Studies on Cooling and Cold Air Drying for Grain Storage (III)

Effect of Cooling and Cold Air Drying for Grain Storage on the Quality of Rough Rice

Abstract

The purpose of this experiment was to investigate the performance of System of Cooling and Cold Air Drying for Rough Rice Storage by measuring the quality of rough rice during storage. Early season rice was used as experimental material. 15°C and 14.5% moisture were adopted as conditions of storage Indices used for judging the quality of rough rice were cracking, germination and free fatty acid.
The main results were as follows.
1) The times required for rough rice with the initial grain temperature of 33.3°C and 21.9% moisture content to reach the above condition were shown below respectively. In division C. (Table 1) the time required for rough rice (200Kg) to reach the above condition was 4 to 6 hours in cooling and 59 to 80 hours in drying under 15-25°C, 55-85% R. H. and 1.23m³/min/100Kg. The average drying rate per hour ranged from 0.13 to 0.09%/hr. In division I. the moisture content of rough rice (200Kg) reduced to 14.5% in 15 hours under 42-46°C, 48% R. H., 10.8m³/min/100Kg, 4 heating periods of 0.5 hour each and 3 intermittent periods of 3 hours each. The average drying rate per hour was 0.5%/hr. In division U. the moisture content of rough rice (20Kg) reduced 14.5% in 24 hours under 35°C, 70±10% R. H. and 10.8m³/min/100Kg. The average drying rate per hour was 0.3%/hr.
2) After the rough rice was dried, all of them were stored for about six months. The grain temperatures and moisture contents of rough rice during storage were 15±2°C and 15±1% in division C. J., 15±0.5°C and 14±1% in divisions I. L. and U. L., 14-32°C and 11-14% in divisions I. O. and U. O., respectively.
3) Cracking was not observed at all in any drying divisions.
4) Harmful insects did not grow in three divisions C. J., I. L. and U. L. In both I. O. and U. O. divisions, it was judged that rough rice was not suitable for eating, because some rice weevils and small weevils grew after about 56 days.
5) The initial rate of germination of rough rice was 33% in dormancy. In divisions I. O. and U. O. the dormancy of rough rice was broken completely after 30 days, but the rate of germination began to decrease after 115 days. In divisions I. L. and U. L. the dormancy of rough rice was broken after 70 days. After 152 days the rate of germination of rough rice in division I. L. showed an increasing trend, whereas in division U. L. it showed a decreasing trend. In division C. J. the dormancy breakage was increased to 85% barely after 200 days, because of the slowest breaking speed dormancy. But it was suppose that the rough rice should have the longest life, because it was confirmed that the rough rice had a germination capacity of 93% in practice.
6) Considering a possibility of nongermination state in spite of its germination capacity, we cannot necessarily conclude that the rough rice is of better quality when its rate of germination is great.
7) The authors considered that free fatty acid of rough rice during storage could be minimized by means of System of C. J.
8) As described above, it was confirmed that System of Cooling and Cold air Drying for Grain Storage was an excellent system which made drying very large bulk of rough rice possible without deteriorating it quality and storing it for a long term. Furthermore, the possibility became apparent of making use of dormancy of grains for establishment a drying and long term storage system.
C.: Cooling and Cold air drying.
C. J.: Cooling and Cold air drying and Jacketed storage.
I.: Intermittent drying.
I. L.: Intermittent drying and Low temperature storage.
I. O.: Intermittent drying and Ordinary storage.
U.: Unheated air drying.
U. L.: Unheated air drying and Low temperature storage.
U. O.: Unheated air drying and Ordinary storage.