oxidation
A wine that’s been exposed to air undergoes oxidation, which causes chemical changes and deterioration. An oxidized wine has a stale, dull, sherrylike smell and flavor; its color takes on a brownish cast. Although oxidation is an asset in wines like sherry and Madeira, it’s undesirable in a table wine and can render it undrinkable.
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.