Buy them when green. When the peels turn yellow with hints of brown, they're ready. They'll be fragile and bruise easily when they’re ripe. If you hang them in a cool area of your kitchen, they should stay fresh for up to a week. If you have overripe ones, freeze them. You can make them part of your next batch of ice cream, banana bread, or muffins. You can also use them to flavor up a smoothie.