Apparently DMS is Still a Thing

DMS-Rich Vienna. Don't let
its yummy appearance
foold you!

I've been brewing since the bad ol' days of the mid-1990s. Back then malt quality is not what it is today, so we had to use a lot of tricks to get good beer. One of these was the 90 minute boil, a necessity when using Pilsner malt (and other minimally-modified malts), to drive off DMS. DMS, for those who do not know, is a sulphur-based compound present in malts which in high enough concentrations gives your beer a cooked-corn aroma and a green-vegetable-like flavour.

Obviously, something you don't want in your beer. But, luckily for us, boiling drives it off...hence the old method of boiling lagers (and other Pilsner-malt rich beers) for 90 minutes.

The good news is that malt quality has dramatically improved over the past 20 years, and the levels of DMS precursors in malt are pretty low compared to historical norms - so low that experiments by Brulosophy found it hard to detect, even after short boils. This improvement in malt quality has led homebrewers (including myself) to do things previously unthinkable - no-boil, 100% pilsner malt sours, 60 minute boils for most lagers, etc. Some of the best lagers I've brewed, like the Vienna & Pilsner I brewed last year, used 60 minute boils with great success.

So imagine my disappointment when I brewed a Vienna this year, using all the same methods and near-identical recipe to last years brew, only to find that the resulting beer had an intense DMS aroma and flavour - probably the worst DMS off-flavour I've had in a beer since the late 1990's. The beer is not undrinkable - in fact, I served it at a recent party and received good feedback - but it is flawed and not up to my normal standards. So what went wrong?

Vienna is prepared in a similar manner to Pilsner malt, meaning it has a similar risk of DMS precursors - but should also be subject to the malting improvements over the past two decades. I've brewed beers previously made of 100% Vienna, with 60 minute boils, without issue. But there is one difference - this was my first time using Weyermann Vienna; all previous batches used Vienna malt from Breiss. Although the character of the malt from each manufacturer is very similar, slight differences in their malting process may have led to different levels of DMS precursors in one malt versus the other - this conceivably could occur even on a batch-by-batch basis within the same manufacturer. That said, a google search failed to find any suggestion that Weyermann had higher levels of DMS in their Vienna than Breiss; although I did find a few reports of DMS in Vienna-heavy beers.

A second issue may have been batch size - I did a 40L batch this year, in place of a 20L batch last year. Because I use the same pot for both sizes of brews, the recent batch had half the surface area:volume ratio, which would slow the volatilization of DMS.

A third issue may have been boil vigour; while I have an over-powered burner on my brewing rig, the larger boil volume, brewing of the beer on a cold day, plus a lot of wind on this years brew day, meant that the boil vigour and rate of boil-off were not as good on the more recent batch.

At the end of the day, I think there are a few things to be learned from this batch. The first is that I probably should return to 90 minute boils for beers brewed using malts with high potential for DMS; especially if brewing larger volumes or on a day where boil vigour may be an issue. The second issue is that I should brew mission-critical beers - e.g. those intended for parties - with a bit more lead time, to allow for additional ageing (or a brewing of an alternative beer) should issues like this arise. And lastly, this beer allowed me to relive my youth, through recreation of flavours that were common in the early years of my brewing "career".