Development of Long-term Rice Storage Techniques for Preserving High Quality at a Temperature below Ice Point

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A new technique for storing rice at a temperature below ice point using fresh chilly air was developed. Freezing temperatures and extents of freezing injury of rice with various levels of moisture content were studied, and effects of temperature below ice point during a four-year storage period on the physiological properties of rice were investigated. Rice with moisture content of less than 17.8% did not freeze even at a temperature of-80° C. Low temperature maintained the vitality of rice, minimized physiological activities and starch deterioration in rice, and preserved rice quality. One thousand tons of rough rice was stored in two silos from the end of November 1999 and was aerated from the bottom to top of each silo using fresh chilly air in January 2000. The rough rice temperature fell below ice point. At the end of July 2000, the rough rice temperature in the center of each silo was still below ice point. The rice quality stored in the silos was preserved at a level similar to that of freshly harvested rice. A combination of rice storage below ice point and utilization of fresh chilly air enables the rice quality to be preserved at a high level without the requirement of a cooling unit or electricity. The use of this storage technique has been increasing in cold regions after the on-farm experiment. In Hokkaido, the northernmost island in Japan, 26 grain-elevators have been constructed since 1996. The storage capacity of rough rice was 115,000t at the end of 2003.