Engineering Aspects of Thermal Processing

The design, operation and choice of sterilizing and pasteurization systems, known as retorts, cookers or autoclaves, for packaged foods depend on a number of factors.

Product characteristics are the first factors to be considered. Acid products with pH less than 4.5 usually require only a mild treatment, and this can be achieved with steam at atmospheric pressure or boiling water. Consequently, the equipment required is much simpler than for low-acid products with greater than pH 4.5. For pasteurization of acid food products, temperatures of the order of 120–130°C are necessary, and pressure vessels will be required to contain the pressure of the steam or maintain the condition of the hot water or other heating medium. In factories that process a wide range of products, pressurized retorts are often used for acidic food products. It is more usual to find atmospheric equipment operating in factories where fruit products are processed in large volumes and where it is possible to have dedicated systems for retorting.