To accelerate the ripen process even faster, place a piece of ripe fruit in with the unripe fruit, or use fruits such as apples which create more ethylene. I did this with peaches. I had a couple peaches that were overripe…like on the border of not being edible. I placed them in the paper bag with hard peaches that I just bought. The very next day the hard peaches became very ripe. I’m talking perfectly soft yet firm where I could bite into it with no problem. I was actually surprised this worked so well. You don’t have to use an overripe peach to help ripen other peaches. You could use a ripe banana, tomato or any other fruit.
How it works
Even though the fruit has been picked, the cells within it are still alive! Starch in the fruit gradually converts to glucose , a sugar, when certain enzymes are present. If you've ever tried to eat a pear before it was ripe, you probably noticed that not only was it very hard but it also wasn't sweet. That's because the starch hadn't yet converted to sugar, which is part of what makes fruit taste so yummy.
Ethylene is a gas that is made by some fruits, and it triggers the ripening process. Ethylene acts like an enzyme by speeding up the conversion of starch to sugar. Bananas make lots of ethylene as they ripen. The ethylene gas that comes out of the banana is trapped in the bag, exposing the other fruits to extra ethylene. The extra ethylene then triggers the ripening process for the pear and the apple. Apples also produce a lot of etylene, and that's why they can also be used to ripen other fruits.