Intra-kernel moisture responses of rice to drying and tempering treatments by finite element simulation

Moisture content patterns inside rice kernels are important in understanding rice fissure formation; especially when glass transition effects are considered. Unsteady and non-linear partial differential equations were employed to describe two-dimensional temperature and moisture distributions within a single rice kernel during drying and tempering processes. Moisture content gradients (MCGs) inside the kernel were examined. Results showed that the maximum MCG (MMCG) appeared in the direction of the short axis. During the tempering process, moisture content on the kernel surface had a much faster and greater change than that at the kernel center. The infra-kernel MCG decreased considerably during the first 40 min of tempering, after which it decreased slowly to approach zero. A duration of about 40 min of tempering at 60degrees C helped eliminate about 90% of the MCGs created inside the rice kernel during drying, and this simulation result correlated favorably with the published tempering data, in the literature. The findings from this study provided useful information for determining optimal drying and tempering conditions of rice to enhance its milling quality.