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 the vicinal diketone content (diacetyl + 2,3-pentanedione) as well as the total diketone content in beer
The method is suitable for filtered beers brewed to any original wort or to any alcohol content as well as for fermenting wort.
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.