Unlocking the Secrets of Smell: Hop Chemists Are Advancing How We Understand and Manipulate Aroma

Feature by | Feb 2015 | Issue #97

Illustration by Andrew Craft

To coax a strawberry smell from his HopPun American Pale Ale, Augie Carton adds a heavy-handed dose of Super Galena hops halfway into the boil. No earlier and no later or its unique hop aroma is lost. “It doesn’t work right at 60 minutes,” says Carton. “And it doesn’t work right at flameout.”

“HopPun is built around dressing up that strawberry notion,” explains the founder of Carton Brewing in Atlantic Highlands, N.J. “We change the time and temperature exposure to get different oils out of the hops at different times,” he says. Finding out through trial and error with which hop to season—and when—was key to developing his HopPun recipe. It’s no wonder Carton compares hop additions to cooking.

“Malts are your protein, hops are your herbs, yeast is your seasoning,” says Carton, reiterating the analogy he made at a recent TED talk. “One of the parts of learning to cook is learning herbs and I think it comes latest. Brewers are just at that phase with hops,” he says. “We’re playing with herbs, with the finishing touches.”

But a brewer can rely too much on the finishing touch. Carton points to a subculture of craft beer that’s fixated on building beers around aromas: the hop bomb. He’s not referring to a resiny, syrupy beer infused with as much hops as possible. To Carton, a hop bomb is a beer designed completely around aromatics. Unlike Alchemist Heady Topper or Alpine Duet IPA, which draw hop character all the way through, hop bombs are stripped down to, in Carton’s opinion,  “short lived aromas through dry hop additions,” whether it’s a dank piney sensation or a tropical punch to the face.

Leaning hard on just one hop aroma can eclipse the complex fragrances beer is capable of, however. Beneath the surface is a smorgasbord of malt character, early-addition hop bitterness, and yeasty esters.

What Ever Happened to Balance?
What’s actually going on when you crack open a hop bomb anyway? Anthony Clark, vice president of biotechnology at the fragrance company IFF, has a few ideas. Clark runs IFF’s research and development arm, finding and creating new aromas and flavors for the fragrance and food industries. As a former laboratory group leader at Carlsberg, Clark knows his beer, too. Naturally, he dives into some chemistry, highlighting—out of more than 300 compounds—some of the most important aroma components found in hop oils.

“Hops are principally terpene and myrcene,” he explains, referring to the volatile, unsaturated hydrocarbons. “Myrcene is kind of spicy, peppery but also plastic-y, floral, fruity. It’s like that top part of a fresh mango. The piney, resiny element in hops comes from mono-terpenes,” he continues. “And then there’s humulene, another terpene, which is more earthy, woody.”

Don’t let the names confuse you. These aroma compounds are being engineered into your beers, so it’s best to get acquainted. Think about them the next time you smell a hop bomb. Does your nose detect anything besides that hop character?

“I’m Scottish,” Clark says. “I want something that is balanced. These hops aromas tend to overpower other characteristics like yeast metabolites. My favorite beer is a Duvel, very strong, a little bit sweet, with a complexity to it. I’m always looking for complexity in beer. I think the hoppy stuff has gone a little bit too far,” he adds. “It’s off the radar.”

Indeed, boutique hops bred for a fashionable character seem anything but unusual anymore. The danger with increasing demand for singular aromas is the pressure this capricious insistence puts on an already overcrowded hop market. So should we expect growers to go big on aroma varieties in coming years? And are voguish craft breweries forgoing the notion of balanced expression at their own peril?

Steve Frazier thinks so. Frazier is head brewer at The Brewer’s Art in Baltimore, Md. Since 1996, he and his colleagues have focused on clean, Belgian-inspired beers with a seasonal nod to new styles. Their approach to beer is more orthodox. Walking through the handsome townhouse that holds their 10-hectoliter brewery, you get a sense of the tradition and grace that shine through in beers like Resurrection Dubbel and Le Canard Belgian Strong Pale Ale.

“Hops are a very important component, but they are definitely not the whole story,” says Frazier, who studied physics. With his insatiable curiosity for scientific explanations, Frazier embodies the analytical approach to brewing. In fact, he’s often found poring over technical brewing literature at the Johns Hopkins library. And his beers show for it. Some of the recipes at The Brewer’s Art have been fine-tuned over decades.

“These aren’t happy accidents,” says Frazier, laughing. Frazier and his colleagues tackle recipes with a methodological mindset. And the hops are just part of the equation, he says. “In truth, the synergistic effects are probably far more important than any one component.”

Can a Sensation be Quantified?
Still, there’s no sign the demand for aromatic hop bombs is slowing down. On the contrary, the trend has sent contracts for varieties like Citra and Simcoe through the roof. Distributors are mailing out experimental hops as fast as they can pick them.

Before those hops go out, Zac German chemically characterizes them with fancy analytical equipment. As technical manager at Yakima Chief-Hopunion in Yakima, Wash., German screens every new hop for its oil content by identifying the levels of around 15 different compounds like myrcene and humulene.

German first extracts the hop oils with steam, then runs them through a gas chromatograph (GC), a machine that vaporizes the solution and measures the relative concentrations of various oil compounds. The science is still a ways away from being able to tell us exactly what a hop will smell like. Rather, this analysis is more valuable for detecting seasonal, regional and grower-specific changes in hops. Measuring the differences in oil levels is a way of fingerprinting them before they’re made available for sale.

Running this analysis on Cascade hop oil, for example, reveals a ratio of 59 percent myrcene to 13.5 percent humulene, along with 12 other compounds at much smaller concentrations. But, German acknowledges, “there really isn’t a good correlation between what you see in a gas chromatography profile and what you perceive with your nose.” It’s difficult to correlate how much a given hop oil contributes to a specific scent. “Our sense of smell is a composite of all we take in.”

Citra, for example, releases a tremendous bouquet of different oils. Specifically, it’s comprised of 60–65 percent myrcene, 11–13 percent humulene, and a bunch of other compounds, many of which are still unidentified. “All the GC readouts have a significant number of unidentified peaks which undoubtedly contribute to the aroma,” says German. “And there are numerous aroma compounds that aren’t detected on the GC.” One smell could be multiple compounds working in concert. As far as we know, the human nose can’t tell how much myrcene is present.

In other words, Citra’s grapefruity melon aroma can’t be attributed to a single hop oil. The causative chemicals are very difficult to tease out. What has surprised hop chemists, however, is the disproportionate effects on aroma that certain hop compounds have at very low concentrations.

“We’re talking parts-per-trillion,” says Tom Nielson, technical lead for flavor and raw materials at Sierra Nevada. “At low parts-per-trillion, sulfur compounds like polyfunctional thiols are driving interesting tropical fruit characters, the papayas, the lychees.” But a compound that lends a tropical character at low concentrations may ruin a beer’s bouquet at higher concentrations. Some thiols released by hops have odors similar to potatoes, popcorn, garlic, cheese and onion.

For Sierra Nevada’s analysis, Nielson has a gas chromatograph with an added benefit: a splitter that can shoot a puff of an isolated hop compound into the operator’s nose. “It’s a really great tool to figure out what is important versus what is noise,” he says. “But after you find the individual components that you think matter, the next level is infinitely complex where you’re combining specific flavors in crazy combinations. The synergisms and antagonism of different flavor combinations are just tremendous and hard to predict.”

So even if we could isolate the precise compound responsible for, say, Mandarina Bavaria’s lychee zest, reverse-engineering that aroma into a new experimental hop and then brewing a beer with it would be almost impossible because of all the hop’s associated oils and chemical interactions. It’s the foremost challenge in taming biology for the benefit of our senses.

“It’s more like fingerprinting a variety and finding outliers, says German. “We really are at this intersection between art and science. And the science still has a lot of complexity to overcome.” For Nielson though, analytical hop chemistry is more than quality control across lots. “[It’s] entering another golden era,” he declares.

But once scientists pinpoint the exact compounds responsible for specific aromas, a world where hops are carefully tailored for beers engineered to satisfy your olfaction seems plausible. Before that happens, the next time you crack open a hop bomb, think about why the brewer chose those hops, what they’re trying to coax out of them, and ask yourself: What did the beers I love used to smell like?