Optimizing combined cryogenic and conventional freezing with respect to mass loss and energy criteria.

The objectives of this work were to evaluate the advantages brought by using cryogenic freezing in comparison to blast air freezing with respect to weight losses and freezing times during food freezing. A mathematical model was then developed to predict the freezing time and the weight loss of food during freezing in very low ambient temperature. The model, first validated with experimental results, was then used to study the combination of cryogenic freezing and conventional freezing on different products such as meat and bread. The influence of the time spent in a cryogenic freezer to the freezing time, the mass loss and the energy consumption was especially evaluated. Results have shown that the behaviour of the product strongly depends on its thermophysical properties and its geometry/size and that there seems to be a linear relationship between the time spent in the cryogenic freezer, the freezing time and the energy consumptions.