Thermal processing using batch or continuous operations is generally used for beer pasteurization, soda processing, low-acid foods, thick or viscous foods, chunky soups, meatballs and other foodstuffs. For example, cans or bottles are filled and sealed and then placed in a pressure vessel (still-cook retort) for the length a time to achieve the required level of microbial kill.

In the past, simplified analyses that only take heat conduction into account have been used to predict the temperature history and lethality of batch sterilization processes. However, the heat transfer taking place inside a can or bottle undergoing sterilization is a complex interaction between heat conduction and convection. Fluent software can be used to more accurately predict the temperature history and lethality or microbial kill in the food product. The kinetics of microbial destruction are computed and thus the efficiency of the sterilization process is estimated. This information can be used to ensure that the required level of sterility is achieved without overcooking which leads to a decrease in food quality.

Continuous food sterilization processes also seek to achieve the desired level of sterility while simultaneously minimizing the loss of product quality. Fluent software is used to simulate continuous flow sterilization for processing at high temperature for short time (HTST). The results show that empirical design methodologies adapted from batch systems can lead to significant overprocessing and unnecessary degradation of product quality.

Fluent software has been successfully used to illustrate complex flow pattern in a beer bottle undergoing the pasteurization process. The beer velocity and temperature distributions are shown on the right. A detailed view of the velocity vectors near the bottle wall are shown on the left.

This example shows the microbial kill or lethality versus time for the slowest heating zone in a can containing a meatball and sauce during sterilization. The curve on the right (dark blue) is the model result when heat conduction only is considered. The curve on the left (pink) shows the result when natural convection is also taken into account. The figure illustrates that the conventional assumption of conduction-only heating significantly overpredicts the amount of time required to reach a certain level of lethality. If the processing time is determined from this curve, it will lead to overcooking and lower product quality.
Courtesy of North Carolina State University