Why does fruit ripen faster in a paper bag?

It is one of the most useful tips in the kitchen: if you have an unripe avocado, banana, or peach, put it in a paper bag and it will ripen faster. This little trick really works, but it can seem mysterious. The paper bag does not provide heat, light, or nutrients. So how can simply placing fruit inside a plain bag speed up the natural ripening process? The answer is an invisible gas.

Many fruits naturally produce a gas called ethylene as they mature. Ethylene acts like a plant hormone, a chemical messenger that tells the fruit it is time to ripen. When ethylene is present, it triggers a series of changes in the fruit: starches turn into sugars, making the fruit sweeter, the flesh softens, and the color and aroma develop. Fruits such as bananas, apples, pears, and peaches release noticeable amounts of this ripening gas as they ripen.

Here is where the paper bag comes in. When a fruit sits out in the open air, the ethylene it produces simply drifts away and disperses into the room. But when the fruit is placed inside a closed paper bag, the gas cannot escape easily. It builds up and becomes concentrated in the small space around the fruit. With more ethylene surrounding it, the fruit receives a stronger ripening signal, and so it ripens noticeably faster than it would on an open counter.

There are a few things worth knowing to use this trick well. Paper is the right material because it traps the gas while still letting some air through. A sealed plastic bag traps moisture as well, which can make the fruit rot before it ripens. You can speed things up even more by adding an already-ripe fruit, such as a ripe banana, into the bag, since it adds extra ethylene. However, the trick does not work on every fruit. Some fruits, like grapes and citrus, do not continue ripening after being picked, so a paper bag will not help them.

This article was written using information from Wikipedia.