Chapter 18 - Thermal processes, methods and equipment

Abstract

This chapter focuses on the thermal processes and methods in which the food is heated and cooled while contained in hermetically closed packages. The hermetic package protects the sterilized or pasteurized food from recontamination. The method is suitable for foods in all physical forms: solids, liquids or liquids with solid particles. The packages can be cans, jars, bottles, trays, tubes, pouches, etc. In the case of pumpable products (liquids, semiliquids, purees, suspensions of relatively small solid particles in liquids), it is possible to apply part or all the thermal treatment process continuously, in heat exchangers, before filling the product into containers. Additionally, bulk heating–hot filling–sealing–cooling in container is the standard method for canning high-acid pumpable products such as fruit juices and purees. The material is heated to pasteurization in continuous heat exchangers and then hot-filled and sealed. The filled containers are cooled by water, usually by spraying. In the case of metal cans, cooling may be accelerated by spinning the container around its axis. The main disadvantage of the method is the relatively long cooling time, resulting in over-cooking of the product and requiring long cooling lines.