Effect of antioxidants on dimethyl sulphoxide reduction and impact on dimethyl sulphide formation during beer storage

Dimethyl sulphide (DMS) can be important in beer aroma. Although primarily formed during wort boiling, it can evolve during fermentation by reduction of its oxidation product dimethyl sulphoxide (DMSO). In this study, a number of antioxidants sulphite, thiols [L-cysteine, L-glutathione (GSH)], gallic acid and ascorbic acid - were tested on DMSO reduction and DMS formation in a buffered model solution [pH 4.3, 5% (v/v) ethanol] together with a Pilsner type beer. In the model solution, significant DMSO reduction and DMS formation were observed for sulphite and the thiols L-cysteine and GSH. Ascorbic acid and gallic acid were not capable of reducing DMSO. During beer storage at 28 degrees C, the highest DMS formation was found with the combined addition of sulphite, GSH and DMSO followed by sulphite/DMSO and GSH/DMSO. In conclusion, the reaction mechanisms of DMSO reduction and their relevance to DMS formation during beer storage are discussed. (C) 2018 The Institute of Brewing & Distilling