People describe a tannic wine as "dry", then get told the wine has no sugar in it, and reasonably conclude that wine people are making things up. They are not. The word is being used for two different things, and separating them is the whole of this article.
What tannins actually are
Tannins are polyphenols. In wine they come from grape skins, seeds and stems, and from the oak the wine is aged in. When you drink them, they bind to the proline-rich proteins in your saliva. Those proteins are what makes saliva slippery, so for a few seconds your mouth loses some of its lubrication and the surfaces drag against each other.
That drag is astringency. It is a tactile sensation, registered by touch, not by your taste buds. Sweet, sour, salty and bitter are tastes. Tannin is a feeling. This is why a bone-dry Riesling can have zero tannin and a lightly sweet red can still grip.
Where the differences come from
Thick-skinned grapes give more tannin because there is more skin per unit of juice. Nebbiolo, Cabernet Sauvignon, Sangiovese, Syrah and Tannat sit at the high end. Pinot Noir, Gamay and Grenache sit at the low end. Winemaking then moves the dial further: a longer maceration on the skins extracts more, a gentler press extracts less, and whole-bunch fermentation adds stem tannin, which feels different again — more herbal, more angular.
White wine is normally pressed off its skins before fermentation, which is why whites have almost no tannin. Orange wines, which are white grapes fermented on skins, are the exception and can be genuinely grippy.
Why tannin softens with age
Tannins are not stable. Over years in bottle they polymerise — small molecules join into larger ones — and once the chains get big enough they fall out of solution. That is the sediment at the bottom of an old red. Less tannin in suspension means less astringency, which is the structural change people mean when they say a wine has "come round".
Worth being clear about the timescale: this is a change measured in years, not minutes. Decanting a young wine mostly helps its aroma and gets the sediment out of an old one. It does not do in an hour what a decade does.
How to use this at the table
Tannin binds protein. Your saliva is not the only protein in the room — so is the steak. Protein and fat in food occupy the tannin before it reaches your mouth, which is why a high-tannin red feels smoother with rare beef or hard cheese than it does on its own. Salt works in the same direction: it suppresses the perception of bitterness and astringency and lets the fruit through.
Two things push the other way. Chilli heat is amplified by tannin and by alcohol, so a big Cabernet with a hot Sichuan dish makes both worse. And umami — mushroom, soy, aged cheese, dashi — raises the perception of bitterness, so a tannic wine can read as harsher alongside it than it did alone.
What this is for
None of this makes high-tannin wine good or low-tannin wine bad. It tells you what a bottle needs in order to show well. If you like the grip, buy it and give it something to hold on to. If you don't, there is a whole category of red — Pinot Noir, Gamay, Grenache — built without it, and choosing that is not a beginner's choice. It is just a different taste.