Tannins are the most confusing and misunderstood flavour or characteristic of wine.
White wines and rosés generally don’t have any tannin so this article is about red wine.
Tannins is a catch-all word for a range of organic molecules found in wine called polyphenols.
They come primarily from the skins of grapes but also from pips, oak barrels, stems and, in some wines, the additions of oak chips or tannin powder.
Polyphenols are present in many plants as well as grapes, for example in tea, cocoa, wood and fruits.
Read more: Wine tips: ‘Acidity is a balancing act with sweetness and tannins’
In wine they perform two important tasks
Firstly they act as preservatives. They react with oxygen in the wine, which prevents the wine oxidising and turning brown, losing its freshness or developing Sherry aromas.
They also inhibit aerobic bacteria from growing, notably the acetobacter which produces vinegar.
Secondly, they contribute to the flavour, body and texture of wines in a complex and often divisive way. The main reason for the complexity is that tannins evolve over time.
They are not alive but their chemical reactions with oxygen and other molecules in wine are very slow, sometimes taking years to achieve.
The whole concept of ageing red wine is about the evolution of the tannins.
Read more: From a French vineyard: The science behind why wine goes bad
Young tannins tend to have an astringent character
Astringency is the drying sensation on our gums and tongue. It should not be confused with acidity, although it often is because acidity causes a similar puckering sensation.
The way to differentiate is to think of whether the sensation is similar to sucking a lemon (acidity) or drinking unsweetened green tea (astringency).
As wine ages, those astringent young tannins will transform into bigger but smoother-feeling tannins.
Wine tastes smoother as tannins mature
Mature tannins still have a presence and texture but not the mouth-drying effect of young ones.
As they evolve into larger molecules they lose their solubility, precipitate and form a sediment in the bottle, making the wine feel softer and smoother.
However, it is important not to stir up the sediment or pour the dregs into your glass. That is one of the reasons for decanting older wines into a carafe.
The other reason being to aerate the wine, which also has the effect of softening astringency if done an hour or two before serving.
Tannins also release complex and interesting aromas and flavours as they age and transform. The appeal of a perfectly aged bottle of fine red wine is not simply that it is smooth.
The aromas of perfumed woods, herbs, spices and dried fruits all come from the transformation of tannins over time and are quite different to those found in young wines.
Read more: Wine tasting basics: describing the smell, the flavour and the texture
Winemakers can control tannin
Winemakers can alter the type and amount of tannin they extract from the grape skins by various means.
As grapes ripen, their skins become less astringent and more flavoursome. Therefore picking grapes that are “phenolically” ripe will produce rounder wines.
The length of time the skins are left in the fermenting wine will also affect how much tannin is extracted.
Finally, ageing wines in oak barrels transforms the tannins by allowing them to combine with oak tannins and with tiny amounts of oxygen, due to the porosity of the barrels.
This has the effect of creating a wine that can not only be kept for a longer period of time but is ready to drink earlier.
Wine industry can fool you
Wines which have the potential to improve with age have more value that short-lived wines.
This led to the conception that any wine that smelled of toasted oak and had a deep colour was a high-quality wine.
The wine industry is particularly good at fooling customers. In the 1990s toasted oak chips became very popular, especially in countries like America and Australia.
They allowed wineries to produce oaky wines much more quickly and cheaply than by storing the wine in costly barrels for a year or two.
An acquired taste
People vary widely in their tolerance and enjoyment of tannin in wine. Younger people and those with little experience of serious red wines often find any amount of tannin distracting and unpleasant.
One can think of tannin as an acquired taste, similar to the bitterness of hops in beer and chillies in spicy food.
In order to attract new and younger customers, wine producers have employed a number of techniques to try to produce ripe-flavoured, full-bodied wines that don’t have the characteristic of tannins.
Shortcuts to remove tannins without ageing
For centuries winemakers have known that adding proteins to barrels in the form of milk or egg whites has the effect of smoothing out the rougher tannins.
Proteins are electrostatically attracted to tannin molecules so when they are stirred into wine they will form a sediment which can be discarded by racking or filtration. The process is known as fining.
Today, many of the world’s biggest selling brands of red wine are softened by adding gelatine, which is a very quick and effective fining agent.
A little sugar added to the wine also hides the bitterness of tannin.
Paul Masson, a Californian wine company, marketed its soft, early-drinking wines in the late 1970s with a famous advert featuring Orson Wells reciting the tagline “We sell no wine before its time”.
However, removing tannins is not the same as allowing them to mature over time.
Red wine with no tannin will not age well. It will go downhill from the day it is bottled and it will never develop the characteristics of a properly aged, traditionally-made bottle of red wine.
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