and procedures must 

be posted in 

conspicuous place or 

be readily available to 

the operator and CSI 

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Prevention of Retort Bypass 

 A system for product traffic control must be 

established to prevent containers from 

bypassing the retort 

 Each crate or at least one container in each 

crate must be marked with a heat sensitive 

indicator 

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Heat-Sensitive Indicators 

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 Paint, tags, tape, or 

ink 

 Color change merely 

indicates heating 

medium contacted 

the container 

 Visual check must be 

performed 

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Other Precautions 

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 Close retort door 

only when ready to 

start the thermal 

process 

 Cans of doubtful 

status must be 

destroyed 

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Coding of Containers 

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 Each container must be coded 

 Codes are embossed or imprinted 

 May be legibly marked on a securely affixed 

container label 

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Coding of Containers 

Code Requirements: 

• Product unless printed on the container 

• Year packed 

• Day packed 

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Coding of Containers 

Importance of Coding: 

• Provides way to isolate and/or retrieve 

questionable product 

• Frequent code changes minimize amount 

of questionable product 

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Initial Temperature (IT) 

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 Temperature of the coldest component in the 

product when thermal process begins 

 Must be determined for coldest container in 

retort 

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Initial Temperature 

The Initial Temperature is a critical 

parameter and is as important to adequacy 

of the heat process as retort temperature 

and process time 

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THERMAL PROCESSING 

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Product Incubation 

FSIS requirements: 

 Temperature indicating device 

 Means of circulating the air inside the incubator 

 Time/temperature recorder 

 1 container per retort load or 1 per 1,000 containers 

 Samples held at 95°F ± 5°F for 10 days (240 hours) 

 Product held until incubation completed 

 May propose alternate plans 

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Questions 

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Questions?

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