There are several ways you can quickly ripen a banana. u003cbr/u003e1. Place it in a brown paper bag for 12-24 hours.u003cbr/u003e2. Put unpeeled bananas on a baking sheet and bake at 300°F for 15-30 minutes. They are done when the peels are shiny and black.u003cbr/u003e3. Poke some holes in the peel with a fork or a knife. Place in the microwave at 30-second intervals until the banana is soft. It may take up to 2 minutes until the banana is ripe.