The freshness of frozen food depends on the cooling rate during freezing. For example, when a cut of fish is cooled down from -1°C to -5°C within 35 minutes, intracellular freezing occurs, and consequently good quality and good taste are maintained. When it takes more than 90 minutes, extracellular freezing occurs, so that the quality is bad. Therefore, it is important to understand the effect of the cooling rate on the cooling and freezing characteristics in the cells in order to control the freshness of food. It is thus necessary to evaluate the processes of flow, temperature and concentration distributions in a single cell, as well as to consider the exchange of heat and mass among cells through the cell membranes.