A combination microwave/vacuum drying system (MIVAC) was used during 1987 to produce puffed dried grapes and other fruits in order to evaluate product quality and MIVAC system performance characteristics. The vacuum reduces the temperature necessary to dry the fruit and minimizes oxidation of the product. The microwave energy provides optimum heating to dry the product. The dried fruit product maintains the characteristics of fresh fruit with respect to color, flavor, and appearance using no chemical treatments for preservation. To improve the throughput and drying efficiency of the MIVAC unit, an oxygen-restricted convection dryer and a liquid medium drying system were tested. During the project, effect of fruit type and composition was evaluated to determine unit performance characteristics. Dried product was analyzed for nutritional value and storage stability. The system was evaluated for technical feasibility and possibility of commercialization.
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