Why Conducting Thermal Validations Test Is So Important In Retorts?
It is described why temperature distribution is important for retort in the reference materials FDA Guide to Inspections of Low Acid Canned Food 22
“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.”
“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.”
In some foreign countries, the food/beverage manufacturers put the new intalled retorts into operation without performing any thermal validations on the retorts, which will have potential risk for the canned food/beverages and is dangerous for the consumers health due to inadequate heat processing.
Retorts must be conducted and operated in such a manner that the finished product will be commercially sterile. Operating procedures, developed by a processing authority or the equipment manufacturer, are established to ensure that the temperatures within the retort are uniform every time the retort is operated.
The purpose of temperature distribution test is to find the area within the retort chamber that has the minimum (coldest) temperature during the normal cycle. Anything that is placed in this area will be the last to reach the sterilizing temperature. This “cold spot” area will be where future heat penetration tests should be undertaken in the retort.
How to carry out the temperature distribution test in retorts?
The temperature distribution test is carried out by placing a number of thermocouples or wireless loggers into the empty chamber of the retort. The temperatures within the different areas of the chamber are measured during the cycle. The area of the lowest temperature reading is defined and documented as the “cold spot” for future testing purposes.
The retort(s) selected should represent the one(s) identified as having the greatest potential for diminished delivery of the scheduled process. Factors that may help identify the test retort(s) include: retort position (at the beginning or end of a line of retorts), container configuration, divider style, and partial loads. It is often necessary to validate every retort in the production area.
The objectives of conducting temperature distribution tests include:
to develop or validate a venting schedule,
to locate cold or slow heating zones in preparation for heat-penetration studies,
in the case of new installations, and
for any changes to an installation which may influence the temperature distribution in the product zone. 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.).
Heat Penetration Test
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.
The study must be designed to adequately and accurately examine all critical factors associated with the product, package and process which affect heating rates.
Before commencing a heat penetration study, where applicable, an evaluation of retort temperature distribution and heat transfer distribution 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.
In the context of this blog, thermal validation is assumed to mean temperature distribution and heat penetration test.
The determination of heating data (time/temperature) should be conducted on a product which simulates commercial preparation. The data obtained from thermal resistance and heat penetration tests are used to calculate a process.
Standard operating procedures for thermal processing systems must be designed to ensure that uniform temperature distribution exists in retorts during operation. Temperature distribution studies are conducted to provide data to support the operating procedures.
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Guidelines for Conducting Thermal Processing Studies (2014), Institute for Thermal Processing Specialists
Guide to Inspections of Low Acid Canned Food 22