Today's diacetyl: the total vicinal diketone profile of beer.

Morrison, N.M. and Bendiak, D.S.

Abstract
The total vicinal diketone (TVDK) profiles of a range of commercial beers has been carried out to provide a market survey. Simple preparation procedures and an automatic gas chromatographic technique (ECD) was used to analyse 86 beers for diacetyl, 2,3-pentanedione, their respective precursors, 2-acetolactic acid and 2-acetohydroxy butyric acid and their products of reduction, acetoin and 3-hydroxy-2-pentanone. These analyses were also used to follow changes in the levels of total, potential and free VDK that occurred when 11 different mutant yeast strains were used to ferment wort. Three general patterns of TVDK profiles were identified. Several microorganisms were TVDK profiled and were classified into three growth rate patterns; 1. rapid growth with the production of large numbers of organisms, typical of Flavobacterium and Enterobacter, 2. rapid growth but low production of organisms, typical of Gluconobacter and Acetobacter and 3. slow but constant growth with the steady accumulation of VDK and little or no reduction, typical of Pediococci. Fermentations using cultured yeast in combination with several contaminants produced distinctive TVDK profiles. This technique can be used to assist in the identification of bacteria responsible for process problems.
Keywords : aeration beer diacetyl gas chromatography microorganism off-flavour vicinal diketones yeast