Category Archives: Brewing

DMS and Boil Time

After writing about the sources of DMS in beer a few days ago, I stumbled upon another quite interesting paper from 1978 that discusses the influence of boil time on the amount of DMS in beer, titled “Control of the Dimethylsulphide Content of Beer by Regulation of the Copper Boil”.

In this paper, the authors put together two different lager malt blends. LMB 1 was designed in such a way that it was kilned at 65 °C, so that it would only contain inactive DMS precursor (see the previous article about active and inactive DMS precursors). LMB 2 on the other hand for kilned at 70 °C and later at 90 °C, so that it would contain substantional amounts of active DMS precursor. With both malt blends, worts of OG 1.037 (9.25 °P) were produced using a single-step infusion mash at 65 °C. The worts were boiled for different times (from 15 minutes up to 2 hours). Each of the worts were split, and fermented with different yeast strains, NCYC 240 and NCYC 1324. The two different yeast strains differ in the amount of DMS they produce: NCYC 240 produces a high amount, while NCYC 1324 produces a low amount.

What was noticeable in the results from the different boil times alone is that there a strong correlation of boil time with decreased amounts of DMS and DMS precursor in the worts. Consistently, LMB 1 had lower amounts of DMS and DMS precursor compared to LMB 2.

When the authors looked at DMS levels after fermentation, the results were quite clear, as well: a longer boil not only brings down the amount of DMS and DMS precursor in the wort, it also consistently reduces the amount of DMS in the resulting beer.

Influence of Boil Time on DMS Levels in Wort and Beer

The paper concludes that the DMS content in beer can be controlled almost impossible from other influencing factors through the right boil length and temperature. There is one exception though: if the DMS comes from another source than DMS precursor, a longer boil doesn’t reduce besides the normal evaporation.

Just like I hypothesized in my previous article, I will mention this again: I think that the literature is quite clear in that the wort boil has a large influence on DMS levels in beer, just like the specific metabolism of the yeast strain has a large influence, and that in the Brülosophy exbeeriment, the experimenters were just “lucky” in getting the right malt with only low levels of DMS and active DMS precursors, and a yeast strain with only low DMS production.

Sources of DMS in Beer

Quite often, when I run into an issue or a question related to homebrewing that is not answered in the usual homebrewing literature or forums, I turn towards scientific literature. One great example is the Journal of the Institute of Brewing, which makes its issues freely available, with literally more than a hundred years of back issues available.

When earlier today, Brülosophy posted lab results about their DMS exbeeriment, their closing statement irritated me a bit:

But, it’s just as possible our understanding of the relationship between DMS and boil length is simply lacking, that our access to modern technology, higher quality ingredients, and better knowledge about brewing processes has reduced the likelihood of problems brewers of yore had to worry about.

That sentence really made it sound like brewing science is only in its infancy. But that’s definitely not the case. Modern brewing science is lots and lots of organic chemistry, microbiology, and even genetics nowadays, so it would be hardly believable that we knew very little about DMS. I vaguely remember seeing an article about DMS on the mentioned journal, so I dug it up, and first posted a link to it in the comment section of that Brülosophy article. But then I thought, why not write about it? Because the paper itself is great.

So, the interesting that I took out of that article is that there are actually two types of DMS precursor. The paper distinguishes them as “active” and “inactive”. Both have different properties, and come from different sources.

“Inactive” DMS precursor is coming directly from the green malt. If you were to product wort from green malt, the precursor would be decomposed, and the wort would end up with large amounts of DMS, and still a certain amount of DMS precursor. During fermentation, parts of the DMS would dissipate through the gases being given off, while the DMS precursor would be metabolized by the yeast. The yeast wouldn’t make DMS out of it, though, hence why that precursor is called “inactive”.

“Active” DMS precursor is the type of precursor that is created out the inactive precursor during the kilning process. After wort production, there would only be a small amount of DMS in the wort, but still a relevant amount of “active” DMS precursor. During fermentation, that DMS precursor is metabolized by the yeast, which makes DMS out of it. Hence the “active”.

This has some interesting consequences. If the kilning can be done in such a way that no “active” precursor is found in the wort, the yeast will not produce any more DMS during fermentation, and the total amount of DMS in the beer is limited by the amount of DMS in the wort right before pitching. It can even be assumed that some of that DMS will be lost during fermentation. The authors suggest that the amounts of DMS formation during wort production need to be controlled, though. In their experience, it is easier to control DMS levels in beer if it’s derived from DMS precursor in the wort, as the final DMS level can be controlled by using a suitable yeast that keeps DMS production low.

And I think the last bit is the crucial point in the Brülosophy exbeeriment: it’s not that a 30 minute boil vs a 60 minute boil doesn’t have any impact for DMS levels, it’s just that both the specific qualities of the malt and the specific metabolism of the employed yeast do matter, and can have a large impact. My guess is: in the exbeeriment, exactly the “right” malt was used (Bestmalz Pilsner malt, apparently), combined with a yeast strain that only produces low levels of DMS (WLP029, a Kölsch yeast strain). And that perfect combination gave a result that made a 30 minute boil indistinguishable from a 60 minute boil in terms of DMS levels. That said, I would really like to see the same experiment done with a different malt (maybe a less modified floor-malted Bohemian Pilsner malt?) and a yeast strain known for greater DMS level, like a lager yeast. W34/70 comes to mind, for example.

Vienna Lager: the Aftermath

The result.
The result.

As blogged previously, I had looked a bit into the historic roots of Vienna lager, a beer style that was quite successful in the 19th century in Europe, but has since then been forgotten in its country of origin, and had only been revived through the US craft beer movement.

In April, I finally managed to brew the beer, and it fermented and matured in the weeks afterwards. It’s been lagering for a while, but a few weeks ago, it was finally ready and also finished carbonating (I had kegged the beer and force-carbonated it). The end result is a good, quaffable lager at 5% ABV, though a bit rough around the edges.

What I do like about the beer is that it just puts the intense maltiness of Vienna malt in the foreground, accentuated by a bit of residual sweetness due to a very poorly attenuating yeast. What I don’t like so much about it is how the hops play together with this residual sweetness: even though I only used Saaz hops as the sole hop addition for bittering, the beer got a very spicy hop flavour. That would be great in a dryer beer, but with 4°P final gravity, it’s just a tad too sweet, and that just clashes a bit. Don’t get me wrong, it’s still a good beer, and I’ll happily drink it, but the next one I’d do differently. Definitely a better attenuating lager yeast, and maybe a different hop variety. I think I really need to research Austrian 19th century hops wrt. to what Anton Dreher used in his beers. As mentioned in one of my previous articles, it’s very unfortunate that Austrian hop land races were (presumably) lost either due to illnesses (which ultimately brought us Styrian Goldings) or a forced stop of any hop-growing activities by the Nazis (as it happened in Mühlviertel, Upper Austria).

Another lesson that I learned was that the WLP820 yeast strain, at least in its first fermentation, is extremely slow. I even employed a quick lagering schedule with which I had had success in previous beers, but it still took 3 weeks until fermentation completely stopped. At least it behaved pretty much as expected, and was only a tiny bit more attenuative than its historic predecessor. Starting at 13°P original gravity, it fermented down to 4°P, while brewing records show something closer to 4.5°P to have been the beer’s final gravity. That’s fine with me, really.

All in all, it was definitely an interesting exercise, with a tasty outcome, and I really learned what works and (more importantly!) what doesn’t with Vienna lagers.

Brewing a Vienna Lager

About a month ago, I posted about some things I found out about Vienna lagers, and how the historic original probably was like compared to modern versions of that style.

So yesterday, we finally got around to brewing it on my own. I compromised a bit in the whole process, though, just to make a few things a bit easier for me. In particular, I decided not to do a decoction mash.

I use a Weck preserving cooker as a mash tun, as it can contain plenty of liquid for the mash, and it’s electrically heatable, allowing to go through specific rest temperatures without having to resort to having to add hot water later. Just don’t trust the internal thermostat, and use a proper food thermometer instead.

I used 20 liters of water at 66 °C, and mashed in 5.3 kg of Vienna malt. The resulting mash was at 62 °C, and from there on I did a simple Hochkurz infusion mash:

  • 30 minutes at 62 °C
  • 20 minutes at 72 °C
  • 10 minutes at 78 °C

For modern malts and a high degree of diastatic base malts (like 100% in this case), that’s good enough to fully convert all starches.

After an iodine test showed that all starches were indeed converted, we continued with lautering. For that, we use a simple bucket from my preferred homebrewing online store, with a Mattmill false bottom.

For sparging, we always employ a colander with a food container lid set in the middle, to sprinkle hot water on the mash. BTW, my hot water is… my boiler. My flat contains a large boiler that actually delivers 80 °C hot water. Perfect for sparging.


The collected wort showed a pre-boil gravity of about 12 Brix, which later turned out to be probably not quite exact. I think I need to recalibrate it with distilled water. *sigh*

Anyway, we boiled it for 90 minutes, with 60 grams of Saaz hops for bittering, and no other hop addition.

After a whirlpool, I moved the wort to a fermentation bucket, and cooled it down to 20 °C with an immersion chiller, then moved it to my keezer to further cool it to 11 °C.

The hydrometer showed a bit more than 13 °P as original gravity, while the refractometer showed 14 Brix. A recalibration really seems necessary.

Finally, in the evening, I pitched a starter of WLP820 yeast. That should give a low attenuation comparable to the lager yeast that was used in the 19th century in Anton Dreher’s brewery. The beer is going to ferment in the next two weeks or so. I’ll use Brülosopher’s quick lagering method, as I’ve had some good experience with it in previous batches of lager brewing.

As soon as the beer is finished lagering and carbonating, I’ll post a report about the final result.