Tannins

Tannins are polyphenolic compounds naturally present in grape skins, seeds, stems, and oak wood. In plain terms, polyphenolic means belonging to the polyphenols: Decanter describes tannins as bitter and astringent chemical compounds belonging to that larger group, found in the bark of many trees and in numerous leaves, legumes and fruits, including grapes. Tannins have a long link with leather: tannin molecules easily combine with other molecules, especially proteins, and Decanter notes that this is the basis of leather production, in which animal hide is tanned using tree barks. The AWRI (Australian Wine Research Institute) describes tannins as a sub-class of phenolics that can precipitate proteins, in other words bind to proteins so they drop out of the liquid, and says tannins contribute to wine texture, particularly astringency, the drying feel in your mouth.

• The OIV (International Organisation of Vine and Wine), in its International Oenological Codex, sorts the tannins used in winemaking into two classes: hydrolysable tannins and condensed tannins
• According to the OIV, condensed tannins are polymers, meaning molecules made by joining many smaller units into longer chains, built from compounds called flavan-3-ols
• Grape tannin and wine tannin are not the same thing: the AWRI says that once extracted, grape tannins begin to chemically rearrange into wine tannins, which can be significantly different in structure

WSET names tannin as one of the big three contributors to how a wine feels in the mouth, alongside alcohol and acidity. In WSET's words, "A red wine with no tannin just wouldn’t taste (or more accurately feel) like wine." Tannin also adds to body, the sense of weight a wine has in the mouth: WSET lists alcohol, tannin and flavour intensity as contributors. Decanter adds that tannins influence wine colour and contribute to ageing potential.

• Colour and tannin are linked: Decanter says the colour of a wine somewhat correlates with its amount of tannin, because some tannins are pigments or precursors of pigment release
• Tannin changes food matches: WSET says wines with more tannin can be smoothed out by serving them with a savoury, high-protein (often meaty) dish
• In nature, Decanter explains, tannins make unripe fruits and seeds unpalatable, which dissuades animals from eating them before they are ripe

Decanter advises describing tannins by the tactile sensations they produce, thinking of mouthfeel rather than aroma or flavour. WSET's tasting tip is to compare two sensations: acidity makes your mouth water, while tannins have a mouth drying effect. Decanter adds that you will often feel tannins on your gums. To practise, WSET suggests tasting a Cabernet Sauvignon beside a Pinot Noir: the Cabernet may have quite a high level of tannin and feel drying and grippy on your tongue, while the Pinot Noir generally has less tannin and may feel softer and more delicate. Serving temperature matters too: WSET warns that serving a red wine too cold may make its tannins feel firmer or more astringent.

• Decanter suggests two groups of descriptors: texture (soft, velvety, silky, or coarse, grainy, chalky) and maturity (green, crunchy and unripe, or juicy, smooth and sweet)
• WSET's texture words include grippy, astringent, fine and smooth (especially in a mature wine), sandpapery, gravelly and cotton woolly
• Astringency and bitterness are different: Decanter explains that bitterness is a taste while astringency is a textural sensation, although tannins can produce both, particularly in young red and orange wines

Because tannins sit mostly in grape skins and seeds, Decanter says varieties with thicker skins generally have the potential to produce more tannic wines. WSET draws the same contrast between thinner-skinned Pinot Noir, which simply has less colour and tannin to give, and thick-skinned Cabernet Sauvignon. Place matters as well as grape. Decanter compares a Barossa Shiraz, likely made with riper fruit and soft, rounded, velvety tannins, with a Rhône Syrah from cooler banks, whose less developed tannins give a grainier, more angular mouthfeel.

• Notably high in tannin, per Decanter: Cabernet Sauvignon, Nebbiolo, Sangiovese, Malbec, Mourvèdre/Monastrell, Syrah/Shiraz, Tannat and Tempranillo
• Less tannic, per Decanter: thinner-skinned grapes such as Pinot Noir, Gamay and Grenache
• Vintage and site change tannin too: Decanter says a cooler vintage yields grapes with less sugar and greener tannins, and that grapes at higher altitude or in extreme wind thicken their skins as a natural defence

Winemakers have a lot of say in how much tannin ends up in the glass. WSET compares red winemaking to brewing tea: temperature and time both play a role in how deeply coloured and tannic the wine becomes during fermentation. Decanter explains that the longer the skins and pips (seeds) macerate, or soak, during and after fermentation, the more tannic the final wine will be, and lists fermentation temperature, length of maceration and even the type of yeast as choices that affect how much tannin is extracted. The AWRI says tannins from skins tend to be more easily extracted than those from seeds, and that the time skins and seeds spend in contact with the juice or wine is probably the most critical factor in defining the wine's phenolic profile (its make-up of tannins and related phenolic compounds) and sensory properties. White grapes can make tannic wine too: orange or amber wines are white wines fermented on their skins, and the AWRI says they have noticeable tannin astringency but are mostly less astringent than red wines.

• Extended post-fermentation maceration leaves skins, seeds and any stems in the wine after fermentation to extract more colour, flavour and tannin; the AWRI says the most commonly reported risks are bitterness and overly astringent tannins
• Tannin can also be added: the AWRI notes that grape and seed tannin extracts, called oenotannins, can legally be added to wine at rates from 50 to 1,000 mg/L to stabilise colour or add astringency or texture
• Oak can add tannin of its own, according to WSET; Decanter says the amount of wood tannin in a wine increases the longer it stays in a wooden vessel, and the amount a vessel gives decreases with each use

Red wines often feel softer as they age. Matt Walls, quoted by Decanter, says tannins often become softer and less astringent over time, which is one of the key reasons certain types of wine are aged before drinking. Why this happens is still being studied: the AWRI's Technical Review No. 207 (December 2013) notes that the reasons are not fully understood and that the explanations suggested have sometimes been contradictory. In an AWRI trial that followed one Cabernet Sauvignon for 24 months in bottle, tannin concentration decreased substantially and tannin size decreased slightly, and the study concluded that red wine texture softens with ageing due largely to a decrease in tannin concentration and tannin size. Decanter describes the change another way: tannin molecules polymerise, joining into longer chains, and eventually precipitate as sediment, after which they no longer give any bitterness or astringency and take some of the wine's colour with them.

• Tannin and colour change together: in the AWRI trial, as total tannin fell, a growing share of it was pigmented tannin formed from the wine's purple anthocyanins (the red colouring compounds in grapes), which contributes to longer-term colour stability
• Winemakers have some control: the AWRI found that lower wine pH (a more acidic wine) and a screw cap liner letting in a slight amount of oxygen sped up colour ageing, giving winemakers some control over tannin and colour development
• Tannin generally helps a wine last: Decanter says tannins generally give wine more longevity, and their grip makes wines feel fresher as the primary fruit aromas fade

Primary sources: https://www.wsetglobal.com/knowledge-centre/blog/2026/the-secret-language-of-wine-what-is-mouthfeel, https://www.wsetglobal.com/knowledge-centre/blog/2021/september/23/what-determines-the-colour-of-wine, https://www.wsetglobal.com/knowledge-centre/blog/2022/september/27/busting-wine-industry-jargon, https://www.wsetglobal.com/knowledge-centre/blog/2019/november/how-to-build-your-wine-tasting-skills/, https://www.wsetglobal.com/knowledge-centre/blog/2023/october/03/how-many-wine-types-and-styles-are-there, https://www.wsetglobal.com/knowledge-centre/blog/2023/july/13/four-rules-to-masterful-food-and-wine-pairing, https://www.wsetglobal.com/knowledge-centre/blog/2026/how-to-pair-drinks-with-spice/, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-oenotannin-addition/, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-extended-post-fermentation-maceration/, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-amber-wine/, https://www.awri.com.au/wp-content/uploads/2011/07/Technical_Review_Issue_207_McRae.pdf, https://www.awri.com.au/wp-content/uploads/2014/12/Measuring-extractable-tannin-fact-sheet.pdf, https://www.oiv.int/standards/international-oenological-codex/part-i-monographs/monographs/oenological-tannins, https://www.oiv.int/. Secondary sources: https://www.decanter.com/learn/tannins-45814/, https://www.decanter.com/learn/tannin-45807/. Last verified 2026-09-28