Influence of Wort Processing on Beer Dimethyl Sulfide Levels

Abstract

The relative importance of dimethyl sulfide (DMS) production by chemical degradation during wort processing and by yeast during fermentation was investigated. The results indicate that DMS in beers arises primarily from the chemical degradation of precursors originating in the malt. Laboratory fermentations confirmed that unboiled extracts of commercial malts cured at final temperatures between 77 and 88°C contain a precursor that can be metabolized to DMS by yeast. In boiled and hopped brewery worts from which free DMS was removed, however, the amount of DMS produced by yeast was small. Similarities between the DMS precursor and S-methyl methionine were observed. Commercially brewed sweet worts contained high concentrations of free DMS and total precursor material, both of which fell markedly during boiling as a result of evaporation and chemical breakdown, respectively. Free DMS levels increased significantly in the hot wort settling tank where residual precursor material is chemically degraded. The free DMS contents of both ales and lagers fell appreciably early in fermentation, and only minimal amounts were subsequently formed by yeast activity. The hot wort settling stage probably is the most important period for determining the DMS level in the final product.