What are tannins, and how do they get into wine?

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Dear Dr. Vinny,

What are tannins, and how do they get into wine?

—John, Sacramento, Calif.

Dear John,

Tannins are a type of naturally occurring molecule called polyphenols, found in many different types of plants. Tannins are in all kinds of things we consume, like berries, coffee, olives, beans, nuts, chocolate, beer and spices. Tannins in wine come primarily from grapes, but also from aging in oak barrels.

Tannins aren’t something you taste, but rather something you feel. They are an important part of a wine’s structure, that sensation of firmness, dryness or tugging on your cheeks. At their most intense, tannins can make a wine seem chewy or drying, and that sensation can come across as bitter. But tannins can also help make a wine feel supple or velvety, even silky.

I find it useful to think of black tea, which also has tannins. The longer you steep a tea bag, the darker and stronger the tea will be, and the more tannins that will leach out. Same with wine. The more exposure the wine has to the grape skins and seeds, the more tannic a wine will be. Red wines have more tannins because they are “steeped” with grapes during maceration, while white wine grapes are typically pressed right away and separated from grape solids. Likewise, the longer a wine sits in an oak barrel, the more tannins it can absorb from the wood.

There are other factors determining tannins in a wine, starting with the fact that some grapes just have more tannins than others. Harvest conditions, fermentation factors and dozens of other winemaking decisions—including the addition of powdered tannins—can affect how tannic a wine is in the end. The type of barrel a wine is aged in (and for how long) adds another set of variables: New barrels are more "potent" than older ones.

One more tidbit about tannins: They can bind with the proteins and fats. When they bind with the proteins in our saliva, our mouths can feel dry. But when you pair a tannic wine with something rich and fatty, those can counteract each other. That’s why wine and cheese is such a classic pairing.

A final (slightly gross) piece of trivia. If you’ve ever been overcome by morbid curiousity and taken a look at the contents of a used spit bucket at a wine tasting, you may have noticed that it looks a bit stringy and globby in there. That's the result of tannins binding with the protein in saliva. You’re welcome!

—Dr. Vinny

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