MECHANISMS OF DRYING OF SKIN-FORMING MATERIALS - THE SIGNIFICANCE OF SKIN FORMATION AND A COMPARISON BETWEEN 3 TYPES OF MATERIAL

Comparisons are drawn between the drying characteristics, and the mech anisms of skin formation on, three characteristic types of material. T he significance of skin formation, which may be a major factor in vola tiles retention in the drying of spray dried products, is discussed. T he optimum drying conditions to achieve the highest volatiles retentio n for each type of skin-forming material are predicted. General compar isons are also drawn between the drying of skin-forming i.e., material s which form a smooth flexible low porosity skin at some stage, and no rmal crust-forming materials. The latter form only a rigid crust with a porosity which is system and drying-condition dependent.