If a fruit is not naturally green, and yet appears to be so, you can be sure it is not yet ripe. Unripened fruit is highly acidic and has a sour taste, which can overwork your digestion and leave you with a stomach complaint. It is a common mistake to think that all fruit at your local fruit store is the ripest you are going to get.
Climacteric fruits may be purchased unripened and left a day or two in the fruit bowl at home to ripen naturally. Some of these fruits include Apples, Apricots, Avocado, Bananas, Rockmelon (but not honeydews or watermelons), Figs, Guavas, Mangoes, Nectarines, Papaya, Peaches, Pears, Plums, Tomatoes.