What are Tannins, Really?

We talk about tannins in wine all the time, but how much do you really know about this versatile chemical compound?
Animation by Matthew Dimas

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?

How Does Oak Really Affect Wine?

How do tannins work?

While tannin is a collective term for various phenolic compounds, all tannins have one thing in common: they bind and precipitate proteins, i.e. separate them out. But what does this mean for the average wine drinker?

Human saliva is full of protein, which is what makes it so slippery. A tannic red wine will bind to saliva—this is what causes the mouth to feel dry. This protein-binding quality is often cited as the reason why red wine and steak are such a good pairing, though this also has to do with how the wine’s astringency counteracts the fattiness of the meat.

Different grapes, different climates, different tannins

Some grape varieties have more tannins than others. Examples that can make really tannic wines include Cabernet Sauvignon, Nebbiolo, Mourvèdre, Malbec, Tannat, Syrah/Shiraz, Tempranillo, Merlot and Sangiovese. Whether the winemaking technique encourages the extraction of the tannins is a question of style. Wines made from grapes like Pinot Noir, Gamay and Grenache, which have much thinner grape skins, are much less tannic.

While grape variety can provide a good idea about the concentration of tannin in a wine, ripeness also matters. A good example is Syrah/Shiraz. It has a lot of tannin, but expresses itself differently, depending on climate and vintage.

A hot climate like Barossa, Australia, produces Shiraz grapes that are superripe, making the tannins particularly smooth, lush and rounded. In the temperate Northern Rhône, the tannins come across as more structured, drying and angular. The tannin structure of Cabernet Sauvignon grapes from Bordeaux in France differ with warmer and cooler vintages. Extraction during winemaking also plays a big role.

Aging freshly fermented wine in new oak barrels requires a wine with sufficient weight and power that won’t be overwhelmed by the oak’s own tannins.

Do tannins help a wine to age?

While often said to help a wine age, plenty of white wines reach a magnificent age without tannin. However, mouthfeel changes as a red wine matures. Initially, the tannins leached into a wine are smaller molecules. With time, these tannins start to combine and form larger chains —a process called polymerization.

One theory is that this aging process reduces the tannins’ reactive surface, which produces a softer mouthfeel. These tannin chains become so long that they fall out of suspension, which creates a deposit and leads to sediment in some bottles.

It’s not clear whether this reaction is the only thing that makes aged wine less astringent. In any case, mature wines are often described as having “resolved” tannins, which are smooth, soft and no longer astringent. However, if a red wine has harsh, bitter and unbalanced tannic structure to begin with, no amount of aging will even them out.

Pigéage, or punch-down, in action / Getty
Pigéage, or punch-down, in action / Getty

The effect of maceration and fermentation methods

Maceration time, or the amount of time red wine spends in contact with its skins during winemaking, has an important influence. A shorter maceration allows less time for tannins and color to leach into the wine as it ferments. Rosé wines, for instance, have a short maceration time, which results in minimal color and little to no tannin. As fermentation continues, more tannins are leached, as the alcohol that develops begins to act as a solvent.

Some winemakers also use grape stems to add structure to wines like Pinot Noir and Syrah. This means that the entire bunch goes into the fermenting vat. This is known as whole-bunch or whole-cluster fermentation.

Known as skin contact, white wines sometimes undergo a short period of maceration—a common practice for aromatic and semi-aromatic grapes like Gewürztraminer and Riesling.

Winemakers can also assist in this process. Pigéage, or punch-down, is a very gentle extraction technique where the winemaker carefully pushes the grape skins that rise to the top during fermentation back into the must. Some wineries have tanks fitted with internal grids that keep the rising grape skins submerged.

Remontage, or pump-over, offers a slightly more effective extraction. The liquid at the bottom of the fermenting vat is drawn off and pumped back over the grape skins.

Délestage, or rack-and-return, is when a fermenting vat’s liquid is separated from the solids and poured back onto them in one motion. Some wineries also have so-called roto-fermenters, which are like giant front-loading washing machines that rotate. The movement helps extract both tannin and color.

Wood barrels bring their own type of tannins / Getty
Wood barrels bring their own type of tannins / Getty

Pressing wine, and the effects of oak

Once red wine has finished fermenting, it’s pressed, which separates the liquid from its solids. Some winemakers press in different batches at different pressures for greater control, wherein the batches under the highest pressure will be the most tannic. Employing a variety of wines with varying degrees of tannic extraction enables the winemaker to achieve a particular blend consistent across numerous vintages.

The best winemakers base tannin management on a multitude of factors, which include the ripeness of the grapes, their skins and the desired wine style.

Aging freshly fermented wine in new oak barrels will leach tannins from the wood into the wine. This requires a wine with sufficient weight and power that it won’t be overwhelmed by the oak’s own tannins.

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 regiment 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.

Published on September 11, 2018
Topics: Wine Basics
About the Author
Anne Krebiehl MW
Contributing Editor

Reviews wines from Austria, Alsace and England

German-born but London-based, Anne Krebiehl MW is a freelance wine writer contributing to international wine publications. She also lectures, consults and translates and has helped to make wine in New Zealand, Germany and Italy. She adores acidity in wine and is thus perfectly suited to her Austria/Alsace/England beat. Her particular weaknesses are Pinot Noir, Riesling and traditional-method sparkling wines.

Email: akrebiehl@wineenthusiast.net.




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