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What are Tannins?

Posted by on June 26th

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What are Tannins?

The dictionary isn’t much help. Here is the definition:

tan·nin

noun a yellowish or brownish bitter-tasting organic substance present in some galls, barks, and other plant tissues, consisting of derivatives of gallic acid, used in leather production and ink manufacture.

Tannins in Wine

What are tannins? It’s a question every wine lover asks sooner or later. 

Not long ago, I was asked about what happens to tannins in red wines as they age. The best ad-lib analogy I could come up with at the time was this: They’re like the Rolling Stones—just when you think they’ll soften up, mellow out and fade quietly into the background, they’re back on tour, on stage, commanding attention and prancing on your palate.

Rule #1

Only wines fermented with seeds and skins will be tannic.

Rule #2

All red wines have tannin.

What is tannin?

At its core, tannins alter the color, structure, and flavor of the wine. The drying, prickly sensation of red wine is tannin. The red color of red wine is tannin, too. The dark fruit flavors? You guessed it, those are derived, in part, from tannin. (for a more in-depth explanation, see the “Science in Wine” section.

I am reminded of the staying power of tannins whenever I taste red wines, irrespective of their age. Young red wines are predictably tannic. But even in wines held for a decade in a wine cellar, tannins rarely melt away like butter.

Why Not Everyone Loves Tannin

Bitterness is not universally beloved. There is a sizable population of people –about 20%– who are genetically predisposed to find high levels of tannin to be distasteful. This grouping is labeled as super-tasters,

This is an evolutionary adaptation in ancient hunter/gatherer communities that still exists today. This was an important survival trait, as most plants with a concentration of bitter compounds are actually poisonous. In the ancient world, super-tasters would have been able essential to the survival of their people.

Color versus Tannins

As it is, tannin types and their presence in wine vary considerably by varietal. Some wines that are lighter in color can be quite tannic, especially if they’re also high in acidity or alcohol, which magnifies tannin levels. Nebbiolo, the great grape of Barolo and Barbaresco, and Pinot Noir are two grapes that can render surprisingly tannic wines, even when their colors are not saturated.

what are tannins in wine
What are tannins in wine?

Tannin in Oak

Tannins are also leached into wine from oak; and the newer the barrels, the stronger the presence, in mouthfeel and flavor.

Tannin Management

The major threat tannins pose, though, is bitterness or astringency. That’s why so much attention is paid to tannin management, starting in the vineyard and extending through fermentation. Harvest dates are crucial. Picking underripe grapes gives tannins a green, herbal edge; overripe grapes can taste raisiny or pruney.

In the Vineyard

Winemakers are constantly rethinking tannins and experimenting with new methods of taming them. Tasting grapes (and chewing the skins and seeds) is the current rage. That gives an indication of a grape’s physiological ripeness and tannins.

In the Winery

Fermentation methods also influence tannic strength. Some winemakers prefer shorter, weeklong fermentations, with an emphasis on extracting color and flavor (and some even barrel-ferment the final phase). Others stretch vinification for weeks, even months, with the goal of softening the tannins and culling flavor. Some even add tannin powder to buff up their wines.

Effect of Age on Tannin

Because tannins act as a preservative, they are one of the most important factors in determining the longevity of red wines. Their enduring presence is also one revelation that comes from drinking older red wines, great or otherwise.

Balance

When you taste a mature wine that has evolved gracefully and maintained a mix of youthful flavors while developing the subtle nuances, you can be assured that it began life in near-perfect balance. That’s why winemakers ultimately define great wines by their balance. Foremost among the factors determining balance are the structure and amount of tannins.

Other Considerations

Concentration, richness, acidity, and alcohol (and sugar in sweet wines) also play vital roles in a wine’s age-worthiness. Moreover, defining what constitutes a mature wine differs for each of us.

Century Old Wines

The last time I tried a pair of 1870 Bordeaux, from Châteaus Lafite Rothschild and Latour, both exhibited the faded, wilted rose petal and dried-fruit scents of their age. I admired the longevity of these wines but was amazed by how persistent the tannins remained. Clearly, these wines aged beautifully because of their tannins and balance.

Those are the exceptions. More often, older wines dry out and lose their fruit vitality. Then tannins are all that remains. You rarely have to look hard to find tannins. They hang around like the Stones. No one knows when they’ll fade away.


The Science of Red Wine

The science of flavor is still in its infancy. Only a handful of the trace elements of wine have been studied, and many flavor compounds -in different proportions-can give distinctly different flavors.

Condensed Tannins

Research indicates that a class of polyphenols has antioxidant characteristics with potential health benefits. These polyphenol antioxidants may reduce the risk of cardiovascular disease and cancer. High levels of polyphenols can generally be found in fruit skins, with some of the highest percentages in grape, apple, and orange skins.

This class of polyphenols is called tannin, which give red wines their astringency and bitter taste. Well, actually they are condensed tannin (anthocyanins) but that really isn’t that important. What is important is that tannins are not water-soluble and will precipitate protein.

To rephrase: eventually the red and bitter stuff in wine will fall to the bottom of the bottle, turning the wine from ruby-red to brick colored… and that is why people age wines! FYI: Tannins are an important ingredient in the process of tanning leather. Oak bark has traditionally been the primary source of tannery tannin, though synthetic tanning agents are also in use today.


Esters

The biggest contributor to flavor is yeast. It is the fermentation process that truly gives a wine its flavors. If conditions are right, acids will combine with alcohol or tannin in the grape to form an ester. These are the flavor compounds in wine.

To rephrase: Esters are the result of a reaction between the grape skins, acids, and yeast during fermentation.

When you say a red wine has  has a berry-like character, or smells like roses, it is because the esters in the wine are mimicking the smell of berries. Please also note that – as we have discussed – flavors such as apple and pear can also come from the acids (tartaric and malic) in wine.

These esters can work together to create new flavors. For example, ethyl butyrate (from the grape) with diacetyl (malolactic fermentation) yields a butterscotch attribute in a wine. Another  example is ß-damascenone which gives an apple, fruity flavor and will elevate other fruity notes (such as a-ionone) in a wine.

Sometimes the esters will clash: a high concentration of methionol will blunt most fruit flavors. Polyphenols
One of the most important flavor elements in wine, especially red wine. Polyphenol translates to  “many phenols” or, more prosaically, “lots of aromatic stuff jammed together”. They are also responsible for the coloring of some plants—for example, the color of leaves in the autumn… and the skin color of red wine grapes.

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