Rate of freezing effect on the colour of frozen beef liver

One problem that arises when freezing liver in plate freezers in the whitish colour acquired by the liver surface when subjected to high freezing rates. The purpose of this paper aims to establish optimum operating conditions for freezing beef liver pieces in a minimum time while maintaining an acceptable colour on the surface. Samples were subjected to different freezing rates and minimum surface freezing time was established in order to obtain an acceptable colour. This was quantified in terms of lightness using a surface colorimeter. Histological analysis of the samples showed that the size of the ice crystals formed on the contact surface with the coolant is the factor that determines the changes in colour as a result of diffused light reflection phenomena. On the basis of mathematical heat transfer models with simultaneous change of phase, the minimum characteristic surface freezing time was related to the process operating variables (initial temperature of the liver, coolant temperature, interfacial heat transfer resistance, thickness of the piece), and the optimum freezing conditions were determined, reducing total processing times to a minimum.