Colorimetric Determination of Total Lactic Acid in Wine

The colorimetric procedure of Barker and Summerson for determining total lactic acid was adapted for use in wines. The method utilizes the oxidation of both D(-)-and L(+)-lactic acids to acetaldehyde and subsequent formation of a color complex with p-hydroxydiphenyl. Tartaric acid, malic acid, citric acid, acetic acid, ethanol, sugar and sulfur dioxide did not interfere with the reaction. The lactic acid of ethyl lactate contributed to the total lactic acid measured by this method: corrections were made by use of boiled neutralized wine. Free and bound acetaldehyde were also measured by this method; however, their levels in wine are normally too low to require correction.