Mass transfer in food and bioprocesses

Abstract

As well as the movement of heat, many processing operations involve mass transfer; this can be the extraction of a product, such as apple juice from apples, or the supply of a material such as the oxygen required by a bacterial fermentation. The principles of mass transfer are similar to those of heat transfer; however, the process is more complicated. This is for a number of reasons, not least because the range of species which may be transferred is much larger. The concept of equilibrium is also more difficult in mass transfer than in heat transfer; whilst for two bodies to be in thermal equilibrium they have to be the same temperature, two phases may be in equilibrium in mass transfer terms even if the concentration of the species transferring is different in both. Before the processes of mass transfer can be described, therefore, it is necessary to discuss the idea of equilibrium between phases, expressed by such ideas as the partition coefficient or the equilibrium constant.