Incidence of open crack formation in short-grain polished rice during soaking in water at different temperatures

The incidence of open crack formation in short-grain polished rice during soaking in water at different temperatures was investigated. Rice with a moisture content of 10.4% (wet basis) was soaked in distilled water for 90 min at 15 °C, 25 °C or 35 °C, and the rate of open crack formation and the moisture content of the rice during soaking were measured. Results show that the rate of open crack formation increased with decreasing the soaking temperature. A model based on the relationship between the tensile stress calculated from the moisture gradient in a rice grain and the tensile strength calculated from the average moisture content of a rice grain provided a reliable qualitative estimate of the difference in the rate of open crack formation at different temperatures. It can be concluded that water diffusion into rice grains should be accelerated to prevent the formation of open cracks.