Determining When to Harvest

Important components to consider when you determine whether the crop is ready to harvest are cluster integrity, sugar, pH and acid. Beginning winemakers often base their harvest decision on cluster integrity and sugar level alone (photo left - enology technician looking through refractometer to read grape juice sugar level).

A grape cluster of good integrity is not rotting, does not have split berries (which may occur after a rain), does not have fruit flies and wasps flying around it, and is otherwise sound.

Wine grapes, particularly Concord, Catawba and Cayuga White, will not usually reach adequate sugar levels (21 - 24 °Brix) in the field, so sugar will have to be added to the juice. In fact, Cayuga White is often harvested from 15 to 17 °Brix to avoid the "foxy" labrusca character. Delaware, Chambourcin, Seyval blanc, Vidal blanc, and Norton/Cynthiana may reach these levels. If cluster integrity is compromised, however, grapes must be harvested before the desired sugar level is reached and the juice must be ameliorated with additional sugar. White grapes should be harvested when the pH is between 3.2 and 3.4 and the acid level is between 0.6 and 0.9 g/100ml tartaric, whereas red grapes should be harvested when the pH is between 3.3 and 3.5 and the acid level is between 0.7 and 0.9 g/100ml tartaric.