Grapes must be harvested at the right stage of maturity to insure high quality. There are several indicators of grape maturity. The color, size, sweetness, and flavor of the berry are the most useful indicators.
Depending on the variety, the berry color changes from green to blue, red or white as the grapes approach maturity. Color alone, however, should not be the sole basis for harvesting grapes. The berries of many varieties change color long before the grapes are fully ripe. At maturity, individual berries are full size and slightly less firm to the touch. As a final test, taste a few grapes for sweetness when berry size and color indicate they are approaching maturity. Harvest the grape clusters when the berries are sweet.
When harvesting grapes, remove clusters with a knife or hand shears. Sound grapes can be stored in perforated plastic bags in the refrigerator for up to two months. Optimum storage conditions are a temperature of 31 to 32°F and a relative humidity of 85 percent.
Uneven ripening of the berries within a cluster is sometimes a problem. Possible causes are over-cropping (too many grape clusters on the vine), a potassium deficiency, moisture stress, or 2,4-D damage. Overcropping is the most common cause for home gardeners.
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