The densities of food products undergoing baking processes in commercial multi-zone band ovens of a local plant were measured with a volume replacement method along with a photographic procedure. Three kinds of cookies were selected as the sample products. It was found that the densities are closely related to the temperature and moisture conteni of cookies during the baking processes. This relationship is statistically represented by polynomial regression equations. The correlation coefficients were better than 0.970. According to the examination of changes in volume of cookies undergoing baking processes, expansion ratios were found to be 2.0-2.5.

The geometrical configuration of many food products may be approximated with an infinite slab, in so far as their heat transfer characteristics are concerned. Several researchers have utilized formulae for predicting transient state heat conduction in an infinite slab undergoing symmetric heat exchange with surrounding medium.However, in a number of food manufacturing processes, the heat transfer rate through one surface of the slab is not identical to that through another surface. There is a published analytical formula available for estimating transient state heat conduction in an infinite slab subjected to nonsymmetric heat exchange with surrounding medium. However, it is impractical because of mathematical difficulty, to apply directly this analytical formula for estimating the temperature of food subjected to nonsymmetric heating or cooling processes. Therefore, computer programs were developed to simplify this application. The programs are for the estimation of characteristic roots, transient state temperature, f and j values and the location of the thermal center. From computational results obtained by using these programs, we then developed a set of charts to simplify the estimation of food temperatures. Examples for the use of the method are included in this presentation.

A computerized procedure was developed for estimating the critical point correction factor, Cf, of come-up heating in thermal processes, which are applied to cylindrical cans of heat conductive foods. Sterilizing values at the thermal center of the can were used as a criterion for this estimation. Fifteen parameters are required to uniquely determine Cf values. These parameters include z value, thermophysical properties, and can dimensions, as well as operational conditions. Through a dimensional analysis, ten dimensionless parameters were selected to estimate Cf values. A fractional central composite experimental design was applied to evaluate statistically the influence of each parameter on Cf. Through this evaluation, several regression equations were developed for their practical uses. A series of heat conduction experiments were conducted by using several different sizes of cans filled with food simulant, 8% bentonite suspension. Fairly good agreement was found between predicted and observed correction factors.