Dimethyl sulfide (DMS) in concentrations greater than 100 μg/l causes a detectable off-aroma in beer. The malting and wort boiling processes have the greatest influence on the amount of DMS in wort and in beer. DMS is formed from DMS precursor (S-methyl methionine). DMS precursor is converted through application of heat to DMS, which is driven out during kilning and wort boiling. The kilning and wort boiling process should be designed to convert the greatest amount of DMS precursor to DMS, in order to achieve the highest level of liberation/evaporation of DMS. The concentration of free DMS in beer should not exceed 100 μg/l in beer brewed exclusively with malt. In beer that has been brewed with adjuncts, the sensory threshold is lower.
Determination of free dimethyl sulfide (DMS) and its precursors in beer
wort
Dimethyl sulfide precursors (DMSP) in the wort are converted to dimethyl sulfide (DMS) by heating under aqueous, alkaline conditions. The DMS is determined using gas chromatography by means of the headspace technique.