DMS - Dimethyl Sulfide in Beer
DMS or Dimethyl Sulfide, is a volatile sulfur based compound which if noticed, will be perceived as cooked can corn, or possibly celery. The flavor threshold is 10-150 ppb which means that it is noticeable. In fact, its part of the flavor profile in most beers, especially lagers.
SMM (S-Methyl Methionine) in malt is the precursor for Dimethyl Sulfide. SMM is found in lightly kilned malts such as pilsner and pale ale. The SMM level in the malt is directly proportional to the Dimethyl Sulfide level in your wort. It is not until the levels becomes excessive that you will notice the typical canned or cream corn flavors and aromas. Below this level, Dimethyl Sulfide is part of the flavor and aroma profile we are all used to in our beer.
British ales are usually lowest in Dimethyl Sulfide at 10-20 ppb and German lagers and all-malt beers are highest at 50-175 ppb. The typical U.S. lager contains 40-100 ppb, falling pretty much in the middle of the range. Lighter beers with high adjunct ratios, or low-gravity beers, will have higher levels of DMS. Whereas in dark German beers, all-malt beers and any other flavorful beer, these cooked corn notes tend to be hidden.
Dimethyl Sulfide is created from the breakdown of SMM in heated wort (above 140 degrees F or 60 degrees C). When the boil kettle is uncovered, most of the DMS produced will be
Some of the remaining Dimethyl Sulfide will be removed during a vigorous fermentation, which is why ales usually have lower concentrations of these off flavors than lagers.
Some causes of excessive cooked corn notes in your beers are covering the boil kettle (which will not allow the chemicals to escape) and cooling the wort too slowly (Dimethyl Sulfide is being produced as long as the wort is above 140 degrees F/60 degrees C). Thus the quicker you can cool the wort, the less cooked or canned corn flavors will be produced. When using all pilsener malt or pale malt, it may be advisable to boil your wort for at least 90 minutes to reduce the Dimethyl Sulfide levels. Ensure that you have a vigorous boil with at least 8% evaporation. Minimize the amount of time the wort sits at higher temperatures and try to cool the wort as quickly as possible.
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