An organic acid, which gives spoiled milk its sourness. Small amounts of pure lactic acid are commonly used as a brewing water additive to reduce pH. Certain types of bacterial infections may produce large quantities of lactic acid during fermentation, imparting a distinct sour flavor to the finished beer. In certain styles of beer (e.g. Lambic, Berliner Weisse, Oud Bruin) some lactic sourness is a desirable characteristic. Result of Malolactic fermentation.