Q: Which wines have the most tannins? How can you tell?
—Debi, Fort Worth, Texas
A: All wines have tannins, which are naturally occurring polyphenols. There are a lot of foods that have tannins, including beans, chocolate and berries. The tannins in wine are absorbed from grape skins, stems and seeds (and a small amount can be absorbed from oak barrels).
Tannins aren't something you taste, but they are something you feel, and are an important part of a wine's structure (that said, a wine with a lot of tannins can taste bitter). Tannins create that sensation of tugging on your cheeks, and can make a wine seem chewy or drying. For those not familiar, it's similar to the mouth-puckering sensation of drinking strong black tea (which also has tannins). But tannins can also be velvety and supple.
You won't know by looking at a wine how tannic it is. But red wines tend to have more tannins than white wines. That's because red wines go through maceration, a process of steeping the grape skins in the wine to extract color and tannins—like a strong cup of tea—while white wines have limited tannins because the juice is typically separated from the grape skins and seeds soon after the grapes are crushed.
Lots of winemaking decisions can impact how tannic a wine is, starting with the grape variety (some varieties have more tannins than others). Harvest conditions, the temperature and duration of fermentations and macerations and other winemaking choices will also affect how tannic a wine is. Winemakers can even add powdered tannins if they feel a wine lacks structure.
The wines that tend to be most tannic are big, dense reds like Nebbiolo, Petite Sirah, Syrah and Cabernet.