Tannins, a group of bitter and astringent compounds, can be found abundantly in nature. They’re present in the wood, bark, leaves and fruit of plants as various as oak, rhubarb, tea, walnut, cranberry, cacao and grapes. Perhaps most importantly, they’re also found in wine.

What do tannins do?

Plants have tannins to make themselves unpalatable. Their purpose in nature is to deter animals from eating a plant’s fruit or seeds before it’s ripe.
Tannins are responsible for that astringent, mouth-coating feeling you get from biting into an unripe pear or plum. Humans have used tannins from various tree barks for a long time to tan animal hides and make leather.
Some foods are also prized for their tannins. Their bitterness and astringency, when managed well, can be rather pleasant. Examples include tea, coffee, dark chocolate and, of course, wine.
Grape skins and residue, also known as pomace, being tipped out of a winery’s stainless steel barrel after the juice has been extracted / Getty GRAPE SKINS AND RESIDUE, ALSO KNOWN AS POMACE, BEING TIPPED OUT OF A WINERY’S STAINLESS STEEL BARREL AFTER THE JUICE HAS BEEN EXTRACTED / GETTY Where do tannins in wine come from? Tannins can stem from four primary sources: the grape skins, pips (seeds) and stems, and the wood barrels used during aging. They provide texture and mouthfeel to wine as well as a sense of weight and structure.
While white wine is made mostly from the juice that’s pressed as soon as the grapes get to the winery, red wine is made from the entire grape. As red wine ferments, skins, pips, juice and sometimes stems are all macerated together. During that process, both color and tannin are leached into the wine. Tannins create the drying sensation in your mouth when you drink a red wine.

How to describe tannins?

It’s important to distinguish between the quality and quantity of tannins.

Texture is useful to describe the quality of tannins, i.e. silky, plush or velvety. When a wine has a pleasant amount of tannins, noticeable but unobtrusive, it’s often described as “grippy.” When tannins are described as “green,” they’re slightly bitter and have unpleasant astringency. “Polished” or “elegant” tannins will be very fine-grained in texture, noticeable but pleasant.
Mature wines are often described as having “resolved” tannins, which are smooth, soft and no longer astringent. Another important element is the difference between bitterness and astringency. Bitterness refers to taste, while astringency refers to tactile sensation.
When you describe a wine, ask these questions: Do tannins immediately coat the mouth, or do they appear slowly? Do they dominate the wine, or are they matched by freshness and fruit? Are they integrated and gentle, or assertive and harsh?
Good tannin management avoids harshness or bitterness, which happens when grapes are not sufficiently ripe or when overextracted. Do white wines ever have tannins, and what about orange wines? Some white wines undergo a short period of maceration. This is known as skin contact. Freshly harvested grapes are crushed and left for a few hours or longer on their skins before they start to ferment. This pulls flavors out of the grape skins—a common practice for aromatic and semi-aromatic grapes like Gewürztraminer and Riesling. There has also been a recent rise of “orange wines,” amber-colored bottlings made from white grapes that are vinified with full skin contact, like red wines. These wines have a tannic element, though not as strong as it can be in reds. What about tannins in sparkling wines? The bubbles in sparkling wines act like millions of little magnifying glasses that highlight each aspect of the wine. Since these bubbles provide a textural element, and bottle-fermented wines also have texture from aging on yeast, additional texture from tannins usually come across as bitter, and the bubbles would exacerbate astringency. That’s why the pressing regimen for high-quality sparkling wine is crucial. The very few red sparkling wines that exist, like sparkling Shiraz or Lambrusco, counteract bitterness with a little sweetness. The wine will still taste dry, but a touch (or sometimes more) of sugar will take the edge off.