If you're a red wine drinker, you're probably familiar with tannins; the pucker-up sensation you get in your cheeks when you take a sip of some red wines. But other than that astringent feeling they leave in your mouth, what are tannins? Where do they come from and what do they do?

What are tannins?
Tannins are present in many foods including tea, pomegranates, berries and of course, wine. They're found in the skins, seeds and stems of the grapes and present in only red wines - white wines are not fermented with skins and seeds intact but with just the juice of the grapes.

While tannins may have negative connotations as they interrupt the digestive process and are possible allergy and migraine triggers, they also contain potent, free-radical fighting antioxidants.

Tannins are a type of polyphenol, the stuff that's said to lower blood pressure and cholesterol, stimulate the immune system and may even help fend off certain types of cancer.

How do tannins get into wine?
Red wine obtains its colour from the skins of the grapes during fermentation. Since the skins contain tannins, or bitter-tasting polyphenols (as do the seeds), they inevitably find their way into the bottle. Oak barrels also contain tannins and will add more tannins to the finished wine if it spends any time aging in the oak barrels - even white wines aged in oak barrels will absorb some tannins.

What tannins do for wine
Tannins serve a very important role in wine making as they give wine structure (sort of like the skeleton of the wine that all the flavours and aromas wrap themselves around). They also serve in the aging process. Acting as a natural preservative that prevents oxidization (breaking down of the wine by oxygen, like apples browning when exposed to air) tannins break down over time which allows some wines to improve with age.

Not all wines can stand up to cellaring for a decade or longer and most available on the market today are meant to be drank within a few years (as they're made with the impatient Western consumer in mind who wants to buy a wine that tastes good now). For these wines, wine makers use gentler ways of extracting the juice from the grapes so as to not crush the seeds and therefore impart only mild tannins into the wine.

Tannins and food
Big, oaky red wines with pronounced tannins serve another purpose. When matched with fatty, luxurious meats like duck, beef and lamb, they help cut through the richness and texture of the meat. Big wines go with big-flavoured food.

Tannins and health
A recent study shows that tannins in the form of procyanidins (a class of flavonoid) have a beneficial effect on vascular health and help prevent hardening of the arteries. Wines from the regions of southwest France (think Bordeaux) and Sardinia are particularly rich in procyanidins. Coincidentally, people from these regions were also found to live longer.

Read more: Debunking 6 wine myths
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Ryan Jennings and David Steele are the authors of Cooking with Booze. For more wine and food pairings visit www.cookingwithbooze.com.