Mass transfer plays a very important role in basic unit operations of food processing, such as drying, extraction, distillation, and absorption. In these physical operations, the resistance to mass transfer is usually the rate-limiting factor, although heat transfer and fluid flow may also be involved. Evaporation of water in concentration processes of liquid foods is normally controlled by heat transfer. However, the stripping of volatile components from liquid foods may depend mainly on mass transfer within the liquid phase or at the liquid/vapor interphase.