sediment
The grainy, bitter-tasting deposit sometimes found in wine bottles, most often with older wines. sediment is not a bad sign but in fact may indicate a superior wine. It’s the natural separation of bitartrates (see acids, tartaric acid), tannins, and color pigments that occurs as wines age. Although generally associated with finer red wines, sediment occasionally appears in white wines, usually in the form of nearly colorless crystals. For port drinkers, the term crust, synonymous with sediment, is often used. sediment should be allowed to settle completely before the wine is decanted into another container so that when the wine is served none of the deposit will transfer to the glass.
The New Wine Lovers Companion, 2nd Edition, by Ron Herbst and Sharon Tyler Herbst. Copyright © (1) 2003, 1995 by Ron Herbst and Sharon Tyler Herbst. Reprinted by arrangement with Barron's Educational Series, Inc.