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So, obviously the ripening of bananas involves changing it’s chemical composition. For example, ripe bananas have a much higher amount of sugar.
It is also known that reaction rates are generally increased with increasing temperature, yet bananas ripen faster in a refrigerator.
Why do bananas ripen faster in the fridge, even though it’s colder? And is there any difference (except ripening time) between ripening a banana in the fridge, and having it ripen in room temperature?
I like bananas, but I almost went bananas doing some research for this question!
Let me post some quotes - too much info to post the sources:
1) Is it safe to store my bananas in the refrigerator? Dr. Brecht: “Never, never, never put bananas in the refrigerator!
2) The answer, far from dissuading me from keeping bananas in the fridge, only confirms my habit. Banana-eaters are divided into two fairly equal camps: those who like the delicate flavour of the green (unripe?) banana and those who prefer the quite different strong flavour of the yellow (over?)ripe banana. Using cold to inhibit the enzymes which aid the ripening process is just what is needed by the 'greens' but should be avoided by the other camp.
3) If they're kept at a cold temperature, the enzymes that enable them to ripen are inhibited. And as those enzymes become inactive, other enzymes operate more efficiently. Some cause cell damage, while others (browning enzymes) cause the skin to blacken. Bananas do best if stored at around 10°C.
4) Bananas require gas, that is ethylene, to trigger the ripening process.
5) Cooler temperatures also slow down the chemical ripening process. Once bananas are ripe to your likening, store them in the fridge.
6) De gustibus non est disputandum
So it seems that bananas do change because of the cold, but the process is not exactly ripening. It does involve a chemical change, which is so complex that it can be predicted and analyzed, but is not useful as a guide to developing a tasty banana for a specific person. Too much variation in the people who eat bananas! I did an experiment some time ago, wondering if the economy of buying green-yellow bananas (with noticeably thick, firm skins) was significantly less than buying bananas with exactly the color for immediate eating (deep yellow for me), where the skins were noticeably thinner, softer. How much weight loss do I incur and pay for, but don't get the benefit of? Not much, it seems, about 10% of the weight of a banana, maybe 15% if you got a green one and let it go almost brown.
So banana color may not be the whole story: enzyme activity occurring at different temperatures may affect taste without being "ripening" - a banana may go from underripe to overripe without ever being exactly ripe! The process of marketing, from green to yellow, is described in some detail, and interestingly, ripening bananas develop heat (and I would guess, ethylene also), so the recommendation was to unpack the banana boxes quickly when they get to the grocery store to reduce the temperature (and C2H4) so the bananas keep longer.
