Structure and Properties of Wine Pigments and Tannins

TLDR

Grape phenolics, including tannins and anthocyanins, are diverse, unstable compounds whose extraction, protein interactions, and reactions during red wine aging drive quality changes, yet their structures and properties are frequently misunderstood. The review highlights that tannin and anthocyanin reactions produce both large polymers and small species, with polymeric pigments susceptible to sulfite bleaching, while astringency loss during aging may result from cleavage, and sensory properties are modulated by interactions with other wine components.

Abstract

Grape phenolics are structurally diverse, from simple molecules to oligomers and polymers that are usually designated “tannins,” referring to their ability to interact with proteins. Anthocyanin pigments and tannins are particularly important for red wine quality. Their extraction depends on their location in the berry and their solubility. All phenolic compounds are unstable and undergo numerous enzymatic and chemical reactions. Color and taste changes during red wine aging have been ascribed to anthocyanin-tannin reactions. The structures and properties of tannins and pigmented tannins from these reactions are often misunderstood. Current research on wine phenolic composition is reviewed, with emphasis on the following issues: (1) reactions of tannins yield both larger polymers and smaller species; (2) anthocyanin reactions can generate colorless species as well as polymeric and small various pigments; (3) some polymeric pigments undergo sulfite bleaching while some low molecular weight pigments do not; (4) polymers are both soluble and astringent, so the astringency loss during aging may involve cleavage rather than polymerization; and (5) sensory properties of anthocyanins and tannins are modulated by interactions with other wine components.