DRYING OF THOMPSON SEEDLESS GRAPES IN THIN-LAYER USING A BIOGAS DRYER

Abstract

A biogas dryer was developed to study experimentally drying behavior of Thompson seedless grapes under Alexandria Governorate, Egypt conditions. Drying experiments are carried out in the month of August 2016. During the experimentation, temperatures of air at various places in the dryer, ambient relative humidity and humidity variation in drying chamber and mass of the dried grape are measured on hourly basis. four kg of Thompson seedless grapes are dried in forced convection heat transfer mode from initial moisture content of 79% (wb) to final moisture content 14% (wb) in 44 hours. The drying was carried out under uncontrolled condition. The average drying chamber temperature was around 51.98 °C. The biogas burner efficiency was 62.06 %. The effect of heating source on color change of the dried grapes was investigated. Color data were obtained using a high-resolution digital camera and lighting box and the images were analyzed quantitatively using Photoshop to get the L, a and b in the Histogram Window. Statistical analysis showed that there was a significant effect of heating source on color data of the dried grapes. Regardless of the heating source, all raisins had varying degrees of brown coloring. The dried grapes by the biogas dryer had lower browning index (BI) of 43.52 indicating good quality. It could be concluded that the farmers can use biogas energy to enhance its utilization to produce good quality raisins.