Veraison is a French term used in viticulture that marks a significant transition in the annual life cycle of a grapevine. This is the moment the vine switches its focus from creating energy for vegetative growth to consuming stored energy to mature the fruit. This stage signifies the beginning of the final ripening process, setting the trajectory for the final quality and style of the harvest.
Defining the Start of Ripening
Veraison is most immediately recognized by the striking visual changes that occur in the vineyard. Before this stage, all grape berries are small, hard, and bright green due to the high concentration of chlorophyll. Ripening begins when the green pigment breaks down, allowing other pigments to become visible.
For red grape varieties like Cabernet Sauvignon or Pinot Noir, this process is particularly dramatic as the berries change color from green to shades of red, purple, or black. This visible shift is caused by the synthesis of anthocyanin compounds within the grape skins. White grape varieties experience a less obvious color change, transitioning from opaque green to a more translucent, yellowish, or golden hue as carotenoids develop.
The physical texture of the grapes also changes noticeably during veraison. The berries begin to soften, becoming more pliable and elastic as they swell with accumulating moisture and sugars. This transition does not happen simultaneously across an entire vineyard. It often starts with a few berries on a cluster and an uneven distribution across the various clusters on the vine.
The Chemical Transformation
Veraison initiates profound internal biochemical shifts within the grape berry. Once ripening commences, the vine begins rapidly transporting sugars, primarily glucose and fructose, from the leaves into the fruit. These sugars, which represent the energy the vine has produced through photosynthesis, can accumulate until they make up over 25% of the berry’s weight.
Simultaneously, the acidity levels within the grape berries begin a sharp decline. Malic acid, which is the tart acid also found in green apples, degrades significantly through a process called respiration. This reduction in malic acid leaves tartaric acid as the predominant organic acid, softening the overall tartness of the grape.
The synthesis of various compounds that contribute to the final taste and aroma of the fruit is also accelerated after veraison. For red grapes, the formation of anthocyanins provides the color, while the development of phenolic compounds, specifically tannins in the skins and seeds, contributes to the texture and structure. Additionally, varietal aroma precursors begin to be synthesized and stored in the grape pulp and skins. As ripening progresses, undesirable herbaceous notes, often caused by compounds like methoxypyrazines, gradually diminish, making way for fruit-forward characteristics.
Importance for Grape Management and Harvest
Veraison serves as a fundamental benchmark for viticulturists, providing a clear indication of where the crop stands in the ripening cycle. Since the period between the start of veraison and full maturity is relatively consistent, it allows growers to accurately estimate the approximate harvest date. Depending on the grape variety and local climate, this ripening period typically lasts between 40 and 60 days.
This stage dictates several management decisions aimed at ensuring even and complete ripening across the entire vineyard. Growers often perform canopy management actions, such as strategic leaf pulling, to ensure the berries receive adequate sunlight exposure. Another practice is crop thinning, where unevenly ripening clusters or those lagging behind are intentionally removed from the vine. This action directs the vine’s energy and nutrient resources to the remaining clusters, encouraging them to ripen simultaneously and reach optimal quality.
Growers also carefully adjust irrigation at this point. They often reduce water availability to slow berry swelling and concentrate the flavors and sugars in the fruit, which is known as managed water stress.