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 that the wines that were available were of high quality and not something that could tarnish the reputation of the Douro. Over the years the system of licensing growers turned into a rating classification operated by the IVDP. The system only pertains the production of Port. A quinta that is growing grapes for both Port and table wines, can do whatever they like with the grapes destined for table wine production regardless of its classification rating. Each year the IVDP classifies and rates the vineyards on an A-F scale with A being the highest level. A quinta's rating will dictate