Many fruits continue to ripen off the tree, including pears, plums, peaches and kiwifruit. When exposed to ethylene gas produced by apples or bananas, these fruits ripen faster. Clemson University notes that fruits such as apples, grapes, citrus, watermelons and cherries do not ripen after picking and require tree ripening for best results. For fruits picked unripe, use a paper bag and an apple to create an environment that speeds ripening.
Place an apple into a paper bag.
Set the fruit for ripening inside the bag with the apple.
Fold the top of the bag over to close and set the bag on a counter to ripen at room temperature.
Check the fruit daily by carefully pressing the side. Remove the fruit from the bag and transfer to the refrigerator once it yields to gentle pressure, indicating ripeness.