Lactic acid is an organic compound with the formula CH3CH(OH)COOH. In its solid state, it is white and water-soluble. In its liquid state, it is colorless. It is produced both naturally and synthetically. With a hydroxyl group adjacent to the carboxyl group, lactic acid is classified as an alpha-hydroxy acid (AHA). In the form of its conjugate base called lactate, it plays a role in several biochemical processes.
In beer brewing some styles of beer (sour beer) purposely contain lactic acid. Most commonly this is produced naturally by various strains of the Lactobacillius bacteria. These bacteria ferment sugars into acids, unlike yeast, who ferment sugar into ethanol. One such style are Belgian Lambics. After cooling the wort, yeast and bacteria are allowed to “fall” into the open fermenters. Most brewers of more common beer styles would ensure no such bacteria are allowed to enter the fermenter. Other sour styles of beer include Berliner weisse, Flanders red and American wild ale.
In distilling, Lactic acid is a common flavor contributor to Whiskey. It provides more mouthfeel with sweet and fatty notes.