Balanced Aroma: Adjusting the Thiol Dial

Modified yeast strains and products such as Phantasm have unlocked the massive aromatic and flavor potential of thiols. Now, brewers are learning how best to tame that power in service of balance and nuance.

Kate Bernot Aug 14, 2023 - 18 min read

Balanced Aroma: Adjusting the Thiol Dial Primary Image

Photo: Matt Graves/

A few years ago, NoDa Brewing co-owner and head brewer Chad Henderson was happy to sit by and watch as the thiol hype train barreled past him. Sure, he knew these compounds—often smelling of ripe tropical fruit—were part of the matrix of contributors to hop expression. Yet when he smelled them in isolation, he thought they were overly sulfuric and off-putting. And, when he tasted other brewers’ initial experiments with thiol-boosting Phantasm powder, he found them to be a bit too one-note.

So, it took some new perspective via thiol-optimizing yeasts to turn him from skeptic to true believer almost two years ago—and help him design two of the North Carolina brewery’s most celebrated new beers in the process.

The Synchronicity of SLURP

Thiols, Henderson came to realize, could be the harmonizing vocals in an IPA, not its screaming lead singer. A growing understanding of just how powerful compounds such as 3MH, 4MMP, and 3S4MP are—they’re perceptible at parts per trillion—is encouraging brewers to make sure thiols are well supported by beer’s other ingredients. Rather than leaning into everything from thiol-promoting yeasts, thiol precursor–rich hops, and products such as Phantasm to provide the totality of a beer’s flavor, Henderson approached the yeast as the starting point around which he could build his hazy IPAs.

He says the lightbulb moment came when he began pairing strains including Omega Yeast’s Lunar Crush, Helio Gazer, and Star Party with hop products such as Salvo, Incognito, Lupomax, and Cryo Hops in the whirlpool, then dry hopping at relatively lower levels. By reducing the amount of physical hop matter added to the beer, Henderson says he’s been able to reduce losses in IPAs to near-lager levels while still blanketing them with layers of hop-, thiol-, yeast- and sometimes fruit purée–derived flavors that become greater than the sum of their parts.


“If I can get a batch of IPA to express thiol as a baseline and make that guide the approach to how we design the beer, I can make a much higher-efficiency beer that’s still really fruity and flavorful,” Henderson says. “This whole concept of trying to isolate the thiols ... indirectly addressed almost every part of why IPAs are so costly and poorly efficient.”

The tangible results of his change in thinking were two IPAs referred to as the SLURP family, originally a playful acronym for “Superior Lupulin Utilization Research Project.” The beers’ marketing reflects thiols’ supporting role: Nowhere does the word “thiol” appear on their cans or website landing pages. In less than a year, they’ve become critical and commercial hits. The double IPA Big SLURP took home bronze in the Experimental IPA category at the Great American Beer Festival in 2022—one of the first beers fermented with thiol-boosting yeast to medal in the competition. (Wye Hill’s Luminous Beings was another, winning gold the same year in Juicy/Hazy Pale Ale.) Big SLURP’s spinoff Lil SLURP would be a top-three-selling beer in NoDa’s lineup, Henderson says, if only the brewery could keep it in stock. It also happens to be his favorite beer that he’s ever released, mainly because it delivered on his efficiency objective: From a 60-barrel batch, Lil SLURP loses an average of just 3.25 barrels between whirlpool and brite tank. Put another way, Lil SLURP is losing only about 5 percent of its wort to hop matter.

“I love the taste of it, but I also love the fact that I pulled it off—the fact that it’s this tasty and aromatic and is that much more efficient of a beer,” he says.

Dialing It Back

This appears to be the future of thiols—an instrument to be balanced, integrated, and layered, but not overblown. Much like the IBU wars of two decades ago or the sour-beer acidity bonanza that followed, craft brewers often see how far they can push a flavor before good sense and the market snap things back into flavor equilibrium.


Even proponents of thiol-boosting products welcome a 202-level discussion that’s less about thiols for their own sake and more focused on how to build recipes and techniques that combine thiol-derived aromas and flavors with complementary ones from hops, malt, yeast, and even fruit.

“At the very start, I talked about Phantasm as MSG for beer, something that would give it an extra pop,” says Jos Ruffell, cofounder of Wellington, New Zealand’s Garage Project and creator of Phantasm, the company that produces Phantasm powder. “But it wasn’t going to be on the front of the label.”

To his surprise, breweries around the world not only splashed the word “Phantasm” across the front of their labels, but one—Santa Cruz, California’s Humble Sea—even went so far as to brew a hop-less IPA using Phantasm. While he’s thrilled to see brewers’ excitement about the thiol-boosting power of Phantasm, Ruffell seems a bit bewildered by the arms race.

“It’s the nature of the industry,” he says. “When something’s new, more is more. We’re still in that phase. There’s been a lot of push to break those boundaries and see how many thiols we can unlock. Now I think we’re starting to see that come back, and it’s going to end up in a place where things are a bit more balanced, a bit more nuanced.”


Much of what is enabling this dialed-in approach to thiols is expanding research on just how potent these compounds truly are. Laura Burns, director of research and development for Omega Yeast, says the sensory threshold for perceiving thiols is 1,000 times lower than that of diacetyl. She likes to use an analogy that begins with an Olympic-size swimming pool, which holds 21,290 barrels of beer. “Put one drop of liquid in that swimming pool, and you’re at the odorant threshold for thiols,” she says.

Omega’s research indicates that yeasts including Star Party, Helio Gazer, and Lunar Crush produce thiols at a level between 5 and 20 parts per billion (ppb) on their own—that’s without additional thiol-boosting products or precursor-heavy ingredients. That’s the same level of thiols in a New Zealand sauvignon blanc; if you want to know whether your beer exceeds that threshold, smell it alongside a glass of that wine and compare their intensities. According to Omega, dialing up thiols beyond that 20 ppb level could produce an out-of-balance beer with diminishing sensory returns.

Deeper Understanding

There are only a few labs in the world with the equipment necessary to measure thiols in their free and bound forms. (Last year, Ruffel says, Phantasm spent roughly $31,000 on analytical testing.) Because quantifying them is well beyond the reach of the average brewery, brewers are essentially driving thiol Ferraris without a speedometer. This makes sensory evaluation absolutely critical to understanding thiols’ impact in a beer: At Omega, Burns recommends that brewers split some wort into a side fermentor to do side-by-side evaluation of a thiol-boosting yeast against its non-thiol-boosting parent strain.

Through these types of controlled sensory evaluations, researchers and brewers alike are contributing to the beer world’s constantly expanding knowledge about thiols and how they’re expressed in beer. While Craft Beer & Brewing Magazine® first covered thiols back in 2018—see “The Complex Case of Thiols,”—Japanese scientist Toru Kishimoto flagged thiols as a potential contributor to tropical-hop aromas 20 years ago. Yet Phantasm has only been available to brewers since 2020; thiol-elevating and so-called "Thiolized" yeasts—the term “Thiolized” is one that Omega Yeast has trademarked—from Omega and Berkeley Yeast debuted the following year. Much is still unknown, but the industry has made huge leaps in a short time.


The past few years have been marked by what Ruffell describes as brewers’ “wild, blind exploration and discovery” of thiol-boosting products. He references the Gartner hype cycle, a technology-industry model that describes a tech product’s life cycle. After the initial “innovation trigger”—the launch of thiol-boosting products—comes the “peak of inflated expectations,” followed swiftly and sadly by the “trough of disillusionment” (which, by the way, would make a fantastic name for a thiol-focused lager).

“In America, we’re sort of getting down in the slope from ‘inflated expectations’ toward the ‘trough of disillusionment’” when it comes to thiols, Ruffell says. “But it’s healthy to go through this.”

Toward Moderation and Diversity of Flavor

There may be no better microcosm of thiols’ current place in brewers’ imaginations than last year’s Phantasm Cup, a first-of-its-kind competition to crown the best beer brewed with Phantasm, held at Chicago’s Half Acre Brewing.

Shana Solarte, advanced Cicerone and a technical writer for Omega Yeast, was one of the judges. While the winning beer—Be Your Future, a hazy IPA collab from North Carolina’s Wise Man and Protagonist—was balanced and invited sip after sip, Solarte says the IPA-heavy field of contenders presented repetitive fruit flavors.


“I’m curious to see [whether] brewers take some lessons from their experiments and trials, and maybe next year’s crop will be more interesting and diverse—not just hitting you over the head with passion fruit,” she says. “They stand out on a tap list, but 10 Phantasm beers side-by-side all using some thiol-enhancing yeast taste pretty similar.”

Solarte says that mixed-fermentation and fruit beers seem like natural applications of thiol-boosting products, but they were rare among the Phantasm Cup entries. In New Zealand, Ruffell says he’s also eager to see more stylistic exploration, making use of yeast blending, Lactobacillus strains—some of which are high in thiol-boosting power—and thoughtful combinations of thiols with esters, terpenes, and other critical aspects of beer aroma and flavor.

Ruffell says he believes that kind of research into better control and integration of thiols will lead to the Gartner hype cycle’s final, desirable stage: the “plateau of productivity.” If thiol-boosting products are going to become brewing tools with staying power, Ruffell says, critical areas include how to incorporate thiols into wort streams, how to preserve them throughout a beer’s life, and how to have them be integrated and complementary to a final beer.

Some of those details are already emerging. As brewers and researchers learn which grains, hops, yeasts, and brewing techniques contribute thiol precursors, they’re also learning which of those ingredients can moderate thiols’ intense sensory effects. A cheat sheet: Barley contributes huge levels of thiol precursors, whereas oats and wheat have not been shown to do so. (Particular varieties of barley and their drying or kilning processes have massive effects on thiol precursor levels, too.) Mash hopping unlocks bound thiols in hops, whereas dry hopping tends to minimize thiols’ sensory impacts. Thiol-boosting yeasts—to varying degrees—free up bound thiols, while blending them with strains not optimized for thiol expression can temper these effects.


Scrubbing the Sulfur

A chief characteristic of the most successful beers Solarte judged at the Phantasm Cup were those that played up thiols’ fruit-flavored contributions while minimizing the perception of sulfur—the aspect of thiols that tends to be most off-putting to drinkers. She emphasizes that clean and complete fermentation is critical for these beers to “scrub up” high levels of sulfur.

Ben Edmunds, brewmaster at Breakside in Portland, Oregon, agrees that excess sulfur is a potential problem—not only because of thiol-boosting products, but also because IPA trends toward pilsner malt as well as late-addition hops with high mercaptan content are making residual sulfur and vegetal notes a larger concern. He suggests pursuing longer boils for IPAs as one strategy to combat this.

“As brewers, we have to find techniques to work these levels back,” Edmunds says. “Extending your boil to drive that off is a really simple one to cut down on unwanted mercaptan, even when we’re using these really heavily sulfur-laden hops.”

He’s also intrigued by the flavor possibilities that can arise from pairing thiol-boosting yeasts with hop varietals that don’t contribute massive doses of thiol precursors. He’s begun thinking about the thiols produced by those yeasts as analogous to the esters of a London ale strain, while conceptualizing hop-forward beers that are built around those esters.


“Rather than playing into the thiol with more thiol,” Edmunds says, “are there routes using less conventional hops—not Cascade and Centennial, but less thiol-prone hops—that would work with these yeasts better?”

How the Strains Do It Differently

One of the top considerations for building recipes that harmoniously integrate thiols is yeast selection. Because thiol-boosting strains vary significantly in their precursor-unlocking power—and because new strains are constantly in development—brewing trials that isolate these yeast strains as the lone variable can give brewers a much better understanding of their varied horsepower.

Some thiol-boosting yeasts—notably Cosmic Punch—make use of a yeast-derived IRC7 gene to promote the expression of more thiols. (They do this by altering the IRC7 promoter, the sequence upstream of a gene that controls its expression, to ensure the gene is always producing the beta‑lyase enzyme that frees thiols from their precursor form.) According to Omega’s Laura Burns, yeasts that use the IRC7 gene result in thiols’ odorant threshold rising from roughly 50 parts per trillion into the thousand parts per trillion range.

“That’s still—depending on the recipe—going to be more of an augmentor,” she says. “It’s not going to take over.”


Then there are the thiol-boosting strains based on the PatB enzyme, derived from Staphylococcus hominis bacteria that’s naturally present on human skin as part of our microbiome. PatB is in many ways comparable to IRC7—except in its intensity. Whereas Cosmic Punch yields a thiol odorant threshold around 500 parts per trillion, Burns says PatB-derived yeasts including Lunar Crush, Star Party, and Helio Gazer “turn that up to 11,” resulting in thresholds of 10 to 20 ppb. That’s another order of magnitude or two beyond Cosmic Punch.

Eric White, head brewer at Mountains Walking in Bozeman, Montana, refers to Helio Gazer as the “nuclear-bomb version of Cosmic Punch.” When he began fermenting a lager with Lunar Crush, from Omega’s Thiolized series, he said the results were immediately “really full on” in their thiol intensity.

During early fermentation, the Mountains Walking team began to worry that the resulting lager—which had been mash hopped with Motueka, Saphir, Hallertau Blanc—might not be drinkable. The thiols contributed an aroma so vibrantly full of pink grapefruit that the beer seemed to have perceived acidity. Thankfully, during the lagering process, those thiols dropped off a bit, and the resulting lager was well received as a new entrant in the brewery’s small-batch lager series.

However, the reception was slightly different when White used Lunar Crush in two other beers—their Nice Fella Italian-style pilsner and Beringia Arctic Pilsner, from their sibling brand New Hokkaido. The results were so potent that White blended batches brewed with Lunar Crush evenly with those brewed with non-thiol-boosting yeast to get them toward more familiar flavor territory.


Even after blending those beers, the brewery received two emails from drinkers who were confused by the unfamiliar flavors; one customer suggested that perhaps the brewery had mistakenly filled cans labeled Nice Fella with an IPA.

“You can go very full-on or you can try to get that nuance, but it seems like no matter what you do, past Cosmic Punch—once you’re using Helio Gazer and Lunar Crush—you're getting those massive thiols,” White says.

White is quick to say he’s early in the process of understanding how best to apply the power of each of these strains. Yet he’s intrigued by the flavor possibilities that thiols open up, especially when applied to the types of beers Mountains Walking wants to be known for: drinkable, exciting beers that entice you into more than one pint.

“The journey continues,” he says. “Whoever figures out thiols and makes them consistent is going to be making some really awesome beers.”