A PHENOL (a kind of compound) derived from the skins, seeds, and stems of grapes and from barrels. The presence of tannin is beneficial, for it gives red wines a firm structure as well as the potential for aging. Tannin is both tasted and felt. When young, highly tannic wines have a slight bitterness (like espresso or chocolate) and a drying, astringent feel. If the wine has been made from mature grapes with ripe tannin, the bitter dry quality will be ameliorated. Excessively dry, harsh, scratchy tannin is a negative and may never ameliorate. Harsh tannin, often called green or unripe tannin, most often results when grapes have been picked before they are completely physiologically mature. Most white wines have only tiny amounts of tannin because they are not fermented on their skins.