Tannins – What are They & How Important are They to Wine?

I am sure most of you have heard someone describe a wine, especially a red wine, as tannic. If you have ever had a cup of very strong black tea then you have definitely tasted tannins. Other foods high in tannins are walnuts, almonds, dark chocolate, cinnamon, cloves, pomegranates and quinces.

When you taste a wine, you can feel the tannin specifically on the middle of your tongue and the front part of your mouth. Depending on how dry your mouth feels, you can determine whether a wine is high or low in tannins. A wine that is high in tannins, is tannic.

Tannin in wine is a textural sensation, something that we feel rather than taste. The effect of tannins in a wine can be described as velvety, plush, silky, supple, smooth, soft, grainy, firm, chunky, grippy,  or powdery. Because it is a textural sensation, you could associate many tannin sensations to the feel of fabrics, such as cotton, suede, silk or satin.

Tannin gives a wine structure, texture and grip. It is a structural element that helps give structure and definition to a wine, a little like what a skeleton does for an animal body, it holds everything together and gives it balance, structure, and length.

Interestingly, the term ‘tannin’ is an old one, and comes from the practice of using extracts from plants to cure or tan leather.

Tannins occur naturally in a wide range of plants and are found mainly in the bark, leaves and immature fruit. The role of tannins in nature is one of plant defence. They have an astringent, unpleasant taste that is off-putting to plant eating insects and animals. As an animal or insect begins to munch on plant tissue, the tannins are released from the plant cells and bind with the proteins in the animal’s saliva making the plant taste unpleasant, bitter and rather indigestible.

In the case of wine grapes, they start out life in Spring as small, green, and extremely bitter berries, due to a combination of searingly high acidity and green, aggressive tannins. The grapes are also coloured green, the same colour as the rest of the plant. For grapevines, the grape berry’s function in life is to act as a carrier for seeds, and it doesn’t want birds to eat them all before they’re ready. The idea is that the palatability and attractiveness of the berry is timed to coincide with the ripeness of the seed. At the right time, the berry changes colour to yellowish green in colour for white varieties, or to reddish purple in colour for red varieties. The ripe berries stand out amongst the green foliage. When grapes are ripe, the acidity has diminished, the sugar has increased and the bitter tannins have softened, all making the grapes far more attractive for birds to eat. The birds eat the berries then deposit the seeds in a new location where a new grapevine may sprout and grow.

So what role do tannins play in winemaking? Wine tannins as we now know, come from grape skins, stems and seeds, but their extraction into a wine during the winemaking process is heavily dependent on what a particular winemaker chooses to do in the winery. Some tannins also are extracted from the tannins naturally occurring in the oak that the barrels are made out of, and are at much higher levels in new barrels.

The amount of tannins present in a grape berry also varies from variety to variety. Some grape varieties have more and some have less. White wines, in general, have lower tannin levels, because for the most part, they are fermented off their skins. In contrast, red wines are fermented on their skins, during which time, both colour and tannins are extracted. Grape varieties such as Cabernet Sauvignon, Shiraz, and Nebbiolo have naturally high levels of tannin. In contrast, grapes such as Gamay and Barbera have much lower levels of tannins, with Pinot Noir, Merlot, Tempranillo and Sangiovese falling somewhere in between.

Tannin ripeness is really important. Unripe tannins give a green, stalky taste to a wine which are often seen in wines made in cooler vintages, where the tannins have not had the chance to ripen and soften fully. In cool years, winemakers have to be extra careful and gentle during red fermentation to ensure they do not extract any unripe tannins and produce wines which are more astringent and bitter.

As with acidity, an important point to remember is that your perception of how tannic a wine is, as with the other flavour components in wine, should not be considered independently. Tannin and acidity seem to reinforce each other. A big, tannic red that is also high in acidity will seem even more tannic and more acidic.