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. Tannin composition therefore varies with its source. 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. 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. 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. 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.
Cold-climate hybrids and measurement
Some cold-climate hybrid grapes produce dark wines with relatively little retained tannin. Watrelot's study of commercial wines found lower tannin in the sampled Frontenac, Marquette, and Petite Pearl wines than in its Cabernet Sauvignon and Pinot Noir comparison wines. Results also varied with the analytical method: abundant pigments and low tannin concentrations complicated common precipitation tests.5. Watrelot (2021), 24 commercial wines, including considerable variation within varieties; the comparison does not isolate ancestry from growing conditions and winemaking. Comparing measurements requires attention to the method as well as the grape and vintage.
What ageing changes
During bottle aging and other 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.
Wine studies identify several simultaneous processes during ageing: 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.6. Sheridan & Elias (2015). Acetaldehyde was added during fermentation; the result documents one reaction pathway under those conditions.
As these reactions and losses proceed, a mature red may seem less drying. 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.
Related topics
Sources
- Aude A. Watrelot, “Tannin Content in Vitis Species Red Wines Quantified Using Three Analytical Methods”, Molecules 26 (2021), article 4923.
- Catherine Peyrot des Gachons & James A. Kennedy, “Direct Method for Determining Seed and Skin Proanthocyanidin Extraction into Red Wine,” Journal of Agricultural and Food Chemistry 51 (2003), pp. 5877–5881, doi:10.1021/jf034178r.
- Olga Pascual et al., “Influence of Grape Seeds and Stems on Wine Composition and Astringency,” Journal of Agricultural and Food Chemistry 64 (2016), pp. 6555–6566, doi:10.1021/acs.jafc.6b01806.
- Kléopatra Chira & Pierre-Louis Teissedre, “Extraction of Oak Volatiles and Ellagitannins Compounds and Sensory Profile of Wine Aged with French Winewoods Subjected to Different Toasting Methods: Behaviour during Storage,” Food Chemistry 140 (2013), pp. 168–177, doi:10.1016/j.foodchem.2013.02.049.
- Hélène Fontoin et al., “Effect of pH, Ethanol and Acidity on Astringency and Bitterness of Grape Seed Tannin Oligomers in Model Wine Solution,” Food Quality and Preference 19 (2008), pp. 286–291, doi:10.1016/j.foodqual.2007.08.004.
- Marlena K. Sheridan & Ryan J. Elias, “Exogenous Acetaldehyde as a Tool for Modulating Wine Color and Astringency during Fermentation,” Food Chemistry 177 (2015), pp. 17–22, doi:10.1016/j.foodchem.2014.12.077.