For the week of Sept. 27 Harvesting grapesHarvesting grapes is an art as well as a science. Commercial growers use a refractometer to measure the sugar content of the fruit, but you must depend on your taste buds. Some suppose erroneously that grapes require frost before they can be harvested. While there is often a light frost before the grapes reach maximum sweetness, it is not a requirement for ripening. Seeds in varieties that have them turn brown as they ripen.
The cluster stems also shrivel slightly and turn brown. White grapes turn from solid green to slightly yellow.
Some varieties drop from the cluster as they mature, so check them frequently to prevent losing fruit on the ground. Ripening grapes are attractive to more than just avid gardeners.
Birds are a serious pest, and there is no way to discourage birds that discover ripening fruit. Netting over the vines or paper bags over the clusters may help.
The fruit does not need light to ripen, so paper bags work well if clusters are not too numerous.
Raccoons also love ripening grapes. If clusters suddenly seem to disappear, check for tracks underneath the vines. Raccoons can be controlled successfully only by trapping and are a major deterrent to gardening in some areas.