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Tannins – What are they and what do they do?

Tannins are a recurring term in wine descriptions and a fundamental part of wine jargon. But what are they and what role do they play in a wine's structure and character?

Your quick reference guide to understanding tannins, their role in wine and how to identify and describe them.

What are tannins?

Tannins are a type of bitter and astringent chemical compounds that belongs to a larger group called polyphenols. They occur abundantly in nature, namely in the bark of many trees and in a variety of leaves, legumes and fruits, including grapes.

Tannin molecules are typically much larger than those found in other types of polyphenols, and they have a unique ability to easily combine with other molecules, namely proteins, causing them to precipitate. This is the basis of leather production, in which the structure of animal hide is changed (tanned) by using various tree barks.

What do tannins do?

Because tannins bind with other proteins, including those in human saliva, they create a characteristic astringent, mouth-coating sensation in the mouth.

Their primary role in nature is to make unripe fruits and seeds unpalatable, thus dissuading animals from eating them.

Where do tannins in wine come from?

Tannins in wine come primarily from the skin, seeds and, to a lesser extent, the stems of the grapes. During fermentation, the juice, skins and pips (and sometimes stems if the winemaker decides to do full or partial whole cluster fermentation) macerate together. As sugar is processed and alcohol produced, colour and tannin are released into the wine – alcohol will dissolve more tannins than water and therefore the longer the skins and pips macerate during and after fermentation the more tannic the final wine will be.

Because white and rosé wines are fermented by excluding or minimising the contact with grape components, tannin levels will be lower than in reds. On the other hand, if a white wine is fermented with extended skin and pip contact (i.e. thus producing a so-called orange wine) the level of tannins can be as significant as in a red wine. White wines contain structures similar to the pigmented tannins of a red wine, but the absence of anthocyanins, the compounds responsible for red pigmentation, explains why they look different and do not impart the same colour.

Tannins can also come from the wood vessels in which a wine is fermented and/or aged. Wood can impart both tannins and flavour to wine.

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How to describe tannins?

Tannins can be best described through the tactile sensations they produce – think more of mouthfeel rather than aroma or flavour. It’s important to consider both their quantity and quality; whether more or less present, tannins can be very different in structure and cause very different sensations when you taste a wine.

There are two useful groups of descriptors to define tannins – according to texture and maturity.

Are the tannins soft, velvety, silky? Or coarse, grainy, chalky? These are examples of textural characteristics that mirror the sensations tannins can cause in your mouth.

Regarding maturity, do they make you think of green, crunchy, unripe fruit? Or of juicy, smooth and sweet pulp? The nature of tannins is closely linked to the grapes’ level of ripeness and, therefore, will mirror the nature of the wine’s fruit profile.

Another important differentiation to make is astringency vs. bitterness. Bitterness is a taste character while astringency is, as already discussed, a textural sensation. Even though tannins are not flavour compounds, they can produce a feeling of bitterness in addition to the mouth-coating grip. This is particularly true for young red and orange wines.

What grapes have high tannins?

Some grapes are naturally higher in tannins than others. In general, and because tannins are predominantly in the skins and seeds of each grape, varieties with thicker skin will have the potential to produce wines with higher tannins. Varieties notably high in tannins include Cabernet Sauvignon, Nebbiolo, Sangiovese, Malbec, Mourvèdre/Monastrell, Syrah/Shiraz, Tannat and Tempranillo. Thinner skinned grapes – such as Pinot Noir, Gamay, Grenache – are therefore less tannic.

This is also true for lighter-skinned grapes. A thick-skinned white variety will also have a relatively high amount of tannins.

Still, growing conditions and winemaking choices have a crucial impact on the development and extraction of tannins and on the amount that actually goes into a wine from a given variety.

This accounts for the dramatic variations in a wine from a given region, produced from the same grapes in different vintages. Or for expressions of the same variety from very different growing regions. Take for example a Barossa Shiraz vs a Rhône Syrah. The former will likely be made with riper fruit at greater alcohol potential and the tannins will, therefore, be soft, rounded and velvety. The latter’s fruit, hailing from the cooler banks of the Rhône, will not be as ripe and the tannins not as developed, for a grainier and more angular mouthfeel.

In terms of winemaking, decisions such as fermentation temperature, length of maceration (how long the juice stays in contact with the grapes’ skins), number and vigour of punch-downs or even the type of yeasts used will have an impact on the amount of tannins that are extracted from the grapes and leached into the wine.

Do tannins help wine age?

Tannins do play an important role in wine ageing. Evolution of grape tannins and the tannins imparted by wood contribute to changing aroma, flavour and textural characteristics over time. The nature and number of tannins change naturally: the tannin molecules will gradually polymerise (combine to form larger chains) and eventually precipitate as sediment.

Once polymerised the tannins will no longer impart any bitterness or astringency effect. But as key structural components, the presence of tannins will give wine more longevity – that ‘grip’ caused by tannic astringency will make wines feel ‘fresher’ as the primary fruit aromas get lost.

What foods are high in tannins?

Tannins are mostly associated with wine – both red and skin-macerated whites (the so-called orange wines). But you will also find them easily in tea, coffee and dark chocolate. While present in many fruits (namely grapes!), nuts, spices, and legumes, they will be in much lower concentrations and therefore not as perceptible.

But taste an over-steeped black tea and you’ll have no trouble identifying the characteristic astringency of tannins.

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