Hydroxycinnamoyl tartaric acid,

The phenolics in the grape berry are monomeric and polymeric molecules and are located in the juice (hydroxycinnamoyl tartaric acid esters), the solid part of the pulp (proanthocyanidins, hydroxybenzoic acids with structures reported in Figure 2.1), seeds (flavan-3-ols, proanthocyanidins, gallic acid) and the skin (anthocyanins, flavan-3-ols, proanthocyanidins, flavonols, dihydroflavonols, hydroxycinnamoyl tartaric acid esters, hydroxybenzoic acids, hydroxystilbens). Their levels in the grape are mainly linked to the variety, but can also be influenced by environmental variables, cultural techniques and the ripening state of the grape. 

Figure 2.2 Hydroxycinnamoyl tartaric acid (CTA, p-CuTA, FTA) esters in grape and the correspondent hydroxycinnamic acids (HCA) found in wine...

Finally, oxidation of hydroxycinnamoyl tartaric acid (HCTA) into hydroxycinnamic acids (HCA), and the successive decarboxylation operated by Saccharomyces yeasts, or reduction and decarboxylation by Brettanomyces yeasts, induce off-flavours due to vinyl phenols and ethyl phenols formation, respectively. 

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