What a sensation to bite into a really ripe peach—the soft flesh, the heady aromas, the sweet juices everywhere, and that incredible flavor. This seduction of the senses is very deliberate on the part of the peach. In fact, it's a matter of survival. Fruits are the seed-bearing ovaries of plants, and their mission is to spread these seeds. When fruits ripen, they become overwhelmingly desirable to animals (man included) so that animals will carry them off, eat them, and spread the seeds.
So how can you tell if a fruit is ripe? Unfortunately, most people don't have orchards and gardens full of fruit ripe for the picking. In fact most of the fruit we buy, at the grocery store anyway, has left the garden far behind, having been picked before its prime to avoid shipping damage and storage loss. All the more reason for us to understand the ripening process and learn some tricks for telling which fruit is ripe now and which will get ripe once you take it home from the market.
As fruits ripen, they go from hard, sour, inedible, near-invisible parts of the plant to stand-out, brilliant-colored, sweet, juicy objects with enticing aromas. They change in color, size, weight, texture, flavor, and aroma (some even produce ethylene gas); these varied attributes can be good indicators of ripeness.
Color is a clue, but not a reliable one. With some fruits, you can tell they're ripe by their color. As the acidity changes, the green chlorophyll breaks down. Some fruits like bananas and apples have bright colors underneath the green chlorophyll layer; the colors show through as the chlorophyll disappears. Others, like tomatoes, make their red-orange compound at the same time that the chlorophyll breaks down. Bluish-red berries become a deeper, more intense red as they ripen. For these fruits—bananas, apples, tomatoes, red berries, cherries—color change is an excellent indication of ripeness.
Aroma hints strongly at flavor. Smell is especially important when color is not a good indicator of ripeness—for example, with most melons. Chemical changes take place in ripening fruits that cause them to produce sensuous, luscious-smelling volatile compounds. Sniff the blossom end of the fruit (the end opposite the stem) and only select fruit that has a full, fruity aroma.
Feel for a tender texture. As fruits ripen, the substances that hold the cells together (hemicelluloses and firm pectic substances) break down and convert to water-soluble pectins, which makes the fruit become softer and softer, so a gentle squeeze is a good test for ripeness. If a plum is rock hard, it isn't ripe. The squeeze test is especially useful with fruit that doesn't have a hard or thick rind, so squeeze stone fruit, pears, kiwis, and avocados. This doesn't work well with melons or pineapples, but even with these rough-coated fruits, a little give is a good sign.
Heavy is good. Weight can be a good indicator of ripe fruit. You'll often see the phrase "heavy for its size" as a positive attribute for fruit. It generally means that the fruit is at least fully mature, which is a good start on the road to ripeness. A heavy tomato or grapefruit, for example, is usually a good one.
If you have a grower nearby who allows you to pick your own or who's a conscientious producer who handles his produce well, by all means take advantage of that locally grown, just-picked ripe fruit. Your local county extension agent can help you find growers and farmers' markets. And speak up to the produce manager of your supermarket, too. Even big companies respond to consumer pressure.