Influence of temperature, air velocity and pretreatments on drying of black currant grape

Drying is one of the most important steps in raisin processing. During this step, initial moisture content is decreased up to 15 – 17 percent (d.b) for suitable storage. Achieving optimum drying conditions can affect the processing time and improvement of raisin quality. Temperature, air velocity and pretreatment are important factors in grape drying process and its quality. In this research, effect of the following conditions on time and drying rate of Black currant grape was studied: temperature at four levels of 50,60,70, and 80 ºC, air velocity at three levels of 1, 2 and 3 m/s, and four pretreatments including hot water, %5 potassium carbonate, %0.4 olive oil, %0.5 sodium hydracids and no pretreatment. Diffusivity and activation energy of all treatments were determined. The results show that factors such as temperature, air velocity and pretreatment have significant effects on drying time and average drying rate. Pretreatment has a significant effect on drying process and decreases the time of drying up to 68 percent in some temperature levels. Also by increasing the temperature, drying time decreases up to 66.5 percent in some pretreatments. Increasing the hot air velocity decreases it about 8.3 percent.