Abstract
In order to discuss the stress cracking of rice during drying process, the effect of the moisture content on the volume change of a rice kernel was investigated.
The densities and specific volumes (dry basis) of many brown and milled rices were determined by means of the liquid-displacement method and the air-comparison pycnometer method at a constant temperature, 34.8±0.3°C. From the relationships between the moisture content and the density of a rice kernel, it was shown that the density of a normal brown rice, which had not been excessively dried, was dependent on its moisture content, regardless of its moisture hysteresis, and that the density of a milled rice was slightly higher than that of a brown rice at any constant moisture content.
In the higher moisture content ranging from 0.08 to 0.43g/g-dry solid, the following equations for the specific volumes (dry basis) of the brown and milled rice were obtained experimentally as v=0.672+0.954w and v=0.661+0.940w respectively.
In this paper by considering a coefficient of hygroscopic expansion defined as the same as the thermal expansion, it could be estimated that the coefficients of cubical and linear hygroscopic expansion were 1.42 and 0.390 (g/g-dry solid)-1, respectivety.
