Definition - What does Veraison mean?
Veraison is a French word that describes the start of the ripening process when the grapes change colors and sweeten naturally. The beginning of veraison occurs in late July for wine growing regions in the Northern Hemisphere and late January for regions in the Southern Hemisphere, but each variety starts their process at their own specific time.
In this process, the energy stores from the roots are moved into the grapes, causing them to swell with sugar and other nutrients that start to change the color of the skin.
WineFrog explains Veraison
During the Veraison season, there are chemical reactions that take place inside the grape that help their characteristics develop, which makes them great for making wine. The chlorophyll (which makes the grapes green) is replaced by carotenoids in white grapes or anthocyanins in red grapes during varaison. These chemicals start to change the green grapes to purple (for red varieties) or golden (for white varieties) when they are filled with glucose, fructose and aromatic properties.
The acid levels also start to fall, and then, as they continue to ripen, the acidity decreases while sweetness increases until they reach the perfect balance for harvesting. The varaison period also signals to viticulturists when to trim their vines, prepare for pests, and keep an eye on the clusters, as some can change color unevenly or faster/slower than others.