Tannins are probably the trickiest thing to understand in wine. All the other structural components – sugar, alcohol, and acidity – are things we encounter regularly in other foods and drink. Some of us do have the occasional run-in with tannin through bitter, papery walnut skins, or an oversteeped cup of tea that makes our gums and the inside of our mouth seem to shrivel up. But for the most part, we really only experience tannin in wine. And only red wine in that.

First of all, what are tannins and where does it come from? Basically, tannins are a group of chemical compounds that occur naturally in many fruits. They’re found in grape skins, seeds, and stems, with skins being the primary source of tannins in today’s winemaking. (That’s why you don’t really find tannins in white wine, which are almost always made without using the skin of the grapes. No skin, no tannin.) If a wine is aged in oak, the wood can impart tannin, too.

Second of all, what does tannin taste like? Well, tannin is as much about feel than it is about taste. Tannin creates a drying sensation in your mouth and a pleasingly bitter flavor. In a well-made wine, this combo will nicely offset the softer, mouthfilling sensation of alcohol and any sugar that might be left in the wine, as well as the richer fruit flavors. Tannin is the taskmaster who keeps the wine’s more unruly impulses in check and gives the wine some consequence. Not enough tannin and the wine tastes like boozy fruit soup and leaves no lasting impression. When you hear someone saying that a wine has excellent structure, they’re likely talking about about its tannins, and how they provide the wine with its backbone.  Tannin also extends a wine’s lifespan. The small percentage of the world’s red wines that age well will have a lot of tannin of them, because tannins do all kinds of cool and delicious things as they age that would require a mini-chemistry lesson on my part to explain fully. As anyone who’s tried a year-old Barolo or first-growth Bordeaux can tell you, this can make these great wines unpleasantly astringent to drink when they’re young.

In my experience, tannins are the number one source of confusion for beginning wine drinkers. They can be hard to distinguish from acidity, as both create a puckering feeling in your mouth. Here’s one way to tell the difference: roll the wine around the sides of your tongue, which is where you’re most sensitive to sour. If the sensation is really strong, and you feel yourself salivating, then what you’re tasting is probably acidity, rather than tannin. Another (slightly gross) trick: take a sip of red wine and spit it out in a clear glass. Take a look at the little thread-like bits – that’s the tannin combining with your saliva. The more threads, and the thicker they are, the more tannic the wine is.

Tannins can also be off-putting to a lot of people. Americans aren’t big on bitter. We love sweet and soft, and tannins are pretty much the opposite of that. When I started drinking wine, I preferred Australian Shiraz, California Zinfandel, and Beaujolais crus, all wines that usually aren’t heavy on the tannins. Gradually, I grew to appreciate more tannic wines, which opened up my choices exponentially. In general, wines made from Cabernet Sauvignon, Cabernet Franc, and Nebbiolo (the grape behind Barolo, Italy’s noblest wine) will have pretty substantial tannins. Pinot Noir has moderate tannin levels, one factor that helps to explain its huge popularity in the U.S.

If you’re stuck with a wine that is too tannic for you, here are a few tricks:

1. Decant it. (Ie, pour it into another vessel at least an hour before serving. You don’t need a fancy decanter. A glass or ceramic water pitcher works great. Avoid plastic or metal, as they will impart some funky flavors.) Exposing the wine to oxygen this way can help soften the tannins.

2. Serve the wine with something fatty, like, say, a rib-eye steak. (You can splurge with all the money you saved from not buying a fancy decanter.) The richness of the food and the astringency of the wine will cancel each other out.