🌿 Grape ripeness

Grape ripeness is the stage of berry development at which grapes are ready to be harvested for a given wine style. Ripening begins at veraison, which starts what the AWRI calls phase 3 of berry development.

In phase 3 the berries expand rapidly and accumulate sugar. Potassium, amino acids and phenolic compounds increase, malic acid is broken down and most flavours develop. Sugar accumulation is faster in the weeks after veraison and usually slows later. Methoxypyrazines, behind capsicum and asparagus aromas, decrease as berries mature, while floral and citrus terpenoids increase. In red varieties anthocyanins start to accumulate in the skins about two weeks before colour is visible; in white grapes phenolic compounds fall to minimal levels.

There is no single definition of ripeness. The AWRI lists several, all used in modern viticulture: juice or pulp maturity (the sugar-to-acid ratio), skin maturity, phenolic maturity (skins and seeds analysed separately), aromatic maturity, which is often not related to sugar ripeness, and seed maturity, meaning full lignification of the seed coat, which often lags behind the other measures. The one chosen depends on the wine style.

Indicative juice composition from the AWRI: sparkling wine 9 to 11 °Baumé with 8 to 12 g/L acidity; full-bodied dry red 12 to 14 °Baumé with 5 to 9 g/L; sweet white 17 to 22 °Baumé with 6 to 9 g/L. Some dry whites need an early harvest, when aroma is at its maximum and acidity is relatively high, and red varieties in hot climates may be picked early because sugar can reach its optimum before other constituents. Bunches picked before veraison generally do not ripen.