I am an Agriculture Teacher in Brisbane, Australia and I was asked by a gentleman if there was any truth in rice speeding up the ripening fruit, as his wife places a handful of rice in a bowl to ripen her fruit. I said I didn't think rice would produce that much ethylene to make a difference and that the rice may act only as a semi enclosure around the fruit that is already producing ethylene. Can you advise if this practice has any truth behind it? (M.K.)
I agree with you, there should be no reason why rice (I assume it is dry) would cause fruit to ripen faster. Dried grain does not produce ethylene. If the rice is wet then it would support mold growth and some molds produce ethylene, which could speed ripening.
You may be on to something supposing the bowl makes a difference, particularly if it is covered in some way. This would act like a ripening bowl, especially if ethylene producing fruits are also in the bowl. One disadvantage to the rice is that it would cause low relative humidity conditions around the fruit and speed the development of noticeable shriveling. I hope this helps.