The Truth About Tannins

An important component of red wines, they can be plush and pleasurable or mouth-scrapingly awful. Why?


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At a party recently, I watched as John bet Chris that he couldn’t manage to swallow a teaspoon of ground cinnamon. I wish I could say that the participants were kids, but they were fully adult members of a Port club. In any case, Chris lost.

Cinnamon is impossibly astringent. On its own, it will make your mouth seize up and refuse to swallow even just a small amount. This makes sense, as cinnamon is derived from the bark of certain trees from Southeast Asia. From the tree’s perspective, it wants to discourage animals (or idiots) from eating it.

It was an amusing and useful demonstration of astringency from tannins, that essential component of fine wines.

Tannins are polyphenols, which are produced by plants, grapevines included. Polyphenols tend to cling to proteins. In our mouths, tannins find protein in saliva—the very proteins that provide saliva’s slipperiness. Formerly saliva-coated mouths turn uncomfortably rough and dry.

Vines have a chance to thrive thanks in part to the defensive properties imparted by tannins. Animals generally dislike strongly astringent experiences, but if this warning is ignored, there is a backup plan: Tannins will sabotage nutrition by seizing crucial digestive enzymes. So the tannins discourage pests with astringency or by reducing its nutritional value—pests “learn” that it’s not worth eating.

Tannins are important to wine in a number of ways: They preserve it for long-term aging; they provide structure (reds with too little seem flabby); they add a slight bitterness for flavor complexity; and their astringency extends a wine’s finish.

But that astringency is what makes many people avoid red wines. Why some people at some times, and not others? One variable is human chemistry—differing levels of salivary proteins and differing abilities to replenish it. Another variable is in the nature of tannins themselves.

Tannins in wine can create sensations in the drinker’s mouth that run a spectrum from velvety plush to silken to neutral to burlap-like to cheek-sucking chalk dust. For years, scientists thought that this spectrum was mostly due to the molecular size of tannins, but that thinking is being revised; scientists are looking into the differing properties that the tannins in the seeds and the tannins in the skins impart once the wine is in the fermenter. And that turns out to be a major mystery. The chemical reactions between tannins and all the other compounds in wine become so complex and unpredictable, University of California (Davis) Wine Chemist Doug Adams calls it a “chemical train wreck.”

Winemakers and growers have any number of methods to to harness the tannins in their wine, but ultimately their great skill and experience is wrestling with chance.

And once the wine is bottled, what actually happens to tannins over time? Why do they mellow? The classic explanation is that their grip relaxes as tannins bind to the wine’s color pigments, ultimately precipitating out of the solution as sediment. But scientists are questioning that conclusion as well. The exact chemistry is still not entirely clear. It’s a mystery, happening in exquisite slow motion.

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