Perennial Wisdom Worried About Ending Up with Sour Grapes?

While some fruits can be easy to harvest because they ripen after being picked, grapes can be more difficult. Grapes typically reach their optimal ripeness on the vine and rely on the amount of light that reaches the plant’s leaves to create the sugars for the fruit, rather than direct sunlight on the fruit. Washington State University (WSU) Extension Master Gardeners recommend the following harvest tips:

Ripeness: Table grapes are pretty straightforward in telling whether or not they are fully ripe, according to WSU Extension Master Gardeners. The berries at the tip of the cluster are usually the last to ripen, so tasting a table grape from that location can tell you if they are ripe or not. Grapes may become sweeter and less acidic the more they mature, with the flavor increasing as they are left on the vine. WSU Exten- sion Master Gardeners warn against leaving them too long though, as it can decrease the grapes’ storage life. Color can be untrustworthy, as many grape types turn a ripe color before they fully sweeten. Howev- er, a fully ripe grape may get a more noticeable natu- ral bloom or whitish coating. Grapes with seeds may also change from green to brown to indicate they are ripe. The stem that supports the cluster also changes from green to brown as the grapes reach maturity. Ripe grapes should also become slightly less firm to the touch, though that can depend on the cultivar. WSU Extension Master Gardeners state that the average temperature must be above 50°F for grapes to continue to mature on the vine.

Tools: Needle-nose pruners are the recommended choice by WSU Extension Master Gardeners for grape clusters, because they allow precise cutting without damaging fruit or vines. For harvesting wine grapes, a refractometer and a pH meter may be useful. Refractometers can be used to determine the grape’s Brix readings, which measure soluble sugars and are normally between 14-25 degrees for table wines. Meters that measure pH determine the amount of acidity in grapes, which is important for the success of canning or winemaking, according to WSU Extension Master Gardeners.

Pests: Wasps and hornets may feed on grapes before they are fully ripe and ready for harvest. Using traps in your grape row can prevent them. Birds can be another major issue; WSU Extension Master Gardeners recommend placing netting over the vines. Growers should also look out for gray mold or powdery mildew. Gray mold can cause fruit rot and may be worse in cool and wet autumns when clusters aren’t exposed enough to sun and wind. Sun and wind also help with preventing powdery mildew

The WSU Extension Master Gardener Program trains volunteers to be effective community educators in gardening and environmental stewardship. Master Gardeners provide information generated from research at WSU and other university systems. Christine Gile, a biologist who lives in Loon Lake, is a current Master Gardener.