It is common for commercial growers to pick fruit before it is fully ripe and treat it with chemicals for preservation until it reaches its destination. In some cases, this can mean your fruit has traveled over 1,500 miles to reach you. Locally grown fruit is less likely to be picked before maturity because of the shorter distance the fruit needs to travel to reach local customers. Of course, home growers have the luxury of picking fruit when it is at its peak maturity and sweetness.
Apple trees (Malus domestica), grown in U.S. Department of Agriculture Zones 4 - 9, need to be fully mature when picked. Apples picked before reaching maturity will not continue to ripen. To determine the maturity of an apple, examine the color of the skin. Immature green apples start off bright green and turn a lighter green when mature. For red apples, examine the color of the skin on the stem. As the apple matures, the stem color will change from bright green to light green and then to yellow. You can also cut open an apple to determine the maturity of the fruit. As the apple matures, the seeds’ coats turn dark brown. Tasting the apple is the easiest way to determine the maturity of the apple. Immature apples will taste slightly starchy while mature apples will be sweet.
Citrus fruits, USDA zones 9 - 11, do not ripen after they are picked. Oranges (Citrus x aurantium), tangerines (Citrus reticulata), lemons (Citrus x limon), limes (Citrus x aurantiifolia), and grapefruit (Citrus x paradisi) are picked when they are ripe and ready to eat. The easiest way to determine ripeness is to taste test the fruit. Unlike temperate zone fruits, citrus fruits can be left on the tree one to two months after they are ripe and the fruit will become sweeter.
Berries and Grapes
Raspberries (Rubus idaeus) and blackberries (Rubus fruticosis) are grown in USDA zones 5 - 7. When picked before turning ripe they are sour and will not reach full sweetness. Strawberries, blueberries, and grapes all grow within USDA zones 3 - 10. Strawberries (Fragaria F. x ananassa) will continue to turn red but they will not get sweeter after they are picked. For blueberries (Vaccinium angustifolium and Vaccinium corymbosum) to reach maximum sweetness, pick them three to four days after they have turned blue. Blueberries that are still tinged with red will not continue to ripen after they are picked. Harvest grapes (Vitis labrusca and Vitis vinifera) only when they are ripe because their flavor will not improve after they are picked. The easiest way to test for ripeness is to taste a grape for sweetness.
Cherries and Apricots
Cherries (Prunus P. cerasus and Prunus P. avium), grown in USDA zones 4 - 9, are harvested as soon as they become ripe. They are ready to be picked when the cherries are slightly soft. Tasting them is a quick indicator as to the ripeness of the fruit. Apricots (Prunus armeniaca), USDA zones 4 - 8, can only be picked when they are ripe. If they are picked before becoming soft and ripe, the fruit will shrivel up and be inedible.