Tannin for wine is dryness. You sense tannin as bitterness, firmness or richness of texture. When you taste a dry wine, you're tasting tannin. Tannin is dry and astringent. You might feel it specifically on the middle of your tongue and the front part of your mouth. if the amount of tannin is high, you might sense it on the inside of your cheeks and on your gums. Unsweetened black tea is a great example of nearly pure tannin dissolved in water.
Tannin is a naturally occurring substance found in plants, seeds, bark, wood, leaves and fruit skins. Tannin exists naturally in the skins, seeds, and stems of grapes. As a characteristic of wine, tannin adds both bitterness and astringency as well as complexity. Tannin levels are far higher in red wines than in white wines. White wines have tannin from being aged in wooden barrels. You may describe a red wine as astringent, firm, or soft.
Red wines have acid as well as tannin. Sensing the difference between the two as you taste a wine can be challenging. Pay attention to how your mouth feels after you’ve swallowed the wine. Acid makes you salivate (saliva is alkaline and will flow to neutralize the acid). Tannin leaves your mouth dry.