For some bakers, the impetus to bake with bananas comes only from realizing that your eating-bananas have ripened past the point of a healthy on-the-go snack. If you regularly find yourself with spotted brown bananas, start baking. If you need to make banana cake in less time than it will take your perfectly yellow, fresh-from-the-grocery-store bananas to turn brown, do not worry. Softening bananas for baking cake can take days or as little as a minute.
If You Have a Couple of Days
Place the hard bananas in a paper or plastic bag with two apples or tomatoes. Apples and tomatoes emit high amounts of ethylene gas, a hormone that affects bananas by causing them to ripen quickly.
Roll the top of the paper bag closed or fold over the top of a plastic bag. If you are using a plastic bag with a zipper-like closure, leave a corner open, cut a small hole in it or fold one side of the top over the other. Oxygen is important for ripening bananas, so do not close off air to the bag completely.
Place the bag in an area out of direct sunlight but also not in the dark. Check the bananas in 24 hours. If they are still not soft enough, put the bananas and apples or tomatoes back in the bag as they were and check in another 24 hours. It shouldn’t take more than two days to soften hard bananas using higher than normal concentrations of ethylene gas.
Peel and mash the bananas with a fork when they are soft enough, as called for in your cake recipe.
If You Only Have a Couple of Minutes
Puncture the peel of the hard bananas one or two times each using a fork or knife.
Place the bananas in their punctured peels inside the microwave. Cook at full power for 30 seconds. Turn the bananas over and cook for another 30 seconds on high.
Cool the bananas until they are cool to the touch. Squeeze the bananas gently to test for adequate softness. Microwave for additional 30-second increments if the bananas are not soft enough, squeeze-testing between each increment.
Peel and mash the bananas using a fork until they reach the desired consistency for your cake recipe.