ABSTRACT

684In the area of food engineering, mass transfer phenomena play679 an important role in many applications, including (1) water (liquid or vapor) in products and air in drying or similar operations, such as osmotic dehydration; (2) aroma components in products during drying and storage; (3) extraction/coagulation (sugar, tea, coffee); (4) salt in products (meat, cheese); and (5) gas and liquid permeation through packaging materials and membranes. The transfer of water is the dominant phenomenon, and most of this chapter is concerned with this and related problems. The terms “mass transfer” and “diffusion” are sometimes used without distinction. This is not correct. Mass transfer may take place in several modes, only one of which is diffusion. These different transfer modes are sometimes treated in the same way as diffusion mathematically (Fick’s law), despite the fact that this is not correct from a phenomenological point of view. In such cases, the corresponding coefficient is called the apparent or effective diffusion coefficient. Distillation is rare in the food industry and is not covered in this chapter.