Relation between the specific Gravity of Unhulled Rice and the Quality of Hulled Rice

Abstract

1. The specific gravity of unhulled grain is mainly determined by the space left between the hull and the kernel. Consequently, the specific gravity of the unhulled grain which involved a fully developed kernel showed a high value. The unhulled grains of normal and white-belly kernels denoted a high value from 1.16 to 1.22 and those of basal-white kernels were ranged between 1.15 and 1.21 in the specific gravity. The specific gravity of unhulled grains of rusty, deformed, milky-white and partially opaque kernels distributed in lower and wider range as compared with that of unhulled grains of normal kernels. Unhulled grains of opaque kernels were ranged in the lowest specific gravity from 1.01 to 1.09. (fig. 5, 6) 2. The unhulled grains of normal, white-belly and basal-white kernels were selected by the specific gravity of 1.15 in company with those of comparatively well developed kernels among rusty, deformed and thin kernels. The unhulled grains selected by this specific gravity were appreciated as the high-grade rice and the remaining ones were recognizecl as the low-grade or trash rice. 3. The specific gravity of unhulled grain of some kernel quality was influenced by ripening condition and that of normal, white-belly or rusty kernel was heavier under well-ripened condition than under worse-ripened condition, but that of partially opaque or opaque kernel scarcely differed on both conditions. (fig. 3, 4) 4. As the moisture content of unhulled grain increase, the kernel involved in the hull expands and space between the hull and the kernel is diminished. Therefore, the specific gravity of unhulled grain became higher or lower as the moisture content increased or decreased and the variation in specific gravity-caused by moisture content was more remarkable in partially opaque and opaque kernels than in normal and rusty kernels. (table. 1, fig. 1, 2)