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.
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.
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