Phenolic acids (especially cinnamic acids) are the major phenolics in grape pulp and juice, and thus in white wines made without skin contact. Anthocyanins are localized only in the skins, except in red-fleshed teinturiers, so that red winemaking requires a maceration phase to extract them into the juice. Flavonols, which are constituents of skins, stems, and leaves, as well as catechins and tannins, which are also present in seeds, are simultaneously extracted. Alcohol, produced by fermentation, greatly speeds up this extraction process. Additional phenolics (including gallotannins and ellagitannins as well as flavour compounds such as vanillin) may also be present in wine as a result of barrel ageing, the use of oak chips, or the addition of oenological tannins. Once extracted into the wine, the anthocyanins, catechins, and tannins are gradually converted to various types of derivatives, including pigmented tannins. These reactions are responsible for the colour and taste changes observed during wine ageing.
