Depending on the vintage, a harvest can start in mid of September, or later in October. Harvesting begins with young vines as they mature first. The grapes are vinified separately.
Taking the vintage into consideration, the decision on when to pick is crucial as it determines the style and character of the wine. The date of the harvest allows the winemaker to produce a wine in the character and style they prefer. When the grapes are picked also determines the level of alcohol, sugar and acidity in the wine.
Waiting to harvest when the berries are fully ripe can be dangerous as the grapes cold be exposed to rain during that period. Ripe fruit is sweeter, potentially higher in alcohol and can deliver darker, fruit flavors and even notes of blueberries along with plusher textures.
Growers that wait too long can harvest grapes that are over ripe, higher in sugar and alcohol and taste similar to raisins and figs, which is not desirable.