Ripen fruit by putting it in a paper bag and then sealing the opening of the bag. Check on the fruit after a few days for ripening.
Fruits produce a molecule known as ethylene, which promotes the process of ripening. By confining it in a sealed bag, the fruit's exposure to ethylene increases, which accelerates the ripening process. Bananas release more ethylene than many other fruits, and adding one to the paper bag can speed up the ripening process.
Rice also harnesses ethylene well. Putting fruit in a container of rice is another way to ripen it. Many Indian households use this method.