What is Tannin in Wine?

"Let's talk about Tannin. Tannin is an acid that is found in the seeds, and skins, and stems of grapes. All grapes, but we usually talk about tannin in a red wine. A white wine can have tannin if the wine has rested on the grape seeds or skins for a while or if it was aged in an oak barrel. You might notice a little bit of a textural drying sensation at the back of your mouth or the tip of your tongue in a white wine. In a red wine, however, I can probably say you will taste tannin. As a matter of fact, the varying levels of tannin in a red wine are one of the major ways we describe the differences in a red wine. You'll feel tannin beginning in the back of your tongue after you swallow and exhale from taking a sip of red wine, however, if you want to bring out the tannin flavor in a wine what you need to do is take a little sip of the wine. When it's in your mouth, draw a little bit of air in like this, "whhh", swallow, and then exhale. It's a little bit embarrassing and not exactly beautiful, but it is what will bring out the tannin texture of the wine. Do it one way. Take a sip of wine, just swallow it naturally. The second time, do the little draw air in and you will be amazed at how much more you can taste and feel the tannin. It will feel like a textural drying sensation, like somebody shrink wrapped or blew dries your mouth. I'll show you how it goes. Ah yes, I can feel a drying sensation on my tongue from the back of my tongue to the tip. That's a wine that's very heavy in tannin. If that drying sensation went up about halfway up my tongue, it would be a medium tannin red wine. If it stayed at the back of my tongue or maybe the back of my mouth, that would be a wine that was low in tannin. Most red wines are at least medium. Some of them are very full in tannin and its part of the thing that we love in wine. It gives it texture, flavor, a little bit of taste, lots of body."