The véraison is the growing phase of the grapevine in which the grapes discolor and the ripening begins. During the véraison, the skins of blue grapes discolor from green to blue due, and the skins of with grapes from green to a white-green, yellowish or transparent hue. This is caused by the replacement of chlorophyll (green pigment) anthocyanins and xanthophylls in blue grapes and by carotenoids in the skin of white grape.
After the véraison, the amount of malic acid in the grapes decreases and tartaric acid becomes the dominant acid. At the same time, sugars start to accumulate in the grapes and the composition of aromas and aroma precursors start to take shape.