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Malic acid is an organic compound with the molecular formula C4H6O5. It is a dicarboxylic acid that occurs naturally in fruits, most notably apples, which gives it its name. The name "malic" comes from the Latin word for apple, "malum." Malic acid exists as a racemic mixture of two enantiomers, L-malic acid and D-malic acid, as well as the racemic mixture, DL-malic acid. L-malic acid is the form found in nature.

In biological systems, malic acid plays a crucial role in the Krebs cycle (also known as the citric acid cycle), a central metabolic pathway for energy production. It is also involved in gluconeogenesis, the synthesis of glucose from non-carbohydrate precursors. Plants also utilize malic acid in CAM (Crassulacean acid metabolism) photosynthesis to store carbon dioxide during the night.

Malic acid is widely used in the food industry as an acidulant, flavor enhancer, and preservative. Its tart taste is particularly desirable in candies, fruit juices, and jams. It is often used as a substitute for citric acid. In cosmetics, it is employed for its exfoliating and skin-conditioning properties. Malic acid is also used in some industrial applications, such as in the cleaning of metal surfaces. It is generally recognized as safe (GRAS) by regulatory bodies for its use in food.

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