Improving the operation of defrost rooms for ready-to-eat foods

Many ready-to-eat foods are stored frozen in commercial stores and then defrosted before dispatch to the retail outlet. Large variations in defrost time can reduce product throughput and lead to variable product quality. We propose that defrost rooms be considered as several zones of different heat flux with only small variations in heat flux in each zone. A type of food is located in a particular zone according to the difficulty of defrosting it. and the types and quantities of other foods being defrosted at the same time. Defrost times for a range of foods in various zones were predicted for a commercial defrost room of a normal capacity of 70 pallets of foods. In practice the quantity of foods to be defrosted varies daily and the room was operated with 45, 47, 57 or 60 pallets of four food types during the tests rather than the expected 70. The average difference between the defrost time to 0 degreesC predicted for the 70 pallet layout and the times measured with each of the four layouts (45, 47, 57 and 60 pallets) decreased from 36.2%, 34.1%, 24.5% to 14.2%. Despite the large differences between measured and predicted defrost times. the model can be used to predict the variations in heating rate through a store and the relative defrost times of different foods. Consequently the method is useful in deciding on the position that food should placed within a defrost store for assured defrost quality and increased throughput. (C) 2002 Elsevier Science Ltd. All rights reserved.