There are two ways to ripen bananas faster. First, if you have a few days before you’re planning to use them, you can place the bananas in a paper bag and leave on your counter until you’re ready to bake.  This traps the ethene gas and helps ripen the bananas faster. Second, if you need them now, you can place the unpeeled bananas on a baking sheet and bake at 300F for 15 to 30 minutes, or until the skin is brown-black and the flesh is soft.  The texture will be a bit softer than naturally ripened bananas but you will get similar taste and sweetness.