Temperature changes can either delay or hasten the ripening of bananas.
The banana is a tropical fruit, adapted to ripen most quickly at a certain stage of its development and at a particular temperature and humidity.
Bananas continue to ripen after they are harvested, with more and more of their starches converted into sugars by the action of enzymes. When harvested, bananas contain about 20 percent starch and only 1 percent sugar. By the time the fruit is ripe, the proportions are reversed.
Bananas also release comparatively large quantities of ethylene gas to help themselves ripen; the gas will even ripen other fruit put in a bag with a ripening banana.
Bananas are usually harvested while still green, cutting off the supply of nutrients at the stem, and then shipped at a temperature low enough to slow the action of the enzymes of ripening.
Later, the bananas are brought back up to a temperature and humidity that let the enzymes become active again. Too high a temperature destroys enzymes, and too low a temperature can break down the cell walls of the fruit so the contents mix and the fruit oxidizes, browns, and softens abnormally.
The optimum temperature and humidity conditions for ripening are 62 to 68 degrees Fahrenheit and 90 to 95 percent relative humidity. Storage temperatures should be 53 to 56 degrees Fahrenheit.