Several years ago, judges at a beer competition in Peru noticed that many entries in the IPA category lacked the level of bitterness they expected. Talking to brewers who made those beers, the judges learned that many of those IPAs were brewed at higher altitudes.
The brewers hadn’t adjusted their recipes to compensate for reduced isomerization at lower boiling temperatures.
Recently, Roadhouse Brewing in Jackson Hole, Wyoming, collaborated on a series of Kush IPAs with multiple breweries. The fifth brewery to participate—Half Acre in Chicago—was the first “to ask me about altitude,” says Roadhouse brewmaster Max Shafer. Jackson Hole is 6,200 feet (1,890 meters) above sea level.
This isn’t a topic that shows up in most brewing manuals, nor one that most brewers would have a reason to talk about, but the information is available. John Palmer, one of those judges in Peru and publications director of the Master Brewers Association of the Americas, followed up with a paper in the MBAA’s Technical Quarterly examining the impact of lower temperatures—whether because of higher altitudes or the whirlpool—on utilization.
“A lot of guys don’t [have time to] read all the literature,” says John Paul Maye, a consultant and former technical director at Hopsteiner. He knows because he wrote about humulinone formation in hops and the implications for dry-hopped beers for Technical Quarterly in 2016. He still gets blank looks when he asks brewers, “Do you know about humulinones?”
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More recently, researchers at Yakima Chief Hops examined whether highly concentrated products such as DynaBoost and HyperBoost produce less bitterness relative to an equivalent dose of T-90 pellets when added to the whirlpool. (Equivalent, in this case, means equal oil content; the concentrated products have high oil-to-alpha ratios.)
(DynaBoost is an extract designed for hot-side additions, primarily whirlpool. HyperBoost is a concentrated hop-oil extract designed to be used anywhere pellets are, including the cold side. Similar products are available from other merchants.)
Like the impact of temperature on isomerization and the role played by humulinones, those products are yet another variable affecting bitterness. To help inform your decisions, there has been more research than you may realize.
Before its first Kush collaboration in 2023, Roadhouse used cutting-edge cultivars and advanced hop products to create a draft-only series of Kush beers.
“An owner wanted to lean into the edgy, cannabis way of talking,” Shafer says of the name. The collaboration cans that followed could double as 1970s psychedelic posters; each labels the beer as “a super heady IPA.”
“The way I like to partner with people is to showcase something about the breweries,” Shafer says. The first collab was Cosmic Kush, with Creature Comforts in Athens, Georgia. The theme of that one was B Corps—companies verified to meet high standards of performance, accountability, and transparency. Both breweries are certified B Corps, as are Mainstem Malt and Roy Farms, the latter of which provided hops.
Another collaboration included USDA experimental cultivars HRC 003 and HRC 004, chosen because both Roadhouse and Odell Brewing of Fort Collins, Colorado, are both voting members of the Hop Research Council. Another collab with Mother Earth, which brews in both Vista, California, and Nampa, Idaho, showcased New Zealand hops because both breweries are among those that hop cooperative NZ Hops has selected to trial experimental varieties. Besides NZ-104, the brewers used Cryo versions of Nelson Sauvin and Riwaka.
Roadhouse and Melvin—which Roadhouse acquired at the beginning of 2023—regularly use many of the advanced products from Yakima Chief Hops, John I. Haas, and Hopsteiner, as well as botanical- and hop-derived products from Abstrax Hops.
Shafer says he appreciates their efficiency, but the primary attraction is increased aroma and flavor impact. “We are very focused on oil composition in the beer,” he says. “We are messing around with the weights of hops used in the whirlpool to make sure we are getting a broader spectrum of oil saturations into the wort, spread between different hop varieties.”
The breweries are big enough that they have in-house equipment to measure bitterness. “We want to make sure we are staying consistent,” Shafer says. “In the hazies, we like bitterness to round out the beer.”
They check the alpha acids in DynaBoost, for instance, and adjust their 60-minute bitterness charge accordingly.
Oils and Alphas
Not surprisingly, the research at Yakima Chief Hops found that when making whirlpool additions, brewers can expect the utilization of bitter compounds to differ based on the type of product.
The researchers added hops in five different forms to 14.7°P (1.060) wort that had cooled to 205°F (96°C). They dosed these worts at the recommended replacement rates:
- T-90 pellets at 5 grams per liter (somewhat more than a pound per barrel)
- Cryo hops at 50 percent
- CO2 extract at 25 percent
- DynaBoost at 10 percent
- HyperBoost at 2 percent
After the researchers dosed each wort, they agitated each sample for five minutes, then allowed it to sit for 25 minutes. They analyzed each wort for humulinones, iso-alpha acids, and alpha-acid content as well as gravity, density, and alcohol content. They also analyzed the beer after fermentation.
Among the findings:
- The iso-alpha yield was higher in worts dosed with T-90 and Cryo pellets.
- The researchers suggest that higher wort temperatures may be needed to get higher IBU utilization from CO2 hop extract because of its high viscosity.
- Worts dosed with DynaBoost and HyperBoost contained no humulinones.
- Post-fermentation, the beers dosed with T-90 and Cryo pellets had a much higher total of calculated bitterness—a measure of the relative impact of iso-alpha, humulinones, and alpha acids—driven by the whirlpool addition.
Ultimately, the researchers conclude that whirlpool additions “will not significantly impact the bitterness of a beer” when kettle additions drive most of the bitterness. However, when most of a beer’s bitterness comes from whirlpool additions, the impact is much more significant.
Graph: Courtesy Suntory
Turning Down the Heat
Brewers who make whirlpool additions at temperatures lower than 205°F (96°C)—and many do, especially in IPAs and other hop-forward beers—should expect different results than in the YCH experiment.
A study in 2005 found that the isomerization rate of alpha acids was primarily dependent on temperature and that none of the other factors tested—glucose concentration, maltose concentration, calcium concentration, and pH—significantly affected that isomerization. The authors constructed a model for isomerization rate as a function of temperature based on test data from 194°, 212°, 230°, 248°, and 266°F (90°, 100°, 110°, 120°, and 130°C), which they used in determining net isomerization at a given temperature.
For Technical Quarterly, Palmer used that model to calculate the net reduction in isomerization at altitude, based on the boiling points at different altitudes and the net isomerization at each boiling point. Brewers who adjust for altitude may want to note, for example, that the net isomerization rate at 4,921 feet (1,500 meters) is 67 percent, versus 100 percent at sea level. Of course, it is not the altitude that affects that rate—it’s the boiling point. At 4,921 feet, that boiling point is 203°F (95°C).
Because temperature is the only significant variable that affects isomerization, brewers could use Palmer’s boiling point/isomerization table to calculate the potential bitterness of whirlpool additions. For example, brewers could expect a 66 percent isomerization rate at 203°F (95°C), 27 percent at 185°F (85°C), or 11 percent at 167°F (75°C).
Of course, aroma is one of the most important reasons to add hops to the whirlpool, and lower temperatures help preserve total oils. However, the content of those individual compounds can vary. For instance, a study at Suntory in Japan found that linalool content is higher when hops are added at 185°F (85°C) instead of 203°F (95°C) or 167°F (75°C). A spider chart capturing sensory qualities (left) shows more citrus and spicy character at 203°F (95°C), but more floral and herbal character at 185°F (85°C).
Humu-what-inones?
Humulinones are not a recent discovery, but few paid much attention to them until brewers began dry hopping at much higher rates.
Humulinones form when alpha acids oxidize, which is why pellets have a higher concentration of humulinones than baled hops. It’s also why varieties with a higher hop storage index (HSI) have a higher concentration. (For more about hop storage and HSI, see Hop-Tub Time Machine.)
Humulinones are about two-thirds as bitter as isomerized alpha acids—but they’re also more soluble than iso-alpha acids, dissolving into beer to increase bitterness. We may perceive that humulinone-driven bitterness differently than we would bitterness that’s more driven by iso-alpha acids.
At Hopsteiner, Maye was among researchers who compared beers fermented with humulinone and isomerized alpha acids, publishing the results in 2016. “The bitterness profile of the humulinone beer, however, appeared smoother, and there was less lingering on the tongue than with the iso-alpha acid beer,” the paper concludes. “This smooth bitterness makes sense given [that] humulinones are more polar than iso-alpha acids and should therefore not stick or linger on the tongue as long as iso-alpha acids.”
Humulinones have a much larger impact in highly dry-hopped beers. The YCH researchers conclude there was not a major impact on bitterness stemming from humulinones added in the whirlpool, but they caution that the hops in their study were fresh. Those that suffered more degradation, resulting in larger amounts of humulinones, could contribute more bitterness. Of course, their influence will vary depending on the quantity of kettle, whirlpool, and dry-hop additions.
Before Maye left Hopsteiner in 2023, he participated in research that discovered a new alpha acid and beta acid in hops. A minor alpha acid, acetohumulone, will add little bitterness to beer. “It’s probably not that important,” Maye says. “It is interesting to discover. You do all this research, you think everything has been discovered, and you find this.”
With researchers finding new things all the time, no wonder it’s so hard for brewers to keep up.
