Seasonal Changes in Storage Conditions of Rough Rice in Steel Bins of a Dry-Store

Abstract

About 40tons of rough rice containing, on the average, 14.5% moisture was stored in each of two storage bins of steel plate (1.6mm thickness) in a dry-store (Satake air sweep flow system, Cap. 500tons) for a period of about 8.5 months from November 26, 1972 to August 7, 1973.
During this period, the grain temperature and the moisture content, which might be the main factors affecting the qualities of rice, were measured, and the changes in quality of the rough rice were examined at monthly intervals.
The results obtained are summarized as follows:
(1) At the biginning of storage in November, the grain temperature was uniformly kept at about 10°C, in the whole depth of the bins. It gradually dropped under the influence of the colder open air in the winter, and attained to the minimum of 4°C. in the middle of February and remained at this level until the end of March.
(2) Thereafter, The grain temperature near the wall and the upper surface rose steadily, being about 5 to 12°C, higher than in the lower and central parts of the bin from the middle of April to the middle of June.
(3) From the middle of July in the last stage of storage, the temperatures inside the air duct and the plenum chamber rose under the influence of the ambient temperature much higher than in the inner part of the bin. As a result, the grain temperature rose rapidly to about 25°C. in the lower and central parts, and the differences in temperature among different parts decreased about 3 to 5°C.
(4) The grain moisture content was kept on the average at 14.5% throughout the whole period of storage, and the rate of germination showed values higher than 95% even at the end of storage, on August 6. The fat acidity values also remained at a low value of 11mg KOH/100g dry matter.
(5) The grain temperature just inside the wall facing southeast and exposed to the direct sun shine rose above 30°C, and exceeded 40°C, several times during the hot period in July. In such a case, the moisture content of the grain was reduced to about 1%, but the rates of germination and crack did not differ from those in the central part of the bin. Also, the fat acidity values remained at 11mg KOH/100g dry matter.
(6) A shelter plate standing outside the bin was effective on falling the temperature of the inside wall but not on the quality of rice which was not deteriorated by the summer heat. The bin was therefore capable of maintaining the qualities of the grain in good conditions even in the hot summer without the shelter plate.