The Wine Blokes

Cabernet Franc grapes undergoing veraison.

Veraison is a French term, but has been adopted into the English literature on viticulture. The official definition of veraison is “change of color of the grape berries.” Veraison signifies the change from berry growth to berry ripening in grapevines.

Process

Many changes occur at veraison. Grape berries follow a double sigmoid growth curve. The initial phase of berry growth is a result of cell division and cell expansion. As berry growth of phase I slows this is termed the Lag phase. The lag phase is not a physiological growth stage, but an artificial designation between the two growth periods of grape berry development.

Degradation of Malic acid results in a decrease of berry titratable acidity. Grapes also possess a small amount of citric acid, but Tartaric acid is another dominant acid. Tartrate accumulates early in phase I of berry growth, while Malic acid accumulates at the end of phase berry growth.

Accumulation of hexose sugars (sucrose, fructose) is associated with the development of xylem cell dicontinuities. The deposition of sugar into the berry depends on the level of leaf photosynthesis, the numer of competing sinks on the vine and sugar importation. Herbaceous aromas are degraded. It is unknown whether the degradation of herbaceous aromas allows fruit aromas to be detected, or if fruity aromas develop later in berry ripening.

The berry then changes in color. Presumably chlorophyll is broken down. In White cultivars carotenoids are formed, while in red cultivars anthocyanins and xanthophylls are formed. The trigger of veraison is unknown.