Elements of Beer: Recycling Hops in the Brewhouse

Think you need to throw out all that fragrant green sludge? Maybe you don’t. A few American brewers are experimenting with reusing spent dry hops, and the results are intriguing.

Stan Hieronymus Apr 24, 2020 - 11 min read

Elements of Beer: Recycling Hops in the Brewhouse Primary Image

Paul Farnsworth was 16 years old when he began working as an apprentice at Truman, Hanbury & Buxton’s brewery in Burton-upon-Trent. By the time he got his Ph.D. from the University of London in 1973, one of the tasks he had performed was calculating how much bitterness could be obtained by boiling hop cones that had already been used in the hop back.

He arrived in the United States in 1976, and ever since he has watched American brewers use hops less and less frugally. Along with teaching at various universities, he built and equipped 50 breweries and fermentation plants around the world, set up quality-control programs for dozens of small breweries, taught brewing, and occasionally brewed himself. Officially retired, he still consults with breweries that interest him.

“The United States changed dry hopping,” he says. At Truman, he was part of a three-man team that dry hopped individual casks, adding Goldings at a rate comparable to six ounces per U.S. barrel. Today there are brewers using more than 15 times that amount. Almost always, the hops are discarded after a single use, although research at Oregon State University recently revealed that they are still rich in compounds brewers covet.

The numbers are downright stunning. Dean Hauser, and others at Oregon State, examined multiple lots of Amarillo, Cascade, and Centennial hops.


They found:

  • Overall, spent dry hops retained 77 percent of alpha acids.
  • Overall, spent dry hops retained 51 percent of total oil.

Josh Chapman at Black Narrows Brewing, on the island of Chincoteague, Virginia, saw those results and knew immediately that he wanted to find a way to capture some of what had been left behind. Put simply, “not getting the most out of our ingredients is wasteful both in practice and ethos.”

Black Narrows, where Chapman brews five barrels at a time, is not the only small brewery to sometimes use spent dry hops to make another beer. At Bosque Brewing in New Mexico, they refer to the process as “second-generation dry hopping.” At Pennsylvania’s Forest & Main, Founders Gerard Olson and Daniel Endicott began occasionally using spent dry hops in a saison after they’d had success reusing fruit.

“Like everybody, you clean the tanks, and you smell all the hops going down the drain,” says Olson. “It smells marvelous.”


OSU’s Hauser, who earned his master’s from Oregon State in 2019, was drawn to food science and technology because of his interest in sustainability. “The reuse of spent hops in particular could provide smaller-scale brewers (who often use more energy and water to produce their product) with a way to mitigate their impact, while at the same time providing a novel, potentially more sustainable product that may differentiate them in a rather saturated market,” he wrote via email.

In a second study, spent dry hops were collected from a local brewery and used to bitter a test batch at OSU’s pilot brewery. Researchers also brewed a trial batch using the same hops varieties in pellet form. The finished beers were then dry hopped with first-use Cascade hops, resulting in four beers. The utilization was higher for spent dry hops than pelletized hops, but from “a sensory perspective, although the spent-dry-hop-bittered beers were significantly more bitter, no consumer preference was found in terms of aroma, overall, or bitterness liking between the two sets of beers.”

The potential benefits are obvious. Larger breweries might save thousands of dollars, and it could be necessary to plant hundreds, or even thousands, fewer acres of hops. Quite honestly, it is not clear this will ever happen. First, more research is needed related to reuse on a larger scale, such as determining the storage stability of spent dry hops and possible methods of preservation.

In addition, although half the essential oil may remain after dry hopping, the percentage of individual compounds changes. A larger percentage of oxygenated compounds, such as geraniol and linalool, are transferred during dry hopping. That leaves behind in the spent hops a smaller portion of those compounds that contribute to the currently stylish bold aromas and flavors.


Hauser points out that both the remaining alpha and oil may vary based on form, process, and even the variety of hops. Nonetheless, while his follow-up research focused on bitterness, all of the brewers who have experimented with second-use dry hops talk first about aromatics.

Challenging Production Schedule

Bosque and Forest & Main both brewed their first beers with second-use hops before learning about the Oregon State research. “We were dropping a cone into the drain,” says John Bullard, chief production officer at Bosque. A former employee commented on the aroma and said, “Man, it would be cool if we could reuse these.”

It wasn’t quite that simple. “The biggest challenge is the production schedule. It isn’t easy to get two beers to finish at the same time,” Bullard says. Bosque has not made Little Tipper, a pale ale, since moving into a larger brewing space with a 30-barrel brewhouse. At the original brewery, it took two 15-barrel brews to produce a 30-barrel batch of Scale Tipper, perhaps Bosque’s best-known IPA. That beer twice won the National IPA Championship, a country-wide bracket-style contest that included 128 IPAs.

Scale Tipper is dry hopped with five pounds of hops per barrel, equal parts Simcoe, Citra, El Dorado, and Mosaic. When it is finished and ready to transfer to a bright tank, it is crash cooled. A 15-barrel batch of Little Tipper, bittered only in the whirlpool, remains at fermentation temperature after reaching terminal gravity, then is transferred to the freshly spent dry hops. “The aromatics are huge,” Bullard says.


In December, Bullard said he expected to brew Scale Tipper again in the spring, and production manager Tim Woodward was already thinking about the logistics of making Little Tipper.

Likewise, production of a relatively low-gravity saison following an IPA at Forest & Main is “always a bit of a juggling thing.” Olson and Endicott add a pound of hops per barrel in the whirlpool for a typical seven-barrel batch of IPA, fermenting it with Boddington’s yeast. They top-crop about two days into fermentation and add a dextrose solution along with three pounds of hops per barrel. They use “cool, sexy hops” such as Citra, Mosaic, and Galaxy.

Olson says that in top-cropping they capture most of the flocculating yeast, and a minimal amount will be left in the trub. “It’s determined by our brewery setup. It’s not how we’d choose to do things if we had a choice,” he says.

The saison, a smaller beer typically starting at about 10°P (OG 1.040), is racked through the bottom of the IPA fermentation tank, mixing with the spent dry hops. The brewers also add a sugar solution to encourage new fermentation. That beer is made with a bit of aged hops in the boil, then 1.5 pounds of a Noble-type hop in the whirlpool. It ferments with a locally foraged yeast.


“We were never a fan of typical New World hops” in saison, Olson says. “Somehow, when we do this, I feel like it softens the saison. It melds nicely.”

Meanwhile, at Black Narrows, Chapman took a cautious approach. He started with a mixed-culture fermented beer, figuring it allowed him greater margin of error. The first run of the beer called Crummy Family takes about three months to finish and spends one month with Mosaic hops to the tune of a half-pound per barrel. After transferring that beer from the fermentation vessel, he racked wort brewed to the same specifications onto the spent hops (and yeast).

“Within two weeks I’d say we had roughly 85 percent to 90 percent the same beer as the first iteration that took three months,” he wrote via email. He missed his target gravity because he didn’t take into account that he would be diluting the wort with what remained in the tank. The second beer was finished in about a month and touched up with a bit more dry hops (one-fifth pound per barrel).

Chapman considered this “fantastic proof of concept” and good reason to create a beer he calls Cruisin’ the J. It starts with Four Mouths, the house IPA brewed with a combination of hops varieties (two parts Mosaic and El Dorado blend, to one part Hallertau Blanc and Callista blend). He adds one pound per barrel in the whirlpool and dry hops with 3.5 pounds per barrel. The grain bill includes 90 percent pale malt, 10 percent flaked oats, and it ferments with an English ale yeast. The final beer is 6.8 percent ABV.

Rather than brew another IPA, Chapman decided to make a pale ale. After transferring Four Mouths from the fermentation tank, he puts a 1.042 OG wort (hopped with a pound of Hallertau Blanc) on top of the remaining trub. As anticipated, the OG drops to 1.038. He does not add any additional dry hops. He doesn’t think the resulting 4.65 percent ABV beer is hops-forward enough to be a session IPA, but it has “a wonderfully aromatic, soft bitterness.”

Customers seem to agree. It is the fastest-selling beer ever at Black Narrows. “We’re at the point now where whenever we brew Four Mouths, we know that on racking day we’re brewing Cruisin’ right on top of it, and you’d be stunned by how many folks are always asking when Cruisin’ is coming back because it’s beating the IPA off the taps,” Chapman wrote.

That would seem to be additional proof of concept.