Veraison is the time of year grapes begin to change color, tannins ripen and astringent malic acid begins to give way to softer tartaric acid. Leaves are often pruned at this time to give grapes more sun and wind exposures. It’s during this time of the year where we like warm days and cool nights. We don’t want any rain during this time of year either.
The weather can dramatically affect the entire growing season at this time. Late rains can dilute sugar levels and excessively high temperatures can lower acidity too much. This can make wines either flat and boring or overly alcoholic. The risk of leaving grapes on the vine for too long must be weighed against the need to develop varietal characteristics.
If you are visiting a vineyard, and notice the grapes turning from a hard green state to their soften color form, you are watching veraison. You might think once the grapes turn they are ready for harvest, but that is not the case. Now is the time they ripen and the sugar levels increase. It’s during this time the grapes develop their sweet and fruity aromas.