The food material is exposed to a much low temperature for the removal of sensible heat or respiration heat depending on the types of food, in order to achieve the desired final product temperature during freezing operation. The latent heat of other food components such as fat is also removed before they could solidify. The temperature at which ice formation begins is defined as the “initial freezing point” of the product.

 

The complexity of the freezing process is demonstrated in the characteristic freezing profile which involves the phase change of liquid to solid in a particular food product due to the removal of heat. Generally, the initial freezing point of the majority food products occurs below 0°C which is the beginning point of the ice crystals formation. The solute concentration within the food product continues to increase as the food temperature decreases. When the temperature is sufficiently low for the solute to become supersaturated and crystallize out, the “latent heat of crystallization” is released. This explains for the slight temperature increase in the food upon reaching its initial freezing point. The temperature of food would decrease gradually towards the freezing medium temperature after the crystallization stage of water and solutes found within the food. Figure 1 shows freezing curve using pear as a model to demonstrate the freezing concept in food systems.