John Kimmich, the mastermind behind The Alchemist brewery and Heady Topper double IPA has little interest in joining discussions about hypothetical differences between IPAs or Double IPAs brewed on the East Coast and the West Coast. “I’ve got to say, I think that [East vs. West] is outdated at this point.” However, the “best IPA” debate does provide context for something more relevant—the effect that yeast selection has on hops aroma and flavor, particularly when it comes to the new “impact” or “flavor” hops.
Kimmich acquired the Alchemist house yeast strain, known as “Conan” as well as VPB1188, when he worked at Vermont Pub and Brewery. Over time it evolved into his own, just as Vermont Pub and Brewery founder Greg Noonan made it his own after acquiring it from English sources. Kimmich particularly likes the apricot and tropical fruit aromas that this strain produces, a combination of the esters that result after yeast creates alcohol and the hops-derived aroma compounds that evolve during the fermentation process (called biotransformations by brewing scientists).
However, Kimmich is pretty confident that he could give Heady Topper a West-Coast hops character more like a Double IPA from San Diego if pressed to do so. How? Well, once, when tasting and discussing yeast experimentation with Shaun Hill (of Hill Farmstead Brewery), Kimmich speculated about fermenting his own beer with White Labs California Ale Yeast (WLP001) instead of his own VPB1188. When asked about why he would do that, he replied, “That’s simple. We [would be] taking Heady to the profile of a San Diego IPA.” To follow his reasoning, let’s look at some recent research on hops and yeast.
Hops Compounds
Scientists have identified more than 400 distinct compounds in hops. Four are most prominent:
- caryophyllene
- farnesene
- humulene
- myrcene
Despite the powerful and seductive aroma of hops, hops oils themselves constitute only 4 percent or less of the cone and often make up no more than 1 to 2 percent. The oils that brewing researchers are currently focused on constitute only .01 to .02 percent of the cone. In Citra hops, for example, 60 to 65 percent of the essential oils are myrcene, compared to about .75 percent geraniol and just less than 1 percent linalool. However, geraniol and linalool affect the aroma of a beer much more than myrcene does. They are responsible for the citrus, fruity, floral, and woody aromas. Although geraniol and linalool may be present individually at levels below human perception thresholds, together they can create distinctive aromas through additive or synergistic effects.
Another oil found in hops, citronellol, naturally exists at low levels in raw hops. By itself, citronellol is described as citrus and slightly green, such as a young lemon or lime. Researchers supported by Sapporo Breweries in Japan set out to determine the role that geraniol metabolism plays in creating citrus and other “exotic” aromas in beers brewed with Citra hops. In this experiment, the citronellol level in the finished beers was much higher than in the raw hops. Researchers determined that citronellol is primarily generated from geraniol when high levels of linalool are present. The synergy of geraniol, linalool, and citronellol contributed to the lime-like flavor found in beers brewed with Citra.
Those same researchers later experimented with blending different varieties of geraniol-laden hops, trying to see whether they could replicate the citranellol qualities found in hops such as Citra. They found that blending hops high in geraniol increased the amount of geraniol and citronellol in finished beer, enhancing the citrus character. For example, a tasting panel perceived a beer made with Apollo and Bravo (high in geraniol) hops as more flowery and citrusy than one brewed with Apollo alone. The same was true of a beer that included a combination of Simcoe and Bravo compared to Simcoe alone.
And Now, Back to the Yeast for a Moment
In another Japanese study, Suntory Liquors found that two different yeast strains pitched into identical base worts produced significant differences in hops-aroma portraits. The scientists explained that this result could be attributed to “metabolites generated from the components derived from hops by different yeasts.” Although more research is clearly needed, this study supports the idea that Kimmich could give Heady Topper a West-Coast hops character more like a double IPA from San Diego just by using a different yeast.
Time to Experiment
Although homebrewers and homebrew clubs may not be able to measure results with the same equipment as advanced laboratories, they can conduct similar experiments and evaluate the outcomes at a sensory level. “Homebrewers have the ultimate efficient lab, making five gallons at a time,” Kimmich says. Although he now makes fifteen barrels (465 gallons) of Heady Topper at a time, blending four of those into a 60-barrel tank for canning and distribution, he’s still experimenting.
“I promised myself that from Day One. The recipe is not set in stone,” he says. Most often, his trials are one-tank experiments, because he doesn’t want Heady Topper to taste dramatically different from one release to the next. “We get to try [each one] by itself,” he says. “We’ve blended many great discoveries into Heady.”
In January, Kimmich dry-hopped two of four tanks of Heady Topper with Citra, just part of the research he is doing on the second beer The Alchemist will release regularly in cans—a 7 percent IPA called Focal Banger. Focal Banger will be hopped with Citra and Mosaic. “They are dynamite in combination,” he says—with a little help from The Alchemist yeast, of course.
The Hops List
Hops with Significant Amounts of Geraniol
Amarillo
Bravo
Cascade
Centennial
Chinook
Citra
Cluster
Mosaic
Motueka
Styrian Golding
Hops with Significant Amounts of Linalool
Amarillo
Bravo
Citra
Glacier
Millenium
Nugget
Pacific
A Short Ancestry Lesson
The researchers who experimented with blending different varieties of geraniol-laden hops made an interesting discovery. They found that the compound they sought is found primarily in hops varieties that include at least a measure of native American hops in their ancestory. The topic of hops ancestry could command an article on its own, but the short version is that hops originated in Mongolia at least six million years ago; a European type diverged from that Asian group more than one million years ago; and a North American group migrated from the Asian continent about 500,000 years later. Most popular new hops varieties, such as Citra, were crossbred from a combination of New and Old World cultivars. Peter Darby, who breeds hops at Wye Hops Limited in England, calls these “impact hops,” and they include selections from Australia and New Zealand as well the United States.