fill level
The level of a wine’s surface in its bottle. In a bottle with a high fill level, the surface will be just below the bottom of the cork. A fill level that comes only midway up a bottle’s shoulders means that more oxygen can reach the wine, causing deterioration through oxidation. Fill levels reduce over time owing to several factors. A faulty cork may allow for leakage, or extreme temperatures can cause the wine’s expansion, which can loosen the cork and cause leakage. It’s a good idea to check the fill level of older wines. See also ullage.
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.