Correlation of Water Concentration in Paste and Drying on Degree of Swelling for Normal Rice Cracker

Abstract

Sembei is a type of traditional Japanese rice cracker (Beika) produced from normal rice and is generally produced by roasting dried rice paste. The degree of swelling after roasting rice paste is generally thought to depend on the drying temperature, drying time and thickness of the rice paste. In the present paper, a general model of the water diffusion accompanying adsorption and desorption at the interface between air and the rice paste is presented, and the average concentrations of water under different drying temperatures and drying times are solved numerically using the model. The effect of drying temperature or thickness of the rice paste on the concentration profiles of water is discussed in terms of the model. The experimental results agreed with those of the numerical simulation and proved the applicability of the model. In the cases of low temperature drying and thin rice paste, the difference in water concentration between the surface and the center of the rice paste was estimated to be small. Low temperature drying seems particularly effective in giving homogeneous and soft swelling properties in the roasting of rice paste.