Thawing of cook-freeze catering packs

Centralised catering facilities using frozen and chilled food in bulk packs require dedicated thawing systems for the frozen supplies. Data on thawing times for foods in such packs are essential for correct design and operation of these systems. The current study initially used computer modelling to identify the fastest and slowest thawing packs from a typical hospital catering range. Estimated heat transfer coefficients and thermophysical properties derived from the manufacturer’s published compositions were used as input data for the model. For the packs identified (chicken Italian and beef curry at nominal thicknesses of 50 mm and 38 mm respectively), experimental thawing (from −20 to 0 °C at centre) and re-cooling (to 3 °C at surface) times were measured.Thermophysical properties of samples of the two recipes were measured and heat transfer coefficients determined for a range of air velocities. These data, and measured rather than nominal pack thicknesses, were used as input to improve the accuracy of the model to an over-prediction of 4.8% for chicken Italian and 5.5% for beef curry compared with the experimental results. The model was then used to produce an extended range of predicted thawing times for varying air temperatures, air velocities and pack thicknesses.