DMS (Dimethyl Sulfide) smells and tastes like sweetcorn or stewed vegetables and is most susceptible and perceptible in light lagers and pilsners.
Stuart Howe describes the formation: “DMS is formed during fermentation from dimethyl sulphoxide which is formed during kilning from the precursor S-methlymethionine [SMM]. The reason it is found more commonly in pilsners is that the more gentle kilning of lager malt removes less S-methylmethionine than that of ale malts.”
SMM is a product of malt germination and the more kilned and roasted the malt is the less SMM there will be in them, this is why pale lagers are more susceptible to DMS than dark ales (interestingly, in the case of a beer like Carling, the malt is kilned to specifically allow a certain higher-than-usual amount of DMS into the beer). When brewing, the malt gets mashed with hot water to create wort. Once the wort has been transferred (with the SMM coming with it – there’s a direct relationship between the levels of SMM and DMS) it is boiled and DMS is produced and then typically it is evaporated out with the boil. If the boil is covered then DMS struggles to escape, so will stay in the wort. If the boil is short then some DMS may still be present, so a long and vigorous boil, uncovered, is the best way to see off DMS. If the beer cools too slowly then more DMS could also be created.
Some people are more sensitive than others to the flavour; I don’t mind it in a lager, where it can be appropriate, but only in small volumes and only if it’s corn-like. If your beer tastes like cold, stewed cabbage then that’s never a good thing. Like most of these characteristics, DMS is naturally present in beer but it’s only when it hits higher perceptible levels that it becomes a problem.
Ever tasted sweetcorn/DMS in a beer?
There’s lots that can go wrong when making beer but thankfully most of them can be controlled. If I’ve missed anything important about DMS then it’d be great if you add it below. Also, this shouldn’t be confused with beers made with corn as an adjunct as that is something different (although DMS can still be present from the usual brewing method). I used this and this to help me out with the post.