Phenolic content in wine - quercetin. Like other flavonoids, the concentration of flavonols in the grape berries increases as they are exposed to sunlight. Some viticulturalists will use measurement of flavonols such as quercetin as an indication of a vineyard's sun exposure and the effectiveness of canopy management techniques. Anthocyanins are phenolic compounds found throughout the plant kingdom, being frequently responsible for the blue to red colors found in flowers, fruits and leaves. In wine grapes, they develop during the stage of "veraison" when the skin of red wine grapes changes color from green to red to black. As the sugars in the grape
Quinta classification of Port vineyards in the Douro the permitted production level of the vineyard and what price the grower can receive for the wine they produce from the grapes. Quintas are given numerical ratings in several categories – age of the vines, altitude, aspect, vine density, gradient, granite content of the soil, schist content of the soil, types of grape varieties planted, overall location of the vineyard, microclimate, mixture, vineyard soil type, vine productivity, and vineyard maintenance. Vineyards that have favorable attributes in a particular category (such as being planted with an optimal low density of vines) are award points while negative attribute (such as having too