Everything you think about tannins is probably wrong, but it’s not your fault. Tannins are complicated little bastards, and the wine world has turned them into one of the least-understood aspects of wine drinking.

Technically, tannins are an evolutionary healing and defense mechanism. They break down proteins in plant life, which dissuades grazing herbivores and helps cut or wounded plants heal. An analogy might be the way various clotting agents in our blood help cuts close and scab.

But we humans kind of enjoy the way tannins affect our mouths, even if we don’t really understand them.

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The confusion starts with the fact that we often talk about tannins as having a taste. They can seem bitter, but are more accurately describe as astringent, meaning that they cause the contraction of various body tissues. The most commonly used term is “dry,” which may accurately describe the drying out of our mouths, but is forever confused with a discussion of sweetness.

The real effect they have on the wine drinker, however, is about touch and texture. Our saliva is full of protein chains, and when the tannins bind with those proteins, they break down the saliva that typically lubricates our mouths. This drying sensation can quickly become overwhelming, which is why typically tannic wines are paired with fatty or protein-rich foods.

Saying a wine is tannic isn’t actually a compelling tasting note. Tannins in wines can come from a few different sources, so a better way to approach tannins in tastings is to explore their causes.

Skin Tannins

Do you ever taste a wine and feel like the dentist has grabbed your tongue with gauze, or that your cheeks are sticking to the sides of your gums? Those are skin tannins working their magic.

Skin tannins start out as astringent. These tannins can make young wines feel really rough and coarse, but they mellow out over time.

A rough rule of thumb is that wines with deeper color are apt to be more tannic, since the extended maceration to draw out those pigment compounds also draws out lots of tannin. That said, Nebbiolo, one of the most tannic varietals out there, is actually very light-colored.

Seed Tannins

Seed tannins aren’t really tannins at all but are similar enough that we lazily lump them together. Seed “tannins” are bitter, which is why grapes are gently pressed, to avoid releasing too many of them.

Cheap red wines, made from heavily pressed grapes, often exhibit these tannins; it’s the reason that these wines are often also made with a surprising amount of residual sugar, which helps mask that astringency.

Tannins from Oak

Oak barrels also have tannins, though they’re much shorter, and tend to integrate into the wine quicker. That said, if you put a wine with fewer skin tannins, like Pinot Noir, into a new oak barrel, the oak tannins can be overwhelming, particularly when the wine is young.

If you’re drinking these wines, you’ll find that decanting them an hour or two beforehand can really help the wine mellow.

Tasting Tannic Wines

Tannins can quickly fatigue your palate, especially if you drink tannic wines without food. If you’re spending a day wine tasting, be warned that after a few tastes of tannic reds like Cabernet Sauvignon, Malbec, or Nebbiolo, you’ll want to reset. Failing to do so can result in signing up for a wine club, and then finding out that when your palate is fresh and sober, that “amazing bottle of wine you just loved” is actually pretty mediocre.

One last thing. Tannin allergy is mostly some nonsense. “O.K.,” you say, “but I get a headache when I drink tannic red wines.” Yes, because tannic red wines are also typically among the highest in alcohol, and you might have heard that alcohol causes headaches.

What’s more, many big, tannic red wines also have a surprising amount of residual sugar in them. This sweetness can counteract the bitterness and astringency, which make them more drinkable, but as you probably learned in your younger days, sugar plus alcohol equals sadness, the next day at least.