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 compound that belongs to a larger group called polyphenols. They occur abundantly in nature, namely in the bark of many trees and in numerous leaves, legumes and fruits, including grapes.
Tannin molecules are usually much larger than those found in other types of polyphenols, and they have a unique ability to easily combine with other molecules, especially 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 they 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 when not yet ripe. Ripening changes the structure of the tannins through polymerization – increase of their overall length due to the combination of smaller molecules – and interaction with pectins (sugar compounds whose presence increases with maturation) and anthocyanins (red colouring compounds). Different harvest dates therefore mean different tannin structure and, ultimately, different tannic structure of the final wine, provided no corrections are made in the cellar.
Where do tannins in wine come from?
In wine, they come primarily from the skin, seeds and, to a lesser extent, the stems of the grapes. During alcoholic fermentation, the juice, skins and pips (and stems if the winemaker decides to do full or partial whole-cluster fermentation) macerate together. As sugar is processed and alcohol produced, colour and tannins are released into the wine. Tannins are soluble in alcohol, but not water; the longer the skins and pips macerate during and after alcoholic fermentation the more tannic the final wine will be. This is why pre-fermentation and carbonic maceration help to add colour (from anthocyanins) and flavour compounds to wine without the simultaneous addition of tannins.
This also explains why the colour of the wine somewhat correlates with the amount of tannins. Some tannins are pigment and/or precursor of pigment release – more tannins therefore contribute to deeper colouring.
White and rosé wines are fermented by excluding or minimising the contact with grape skins and tannin levels are therefore lower than in reds. However, if a white wine is fermented with extended skin and pip contact (i.e. producing a so-called orange wine) the level of tannins – colour from yellow to amber – can be significant.
Wood vessels, if used for fermentation and/or ageing, will also contribute to the tannic content of the wine. Different types of wood (oak, acacia, chestnut, etc) have different levels of tannin that leach out into the wine; the amount naturally decreases with each use of a given vessel.
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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 maturation at harvest and, therefore, will mirror the nature of the wine’s fruit profile.
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Source : https://www.decanter.com.master.public.keystone-prod-eks-euw1.futureplc.engineering/learn/tannins-45814/
