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
Wine Grapes franc may have originated in Basque country of Spain. Additionally the origins of the assumed to be French varieties of Mourvèdre, Grenache and Carignan are shown to likely be Spanish instead. Another detail revealed by DNA testing and reported in "Wine Grapes" is that several northern Italian white wine grape varieties including Favorita, Pigato and Vermentino are genetically the same grape vine which is known under the synonym of "Rolle" in France but has no genetic relationship to the Rollo grape of Liguria. A number of grape varieties are illustrated by reproductions of colour plates from "Ampélographie. Traité général de