malic acid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A colorless, crystalline compound, C₄H₆O₅, used as a flavoring in foods and beverages. The levorotary form occurs naturally in wine and in many fruits, including apples, cherries, and tomatoes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry A colourless crystalline dicarboxylic acid, hydroxy-malonic acid, found in wine, apples and other fruit; it is converted to lactic acid by malo-lactic fermentation.