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
Phenolic content in wine the vanilla notes in wines that have been aged in oak. Trace amounts of vanillin are found naturally in grapes, but they are most prominent in the lignin structure of oak barrels. Newer barrels will impart more vanillin, with the concentration present decreasing with each subsequent usage. Oak barrel will add compounds such as vanillin and hydrolysable tannins (ellagitannins). The hydrolyzable tannins present in oak are derived from lignin structures in the wood. They help protect the wine from oxidation and reduction. 4-Ethylphenol and 4-ethylguaiacol are produced during ageing of red wine in oak barrels that are infected by brettanomyces