Identifying off-flavours in beer: Dimethyl sulfide (DMS)

This article is the second instalment of a mini-series on the most important off-flavours and compounds that a homebrewer should know. Last month we talked about Diacetyl. This month, we turn our gaze to DMS.

DMS

Short for dimethyl sulfide, DMS is most commonly known for tasting and smelling like creamed corn. In large quantities, though, and if not mitigated properly, it can be perceived as cooked cabbage, canned vegetables, or even oysters or farts. That’s because (you guessed it!) it is a sulphur compound.

Chances are you have experienced DMS, whether you knew it or not. That’s because it is a fairly common and sometimes even desired flavour in almost all pale lagers, Pilsners, and cream ales. BJCP even states it is perfectly acceptable in low quantities in some of these beers.

Dimethyl sulfide occurs naturally in the germination process of barley and other grains, being found in its highest quantities in Pilsner malt, six-row malt, and (surprise!) adjuncts like flaked corn. You have probably now clued into why the before-mentioned styles allow an acceptable level of DMS—European lagers use Pilsner malt, North American lagers historically used six-row and flaked corn.

While DMS is more prevalent in Pilsner and six-row, it still shows up in Pale Ale malt, two-row, and other base malts, so you need to still keep an eye on your brewing habits. DMS might be acceptable in pale lagers but it has no place in pale ales, ambers, or anything dark, caramelly or hop forward.

While you can’t always eliminate DMS 100%, there are a number of things you need to do to mitigate its presence and ensure it doesn’t overwhelm your brew with its danker essence. Some pro tips to keep in mind are:

  • If using Pilsner or six-row malt, extend your boil time to 90 minutes instead of the standard 60. Don’t forget to calculate for the extra water evaporation loss or you will get a slightly higher starting gravity than you will have calculated for.
  • Make sure you have a vigorous, open boil. The steam coming off will carry away the sulphur compounds. Using a lid or cover creates a situation for condensation and DMS to drip right back into your wort. Keep your lid away from your brew during all stages of the boil, including your rest and cool down.
  • Over-sparging can leach out more of the sulfur compounds in your grain, so if doing an all-grain brew, make sure you don’t use more sparge water than what you calculated for.
  • Crash your wort down to your yeast-pitching temperature as soon as you are finished with your boil and/or hop stand. DMS develops best in warm, non-boiling temperatures, and leaving your wort to drop its temperature for too long will allow the compounds to develop in excess.
  • If you are concerned you can’t mitigate the development of DMS using the recommendations above, you can always decrease the amount of Pilsner malts in your recipe and replace it with some two-row.

As with all your brews, keep your tasting notes, brew logs and fermentation logs all together, and refer back to them to see any patterns or insights. Happy brewing!

David Boggs has been homebrewing for over 10 years and currently works as a professional brewer in Edmonton. He holds a certificate in Applied Craft Brewing and is a Recognized BJCP Judge. He is a fan of Belgian ales and anything barrel-aged.

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