Rice is generally cooked once a day in the ordinary Japanese home. After the rice is cooked it is transfered into a wooden rice tub “Hitsu”.
Nowadays, the jar which is a kind of vacuum-bottle seems to be effective for preserving the temperature of this cooked rice has a rising demand on the market.
Though it is well known that the jar is much more heat-effective than the rice tub, putrefaction is promoted because the optinum growth temperature of bacteria is maintained. For this reason in order to investigate preservation of cookd rice kept in the jar, the authors have attempted to clarify the relation between preservation temperature of the jar and multiplication of bacteria.
In this experiment some respects concerning multiplication of bacteria such as jar-size, rice cooked at three different time of the day i. e., for breakfast, lunch and dinner were taken into consideration and a comparison was made.
Experimental:
Bacteria growth was inhibited in case jar temperature was maintained over 50°C. Therefore bacteria. multiplication could first be observed in samples which came below 50°C more rapidly than others. However, in seasons like spring, autumn and winter when room temperature does not reach the optimum growth temperature of bacteria, bacteria multiplication declined in accordance with the temperature of the rice approaching room temperature. However, in contrast to this it should be noted that though bacteria multiplication is delayed when cooked riceis preserved at a temperature exceeding 50°C for a long period, after the lapse of time it is promoted and putrefaction occurs earlier than in the former case. This is due to the prolonged duration of optimum growth temperature.
Thus it is quite natural that rice preserved in the wooden rice tub showed much better results than in case of using the jar.
In contrast to this, in summer when room temperature is most suitable for bacteria growth, bacteria multiplication commenced at a later period, especially in case of samples maintaind over 50°C for a long period.
It is thus assumable that putrefaction occurs at an earlier period in the wooden rice tub.
In winter when room temperature is lower than optimum bacteria growth temperature, multiplication showed the same trend as in spring and autumn.
Conclusion:
It is concluded that putrefaction of boiled rice is prevented by preserving the rice in the jar at temperatures exceeding 50°C for a longer period and thereafter, when the temperature comes below 50°C the jar lid should be taken off and the contents left to cool.
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