Effect of mixing, tempering and multistep thin layer drying on milling quality of parboiled paddy

Abstract

Convective air drying studies were conducted on a laboratory model thin layer dryer. The parameters studied were 70-150°C drying air temperature, 0.5-2 m/s air velocity and 5-20 cm grain bed depth. The effects of mixing, tempering and multistep drying process on milling quality were evaluated. Mixing, tempering, multistep drying and control of grain temperature enhanced the milling quality while reducing the drying time and specific energy requirement. To achieve maximum head yield, minimum specific energy and minimum drying time, the optimum process parameters were grain bed depth 7-10 cm, air velocity 0.55-0.68 m/s and drying air temperature 112-116°C. This combination gave 65-68% head yield and specific energy consumption of 8.5-10.7 MJ/kg of water removed.