Dehydration I – Tray Drying of ApplesTray Drying Of Apples
Objectives And Learning Outcomes
Describe the drying process for a tray drier and indicate relevant variables that are used to control the process.
Calculate the drying times for different periods of a drying process.
Dehydration is a food unit operation that is used to extend the shelf-life of a foodstuff by reducing its water activity (aw). Drying with hot air using a tray or cabinet drier is one of the methods of food dehydration. Heat transferred to the surface of a foodstuff exposed to hot air, provides the latent heat of vaporization to evaporate moisture from the food surface. Water vapor diffuses through the film of air that is formed at the food surface and is subsequently removed by the circulating air. A region of low vapor pressure thus forms at the food surface, establishing a vapor pressure gradient between the inner humid layer and the outer layer of dry air. This gradient acts as the driving force of the drying process (Geankoplis, 1993, Heldman...
KeywordsFall Rate Period Food Surface Apple Slice Critical Moisture Content Constant Rate Period
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