Mass transfer of food constituents occurs during food processing and may cause changes in food quality in terms of nutritional value, texture, color and taste. The aspects which are important for mass transfer modeling, aiming at estimating the rate at which mass transfer occurs in one or more prevailing directions, are driving force and structure. In this paper the driving force which in the opinion of the author should be a gradient in the chemical potential of the transported component is discussed. The measurability of the property of chemical potential is possible using methods that are briefly presented. The practical implications of using the chemical potential rather than the concentration are discussed.