It's chewy and vigorous but it can get soft; it can be dusty or velvety, and it can come across as thick or thin; sometimes it's strong, sometimes its light, it can even be ripe, but mostly it's bitter and/or astringent.  Believe it or not, we are talking wine tannin here.  How can one thing have so many descriptors!

First, I want to strip the snobbish veneer off of the word 'tannin' because it is frequently bandied about at wine tasting events as though pretense of understanding it suggests a person knows the 'revealed truth' about wine.  Let's be clear. Tannin is the most common, secondary plant compound among all botanical life in the entire world, and is essentially a plant molecule.



Broadly speaking, tannin molecules in the bark of trees protect the trees from insects, bacteria and even fire.  Humans happily discovered that they could extract and use it on animal hides since tannin alters the protein structure of skin so that instead of decomposing, the hide is preserved and turned into leather.   (Hold on to the idea of tannins as a preservative)

Tannin comprises the majority of many victuals - tea, coffee and chocolate to name a few and are found in edibles like nutmeg, walnut skins, blackcurrants and pomegranates and, most importantly for wine, in the skins and seeds of berries including grapes.  

Grape Tannins & colour

It is difficult, though not impossible, to discuss tannins without mentioning anthocyanins (antho sigh anins).

Tannin is found in the seeds and in the skins of grapes whilst anthocyanin is produced in the grape skins as the grape ripens over the long season.  Over a period when grapes ripen, and the acid levels decrease whilst the sugar levels increase, tannins mature or ripen by becoming less astringent.  At the same time the anthocyanins (colour) and flavours develop in the grape.  This is what is referred to as phenolic (fee nolick) or physiological  ripeness.

The term tannin is often used, mistakenly, to describe the phenolic compounds (e.g. colour and tannin) that wine is made up of besides water, ethanol, sugar and acids.

Let's get it straight here -
·   Phenolics in wine are composed of anthocyanins, or the colour components of wine.
·   Tannins, on the other hand, are responsible for astringency, stability (preservation) and structure of a wine.

Harvesting a ripe grape

A viticultural aim of every grower/producer is to provide grapes for harvest that are physiologically ripe.  If however, physiologically ‘unripe' grapes are made into wine, the unripe skin-tannins in grapes can be sensed and are referred to as ‘green' tannins.  This is a "not too desirable" quality since the green taste is very astringent and unrefined.

Hence, truly dedicated winemakers do not only rely on laboratory measurements of grape ripeness when making decisions when to harvest - but they rely on their palate - spending hours walking up and down rows of vineyards, plucking berries and tasting them to determine whether there is a convergence of ‘phenolic' maturity and sugar ripeness, so that a good wine can be produced. 

This may seem odd, but this simple, human and accurate interactive-way of determining ripeness is often relegated to the winery laboratory where chemical analysis decides when a grape is ripe.  The laboratory route is both time consuming and the analysis can sometimes be skewed.  This is because there may be adequate sugar levels in the flesh of the grape, but the pip is still green...hence green tannins and astringent qualities.



Extract the desirable tannins during winemaking

Winemakers are aware that they have to optimize not only the quantity of tannin extracted, but also the desired level of tannin in the wine. Tannin from seeds can make wine excessively astringent whilst high skin tannin levels may cause herbaceous characters and bitterness in the final wines.

Because of this, winemakers like to use skin contact, or maceration (mass aeration), that extracts a higher proportion of skin-derived tannins to seed tannins.  The overall result is a taste of "riper" tannins, particularly when compared to tannins found in the seed alone. By using maceration, winemakers also get to extract the colour from the skins.

As such, the choice of a style of wine to make predetermines if that wine will have high or low tannin. Beaujolais Nouveau has a very short period of skin contact using a method called "carbonic maceration" that yields a wine with low tannin content. (This is a topic for another article...)

At the other extreme are Bordeaux and Cabernet Sauvignon wines that are made via an extended period of maceration on the skins which yields much more tannic, and colour extracted wines.

That said, some grapes are naturally high in tannins and hence the desired style is to ‘go with the flow' and make a tannic wine (Bordeaux, Barolo, Barbaresco, Cabernet & Syrah).  Other grapes are less tannin (Dolcetto, Barbera, Pinot Noir, Gamay, Nero d'Avola and Tempranillo) and so is the resulting wine.

Pinot Noir, a grape with naturally low anthocyanins and tannin, is sometimes charged up with more tannins deliberately. Winemakers first give the grapes a ‘cold soak' and sometimes add the stalks and stems back to the fermenting juice.




The above graph illustrates the relative change in color, anthocyanins, total tannins, and polysaccharides that occurs when grapes are given a cold soak, and then fermented and finally, allowed to macerate further for additional colour/tannin extraction.

Indeed, winemakers can juice up a wine's tannic heft.  Powdered grape tannin exist in the marketplace and winemakers can add them to juice and wine for various purposes. Yes, besides correcting unripe grape tannins, the addition of tannin to wine does many other things.  It can enhance the structure and mouth-feel of the wine, increase the effectiveness of microoxidation, help precipitate proteins, enhance the aging (preservation) potential of wine, and help stabilize red wine color.

In short, tannins do a lot for wine!

What happens when wines taste too tannic?

Winemakers can remove tannin by a fining process of adding gelatin, or casein (milk).  A more modern "fine-tuning" technique to modify tannin in wine is micro-oxygenation. This involves exposing the wine to minute quantities of oxygen in order to alter positively, the structure of red wines. 

Winemakers who age wines in barrel achieve a similar micro-oxygenation because the barrel allows a gentle oxygen exchange with the wine over time.  But the modern method accelerates this process by feeding (introducing) a tiny stream of air-bubbles into the wine storage vessel to stabilize, and oxygenate a wine very slowly.

Role of tannin in wine

For the wine drinker and wine collector, tannin is welcomed.  Tannins prevent oxidation and are in part responsible for a red wine's aging potential.  Like the hides I first mentioned...tannins help preserve.

Wines with strong tannins will produce a clawing sensation the cheeks (as in chewing on banana skins or sipping strong tea), and are deemed "tannic".  Wines that taste ‘smooth' are described as having silky soft tannins, or velvety or fine-grained.  Taste enough wine with this in mind and you'll soon see that there is a difference between velvet and fine-grained tannins!


The Australian Wine Research Institute has conducted extensive research on wine tannin so I turn to them for useful terms to describe tannin and its effect in wine.

Drying:    numbing, parching dry
Harsh:     agressive, abrasive
Dynamic: puckering, chewy, grippy
Unripe:   green, sappy resinous
Particulate:  powdery, dusty
Complex:  soft, supple, fleshy, rich

Ed Soon 23/04/09