Wine Arcana

Concept

Tannin

Also known as Wine tannin

Tannin is a loose wine term for phenolic compounds that can make a wine feel drying or rough and, in some cases, taste bitter. In grape wine, the main tannins are condensed tannins, also called proanthocyanidins. They come chiefly from skins and seeds. Oak contributes a different family, hydrolysable tannins called ellagitannins. Their effects depend on what the wine extracts, what reacts or precipitates later, and how the whole wine changes perception.

Where tannin comes from

Seeds contain a different profile of proanthocyanidins, with more galloylated material and no skin-derived prodelphinidins. The distinction matters because source is part of tannin's composition, not just its amount. A commercial-scale fermentation study found that seed and skin proanthocyanidins retained different subunit patterns as they entered the wine, allowing the researchers to estimate their contributions directly.1. Peyrot des Gachons & Kennedy (2003).

Juice made by pressing away the solids extracts little grape tannin. Red fermentation keeps skins and seeds in contact with the fermenting juice, so alcohol, temperature, time, crushing, cap management, and pressing determine which compounds dissolve and how much remains in the wine. Ethanol can increase extraction from seeds as fermentation progresses, while extraction from skins follows a different pattern. Ripeness and berry condition also change the material available and its extractability. A longer or more forceful maceration therefore changes a wine's phenolic composition.

A controlled Cabernet Sauvignon experiment illustrates the interaction. Wines fermented with added seeds contained more seed-derived flavan-3-ol compounds and showed increased astringency and bitterness; seed addition also increased colour intensity in that experiment.2. Pascual et al. (2016). The study used decoloured juice and a four-day macerated juice from Cabernet Sauvignon, with experimental seed or stem additions. The same physical principle underlies skin-contact white wine: keeping skins and sometimes seeds with the juice can add phenolic texture and colour, even when the grape is white.

Oak supplies ellagitannins from the wood, alongside aroma-active compounds. Toasting degrades some of the wood's native ellagitannins while creating or concentrating other extractives, so a more heavily toasted barrel does not simply contribute more tannin. Species, tree, seasoning, toast, barrel age, wine composition, and contact time all matter. In a controlled study using French oak winewood, ellagitannin extraction was fastest in the first two or three months and declined later; the wines with more ellagitannins were also rated more bitter and astringent by the trained panel.3. Chira & Teissedre (2013). The study used French Quercus robur winewood under specified toasting treatments and a defined storage experiment.

Astringency, bitterness, and colour

Astringency is principally a tactile response, not a basic taste. Tannins bind salivary proteins and reduce lubrication in the mouth, producing the drying, rough or constricted sensation associated with a tannic wine. Bitterness is a taste response, and phenolics that contribute to it are not identical in effect to those that drive astringency. The two sensations can rise together, but they need not: a model-wine study found that pH changed astringency while ethanol affected both astringency and bitterness, especially at typical wine alcohol levels.4. Fontoin et al. (2008). The findings came from grape-seed tannin oligomers in model wine solutions assessed by a 16-person sensory panel.

Wine's matrix changes the result. Acidity, alcohol, sugars, polysaccharides, pigments, and other phenolics can modify tannin–protein interactions and the way a taster integrates taste with texture. This makes “high tannin” an incomplete explanation of a sensation. The same measured tannin concentration can feel different at another pH, alcohol level, or stage of the wine's life.

Colour is a separate property. Red colour comes mainly from anthocyanins and their later derivatives, while tannin is a major partner in colour chemistry. A dark wine need not be highly astringent, and a pale wine can still contain substantial tannin. During fermentation, tannins can bind or react with anthocyanins, changing the amount and stability of colour. Seed and skin extraction can consequently affect both colour and astringency without making the two properties equivalent.

What ageing changes

During maturation, grape tannins can react with anthocyanins, acetaldehyde and other wine constituents. Some products remain dissolved, some bind into larger or differently structured material, and some become insoluble and form sediment. Oak ellagitannins can also react with wine phenolics or decline as they are transformed. Oxygen, sulfur dioxide, temperature, vessel, and storage determine which paths matter.

“Polymerization” is therefore a useful shorthand for some reactions, but a poor complete story of ageing. It suggests that small tannins simply join into ever-larger, softer chains. Wine studies instead find several simultaneous processes: direct tannin–anthocyanin products, acetaldehyde-linked compounds, oxidation, adsorption, and precipitation. In a fermentation experiment, adding acetaldehyde increased polymeric pigments and reduced protein–tannin precipitation, but that result describes a specific treatment and does not show that all bottle ageing follows the same route.5. Sheridan & Elias (2015). Acetaldehyde was added during fermentation; the result is evidence for one reaction pathway, not a general model of all ageing.

As these reactions and losses proceed, a mature red may seem less drying even though its tannin has not simply “turned soft.” Some reactive compounds have left solution, some have changed their affinity for salivary proteins, and fruit, acidity, aroma, and colour have changed around them. The direction and pace vary with the starting wine and storage.

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