Changes

Yeast species/strain, temperature, pH, wort composition, and open/closed fermentation vessels contribute to how much DMSO gets converted into DMS. For example, ''S. uvarum'' (potentially reclassified to ''S. bayanus'') produces less DMS than ''S. cerevisiae'', as does ''S. pastorianus'' <ref name="bamforth"></ref>. DMSO is converted to DMS by yeast more readily at lower temperatures than warmer temperatures with five times as much at 8°C than at 25°C. Higher gravity worts (1.033 vs 1.060 in the linked reference) also produce more DMS from DMSO during fermentation. A higher pH of wort also leads to more DMS production; for example lager wort pH is typically 5.4-5.7, while ale wort pH is typically ~5.1. This might explain why DMS is present more in lager beers. Anderson et al. and Booer & Wilson showed that open fermentation leads to less DMS production compared to closed fermentation <ref name="Anness"></ref>.

Many types of microbes are capable of producing DMS from DMSO as a secondary metabolite of fermentation. Microbes that can produce high amounts of DMS include gram-negative, facultative anaerobes in the [https://en.wikipedia.org/wiki/Enterobacteriaceae ''Enterobacteriaceae''] family, which includes species of ''Klebsiella'', ''Citrobacter'', ''Enterobacter'', ''Obesumbacterium'', ''Proteus'', ''Salmonella'', and ''Escherichia'', as well as gram-negative aerobic bacteria such as ''Pseudomonas aeruginosa'' <ref>[http://mmbr.asm.org/content/77/2/157.short The Microbiology of Malting and Brewing. Nicholas A. Bokulicha and Charles W. Bamforth. 2013.]</ref><ref name="zinder">[http://www.ncbi.nlm.nih.gov/pubmed/347031 Dimethyl sulphoxide reduction by micro-organisms. Zinder S.H., Brock T.D. 1978.]</ref>. Gram-positive bacteria can also produce high amounts of DMS, such as ''Bacillus subtilis'' <ref name="zinder"></ref>. Many other bacteria such as species of ''Clostridium'', ''Streptococcus'', and ''Staphylococcus'' produce only small amounts of DMS (much less than ''S. cerevisiae'' even) <ref name="zinder"></ref>. All bacteria that can produce DMS from DMSO do so using a different enzyme than yeast, which might account for the ability of some bacteria to convert a higher percentage of DMSO to DMS than ''S. cerevisiae''. The DMS production by facultative anaerobic bacteria is encouraged by the lack of oxygen <ref name="Anness"></ref>.