a comparative study of raisin production by solar dryer and other drying methods

in recent years immense interest has been focused on the use of solar dryers especially when taking into consideration economical and ecological aspects and increasing in fuel costs. the aim of this study was to compare the qualitative factors of raisins made by five different drying methods. at the first step, pretreatments were applied to grapes (var. sultanas) and then the grapes were dried by five methods, including open-sun drying, shade drying, drying by industrial cabinet dryer and two different modes of solar drying namely mixed and indirect type. the shortest drying time was obtained with industrial cabinet drying, but mixed and indirect solar drying were more effective than open-sun drying and shade drying. moisture content, acidity, sensory properties (color, texture, flavor and overall acceptance) and microbial level of the produced raisins were determined and compared. the texture of the raisin samples was evaluated by texture analyzer device as well. the color of the samples was measured and analyzed by a novel digital imaging method for measuring color of foods.the results indicated that the solar dryers were not only able to produce raisins similar to other drying methods but also the raisins produced by these dryers were in some qualitative factors (consumers overall acceptance and color) better than the other raisins.