In my humble opinion, green bananas are just eeew! Sometimes you wait and wait and wait for those bananas to ripen but they seem to become hard green bananas instead of soft yellow ones. If you place your bananas in a paper sack with an apple, then close the sack, your bananas will be ready in say 1-3 days, depending on how ripe they were to begin with. How does this work? Chemistry. Apples emit a chemical that causes other fruit to ripen.