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Commercial sterilization of low-acid food in hermetically sealed containers: retort systems

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1. Introduction

The following provides recommended preventive controls for the thermal processing of commercially sterile low-acid food in hermetically sealed packages (containers) stored at room temperature.

Retorting is the in-container sterilization of food to render it shelf stable at room temperature (commercially sterile).

The safety of thermally processed low-acid food is dependent primarily upon 4 conditions:

  1. The scheduled process is adequate to control Clostridium botulinum for the product and processing system;
  2. The product adheres to the scheduled process parameters and heat is applied to all points in the product for a time and at a temperature sufficient to produce commercial sterility;
  3. Container filling adheres to the scheduled process parameters, and container sealing prevents microorganisms from entering and contaminating the sterilized product; and
  4. Post-process handling procedures protect the finished closures from contamination or damage – which can lead to leakage or re-contamination – through to distribution to the consumer.

2. Record keeping

In a Preventive Control Plan (PCP), it is important to maintain and keep records of activities which demonstrate that the PCP is implemented and working effectively. Records can be in either a hard copy or electronic format. Refer to Record keeping for your preventive control plan for guidance on how to ensure the integrity of recorded processing data, including data captured via electronic recording systems.

3. Process design

Temperature distribution

A temperature distribution test identifies the location of the slowest heating point (the "cold spot") in the retort. This "cold spot" is taken into consideration when conducting subsequent heat penetration studies to establish the scheduled process.

Scheduled process

A scheduled process is determined using heat penetration studies or other equivalent scientific methods by persons having scientific knowledge and expertise (competency) in thermal processing, for example, a process authorityFootnote 1. These tests are carried out using the most adverse conditions that could occur during normal production.

Thermal process design records

4. Thermal processing equipment

Refer to the following documents for more information on thermal processing equipment specifications:

5. Incoming material control

The ability of a thermal process to reduce the microbial load to an acceptable level is influenced by the number of bacteria present in the product before heat treatment begins.

Commonly used containers include rigid containers such as cans and glass jars, and semi-rigid or flexible containers such as pouches and cartons. A container must be able to withstand the thermal process and maintain its hermetic seal for the shelf life of the product.

6. Empty container control

Empty container handling

Container cleaning

Empty container records

7. Product preparation and blending control

Critical factor control

Product preparation and blending records

8. Filling control

Filling of containers

Filling records

Filled unsealed container handling

Extraneous material contamination control

9. Container closure control

Container closure

Metal can seaming

Glass capping

Pouch sealing

Vacuum-packed foods

Visual and destructive examinations

These examinations should be performed only by individuals that are competent in identifying container defects.

Refer to the container and/or sealing equipment manufacturer's instructions for closure specifications and guidance on how to conduct these evaluations. Other resources include the CFIA's Metal can defects manual and the Flexible retort pouch defects manual, as well as section 7.4.8 of the Codex Code of hygienic practice for low-acid and acidified low-acid canned foods (CAC/RCP 23-1979) (PDF - 1,158 kb).

Container closure control records

10. Pre-thermal process control

Sealed container handling

Maximum time lapse

Retort loading

Traffic control and process indicators

11. Process control

Retort systems should only be operated by, or under the continuous supervision of, an individual competent in thermal processing.

Initial temperature

Operating procedures

Vent control

Process time control

Process temperature control

Thermal process control records

12. Post-process control

Cooling controls

Cooling water control

Cooling water records

Container handling and drying

Post-process container integrity verification

Post-process container integrity records

13. Incubation

Incubation testing

Incubation testing is the holding of samples of hermetically sealed, processed foods at a specified temperature for a specified period of time, before examination for signs of spoilage. It is useful when establishing a scheduled process (validation), to help diagnose spoilage issues and for verification purposes.

Incubation testing records

14. Deviations and corrective actions

Deviation control

Corrective action

Deviation and corrective action records

15. Verification of product safety

16. References

CFIA references

Other references

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