Ross Koenigs didn’t mean to shake the foundation of craft beer in January, but that’s what he did. “This style is more American than American IPA,” he told an overflow crowd of brewers and beer geeks during a seminar at the Big Beers, Belgians and Barleywines Festival. “I’d like to see this style as the new American IPA.”

Koenigs, a brewer who specializes in the research and design of new beers at New Belgium Brewing, was talking about — what else? — hazy, New England-style IPAs. He and the owners of Cerebral Brewing, Weldwerks Brewing and Outer Range Brewing (all Colorado breweries) were there to suggest that the traditional way of measuring bitterness in hops, IBUs, might be outdated or too simplistic, to point out that American tastes were changing, and to school the attendees on the scientific research backing up their claims.

Koenig’s comments silenced the room. But they had a far-reaching effect.

Julia Herz, the craft-beer program director for the Brewers Association, which hadn’t yet officially recognized these beers as a “style,” tweeted: “IBU as we know it defined as a measurement is about to have to change.” Weeks later, some of the breweries who’d been in attendance were still thinking about — and talking about — that idea. And in March, the BA formally added not one, but three categories encompassing the controversial style to its 2018 list of beer style guidelines: Juicy or Hazy Pale Ale, Juicy or Hazy IPA and Juicy or Hazy Double IPA.

EXPAND Sean Buchan (left), Neil Fisher, Lee Cleghorn and Ross Koenigs made for a hazy brain trust at Big Beers last January. Jonathan Shikes

The validation was nice, but Koenigs and the brewers who specialize in New England-style IPAs hadn’t been waiting around. In October 2017, just before the Great American Beer Festival in Denver, Koenigs was chatting with Neil Fisher, the founder of Weldwerks Brewing, who is one of the foremost experts in juicy, hazy New England-style IPAs in Colorado and nationwide. Typically marked by very low bitterness, a creamier mouthfeel than traditional IPAs and intense tropical or citrus flavors and aromas (not to mention the cloudy appearance), these beers have become immensely popular over the past two years. Brewers usually get their desired effects by adding hops much later in the brewing process, at a point after the wort (unfermented beer) has cooled, rather than during the boil. This also enables them to add far more hops than they otherwise would for a standard IPA.

But Fisher told Koenigs he was starting to get some unintended bitterness in some of his heavily hopped beers, though the bitterness couldn’t be measured by the traditional IBU method. “He asked if New Belgium’s chemistry lab would be willing to run some baseline analytical numbers,” Koenigs says. “That’s something we like to do on a regular basis anyway for our friends and colleagues in Colorado and elsewhere, so we said yes.”

At New Belgium, Koenigs brewed the same beer four ways, changing the amount of hops that were added during the boil and the amount added afterward. The results showed that there was something going on aside from simple isomerization, a process in which the molecules in hops change in boiling water and create iso-alpha acids. Iso-alpha acids are what chemists use to measure International Bittering Units, or IBUs, which is the scale that brewers in turn use to communicate to customers how bitter each individual beer will be.

“Intuitively, you would think that if you are stepping up the volume of hop material, that you would see a nice linear growth of concentrations of both aroma and bitterness. But in reality, the chemistry starts getting a lot more complex than that,” Koenigs says. In addition, hops that are added after the boil also lend a certain amount of bitterness, but not the same kind. Understanding the difference and being able to define it could make the notion of IBUs obsolete. It could also help brewers of New England-style IPAs, who are trying to limit bitterness in their beers, understand why some beers turn out better than others.

EXPAND Ross Koenigs sampled one of his experimental beers at the Big Beers festival, alongside other hazy IPAs. Jonathan Shikes

Scientists and graduate students at Oregon State University are currently studying the process, and two of them will present their findings at the Craft Brewers Conference in Nashville in May.

New Belgium will also continue to study the process through experimentation — and with the help of brewers from Weldwerks, Cerebral and Outer Range. “Our guiding philosophy at New Belgium is that if we can’t measure it, we can’t understand it — and New England-style IPAs have made us realize how much we don’t understand,” Koenigs says. “We want reliable math that says, ‘If we add X number of hops at this point in the process, we can reliably get Y amount of bitterness — and have everyone agree on that.”

That reliable math may be a few years down the road, however. New Belgium will continue to study the chemistry — and maybe help publish a paper at some point in the future. In the meantime, though, brewing New England-style IPAs will continue to hover at the intersection of art and science, he adds. “Right now it's more art than science, though.”

Oh, and as for his comments at Big Beers, Koenigs says he wishes he’d been a little more clear. He didn’t mean to suggest that New England-style IPAs should replace classic IPAs in the BA's “American” category.

Rather, he wanted to point out the truly American characteristics of juicy IPAs. While American IPAs are a variation of India Pale Ales invented centuries ago in England, juicy IPAs are typically brewed with hops varieties that have been tested in American hops yards over the past fifteen years and “custom bred” for American tastes.

The beers themselves are usually brewed with extreme quantities of hops — “something only Americans would try,” he says with a laugh. "They’re hazy and weird, and most people would think we were insane for doing something like that. But pushing the envelope is as American as apple pie.”