Malic acid is a naturally occurring acid, especially in apples, which contributes a tart, sour taste. It is widely used in food processing as an acidifier and flavor enhancer. The flavor of malic acid is a major component of "green apple" sourness.
Malic acid is less sour than citric acid and lingers longer on the tongue. It is often included as part of an acid mixture to create a more rounded taste sensation.