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Diacetyl (2,3-butanedione) and 2,3-pentanedione are detected photometrically in the beer after steam distillation. It is also possible to determine precursors in green beer.

Beer is thermally treated to cause the precursors present in the sample to transform into their respective vicinal diketones. Using the headspace technique, the concentration of total diacetyl is determined using gas chromatography. The linearity of the detector and the determination of the concentrations of analytes in the sample are achieved by using multiple concentration levels within their relevant range and through evaluation of the relative area under the peaks. Depending upon the operating conditions of the chromatograph, the relative areas under the peaks can also be used to determine the concentrations. The method is suitable for beer brewed to any original gravity or to any alcohol content.

Diacetyl, 2,3-pentanedione and their precursors are determined by means of gas chromatography. A sample from the headspace – in equilibrium with the beer at 35 °C – is analyzed. Precursors are converted to the corresponding diketones through aeration and heating the beer to 60 °C. The evaluation of the results is performed by comparing the height of the peaks of diacetyl and against the peak for hexanedione as the internal standard.