Stay at Home(Brew) Off-flavor: DMS

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:

Windsor Homebrew Supply Co.

743 Baker Street, Suite D, Costa Mesa

1045 N Armando, Suite E, Anaheim

Phantom Ales Pub & Home Brew Shop

1211 N Las Brisas St., Anaheim

O'Shea Brewing Co.

28142 Camino Capistrano #107, Laguna Niguel

Brewers Hardware (for large production)

5692 Buckingham Drive Huntington Beach

Cheers and happy homebrewing!

-Gilbert “Charlie” Perez, Advanced Cicerone®

Vocabulary Lesson – Dimethyl Sulfide (DMS)

Dimethyl Sulfide, more well-known by its initials (DMS), is a compound causing flavors and aromas considered an unacceptable in most beer style. DMS causes a creamed corn or cooked vegetables flavor and aroma when found in beer at detectable levels. When present at high concentrations, DMS can cause more of a rotten vegetable aroma and taste. Although it is considered an off-flavor in most styles, DMS is actually a desirable trait and/or acceptable in small quantities (complementary and adding to complexity) in most pale lagers, such as a German Pils and Munich Helles, and some light-colored ales, like Cream Ale.

The most common way to form DMS is in the brew kettle. The precursor of DMS is the compound S-Methyl-Methionine (SMM), an amino acid formed in barley during the germination stage of malting. Once the germination (tricking barley into sprouting) is complete, the malt is then kilned (heated) to remove moisture then kilned even further depending on the type of malt that is being created. SMM is a thermally liable compound, which means that it reacts at a certain temperature and creates something else. Lightly kilned malts, such as Pilsner Malt, are not subjected to excessive heat for large periods of time and retain much of the SMM found within. Mashing (steeping malt in hot water) is usually done at a temperature that does not create DMS. However, it will release SMM into the wort (sweet liquid created in the mash) and is carried over into the kettle. When SMM is in the kettle and the wort is boiling, it create DMS.

Along with SMM, there is another compound is responsible for DMS. Dimethyl Sulfoxide (DMSO) is created when DMS gets oxidized and this can happen either in the kettle or already be present in the malt. 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. Since top-fermenting (ale) yeast tends preform more vigorous fermentations, the production of Carbon Dioxide (Co2) can literally scrubs away some of the DMS compounds out of the fermenter via the blow-off valve. Conversely, bottom-fermenting (lager) yeasts preform much slower so 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 higher levels of DMS compared to other styles.

DMS is quite volatile and generally escapes the brew kettle as steam with no issue. Homebrewers will encounter this as a problem if they cover the pot of boiling wort or before it has cooled down. The condensation collected on the cover is full of DMS and simply falls back into the wort. Other major contributors are a the use of high-protein malt such as those made from 6-row barley, lack of a vigorous boil, not cooling down the wort quickly enough, or bacterial infections from bacteria such as Enterobacter.

Thanks for reading. I hope you enjoyed it and learned a thing or two. Class dismissed!

Cheers,

Gilbert “Charlie” Perez, Certified Cicerone®


References:

https://beersensoryscience.wordpress.com/tag/dms/
"Beer: Quality, Safety and Nutritional Aspects" by by Paul S Hughes (Author), E Denise Baxter
"Malts and Malting" by D.E. Briggs