Determination of parameters and pretreatment solution for grape drying

The drying of Iranian seedless white grapes (sultana) was investigated in a batch operation in a laboratory dryer. The effect of pretreatment and temp erature on the drying rate of grapes at constant air velocity were studied. Pretreatment solutions contained different alkaline materials in different concentrations and temperatures. Dipping grapes in an alkaline solution in creased the drying rate substantially. Increasing the air temperature in th e dryer from 60 to 70 degreesC accelerated the drying rate (for a decrease in drying time) of the pretreated grape. Grapes dried in 450-900 min depend ing on pretreatment and air temperature. The shorter drying time and best q uality dried product were obtained with grapes dipped in a solution of pota ssium carbonate of 5% at 42 degreesC. The mean apparent diffusivity of mois ture for K2CO3 pretreatment was calculated at 50, 60, and 70 degreesC, and the values were fitted to an Arrhenius type model. Moisture sorption isothe rms of currants were determined at 20, 30, and 40 degreesC using static gra vimetric methods. A modified Halsay equation was used to predict experiment al data for water activity in a range of 0.1-0.85.