How Tannin Affects Red Wine’s Taste
Tannin is a substance that exists naturally in the skins, seeds (or pips), and stems of grapes. Because red wines are fermented with their grape skins and pips, and because red grape varieties are generally higher in tannin than white varieties, tannin levels are far higher in red wines than in white wines. Oak barrels can also contribute tannin to wines, both reds and whites.
To generalize a bit, tannin is a backbone of red wine (acidity is a backbone to white wine). Tannins alone can taste bitter, but some tannins in wine are less bitter than others. Also, other elements of the wine, such as sweetness, can mask the perception of bitterness. You sense tannin — as bitterness or as firmness or richness of texture — mainly in the rear of your mouth and, if the amount of tannin in a wine is high, on the inside of your cheeks and on your gums. Depending on the amount and nature of its tannin, you can describe a red wine as astringent, firm, or soft.
Red wines have acid as well as tannin, and distinguishing between the two as you taste a wine can be a real challenge. When you’re not sure whether you’re perceiving mainly tannin or acid, pay attention to how your mouth feels after you’ve swallowed the wine. Acid makes you salivate (saliva is alkaline, and it flows to neutralize the acid). Tannin leaves your mouth dry.