Malic Acid is the active ingredient in many sour or tart foods.

Malic Acid is a colorless, crystalline compound, that occurs naturally in a wide variety of unripe fruit, including apples, cherries, and tomatoes, and is used as a flavoring and in the aging of wine. Malic acid contributes to the sourness of green apple. Malic acid is present in grapes. It confers a tart taste to wine, although the amount decreases with increasing fruit ripeness. The process of malolactic fermentation converts malic acid to much milder lactic acid.

Malic acid, when added to food products, is denoted by E number E296. Malic acid is the source of extreme tartness in so called "extreme candy", for example Mega Warheads or Sour Punch candies. It is also used with or in place of the less sour citric acid in sour sweets such as Jolly Ranchers, SweeTarts and Salt & Vinegar flavor potato chips. These sweets are sometimes labeled with a warning that excessive consumption can cause irritation of the mouth.

Malic acid is both derived from food sources and synthesized in the body through the citric acid (Krebs) cycle. Its importance to the production of energy in the body during both aerobic and anaerobic conditions is well established. Under aerobic conditions, the oxidation of malate to oxaloacetate provides reducing equivalents to the mitochondria through the malate-aspartate redox shuttle. During anaerobic conditions, where a buildup of excess of reducing equivalents inhibits glycolysis, malic acids simultaneous reduction to succinate and oxidation to oxaloacetate is capable of removing the accumulating reducing equivalents. This allows malic acid to reverse hypoxias inhibition of glycolysis and energy production. This may allow malic acid to improve energy production in FM, reversing the negative effect of the relative hypoxia that has been found in these patients.

Soft drinks have a high phosphorus content, which also reduces magnesium levels in the body. Even high-calcium supplementation, without adequate magnesium, will deplete the body's level of magnesium. Malic Acid Aluminum toxicity may play a role in symptoms experienced by magnesium-deficient FM patients.