Explanation of Method of Pressure Control of Retort Equipment used for Heating of Plastic Food Containers

Abstract

To prevent the deformation of pressurized food containers during temperature changes, retort pressure control methods are used to maintain an appropriate pressure within the container gas headspace. The simplest of these, known as the Taguchi method, involves manual control of the retort pressure based on the measured temperature within the container. There is, however, a lack of understanding concerning the applicability of various types of containers and retort methods, and selection of the location of temperature measurement and respective offset values proposed by Taguchi. This study resolved these issues and provides an explanation of them. Three types of plastic cups with different thicknesses of gelatinized starch were used. Temperature within the cups was measured in the central vertical direction during a thermal process in which the cups were heated to 120°C for 30 minutes using a hot-water shower-type retort. The pressure calculated based on the temperature of the air within the cups during the heating process showed better consistency with the measured pressure than that measured at other locations. During the cooling process, the pressure calculated from the temperature within the retort chamber was strongly consistent with the measured pressure. The reason why the chamber temperatures and offset values are used in the Taguchi pressure calculation is attributed to the good heat conductivity of the contained air.