Why do fruits ripen faster when kept in a rice container

Fruit ripening is governed by a number of factors; the primary ones among them being the temperature of storage and the concentration of the gaseous plant hormone, ethylene. Mature unripe fruits start to emit ethylene when they start to ripen. Storing them in a closed container, even a paper bag, would enhance ripening due to the accumulation of ethylene.

The primary reason why fruits ripen quicken when stored in a rice container is due to ethylene accumulation. Differences in the rate of ripening between fruits kept in a rice container and a wheat container might be due to the differences in carbon dioxide emission and self heating nature of these grains.

Both wheat and rice grains (esp. brown rice) when not completely milled, still actively respire, thus releasing carbon dioxide and energy. Carbon dioxide is a known inducer of ethylene biosynthesis in a number of fruits e.g. tomato.

Respiration also leads to increase in temperature. Both these factors promote fruit ripening. Wheat and rice grains differ in their seed dormancy which is known to affect seed respiration rates.

Rice grains without a husk typically have no dormancy and thus respire more at normal storage conditions. Most wheat grains have moderate to high dormancy periods (red wheat is more dormant than white wheat) and respire less at normal storage conditions. This is the reason why fruits stored in a rice container ripen faster than the ones stored in a wheat container.