Freezing of a parallelepiped food product. Part 1. Experimental determination

Abstract

A number of procedures are used to predict the freezing time of food. The objective of the project reported here was to test the adequacy and applicability of the various mathematical models and methods used to predict the freezing time of a small, parallelepiped food product. The approach was to compare experimental and predicted freezing times. In this paper the experimental methods and results are described; the freezing time and the thermophysical properties of both the frozen and non-frozen food were determined. Comparison between experimental and predicted freezing times will be given in a subsequent paper. The experimental conditions consisted of individually freezing the product in an air blast; the food product was french fries. The time required to lower the temperature of a french fry from 31 to −18°C in the −29°C air blast freezer used was approximately 1200 s. The mean moisture content of the fries was 73.7%. The average densities of the non-frozen and frozen fries were 1069 and 1012 kg m −3, respectively; the average thermal conductivities were 0.50 and 1.0 W m −1 °C −1; and the heat capaciti were 3420 and 1870 J kg −1 °C −1. The overall surface heat transfer coefficient of a parallelepiped object in the air blast freezer used for these experiments was 21.0 W m −2 °C −1. The low surface heat transfer coefficient resulted in a flat temperature profile within the fries.