Do you know that feeling when drinking a glass of Cabernet Sauvignon that causes the inside of your cheeks to pucker and dry out? If you answered "yes," then you've experienced tannins at work. Technically speaking, tannins are a group of organic compounds present in a wide variety of plants, including grapes, that are capable of binding to and precipitating proteins. Tannins can contribute both a drying sensation and astringency to a wine, and are also tied to the perception of body. Wine isn't the only place you'll find tannins – if you leave a bag of Earl Grey steeping a couple minutes too long, you'll encounter a similarly tannic experience. The majority of tannins perceived in tasting a wine derive from the skins of the grapes, however tannins can also be extracted from grape seeds and stems, as well as from oak barrels. Generally, the discussion around tannins tends to be limited to red wines, however skin-contact white wines (or "orange wines") and rosé wines can be noticeably tannic as well. Some grapes, such as Cabernet Sauvignon and Syrah , are naturally rich with tannins, while others, such as Pinot Noir and Gamay , are not. Together with acidity, alcohol, and sugar, tannins are one of the chief factors that contribute to a wine's ability to age. While highly tannic wines can taste austere in their youth, over time in bottle, tannins will bind and form chains (or "polymerize") and precipitate out of the wine as sediment. They can also bind to your food – namely proteins. Why does Cabernet Sauvignon taste so good with steak? We have tannins to thank for that winning combo.