Malic acid is an organic compound with the molecular formula C4H6O5. It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Here are some key points about malic acid:

• It is the main acid in many fruits, including apricots, blackberries, blueberries, cherries, grapes, mirabelles, peaches, pears, plums, and quince, and is present in lower concentrations in other fruits, such as citrus.
• It contributes to the sourness of unripe apples, and sour apples contain high proportions of the acid.
• Malic acid is also present in grapes and in most wines, with concentrations sometimes as high as 5 g/L. It confers a tart taste to wine, and the amount decreases with increasing fruit ripeness.
• Malic acid is used in foods and cosmetics, and sometimes as medicine.
• It is an alpha hydroxy acid found in certain fruits and wines, and is said to be a natural exfoliator. It may be used to smooth wrinkles and fine lines, improve skin hydration, and improve skin smoothness and tone.
• Malic acid is also involved in the Krebs cycle, a process the body uses to make energy.
• Malic acid is approved for use as a food additive in the EU, US, and Australia and New Zealand, where it is denoted by E number E296.
• Malic acid is a potent metal chelator, which binds to the toxic metals accumulated in the liver and deactivates them. It is also beneficial in breaking up gallstones and cleanses the liver.

Overall, malic acid is a versatile compound with a variety of uses in food, cosmetics, and medicine.