Factors Influencing the Levels of Polysulfides in Beer

Abstract

This study was done to identify the factors that influence the concentrations of dimethyl polysulfides, which are important contributors to the sulfury character of some Canadian beers. The brewing process was monitored using established methodology, and malt was found to be the major source of these compounds in wort. Yeast was important in reducing their concentrations during fermentation to low levels that did not change during normal maturation. Packaged beer stored for prolonged periods at room temperature or for a few days at 45° C showed marked increases in the trisulfide and tetrasulfide levels. Headspace air and, particularly, sulfur dioxide had influence on the formation of the higher sulfides. Pilot scale trials have shown that, as the level of antioxidant (sodium metabisulfite added during maturation) is increased, the formation of polysulfides also increases. The residual sulfur dioxide in the malt, probably due to the sulfuring of malt during the kilning process, and the polysulfide levels found in worts are directly related. The interaction of sulfur dioxide (or bisulfite) with wort and beer constituents is a major factor in the formation of dimethyl polysulfides. These compounds may include S-methylmethionine, which is a precursor for dimethyl sulfide, and methionine.