Beer sulphur components
The main sulphur components impacting on beer flavour are sulphur dioxide (SO2), hydrogen sulphide (H2S), dimethyl
sulphide (DMS) and mercaptans (Van Haecht & Dufour, 1995). The two main compounds that are influenced by yeast metabolism are H2S and SO2 (Fig. 3). Reduced sulphur is an essential constituent of proteins (sulphur-containing amino acids such as cysteine and methionine), coenzymes (CoA, biotin, thiamine and pyrophosphate) and other cellular metabolites (glutathione, sulphides and thiols). Radiochemical tracer experiments showed that all of the SO2 formed during fermentation is derived from the inorganic sulphur source, sulphate, in wort. SO2 production during fermentation should be controlled due to possible negative flavour impacts. However, sulphite can function as an antioxidant and can react with stale-tasting carbonyls (acetaldehyde and trans-2-nonenal) to form flavour-inactive carbonyl-sulphite adducts.