Over the course of primary fermentation, the compounds 2-acetolactic acid and 2-acetohydroxybutyric acid occur as by-products of yeast metabolism, and from these by-products, the substances diacetyl (2,3-butanedione) and 2,3-pentanedione are formed through oxidative decarboxylation. Diacetyl produces an off-flavor in beer in concentrations over 0.10 mg/l.
Determination of total diacetyl in beer.
The method is suitable for beers of all original wort ranges and alcohol contents.
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.