Preservation is the main reason but not the only reason for dehydrating foods. Food may be dehydrated for other reasons also viz. to decrease weight and bulk; to retain size and shape of original food; to produce convenience items. Dehydration/ drying is advantageous for being cheaper than the other methods of preservation with less requirement of equipments. Storage of dried food products does not require special facilities like refrigeration etc. Dried food products are simple to store and pack because of their low volume.
Dehydrated foods however, are less popular because of some undesirable changes in colour, taste and flavour during storage and distribution. Dehydration techniques have been improved to overcome most of these defects.
Factors in control of drying: Various factors affecting rate of drying in a fresh produce include the following:
Composition of raw materials: Foods containing high amount of sugar or other solutes dry slowly.
Size, shape and arrangement of stacking of produce: Greater the surface area greater is the rate of drying.
Temperature as well as humidity and velocity of air: Greater is the temperature differential between the product and the drying medium faster the product dries. Lower the humidity of environment the faster the drying will be.
Pressure (atmospheric or under vacuum): Lower the atmospheric pressure the lower the temperature required to evaporate water.
Heat transfer to surface (conductive, convective and radiative): The fastest method of heat transfer is radiation consecutively followed by convection and conduction.
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