An organic acid profile provides valuable information regarding authenticity of apple juice. The presence of D-malic acid is a clear indication of adulteration because this isomer does not occur naturally. Fumaric and citric acid levels above trace amounts are also inconsistent with pure apple juice; therefore, measurement of these organic acids may also be used as an authenticity check. Citric acid, total malic acid, and fumaric acid were determined in a single scan by liquid chromatography (LC) for 30 known pure apple juice samples. The L-isomer of malic acid was measured by an enzyme-specific method, and the D-isomer was calculated as the difference between total malic acid and L-malic acid.