The only true and meaningful way in which to assess the flavor of beer is through organoleptic analysis. Nonetheless, analytical control of complex technological processes may be needed as backup for large breweries. DMS is a substantial contributor to the aroma of many lager-style beers. Typical values of DMS in beer vary between 15-150 µg/L while the sensory threshold for the human nose is about 30-45 µg/L. DMS can be derived in beer from two sources: the thermal decomposition of S-methyl-methionine (SMM) produced in the embryo of barley during germination, or the reduction of dimethyl sulfoxide (DMSO, derived from the breakdown of SMM during the curing of malt) by yeast. The enzyme that affects DMSO reduction is a reductase whose primary function is the reduction of methionine sulfoxide and which competes for reducing power with several other cellular systems. Control of DMS production is achieved by specifying precursor levels in malt, attending to the vigor and duration of the boil, controlling the length of the whirlpool stand, specifying yeast strain, and maintaining other parameters.

The isotope-dilution SPME GC-MS method for analysis of DMS in wort and beer was developed following a request from a local brewery.

Instrumental. DMS in wort and beer samples was analyzed using the GC-MS which consisted of a 5973C single-quadrupole mass spectrometer coupled with a  7890B gas chromatograph (Agilent). The mass spectrometer was operated in EI mode using helium as a carrier gas. The GC-MS system was equipped with a CTC PAL autosampler operated in the SPME sampling option. Quantitation of DMS was carried out by isotope dilution method using CD3-S-CD3 (DMS-D6) as an internal standard. The mass spectrometer was operated in selective ion monitoring mode (SIM). The ions m/z 62 (quantitative) and 61 (qualitative) were selected for DMS, and m/z 68, and 66 for DMS-D6. The compounds were separated on BPX-Volatiles (SGE, 60m×0.25mm, 1.4μm) capillary column. Analytes were sampled from the headspace using SPME (fiber – Carboxen/PDMS).