Ask for anyone’s short list of beer flaws and invariably you will hear “DMS—dimethyl sulfide,” bested only by the other D-word “diacetyl.” Unlike diacetyl, which is created during fermentation, the cause and cure for DMS happen before yeast ever touches the wort.
For those who have never had the pleasure of encountering this “flavor attribute,” DMS is often described as a cooked-corn flavor, but you may also be reminded of the inside of a can of black olives or canned tomato paste. If you ever have the chance to taste a particularly potent example, you may be able to then find it in a surprising number of beers, both commercially brewed and homebrewed.
DMS is a sulfur compound that is created by s-methylmethionine (SMM) sometimes called simply “DMS precursor.” SMM develops during the germination of barley and is therefore present to some degree in all malt. Most of it, however, is broken down to DMS during malting and is volatilized during kilning. The darker the kiln, generally the lower the SMM level in the finished malt. Very pale malt such as Pilsner, however, still contains appreciable amounts of SMM, which breaks down into DMS when exposed to the heat of the boil. That makes it tricky to get a DMS-free very light colored wort using 100 percent barley (using adjuncts such as corn and rice can decrease the SMM/DMS load). In this article, I discuss a novel approach that attempts to do just that.