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Tannins in wine, tea, whisky and coffee - where astringency comes from

That characteristic, astringent, almost dry sensation in the mouth that strong red wine, strongly brewed tea, cask whisky or some coffees leave behind has a common source: tannins. Although we associate them mainly with wine, the same compounds link four of the most popular drinks in the world, giving them astringency and structure. Understanding what tannins are, where their astringent character comes from and why it is not the same as bitterness changes the way we perceive these drinks. In this cross-niche post we will look at tannins in wine, tea, whisky and coffee: you will learn the common mechanism of astringency, the differences between the drinks and practical ways to come to love this flavour. It is a journey through one compound linking four different worlds of tasting.

What tannins are

Tannins are a group of chemical compounds belonging to a larger family of polyphenols. They are characterised by a bitter and astringent taste. Tannin molecules are usually much larger than other polyphenols and have a unique ability to combine with other molecules, especially proteins, causing them to precipitate. It is precisely this ability to bind proteins that lies at the root of their characteristic action in the mouth. Tannins occur abundantly in nature: in the bark of many trees, in numerous leaves, legumes and fruits, including grapes. Besides wine, we find them in tea, coffee and dark chocolate. They are among the most important compounds affecting the flavour and feel of many drinks and products. Understanding what tannins are is the key to grasping why such different drinks as wine, tea, whisky and coffee can give a similar, astringent sensation in the mouth. It is a common chemical denominator linking these worlds.

Where astringency comes from

The secret of the astringency of tannins lies in their ability to bind proteins. Because tannins combine with other proteins, including the proteins present in human saliva, they create a characteristic, astringent, mouth-coating sensation. The mechanism is fascinating: our saliva contains proteins that normally moisten and lubricate the mouth. When tannins bind with them and precipitate, the saliva temporarily loses its lubricating properties, and we feel dryness, roughness and a puckering. This is what we call astringency. It is not a taste in the classic sense, but a tactile sensation in the mouth. That is why we feel astringency across the whole oral cavity, rather than only on the taste buds. This precipitation of saliva proteins by tannins is a universal mechanism, the same in wine, tea, whisky and coffee. Understanding that astringency is a physical reaction of tannins with saliva, rather than a taste, is the key to grasping this sensation in all drinks.

Astringency is not bitterness

A common misunderstanding is confusing astringency with bitterness, and these are two different things. Bitterness is one of the basic tastes, detected by the taste buds on the tongue. Astringency, on the other hand, is a tactile sensation, that is the puckering, dry feeling across the whole oral cavity, resulting from the binding of saliva proteins. Tannins can give both sensations at once, because they are sometimes both bitter and astringent, which further complicates matters. But it is not the same. You can have a drink that is very astringent but not very bitter, and vice versa. Distinguishing these two sensations is an important step in tasting: by learning to separate them, you better understand what you really feel. When a strong tea seems unpleasant to you, it is worth asking whether it is bitterness or astringency, because they flow from different sources and are softened in different ways. Understanding that astringency is a physical sensation and bitterness is a taste orders the impressions and makes tasting more conscious in each of the four drinks.

Tannins in wine

Wine is the most obvious home of tannins, especially red wine. They come mainly from the skins, seeds and stems of grapes, and also from the oak casks in which the wine matures. It is tannins that are largely responsible for the astringency of red wines and for the impression of dryness and roughness. They also play a positive role, however: they give the wine structure, a backbone and aging potential. Young, strongly tannic wines, like Cabernet Sauvignon or Nebbiolo, can be downright aggressively astringent, but with age the tannins soften, polymerise and smooth out, making the wine softer and more harmonious. That is why many great red wines require years of maturing. Tannins in wine are not a fault, but the foundation of its build and ability to evolve. White wines have far fewer of them, because they are made without contact with the skins. Tannins are one of the key elements of wine tasting. We write more about how wine is made in our post how wine is made.

Tannins in tea

Tea is the second great world of tannins, though here the mechanism is somewhat different. The astringency of tea comes largely from catechins, that is a group of polyphenols related to tannins, especially abundant in green tea. It is they that give that puckering, dry sensation, especially in strongly or too long brewed tea. Astringency in tea is strongly dependent on the way of brewing: water that is too hot and a steeping time that is too long draw out more tannic compounds, making the brew unpleasantly astringent and bitter. That is why delicate green teas are brewed with cooler water and for a shorter time. Tannins in tea, in the right amount, add structure and character, but in excess they spoil the brew. Skilful brewing is the art of controlling their extraction. Understanding the role of tannins and catechins explains why the same tea can be delicious or undrinkable, depending on the brewing. We write more about this in our post on why your tea tastes bitter.

Tannins in whisky

Whisky is a less obvious but real source of tannins, coming from the oak cask in which the drink matures. Oak wood contains tannins, which during years of maturing pass into the whisky, giving it structure, a pleasant dryness and a note of spice. They co-create the flavour skeleton of a mature whisky, alongside the vanilla and lactones from the same wood. Oak tannins account for that astringent, slightly puckering sensation felt in many whiskies, especially those aged long in active casks. In excess, with too long maturing, they can make a whisky overly tannic and drying, much like too strong a tea brew. In the right amount, however, they add depth and balance to the drink. It is a good example of how the same compound, tannin from oak, shapes both wine and whisky, because both mature in wood. We write more about the role of the cask in our post on how the cask makes whisky.

Tannins in coffee

Coffee is the fourth drink in which tannins and related compounds play a role. Coffee contains polyphenols, including compounds of a tannic character and chlorogenic acids, which contribute to its astringency and puckering sensation, especially with over-extraction. Coffee brewed too long or too hot becomes astringent and bitter, much like over-brewed tea. Astringency in coffee, however, tends to be less prominent than bitterness or acidity, which is why it is talked about less often. Even so, the puckering sensation after drinking a strong, dark-roasted coffee is partly the work of these compounds. Proper extraction, that is the right grind size, time and temperature, lets you control the astringency, so the coffee is balanced rather than rough. Tannins in coffee are another example of the same mechanism of astringency that links it with wine, tea and whisky. We write more about coffee flavours in our post on types of acidity in coffee.

Why plants make tannins

Why do plants produce tannins at all? The answer lies in their defensive biology. Plants make these compounds to protect themselves from UV radiation, provide pigmentation, prevent microbial infections, control growth and support other important life processes. The astringent, puckering taste of tannins also discourages animals from eating unripe fruit and leaves, acting as a natural protection. That is why unripe fruit can be so astringent: the plant protects the seeds until they are ready. When the fruit ripens, the tannins often soften, signalling readiness. This defensive function explains why tannins are so widespread in the plant world, from grapes, through tea leaves, to oak bark. What for the plant is a survival mechanism, for us became an element of flavour and structure of our favourite drinks. Understanding the biological role of tannins adds depth to appreciating them: drinking astringent wine or tea, we taste a plant defence mechanism transformed into the pleasure of tasting.

How to come to love astringency

Astringency can be difficult at first, but it can be learned and come to be loved. Let us gather practical ways to tame tannins in the four drinks:

The table shows that the key is controlling extraction and the right serving. An important, shared trick is combining astringent drinks with food rich in protein and fat, like cheese or meat. The proteins in the food bind the tannins before they reach your saliva, softening the puckering sensation. That is why a strong red wine tastes so good with fatty meat or cheese.

The common denominator of four drinks

Tannins are a fascinating example of a compound that links four of the most popular drinks in the world. The same mechanism, that is the binding of saliva proteins giving a puckering sensation, works identically in wine, tea, whisky and coffee, even though they are drinks from completely different worlds. They differ in the source of the tannins: in wine it is grape skins and seeds and oak, in tea the leaves and their catechins, in whisky the oak cask, in coffee the bean and chlorogenic acids. But the effect in the mouth is related. This shows how chemistry links seemingly distant fields of tasting. Understanding tannins in one drink helps understand them in all the others, and the ability to recognise astringency is a universal tasting tool. Astringency, once a plant defence mechanism, became a common language of the flavour of wine, tea, whisky and coffee. It is one of the most beautiful examples of how the same chemical principle manifests in four different, beloved drinks of the world.

The key points in a nutshell

Tannins are polyphenols of large molecules that bind with proteins, including saliva proteins, giving the characteristic, puckering, dry sensation called astringency. It is a tactile sensation, rather than a taste, so it differs from bitterness, although tannins can give both at once. They link four drinks: in wine they come from skins, seeds and oak, in tea from leaves and catechins, in whisky from the cask, and in coffee from polyphenols and chlorogenic acids. Plants produce them for defence. Astringency can be softened by proper extraction, decanting, time and food rich in protein and fat. Want to record astringency impressions in different drinks? Keep notes in the GustoNote app. See also our posts on oak tannins in whisky and tea astringency.