To pick grapes properly, pick from both shaded and unshaded clusters on the upper and lower parts of the vine, examine their color, test their firmness and flavor, cut the cluster from the vine with gardening shears, and place them gently in a container to avoid bruising. When picking grapes for wine making, measure the pH of the juice using a digital pH meter.
To ensure the ripeness of a grape harvest, pick many grapes from several clusters to test. Test the color of the grapes by looking for rich colors, such as near-blue purple, deep red or crisp white, depending on the variety of grape. To test the shape, squeeze the grapes between a thumb and forefinger. When ripe, a grape pops with juice when squeezed. Unripe grapes shrivel and dribble juice when squeezed.
To test the flavor, eat grapes one at a time, looking for the appropriate flavor for the grape. When taste-testing a ripe chardonnay grape, for example, look for crisp melon, grass and lemon flavors. Unripe grapes may taste acidic, sour or overly tannic. When you are ready to remove a cluster of grapes, cut it from the vine using garden shears, leaving half the stem attached, and place it gently in a basket to avoid bruising.
For wine making grapes, use a digital pH meter to determine the sugar content. The pH of grape juice decreases as its sugar content increases. Ripe red wine grapes should measure between 3.3 and 3.5, while white grapes should measure between 3.2 and 3.4.