When it comes to flavors, red wines have a characteristic whites don’t have: tannin. Tannin is a compound that gives reds their distinctive bitterness. While this sounds more bad than good, tannin also has the positive effect of helping red wine age.

The reason red wines have tannin is due to winemaking practices. Virtually every grape in the world—whether used to make wine or not—has juice that is colorless. Thus, for a red wine to have color, the skins, which contain tannin, must remain in contact with the juice during fermentation. When making white wines, the skins are discarded before fermentation.

Some reds have more tannin than others. This is because grapes vary in the amount of tannin they have. For example, Pinot Noir grapes have lower levels of tannin than Cabernet Sauvignons. To taste the difference, try two wines—a Cabernet Sauvignon and a Pinot Noir—from the same vintage. Don’t focus on aromas and flavors but rather on the feel of the wine as you drink it. The Pinot Noir, with less tannin, seems smoother; it glides across your palate. In contrast, the Cabernet Sauvignon has a drying sensation in your mouth, and the finish of the wine (the sensation as you finish swallowing it) is shorter than that of the Pinot Noir.

Note that this bitterness decreases over time. The finish on a Cabernet Sauvignon rounds out and is smoother as you continue to taste it. Because of its high tannin levels, red wines such as Cabernet Sauvignon can age from 5 to 25 years, depending on the vintage and intensity of the wine.

Tannic red wines must be matched with foods that can stand up to the bitterness in the wine. Fat and tannin marry beautifully, so cheddar cheese and prime rib are superb with them.