Bananas ripen quickly and cause other fruits close by to ripen faster too. The fast ripening of bananas is caused by ethylene emission, gases that are naturally released by the fruit itself. Putting bananas in the refrigerator does at least two bad things to an innocent, unripened banana. It slows the ripening process, and turns the peel black. If you want to delay the ripening of bananas, keep them cool (not cold), and separate them from each other. Separating bananas will reduce the amount of ethylene each banana is exposed to from the other fruit, thereby slowing the ripening.