Tannins, a group of bitter and astringent compounds, are found abundantly in nature. They are present in wood, bark, leaves and fruits of plants, such as oak, rhubarb, tea, walnut, cranberry, cocoa and grapes. But most importantly, they are also found in wine.
What are tannins really?
Plants have tannins to make themselves indigestible. Their purpose in nature is to keep animals from eating a plant's fruits or seeds before they are ripe. Tannins are responsible for the astringent mouth covering sensation you get from biting into an unripe pear or plum.
Humans have long used tannins from various tree bark to tan animal hides and make leather. Some foods are also valued for their tannins. Their bitterness and tautness, when properly managed, can be quite pleasant. Examples include tea, coffee, dark chocolate and, of course, wine.
Grape skins and residue, also known as pulp, are removed from the stainless steel barrel after the juice is pressed.
Where do tannins in wine come from?
Tannins can come from four primary sources: the grape skins, pips (seeds) and stalks, and the wooden barrels used during aging. They impart texture and mouthfeel to wine, as well as a sense of weight and structure.
While white wine is usually made from the juice pressed as soon as the grapes reach the winery, red wine is made from the whole grape. For red wine, skin, seeds, juice and sometimes stems are all soaked together. During that process, both color and tannins are determined in the wine. Tannins create the dry feeling in your mouth when you drink a red wine.
How do you describe tannins?
It is 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 is often described as "grip."
When tannins are described as "green," they are somewhat bitter and have an unpleasant astringency. "Polished" or "elegant" tannins have a very fine grain structure, noticeable, but pleasant.
Ripe wines are often described as having "dissolved" tannins, which are supple, soft and no longer astringent.
Another important element is the difference between bitterness and tautness. Bitterness refers to flavor, while tautness refers to palpable sensation.
When describing a wine, ask these questions: Do tannins cover the mouth immediately, 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 do tannins work?
Although tannin is a collective name for several phenolic compounds, all tannins have one thing in common: they bind and precipitate proteins, i.e., excrete them. But what does this mean for the average wine drinker?
Human saliva is full of proteins, which is what makes it so smooth. A tannin in red wine will bind to saliva - this is why the mouth feels dry. This protein-binding quality is often cited as the reason why red wine and steak go so well together, although it also has to do with how the tautness of the wine counteracts the fatness of the meat.
Different grapes, different climates, different tannins
Some grape varieties have more tannins than others. Examples that can make truly tannic wines include Cabernet Sauvignon, Nebbiolo, Mourvèdre, Malbec, Tannat, Syrah / Shiraz, Tempranillo, Merlot and Sangiovese. Whether the winemaking technique encourages the extraction of tannins is a matter of style. Wines made from grapes such as Pinot Noir, Gamay and Grenache, which have much thinner grape skins, have much less tannin.
While grape variety can give a good idea about the concentration of tannin in a wine, ripeness is also important. A good example is Syrah / Shiraz. It has plenty of tannin, but expresses itself differently depending on climate and vintage.
A warm climate such as Barossa, Australia, produces Shiraz grapes that are super-ripe, making the tannins particularly supple, lush and rounded. In the temperate Northern Rhone, the tannins appear more structured, dry and angular. The tannin structure of Cabernet Sauvignon grapes from Bordeaux in France differs with warmer and cooler vintages. Extraction during winemaking also plays a big role.
Do tannins help a wine age?
Although often said to help a wine mature, many white wines reach a wonderful age without tannins. Mouthfeel, however, changes as a red wine matures. Initially, the tannins leached into a wine are smaller molecules. Over time, these tannins begin to combine and form larger chains - a process called polymerization.
One theory is that this aging process reduces the reactive surface of the tannins, producing a softer mouthfeel. These tannin chains become so long that they separate from the wine, creating a deposit and leading to sediment in some bottles.
It is 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 "dissolved" tannins, which are supple, soft and no longer astringent. However, if a red wine has a hard, bitter and unbalanced tannin structure to begin with, they will not age.
Pigéage or punch-down, in action
The effect of maceration and fermentation methods
Maceration time, or the amount of time red wine spends in contact with its skin 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 example, have a short maceration time, resulting in minimal color and little to no tannin. As fermentation continues, more tannins are leached out, while the alcohol that develops begins to act as a solvent.
Some winemakers also use grape stalks to add structure to wines such as Pinot Noir and Syrah. This means the entire bunch goes into the fermentation vessel. This is known as 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 such as Gewürztraminer and Riesling.
Winemakers can also help with this process. Pigéage, or punch-down, is a very gentle extraction technique in which the winemaker gently pushes into the must the grape skins that rise to the top during fermentation. Some wineries have tanks equipped with internal grates that keep the rising grape skins submerged.
Remontage or pump-over offers a slightly more effective extraction. The liquid at the bottom of the fermentation vessel is extracted and pumped over the grape skins.
Clearance, or rack-and-return, is when the liquid of a fermenting vessel is separated from the solids and poured back onto it in one motion. Some wineries also have so-called roto-fermenters, which resemble giant front-loader washing machines that rotate. The motion helps extract both tannin and color.
Wood barrels bring their own type of tannins.
Pressing wine, and the effects of oak
Once red wine is fermented, it is pressed, separating the liquid from the solids. Some winemakers press in different batches at different pressures for greater control, with the batches under the highest pressure having the most tannins.
By using a variety of wines with different degrees of tannins, the winemaker can achieve a particular blend that is consistent across vintages. The best winemakers base tannin management on many factors, including the maturity of the grapes, their skins and the desired style of wine.
When freshly fermented wine is aged in new oak barrels, tannins will leak from the wood into the wine. This requires a wine with sufficient weight and strength that will not be overwhelmed by the oak's own tannins. Good tannin management prevents harshness or bitterness, which happens when grapes are not sufficiently ripe or when they are over-extracted.
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 on their skins for a few hours or longer before they begin to ferment. This extracts flavors from the grape skins - a common method for aromatic and semi-aromatic grapes such as Gewürztraminer and Riesling.
There has also been a recent emergence of "orange wines," amber-colored bottlings made from white grapes vinified with full skin contact, like red wines. These wines also have a tannin element, although not as strong as it can be in reds.
What about tannins in sparkling wines?
The bubbles in sparkling wines act as millions of tiny magnifying glasses that highlight every aspect of the wine. Because these bubbles provide a textural element, and bottle-fermented wines also have texture from aging on yeast, additional textural tannins usually come across as bitter, and the bubbles would exacerbate astringency.
Therefore, the urgent regime for high-quality sparkling wine is crucial. The very few red sparkling wines that exist, such as sparkling Shiraz or Lambrusco, combat bitterness with a little sweetness. The wine still tastes dry, but a touch (or sometimes more) of sugar will take the sharp edge off.
By Anne Krebiehl MW / @WineEnthusiast / Illustrations by Mathew Dimas / Photos by Getty
