Bananas ripen when exposed to ethylene gas. This is a gas produced by other ripening fruits on the tree and is a way for the tree to send a signal for all of the bananas to ripen at once. To harness the natural ethylene gas produced by ripe bananas, place unripe bananas into a paper bag with a fully ripe banana or banana peel. Close the bag and store it in a warm, dark place. Check the bananas daily and remove them as they turn yellow and spotty. Avoid using plastic bags or airtight containers, both of which promote mold growth.
To speed the ripening of bananas in a paper bag, wrap a damp paper towel around the bunch of bananas before putting it into the bag. Check the bananas daily. The paper bag should allow for enough air flow to discourage mold formation. Do not use this technique with a plastic bag, as it will trap the moisture. Keep the paper bag filled with bananas at room temperature since refrigerating the bananas will stop the ripening process.
If you are in a hurry to get mushy, fully ripe bananas for use in baked goods like bread, use the oven. Heat the peeled bananas for 10 minutes at 450 degrees Fahrenheit on a baking pan or until soft. The bananas will then be ready to mash or puree for your recipe. However, do not use this technique if you want the ripened bananas to maintain their shapes. Instead, opt for a slower, more gentle ripening method.
Knowing when you have properly ripened bananas will ensure the best flavor for your recipes. To determine the banana's ripeness, look at its coloring. The banana should be yellow with an even coating of brown spots, indicating an elevated sugar content. Use a toothpick to test the banana as you would test when a cake is finished baking. Insert a toothpick into the top of the banana at the base of the stem. The banana is properly ripened if the toothpick can be inserted with ease and comes out clean.