Drying of solids involves complex coupling of transient transport phenomena with material science. The objective of any drying operation is not just to remove water (or any liquid) as rapidly as possible but to do so while ensuring that the desired dried product specifications are met. Typically, constraints of quality override the best conditions for heat and mass transfer. More often than not, the physical structure of the dried product is one of the key quality requirements. For food materials, physical structure affects not only the rehydration ability but also the shape, texture, appearance, and strength of the product. The structure is affected by nearly all of the dryer parameters and operating conditions employed for any given material. Thus, the dryer type and operating variables like temperature, humidity, drying medium used, mode of heat transfer, operating pressure, and rate of drying can affect the development of structure and even the shape of the product. It is not possible to make quantitative generalizations about the effect of various parameters on the structure of a given product in a specific dryer type. Some qualitative generalizations can be made for some products. This brief article will attempt to summarize the more commonly known effects for select food materials.
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