Changes

'''Dimethyl sulfide (DMS)''', sometimes spelled "dimethyl sulphide" <ref name="pubchem"></ref>, is the simplest type of [https://en.wikipedia.org/wiki/Thioether thioether] <ref name="Scheuren2016">[http://onlinelibrary.wiley.com/doi/10.1002/jib.301/full Evaporation behaviour of DMS in an aqueous solution at infinite dilution – a review. H. Scheuren, M. Baldus, F.-J. Methner and M. Dillenburger. 2016]</ref>, which are sulfur containing oils that are generally considered off-putting in beer <ref>[https://en.wikipedia.org/wiki/Thioether Wikipedia. Thioether. Retrieved 03/01/2016.]</ref><ref name="Anness">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1982.tb04101.x/abstract DIMETHYL SULPHIDE—A REVIEW. B. J. Anness andC. W. Bamforth. 1982.]</ref>. The flavor and aroma of DMS have been characterized as being like cooked sweetcorn, tomato sauce, celery, or sauerkraut. In beer, it is sometimes confused with methyl thiocetate, ethanethiol, and dimethyl trisulphide. DMS in beer originates from malt-derived precursors, S-methyl methionine (SMM) and dimethyl sulphoxide (DMSO), and to a lesser extent can be formed during fermentation by certain microbes <ref name="aroxa">[http://www.aroxa.com/beer/beer-flavour-standard/dimethyl-sulphide/ Aroxa. Dimethyl sulphide. Retrieved 03/01/2016.]</ref>. Small amounts of DMS have also been found in hops, which is volatilized during boiling <ref name="Scheuren2014">[http://onlinelibrary.wiley.com/doi/10.1002/jib.156/abstract Decomposition kinetics of dimethyl sulfide. H. Scheuren, J. Tippmann, F.-J. Methner, and, K. Sommer. 2014.]</ref>. The flavor threshold of DMS is 30-50 µg/liter. Low levels above threshold between 30-100 µg/liter are considered acceptable and even beneficial to some lagers in the United Kingdom (but not in Germany) <ref name="beersmith"></ref> (~25 minutes in), and maybe some traditional farmhouse ales that are not boiled (see [[Dimethyl_Sulfide#Considerations_for_Historical_Examples_of_Raw_Ale|Considerations for Historical Examples of Raw Ale]]). However, amounts above 100 µg/liter are generally considered offensive for any beer. Ales typically have below the flavor threshold of DMS <ref name="Anness"></ref>. The basis of the understanding of DMS and it's creation in beer was uncovered in the late 70's and early 80's. DMS is a common compound found throughout nature, including having an importance in cycling sulfur in ecosystems involving algae and other microbes, helping the navigation of seabirds, and is found in many foods such as corn, cabbage, parsley, asparagus, potatoes, beef, Camembert cheese, fish (carp), tea, cocoa, milk, wine, rum, beetroot, black truffles, and seafood <ref name="Scheuren2016"></ref><ref name="bamforth">[http://www.asbcnet.org/publications/journal/vol/abstracts/ASBCJ-2014-0610-01.htm Dimethyl Sulfide – Significance, Origins, and Control. Charles W. Bamforth. 2014.]</ref>.

While malted barley contains small but not insignificant amounts of DMS (more than 10 ppm) <ref name="Scheuren2016"></ref>, the primary source of DMS are the precursors S-methyl methionine (SMM) and dimethyl sulphoxide (DMSO), both of which are present in malted barley <ref name="Anness"></ref>. When listed on malt analysis sheets they are usually listed as a combined value as "DMS-P" or "DMSP". This value should be between 5-15 ppm for pilsner malts, and less for fully modified malt <ref>[http://morebeer.com/brewingtechniques/bmg/noonan.html Understanding Malt Analysis Sheets -- How to Become Fluent in Malt Analysis Interpretation. Greg Noonan. Retrieved 03/02/2016.]</ref>. DMSP is rarely included on modern malt analysis sheets because it is viewed as much less important than the brewing process <ref>"Unraveling the Malt Puzzle." Joseph Hertrich. Michigan Brewers Guild MBAA – District Michigan Winter Conference. 01/13/2012. Retrieved 08/04/2016.</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 CO₂. 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>.

DMS is a very volatile compound. Scheuren et al. (2016) determined that there is not a significant difference in DMS evaporation in water versus wort, and came up with equations for determining the evaporation of DMS in water using the laws of thermodynamics. They presented a somewhat counter intuitive result that DMS actually volatilizes more readily as temperatures drop, until about 50°C (volatilization of DMS drops significantly under 50°C). Their calculations state that 3.2% of the total wort volume needs to be evaporated for 90% of the DMS to volatilize at 100°C, whereas only 1.3% of the total wort volume needs to be evaporated for 90% of the DMS to volatilize at 80°C (keep in mind that the rate of evaporation at 80°C is much slower, and thus it takes more time to reach 1.3% evaporation). This indicates that some amount of DMS is evaporating off at temperatures below boiling until 50°C is reached <ref name="Scheuren2016mbaa"></ref><ref name="Scheuren2016"></ref>.