We’re going to answer the question “why do I have Dimethyl Sulfide (DMS) in my beer?”, today. My recent off-flavors in beer content, has been well received
So, I decided to a deep dive into all common off-flavors. This is the second article in the series with Acetaldehyde being the first one.
Dimethyl Sulfide is often found beer, as it’s easily picked up, if a brewery’s processes aren’t quite right. In some beers like German lagers, at lower-levels it can actually be appropriate to style
The logically first place to start is with, what does this off-flavor smell/taste like…
Why Do I Have Dimethyl Sulfide (DMS) in My Beer? Description
Dimethyl sulfide which brewer refer to “DMS”, for ease of use, is perceived and described with following characteristics
- Sweetcorn
- Tomato juice/sauce
- Cooked broccoli
- Cabbage
- Creamed corn
- Parsnips
- Seaweed/Sea vegetables
- Plus having an “oily/creamy” mouthfeel
The main descriptor and the one most people associate with DMS, is sweetcorn in aroma and to a lesser degree in the taste of the beer for lighter beers.
The approximate flavor threshold of DMS is 0.025mg/l (milligrams per liter). As noted earlier in some beers such as German lagers, at low-levels its appropriate to style.
Generally British ales have the lowest Dimethyl Sulfide levels at 0.01 to 0.02 mg/l. While German lagers and all malt beers are highest, at 0.05 to 0.175 mg/l DMS levels.
For further reference, a typical US lager contains 0.04 to 0.1 milligrams per liter, levels of Dimethyl Sulfide.
In darker or flavorful all malt beers, the DMS is often hidden, but will likely present as tomato-like or vegetal, if noticeable.
In lighter, “more naked” beers, DMS is more easily picked up by the drinker. Presenting as more “corn-like”.
How To Understand This Off-Flavor?
I guess one of the easiest ways to cook up some canned corn. Strain the liquid from the corn, and maybe used the corn for your lunch/dinner.
Take the strained liquid and add some to a neutral lager. Have the control base liquid, the lager without the “corn juice” and compare the sensory to the beer where you’ve added the liquid.
There are beer off-flavor kits, however they can be expensive. This is a quick, cheap way to give you a sense off how this off-flavor present in pale lagers.
In a commercial beer Rolling Rock is well known to have high levels of DMS in it. Please note, this is referring to other sources online, it’s been a long time since I’ve had a Rolling Rock so, not sure if this still holds true.
What Causes DMS?
Barley does contain DMS, but in very small amounts. However, barley does contain the precursors to Dimethyl Sulfide, S-methyl methionine (SMM) and dimethyl sulphoxide (DMSO).
On a modern malt analysis sheet; the values of these precursors often aren’t listed. If they are, it would be as a combined value of “DMS-P” or “DMSP” with a rate of 5 to 15ppm for pilsner malt, and less for fully modified malt.
Why Do I Have Dimethyl Sulfide (DMS) in My Beer? SMM Precursor
So, the primary source of DMS in beer is caused by the decomposition of S-methyl methionine (SMM) into DMS.
This decomposition happens by heating above ~80°C. In raw barley SMM levels are initially low, but as the barley is malted the SMM precursor is formed in the malt.
In malted barley, SMM amounts are correlated with nitrogen amount. With the longer the barley being stored before malting, increasing the SMM levels.
During kilning where temperatures are above 70°C the SMM is partially broken down into DMS and homoserine (isothreonine).
If the kilning temps are higher then DMS can be driven off, as its quite volatile (as we will see later). However, with lower kilning temperatures, such as with pilsner malts, more of the SMM precursor is retained in the malted barley.
Please also note: Adjunct grains such as corn, contain high levels of SMM
Why Do I Have Dimethyl Sulfide (DMS) in My Beer?
During mashing-in, the SMM precursor in the malt is liberated into the solution. As it’s easily dissolved into the wort during the mashing process.
Dimethyl sulfide is the created with the breakdown of SMM, when the wort is heated (above 60° C or 140° F). DMS is continuously created in wort while it’s hot. The process looks like this:
SMM > Dimethyl Sulfoxide DMSO > DMS
However, it’ll be driven off with a vigorous boil, as DMS is a volatile compound. Furthermore, some of the remaining DMS will be removed during a vigorous fermentation.
Which explains why ales fermented warmer have lower concentrations of this off-flavor than lagers. Plus, as we said earlier, pilsner malt contains higher levels of DMS precursors too.
This why in the past, pilsner brews, were boiled in the brew kettle for longer (90-minutes+) than ales (60-minutes).
With today’s modern modified malts, some brewers no-longer boil pale lagers for longer. As they don’t deem it necessary.
Other brewers still do 90-minute boils for lagers, it’s very much personal preference.
Side note
If brewing raw ales, try to keep wort temperatures below 80°C (176°F). Going above this threshold, will see DMS forming at a much quicker pace.
Cooling Wort – Why Do I Have Dimethyl Sulfide (DMS) in My Beer?
After a vigorous boil in the brew kettle, which has allowed the brewer to drive off a lot of this volatile compound. The next step in the process, is to cool the wort down to fermentation temperatures.
It’s important to cool the wort down as quickly as possible. If not, these compounds will not be removed from the wort, and actually dissolve back in.
- Likewise, keep an eye on your whirlpool times and temps. Reducing the times where wort sits above 80° C will help reduce the amount of DMS in finished beer.
- Higher moisture content in malt will increase SMM levels. Therefore, ensure your malt is stored in a dry, cool place.
- Over-sparging during wort collection to the kettle can lead to increased DMS. Keep an eye on the final running’s gravity and pH.
- Furthermore, sparging at temperatures below 71°C (160°F) aren’t recommended. Ideally, you’ll keep spare temperatures near 168°F (75.5 °C).Â
Ensure a Vigorous Boil in the Brew Kettle
To reiterate the point, you want to have a vigorous boil in the brew kettle. Many brewers like to have at least 8% evaporation rate, when using pale lager malts for example.
Make sure you’ve enough room in the kettle for a vigorous boil (or use antifoam if needed).
Furthermore, Ensure the steam can be vented out. If you don’t have a flue/stack to the outside or a condensation stack, keep the lid to the kettle open.
Furthermore, keep an eye out for boil-overs. You don’t want the condensate falling back in the boil.
Less important with modern modified malts, however in the past brewers used to boil lagers brews for longer (90-minutes) than ales brews (60-minutes).
As pilsner malt contains a lot more of the DMS precursor SMM. It’s worth noting; if using a percentage of adjuncts like corn in your mash, be aware they contain more of the precursor SMM as well.
Sanitation and Cleanliness – Why Do I Have Dimethyl Sulfide (DMS) in My Beer?
It also goes without saying, always carry out proper sanitation when working in a brewery too. Make sure you have solid CIP (clean in place) procedures, especially on the cold side.
- Avoid equipment which can’t be properly sanitized like wood and soft plastic items. Bacterial or wild yeast infection, usually Obesumbacteria Proteus. Please, also see Zymomonas, another beer spoilage bacterium
Obesumbacteria Proteus is a bacteria which only grows during the lag phase of fermentation, when wort pH is 4.4 or higher. It can be a problem, if fermentation is sluggish or the lag phase is longer than 24-hours.
Yeast Management
Ensure you pitch enough yeast to minimize lag phase. The general rule of thumb is, one-million cells per milliliter of worth per degree Plato.
This chart was taken from Wye Labs Website Here. Click the Link For Expanded View.
However, a study by George Fix concluded 0.75 million cells/milliliter of wort/degree Plato was a suitable pitching rate for (most ales).
Furthermore, 1.5-million cells/milliliter of wort/degree Plato was a better pitching rate for lagers. This is a good starting point and was based on commercial re-pitching.
However, if using fresh yeast for your brews, then these figures could possibly be halved, and still result in a successful fermentation.
Why Do I Have Dimethyl Sulfide (DMS) in My Beer? Conclusions
DMS is an off-flavor which you don’t want in your beer. There will be some, but you’ll want it to be below the flavor threshold.
The main way to guard against DMS in a brew, is ensuring a vigorous boil, is carried out. Where the steam can leave the kettle via a stack or through the open kettle.
For pale lagers, an evaporation rate of 8% is a good marker, to guard against DMS.
When the boil is done, the quicker the wort is cooled and sent to the fermentation tank the better. As extended times above ~80°C, will allows DMS dissolve back into the wort.
If you’d like to learn more about other common off-flavors in beer, then please feel free to download our guide.
Need Some Advice on Beer Processing or Brewery Project?
Need some advice on beer processing? As your having issues. For example, I was recently contacted by a brewery having issues with acetaldehyde in his beer.
Then feel free to get in contact. I’ve been brewing for 25-years around the world from small brewpubs to production craft breweries. I’ve also overseen several brewery installations too.
I’m currently assisting on projects in Sweden, Australia, Africa and the UK. Helping put equipment lists together, and sourcing brewing equipment within the budgets given.
I would love to hear about your project or happy to have a chat about any beer processing issues you may have. Please email me at:
neil@asianbeernetwork.com
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For now, thanks for reading, happy brewing and have a great day.
