APPLICATION OF NITROGEN-PURGING OF MALT EXTRACTS TO MEASURE 2 DIMETHYLSULFIDE PRECURSORS BY HEADSPACE GAS-CHROMATOGRAPHY

Dimethylsulfide (DMS) in beer can arise from S-methylmethionine (SMM) by heat degradation during malt kilning and wort boiling, or from the reduction of dimethylsulfoxide (DMSO) by yeast during fermentation. Bo th SMM and DMSO originate from malted barley. A gas chromatography (GC ) headspace technique was applied to analyze SMM and DMSO in malt. Nit rogen-purging was used to remove free DMS from the malt extract, there fore only SMM was determined following heat treatment in alkaline solu tion. The accuracy and precision of malt SMM analysis were improved in comparison with the traditional subtraction method, where the SMM val ue was based on subtracting free DMS in the untreated sample from tota l DMS in a heat-alkaline-treated sample. Similarly, for DMSO measureme nt, free DMS and SMM could be removed by nitrogen-purging of the aqueo us sample after heat-alkaline treatment. DMSO then was reduced with st annous chloride into DMS for GC analysis. A small amount of DMS was ox idized to DMSO in a sealed system under heat treatment. This indicated that DMSO could be formed from oxidation of DMS during malt kilning. The level of DMSO present in malts was found to be similar to that of SMM.