The three-dimensional transient heat transfer phenomenon occurring in a rectangular brick-shaped frozen food when subjected to diverse functional forms of variation in the storage temperature is solved by computer simulation in order to analyse the behaviour of the thermal centre in comparison with that of the geometric centre, characterisation being made through the evolution of two dimensionless parameters: the initial time when separation appears and the maximum temperature difference between both centres. Also, influences of product thermal properties (heat capacity and thermal conductivity) and convection due surface heat transfer coefficient are studied.