It might seem like there isn’t a lot in common between tomatoes and bananas, except that they are both fruit that shouldn’t be refrigerated. However, this can be deceiving, especially when it comes to the ripening of the fruit. In fact, it is the reason bananas and ripe tomatoes shouldn’t be stored together.
Green bananas release a gas called ethylene when they ripen. Green tomatoes release very little ethylene when they ripen, so it would appear that again, there isn’t much in common.
When stores get bananas and tomatoes from suppliers, they often arrive partly or completely green. They are less susceptible to bruising and damage in transit when they are green. Quite often, the boxes that contain the bananas are lined with plastic or are waxed, though. This concentrates the ethylene so that the bananas ripen faster.
This, in itself, can be useful information. If you buy ripe bananas in a store, don’t leave them in a bag. If you do, the ethylene will still be concentrated and the bananas will become over-ripe very quickly.
Larger stores that can afford to do so often ripen green tomatoes rapidly by pumping a gas over and around the tomatoes. Guess what the gas is that is used? Yep, it is ethylene. Although ripening tomatoes don’t produce much ethylene, this gas still causes them to ripen quickly. This is why bananas shouldn’t be stored with ripe tomatoes. The tomatoes continue to ripen fast if they are subjected to the ethylene that the bananas are emitting.
This fact can be used in another way, though. If you have tomatoes that are still a little green and want to ripen them fast, put them in a paper bag and include a banana in the bag. Paper is recommended rather than plastic because paper bags “breathe”. The tomatoes are less subject to rotting before they can ripen.
Check the tomatoes fairly often, though, so they don’t get too ripe.
This is especially helpful for people who grow tomatoes and who, for one reason or another, find themselves with a lot of green or nearly green tomatoes. You can ripen them more quickly by using a banana.
Incidentally, this is also why you can slow down the ripening of bananas by wrapping the stem end with plastic. The stem end produces the most ethylene, so by wrapping it in plastic, you are preventing a majority of the ethylene from getting to the rest of the fruit.
It should also be mentioned that putting an apple with green tomatoes will also cause them to ripen faster because apples also produce ethylene gas. For exactly the same reason as mentioned in regard to bananas, tomatoes and apples shouldn’t be stored together. This is a little easier, though, because apples can be stored safely in the refrigerator while tomatoes (and bananas) shouldn’t be.
One final thought about why bananas and tomatoes shouldn’t be refrigerated, though this has been written about before. Both bananas and tomatoes are warmth-loving fruits. When they are refrigerated, it causes sugars in the fruit to turn to starch, which has far less flavor. This is the reason store-bought tomatoes are usually far blander than garden-fresh tomatoes. Suppliers usually ship them refrigerated and the stores keep them cold, probably because they don’t know any better. You can easily test this yourself if you have access to garden-fresh tomatoes. Try putting one of those tomatoes in the fridge for a few days, then taste it. It will probably taste almost identical to store-bought tomatoes; bland.