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The Analysis of Dimethyl Sulfoxide in Malt, Wort and Beer using Headspace Gas Chromatography combined with Pulsed Flame Photometric Detection (HS-GC-PFPD) - Methodology and Applications
M. Baldus, T. Kunz and F.-J. Methner

Besides S-methyl methionine (SMM) as the thermal precursor for the unpleasant aroma compound dimethyl sulfide (DMS) in the brewhouse dimethyl sulfoxide (DMSO) is a further potent precursor during fermentation. In this paper a short and sensitive method for its analysis is introduced. In the first step DMSO is reduced to DMS by sodium metabisulfite and the generated free DMS is subsequentially analysed employing HS-GC-PFPD. In comparison to other substances sodium metabisulfite emerged as an efficient reducing agent whereby SMM and other potential precursors of volatile sulfuric compounds are not contributing to DMS under the applied conditions. In saturation of sodium metabisulfite the reduction of DMSO is exposed to be independent of its initial concentration and the recovery rate is constantly above 95 % in its usual wort- and beer concentration range. In first applications of the developed method DMSO and DMS levels are tracked during fermentation. The DMSO reduction was about 11?%, which is consistent with the accordant literature. Additionally, a non enzymatic pattern of DMS formation by reduction of DMSO with sulfite is proofed and discussed. The described method is easy to integrate to standard DMS analyses. Thereby breweries and related sectors have the possibility to upgrade their existing system without high financial and technical effort.

Descriptors: DMSO, DMSO analysis, DMS, S-methyl methionine, DMS precursor, sulfite, wine, SO2, thiols, fermentation, oxidation, reduction

BrewingScience - Monatsschrift fr Brauwissenschaft, 66 (September/October 2013), pp. 154-161