The saying goes that by Saint Joaquin and Saint Ana the grapes get coloured; with the sun as a witness, in the second half of July the vineyard is in one of its crucial points, perhaps the most important process after flowering. The berries are green and develop a photosynthetic activity as if they were leaves. Its sugar content is low and acidity is too high, the grain is inedible, precisely because of the high content of acids.
With veraison process begins the great transformation in the cluster: acids (mainly malic acid, tartaric acid, and a lesser presence of citric acid) are yielding in favor of sugars (fructose and glucose) as a result of photosynthesis and from reserves that were being accumulated in the wood of the plant. This is one of the reasons that older vineyards have higher quality and more regular maturation within the same plot.
This process not only occurs in the biochemical composition of the fruit, but also it is visible in the visual aspect of the cluster, by causing a color change from green to yellow in white varieties or to the black-bluish color in red varieties.