Veraison is the term used in viticulture (wine-growing) to indicate one of the stages in the course of maturing. It is originally French, but has been adopted into English use. It marks the transition between the growth and the ripening of the grape and it can be easily recognized for the change in the colour of the fruits. From this moment, the grape pigment ceases to be green, the Red wine varieties will turn either red or blue while the White wine varieties become golden or yellow.
The process will always take place in summer and allows to roughly estimate the moment for harvest, which will occur in 40 to 50 days after Veraison, always depending on the grape varieties and the climate of the different areas.
As the grape grows, it undergoes changes both morphological and physiological, that will allow the fruits to accumulate substances such as sugars, acids, primary aromas and phenolic compounds (responsible for the colour, flavour and structure), all of which are decisive for the grapes to fully mature and develop. Whenever there is a good balance among them, that will be the moment of harvest.
The most important parameters to decide the optimal ripeness point and, therefore, to begin with the harvest are: the concentration of sugars, which will later become alcohol through fermentation, the concentration of acids and the condition of the skin.
In the past, farmers used to taste the grapes from Veraison, valuing the sweetness (sugar) and the decrease of acidity to determine the exact moment for the harvest. It was a totally empirical process.
That is why the Veraison is so important, as indicative factor to approximate the timing of the harvest, which can vary greatly depending on the weather and the grape variety.
Pure viticulture begins at the Veraison.