Jen Blair tilted her body slightly toward the sample cup of beer, sniffed, and felt a sensory association dislodge itself from her memory.
Perm solution.
Blair, a Master Cicerone and master BJCP judge, is accustomed to using a wide vocabulary for aromas and flavors while judging beer competitions. But even she has to admit that perm solution—like the kind you’d smell in a hair salon—was a new one to her.
The other judges at the table—all men who had, perhaps, not subjected their hair to curl-producing perm chemicals any time recently—were slightly puzzled by Blair’s descriptor. They all described an off-aroma wafting from the beer, but they were struggling to pinpoint it. Later, Blair spent some time researching which chemicals, exactly, were in those hair solutions. It turns out that her sensory association had a scientific underpinning: The odor-active chemicals in perms are sulfurous.
“Now I know, when my brain is telling me ‘perm solution,’ I’m probably smelling some kind of sulfur compound,” Blair says.
It’s not surprising that Blair had such an immediate reaction to the beer’s aroma. Sulfur compounds are aromatic red flags. There are good reasons why humans have evolved to detect some of them at parts-per-trillion concentrations. Certain sulfurous compounds denote rotting food, sewage, skunk spray, and other highly undesirable things. While there are pleasant sources of sulfur, too—such as alliums and strawberries—human brains seem to prefer to err on the side of caution when encountering this general aromatic family.
As Randy Mosher writes it in his new book Your Tasting Brain, sulfur is “sometimes horrid, often polarizing.” He cites the example of sulfur-rich truffles to encapsulate “this conflict between the profane and the transcendent.”
Another example of that push-pull? Hop-forward lagers.
While lager fermentation character is often portrayed as neutral, that’s not always the case. Some lager yeast strains—in combination with malt, hops, and water—produce sulfur compounds that can include sulfur dioxide, hydrogen sulfide, and mercaptans. Sulfur dioxide (SO2) is the most pleasant of these, responsible for that struck-match quality that many consider to be characteristic of certain hop-forward European lager styles. (SO2 is also one of the primary products of a volcanic eruption, an example of the association between sulfur—called brimstone in the ancient world—and the menacing underworld.)
When fermentation-derived sulfur, meanwhile, combines with the sulfurous components present in hops, the effects can compound. And if a brewer wants to enhance the perception of bitterness and dryness by using higher-sulfate water, well… add another layer to the sulfur stack.
That tees up yet another brewing balancing act. Humans are deftly attuned to aromatic sulfur compounds, and we often find them highly off-putting. Yet, some pleasant elements of beer—fruity thiols or a lager’s hallmark flintiness—are often desirable and add complex layers to the drinking experience.
Walking that tightrope is a tall order and requires precise attention to fermentation, dry-hopping techniques, and recipe formulation. Then there’s the fact that sulfur is highly volatile—arriving in the nose like a wisp of smoke and disappearing just as quickly—and it’s easy to see why the quest for desirable levels of sulfur character can be so tricky… and so beguiling.
Setting the Target
How much sulfur is too much, and how much is just enough? Some of this Goldilocks question comes down to your personal preference as a brewer, and some down to the style of lager you’re brewing.
Alex Tweet, cofounder and brewmaster at Fieldwork in Berkeley, California, says he also takes drinker preferences into account. He acknowledges that some sulfur dioxide is a hallmark of lager fermentation—“a feature, not a bug”—that adds layers of aroma and flavor. But he also knows that some drinkers might find it off-putting, so he generally tries to minimize its presence in Fieldwork’s beers.
“As a brewery, you have to make that decision: Do I want to have this component that might add complexity but also be seen as a negative?” Tweet says. “Sulfur can contribute to the overall complexity of the hop profile, but I think it’s more likely to detract from it. So, in a beer you’re referring to as ‘hoppy lager,’ I would avoid sulfur as much as you can.”
Not all brewers see it the same way. Natalie Baldwin, brewmaster at Wayfinder in Portland, Oregon, distinguishes between hop-derived and fermentation-derived sulfur compounds, and she says both can enhance each other. Some of the lager fermentation character helps to carry the hop aromas, she says, while the hop aroma can help soften the edges of the struck-match quality. She distinguishes between the negative descriptors of hydrogen sulfide (H2S) and the more pleasant notes of hop-derived sulfurs, which can read as cannabis-like dankness.
“It carries this intensity,” she says. “We’ve seen that with different hops like Strata, Comet, and Krush in lagers, or even Nelson [Sauvin]. We’re choosing these intense, diesely hops, and the beer has two different phases of its life: when the hop sulfur is really intense, and then when it mellows. Sometimes I like it when it’s intense, and sometimes I like it when the hop sulfur mellows out, and when just the guts of the hop flavor are there.”
There’s perhaps no more vocal proponent of sulfur dioxide in lager fermentation than Ashleigh Carter, cofounder and head brewer at Bierstadt Lagerhaus in Denver. As a brewer of almost exclusively German-style lager, Carter says those styles of beers just don’t read as deeply authentic to her without a perceptible match-struck component. Also, because sulfates act as a preservative in beer and wine, that aroma signals freshness to her.
“I’m about to head to Munich, and every one of those lagers sometimes has a pretty overwhelming amount of sulfur,” Carter says. “I’ve had some wildly sulfury Augustiner Helles in my life. To me, it’s not going to taste like pale German lager without that flinty sulfur.”
Ultimately, the choice of whether to enhance or downplay sulfur—and to what degree—is the brewer’s own, informed by personal preference, stylistic decision, other elements of the recipe, and drinker preferences. Beginning with a goal for a lager’s sulfur component helps to inform the fermentation process.
Choosing the Right Yeast for the Job
Whatever your desired sulfur threshold, choosing the right yeast and treating it well will get you most of the way there.
For Fieldwork’s Tweet, who wants to minimize sulfur in his hop-forward lagers, that means starting with the low-sulfur Fresh Andechs strain from Berkeley Yeast. “You start with [yeast] that’s not going to create a lot of sulfur and then, if your process supports it, you should end up with a hoppy lager that doesn’t have much sulfur at all,” he says.
Brewers curious about how yeast selection and management affect sulfur levels might take a page from Whitney Burnside’s book.
The cofounder and brewmaster at Grand Fir in Portland, Oregon, uses the Andechs strain to ferment her West Coast pilsner, Cold Cutz, which recently won silver at the World Beer Cup. However, a spring collaboration with pFriem of Hood River, Oregon, offered the chance to ferment a West Coast pilsner with the popular 34/70 strain.
Tasting them side by side crystallized Burnside’s hunch that the two strains lent themselves to different hops, based in part on the beers’ sulfur expression: The clean, distinct sulfur dioxide she perceives from 34/70 plays especially well with Simcoe and Mosaic, while she feels the Andechs is a bit softer and invites candied lemon and peach notes.
The 34/70 strain, “with more of that sulfur dioxide, can help when you’re using varieties like Mosaic,” Burnside says. “It’s going to just meld better with that profile. But with Andechs, I’m getting this really fun tropical vibe, so I’m using like a pinch of Centennial Cryo at cool-pool along with some Citra and a little pinch of Krush.”
Before she came to Wayfinder, Baldwin brewed at Portland’s Breakside, where she typically fermented lagers with the Augustiner yeast strain. For the past three years or so at Wayfinder, however, she’s used 34/70, and returning to the Augustiner strain highlights the contrast in their sulfur production.
“Now when I go back, the sulfur on Augustiner smells so much different because I’m so familiar with 34/70,” she says.
She cautions fellow brewers not to judge a yeast strain by its first pitch, noting that they often need a few brews to start settling into their best performance. She says she finds that even a healthy lab pitch will sometimes not finish dry enough, or it might throw a bit more sulfur before subsequent generations “get their feet under them.”
No matter the strain, it almost goes without saying that a healthy pitch and proper fermentation management are critical to inhibiting undesirable sulfuric compounds.
Tweet says he suspects that under-pitching is responsible for a good amount of overly sulfuric beers. He also praises Fieldwork’s Aber Perfect Pitch—a portable yeast-management skid that can count live cells—as “the best investment we ever made.”
Turning Up the Dial
As with seemingly any aspect of lager fermentation, brewers can manage sulfur expression through temperature adjustments.
It may run counter to conventional wisdom, but fermenting lagers slightly warmer can aid in sulfur reduction, as well as clean up diacetyl and other undesirable aromas.
“I have a firm belief that getting just a little earlier on that diacetyl rest while it’s still slightly exothermic is going to aid a lot in cleaning up some of those compounds produced during fermentation that you don’t want in the finished beer,” Tweet says. He adds that strains such as 34/70 and Fresh Andechs perform just fine for him at slightly warmer temperatures.
At Transmission Brewing in Ventura, California, owner and head brewer Carey Jonker treats his West Coast pilsner differently than any other beer: It’s the only one that receives a diacetyl rest, with temperatures creeping into the upper 50s °F (14–15°C). That’s mostly to increase hop extraction, but then it becomes important to get the beer off the yeast as soon as possible to reduce mercaptan, which can produce a garbage-like taint.
“Because coming up in temperature and then down again can kind of beat up yeast, if it stays in the tank and you can’t get it all out, you end up with some of that mercaptany character,” Jonker says. “With the lagers that we dry hop before crashing, we shorten the lager time, so we’ll go three weeks instead of four to six. Where we have had that temperature increase … we want to get it off of there faster.”
Moving Beyond Qualitative Evaluation
Most brewers are evaluating their sulfite levels based on sensory analysis, but they can be quantified. The nose may know, but a spectrometer measures.
Joe Shubert, quality and innovation manager at pFriem, uses the brewery’s UV-Vis spectrometer to measure sulfites, the vast majority of which are SO2. The desired levels depend on the style of beer.
For West Coast pilsners and IPAs fermented with lager yeast, the brewery targets the lower end of sulfite content—about 3 to 3.5 parts per million. Adjunct lagers, such as those with corn or rice, are designed to fall within the 4.5 ppm range. German pilsner might push the needle to 6 or 6.5 ppm. Shubert says that for breweries that have spectrometers, adding sulfites as an assay is relatively simple and goes a long way toward creating consistency for drinkers.
“It’s pretty hard to be a doctor to something that you can’t really see or talk to,” Shubert says. “So having all these different analytes—such as sulfur-dioxide production—is just another tool in the tool belt to understand yeast performance.”
When pFriem’s brewers spot a sulfite spike, it’s time to troubleshoot. That might involve starting a new propagation, adding lipid nutrient, or going back to the drawing board on the recipe itself.
“Whether you’re brewing a German pils or a hoppy lager, having a consistent value within SO2 production ensures you’re having consistent fermentations,” he says. “That would be the largest indicator to consumers that you’re getting a consistent product time and time again.”
Addendum: Is Copper King?
It’s well established that copper ions convert H2S into copper sulfide, eliminating its rotten-egg smell. Some brewers swear by introducing a small copper pipe or plate to hot wort to eliminate sulfur compounds.
Bierstadt’s Ashleigh Carter says she can’t speak to whether that small amount of copper will do the trick—but she knows her copper tanks sure do.
“Because beer does actually scrape the bottom of it, and it’s part of the yeast nutrient, I do think it helps avoid too much of the wrong kind of sulfur.”
