Heat Penetration Testing

Heat penetration testing provides the fundamental information used by the process authority to design thermal processes for terminally heated containers of food products. The data from heat penetration tests are used by the process authority to calculate matrices of optional time-temperature process schedules that will deliver an appropriate sterilizing value (F0) to the food product. The objective of heat penetration testing is to first, determine the zone in the container geometry that is the “cold spot”, i.e. the zone with the slowest heating rate. This is done by doing a set of tests in which thermocouples or other suitable temperature measuring probes are set into zones of the container at varying heights or depths into the product mass or covering liquid. The product is heated either in a test simulator or in the actual commercial scale vessel; and the data is collected and evaluated. If a “cold spot” can be determined with that data set, a confirmatory set of tests is done in which the probes are all placed in the “cold spot” of each test container. Depending on the quality of the data obtained from the confirmatory tests, the investigator might run enough tests to get data from 16-32 containers.

Most food products heat according to one of the two of the physical models, either by conduction or by convection. Some, however, heat convectively during one phase of their cooking cycle, and conductively during another portion. Some heating histories are even more complex.

Heat penetration tests are designed by the process authority to provide very conservative representations of the industrial practices. It is the responsibility of the process authority to carefully define all product-related and process equipment-related critical factors that can affect the safety of the process; and to take into account the innate variability of each unit operation that comprises the manufacture of the product under consideration. The process authority is responsible for defining how the process will be applied and under what specific conditions it will be valid. Heat penetration testing is one of the critical first steps to be taken in process design.