Thin Layer Infrared Drying of Crimson Seedless Grapes

Abstract

The drying characteristics of crimson grape (vitis vinifera L.) were investigated using laboratory scale infra-red dryer at four levels of infra-red radiation intensity (0.861, 0.973, 1.039 and 1.161 kW/m 2 ). The drier was also equipped with three axial flow fans to supply air over the samples to carry the evaporated moisture. The passing air was adjusted at three different temperatures (40, 50 and 60 o C) and constant air velocity of 2 m/s. During the experiments, grapes were dried to final moisture content (19.96 – 13.87) % from 292.46 ±1 % dry basis. It has been found that, both air temperature and infra-red radiation intensity affect the course and rate of drying. The gained data were fitted to two thin layer drying models: Lewis model and Henderson and Pabis's model. The examined models were compared using R 2 , SE, χ 2 , MBE and RMSE. Lewis’s model is the best for describing the drying curve of Crimson seedless grapes. A diffusion model was used to describe the transfer of moisture and the effective diffusivity at each drying temperature and radiation intensity. The effective diffusivity; varied between 6.8632x10 -11 to 6.4057x10 −10 m 2 /s and was significantly affected by radiation intensity. The average value of activation energy was 4.2515 kW/kg. The Crimson seedless grape dried at radiation intensity of 0.973 kW/m 2 and air temperature of 60 °C recorded the highest quality of the dried samples in terms of, TSS, total sugar, reducing sugars and remained SO 2 .