Malic acid, or its ionized form, malate (C4H6O5) (from the Latin malus domestica meaning apple) is one of the most abundant acids in nature and is easily metabolized by microorganisms. Malic acid is a main part of the Krebs cycle. It is found mostly in sour foods or flavored acids. When eaten, it produces a mild and persistent bitter taste. The most common source of this compound is the apple.