Tannin, the grip of red wine.

Take a sip of a young Barolo or a young claret and wait a few seconds. Your gums feel dry, your teeth slightly rough, the inside of your cheeks faintly puckered. That grip is tannin. Tannins in wine shape how a red feels, how long it can live and which dishes it suits.

You feel tannin more than you taste it. Learning to judge it, both how much there is and what kind, is one of the most useful skills for anyone who buys red wine to keep.

Where tannins in wine come from

Tannins are a family of compounds found in grape skins, seeds and stems. Red wine is fermented with its skins, often for days or weeks. The longer the contact, the more tannin passes into the wine. White grapes carry much less tannin to begin with and white wine is usually pressed off its skins before fermentation, which is why it has so little.

Where the tannin comes from changes how it feels. Seed tannins are smaller molecules and taste more bitter; the larger tannins from the skins do more of the drying. Winemakers tend to handle seeds gently for that reason. Stems carry tannin too, so some growers ferment part of the crop as whole bunches, stems included, to add structure to a grape as low in tannin as Pinot Noir.

Oak is the other source. New barrels give up tannins of their own, although far less than the grapes do: in a red wine, the grapes supply the great majority.

How tannin feels

Tannin binds to proteins, including the proteins in your saliva that keep the mouth lubricated. As they bind and drop out of solution, the lubrication goes and you feel dryness and friction on the gums, the teeth and the inside of the cheeks. Scientists call this astringency. It travels through the nerves of touch rather than the taste buds, which is why you feel it on the gums and cheeks as much as on the tongue. Tea left to brew too long works the same way.

Some tannin tastes bitter as well, the smaller molecules especially, but the grip is what to judge. Acidity changes how it feels too. A young wine high in both can feel severe; young Nebbiolo is the classic case. Judge acidity in wine and tannin together, never one without the other.

Quantity and quality

Tasters describe tannin by its texture as much as by its quantity. At best it is fine-grained, silky or powdery. At worst it is coarse, rough or green, with a bitter, stalky edge. Ripe tannin can feel like fine sand or suede; unripe tannin feels more like sandpaper.

How much tannin a wine has matters less than what kind of tannin it is.

A great young Bordeaux or Barolo can carry a great deal of tannin and still feel refined because the tannin is ripe and fine. A lesser wine with far less can feel harsh. When you taste, note two things: the amount (from low to high) and the texture. The second tells you more about quality.

The grape sets the starting point:

• High tannin. Nebbiolo, Cabernet Sauvignon, Syrah and Tannat, the grape of Madiran in south-west France and Uruguay's national variety.
• Lower tannin. Pinot Noir, Gamay and Grenache.

Colour is no guide. Nebbiolo, the grape of Barolo and Barbaresco, makes pale wines with fierce tannin and catches out anyone who judges a red by its depth of colour. Winemaking then pushes any grape one way or the other: long maceration builds tannin, gentle handling keeps it in check.

How tannin changes with age

Tannin is part of what lets a red wine age. It helps protect the wine from oxygen and gives it a frame that outlasts the first rush of fruit.

In the bottle, tannins slowly react with one another and with the wine's colour pigments to form larger molecules. Some grow too large to stay dissolved and fall out as sediment, taking colour with them. What remains feels softer and rounder. That softening is one of the main reasons to cellar serious red wine at all.

The risk is a wine whose fruit fades before its tannin softens. It ends up dry and dusty, all frame and no picture. Tannin alone does not make a wine age well: it needs fruit, acidity and concentration in proportion. Which wines improve with age maps the styles that have that balance.

Tannin at the table

Tannin needs something to work on. Protein and fat give it that: a steak or a slice of roast lamb makes a young, tannic red feel noticeably smoother. Salt may do even more: it damps both the drying and the bitterness, so a well-seasoned dish does more for a tannic wine than a bland one.

Fish is the famous exception. Oily fish and some seafood can leave a metallic, fishy aftertaste with red wine. Tannin usually takes the blame, but a study of red and white wines tasted with scallops traced the effect mainly to iron in the wine reacting with the oils in the seafood. Heavy tannin still overwhelms delicate fish on its own terms, drying the palate and flattening the flavour. With steamed fish, a white or a light, gentle red remains the safer choice.

Umami pushes the other way. Mushrooms, eggs and other foods rich in umami but low in salt can make tannin seem harder and more bitter, so a mature red whose tannin has softened is an easier partner than a young one. In Cantonese cooking, where soy, oyster sauce and steamed fish can all appear at one meal, the point comes up again and again; pairing wine with Cantonese food works through it dish by dish.

Tannin in white and orange wines

White wines have little tannin because they spend little or no time on their skins. Some pick up a trace from skin contact before pressing or from new oak, felt as a faint firmness rather than a grip.

Orange wines are the exception. Made from white grapes fermented with their skins, the way a red is made, they can carry real tannin. That surprises anyone who expects a white wine to feel soft. The same rules then apply as for a red: protein and fat will soften the grip.

Reading tannin, glass by glass

• Taste for texture. Note the amount and the grain. Fine, ripe tannin with fruit to match is the profile that ages. Coarse tannin over thin fruit rarely improves.
• Decant young reds, but know why. A few hours in a decanter will not soften the tannin itself; that takes years. Air changes how the wine comes across, opening the aromas and blowing off anything stuffy, so the wine seems more generous and the grip easier to read. How long to decant depends on the wine, so taste as you go.
• Mind the temperature. Chilled too far, a tannic red tastes harder and more bitter. Medium and full-bodied reds show best at 15 to 18°C.
• Be patient with the grippiest. Young Barolo, classed Bordeaux and Northern Rhône Syrah soften over years, not hours.

To feel the change for yourself, taste a young and a mature bottle of the same wine side by side. The difference in the grip teaches more than any description; a four-step tasting routine gives you the words for it. Mature vintages matched course by course with food are the point of our vintages dinners.