Moisture distribution in a rice kernel during tempering drying

Abstract

The intra-kernel moisture content profiles are important in understanding the effect of tempering process on the moisture content gradient and rice fissuring. Intermittent drying of long-grain (var. L201) and short-grain (var. Akitakomachi) rough rice was performed and the moisture content distributions within a rice kernel were estimated by a simplified sphere drying model. The results showed that the model was capable of accurately simulating drying and tempering processes of grain. Moisture content gradients were produced during drying periods, which remarkably decreased at the early stage of tempering processes and then decreased gradually. Tempering at 50 °C for 120 min removed about 80% of the moisture content gradients created in a rice kernel during drying. Moreover, moisture contents of the internal layers of the kernels always decreased in the whole intermittent drying while that of the outer layers of the kernels decreased during the drying periods and increased during the tempering periods.