13,700
edits
Changes
added percentage conversion examples for DMSO in bacteria
====Spoilage Organisms and Spontaneous Fermentation====
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>. These bacteria species can convert 17-37% of DMSO into DMS, whereas ''S. cerevisiae'' converts around 5% of DMSO into DMS. Many other bacteria such as species of ''Clostridium'', ''Streptococcus'', and ''Staphylococcus'' produce only small amounts of DMS (much less than ''S. cerevisiae'' even1% of DMSO converted into DMS) <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>.
In [[lambic]] production where the pH of the wort is not lowered to less than 4.5 before entering the [[coolship]] for [[Spontaneous_Fermentation|spontaneous fermentation]], ''Enterobacteriaceae'' are responsible for high amounts of DMS production. No DMS was found in the referenced study before the wort was cooled in the coolship, which might be due to the lengthy boil of the wort due to the [[Turbid Mash|turbid mash]]. After two weeks of fermentation, 450 ppb of DMS were found, far more than the 30 ppb taste threshold, and the vegetal aroma of DMS could be detected during the fermentation at this time. After two weeks the fermentation of ''Saccharomyces'' begins, and the DMS levels decline due to the formation and blow-off of CO<sub>2</sub>. At 6 months the DMS was down to 100 ppb, and a range of 25-75 ppb of DMS found in bottles of lambic (and at 16+ months), which is a typical amount for regular ales and lagers <ref>ORIGIN AND EVOLUTION OF DIMETHYL SULFIDE AND VICINAL DIKETONESDURING THE SPONTANEOUS FERMENTATION OF LAMBIC AND GUEUZE. D. Van Oevelen, P. Timmermans, L. Geens and H. Verachtert. 1978.</ref>.