Stay at Home(Brew)
Off-flavor: DMS
During these times where we are at home for an extended period,
homebrewing is seeing an uptick. Whether it be former homebrewers picking up
the hobby once more, the avid upping home production, or those taking up the
hobby for the first time it can be very rewarding. When homebrewing, one must
take care to watch out for common off-flavors that could show up on your
finished beer that could put and asterisk on your hard work. Let’s talk about
DMS.
Dimethyl Sulfide, or better known by the acronym DMS, is a compound
characterized by its distinctive creamed corn or cooked vegetable aroma and
flavor. In some extreme cases, it may be reminiscent to rotten vegetables or
dead shellfish. Very unappealing in those large quantities.
DMS isn’t always an off-flavor, though. In certain beer styles, a
slight note of DMS is acceptable, if not welcomed, and sometimes expected to be
there. The American lager family and Cream Ale are great examples of that. Other
examples include Kölsch, Helles, German Pils, and other styles may also have a
slight hint of DMS as well as other similar styles that may fit the bill.
With that said, it is not a required flavor and not all examples have
it. It’s not a flaw if there’s a slight corny note in the background of these
styles, although it is not necessarily essential. However, a large presence of
DMS is always a flaw.
The origin of Dimethyl Sulfide is found in the grain used to make beer,
barley. A compound known as S-Methyl-Methionine (SMM), an amino acid formed in
barley during the germination stage of malting is the precursor to DMS. Once
germination is completed and the barley begins to sprout, it is then heated, or
kilned, to remove moisture. From there it can be kilned further to create a
verity of malts. The lightest of kilned malts are only heated for a short while
at about 170*F. Not enough heat or time to degrade much of the SMM.
The SMM is released into the wort during the mash but is not converted
into DMS until it gets into the boil kettle. SMM is thermally liable and, as it
turns out, boiling temperatures are enough to convert it into something else.
And that something else is -you guessed it- DMS.
Homebrewers beware: During production, the steam created during wort
boil caries a ton of DMS. You may experience a large amount of DMS if they
cover their kettle to speed up the boil or to make it more vigorous. All the
steam condensates on the lid and drips concentrated basically liquid DMS back
down into their boiling wort. A long 90-minute boil is highly recommended.
Leave your kettle uncovered!
Commercially, this is an important reason why fans and flues are used
to carry the steam away into the atmosphere and not allowing it to condense
back into the kettle. A broken or improperly working fan or flue causes the
same effect as a covered homebrew kettle.
There’s another compound called Dimethyl Sulfoxide (DMSO) that is
created when DMS is oxidized usually in the kettle. DMSO is not as volatile as
DMS and is not heat sensitive, therefore, it would remain dissolved in the wort
even after boiling. DMSO is then reduced into DMS in the fermenter by yeast during
fermentation. There have been instances where this can kick-started during
dry-hoping, so watch the oxygen exposure.
Since top-fermenting (ale) yeast usually produce a vigorous
fermentation, the production of Carbon Dioxide (Co2) literally scrub away some
of the DMS compounds out of the fermenter via the blow-off valve or airlock. On
the other hand, bottom-fermenting (lager) yeast work much slower. More of the
DMS created from DMSO during fermentation can remain in the beer because the
Co2 production is not as energetic. This is yet another reason why pale lagers
tend to have elevated levels of DMS compared to other styles.
The use of six row barley also tends to increase the production of DMS
as well as some bacterial infections if sanitation becomes an issue. The
addition of adjuncts such as flaked maize or corn sugar may enhance or confuse
the perception of DMS in a finished beer. So that’s something else to keep in
mind.
Support local homebrew shops:
743 Baker Street, Suite D, Costa Mesa
1045 N Armando, Suite E, Anaheim
1211 N Las Brisas St., Anaheim
28142 Camino Capistrano #107, Laguna Niguel
5692 Buckingham Drive Huntington Beach
Cheers and happy homebrewing!
-Gilbert “Charlie” Perez, Advanced Cicerone®