Acetic acid, also known as acetic acid, is an organic compound with the chemical formula CH3COOH. It is an organic monobasic acid and is the main component of vinegar. Pure anhydrous acetic acid (glacial acetic acid) is a colorless, hygroscopic liquid with a freezing point of 16.6 ℃ (62 ℉). After solidification, it becomes a colorless crystal. Its aqueous solution is weakly acidic and highly corrosive, with strong corrosion to metals. Steam has a irritating effect on the eyes and nose. Acetic acid is widely distributed in nature, such as in fruits or vegetable oils, where it mainly exists in the form of esters. Acetic acid also exists in the form of free acid in animal tissues, excreta, and blood. Many microorganisms can convert different organic compounds into acetic acid through fermentation.