From Vol. 2, No. 10, February 2018
When Paul Farnsworth first graduated college in the 1960s and began working in English breweries one of his first tasks was calculating how much alpha was left in whole cones after they had been used in the hopback. Brewers today are less frugal. Were they focused on using hops more efficiently they could sell beer for less. In addition, farmers could devote fewer acres to hops. Just to be clear, the discussion is about using fewer hops to create the same aroma and flavor, not lesser beer.
With that in mind, this month’s newsletter has less “wow” science/data and a little more about what motivated research first presented at the sixth international Young Scientists Symposium in Germany last September. The conference is for students and young professionals working the fields of malting, brewing, and distilling. These sorts of gatherings are important because sideways thinking in science is as important in driving innovation as wacky new ideas brewers might come up with.
Dean Hauser’s interest in the efficiency of dry hopping began in 2015 when he was an undergraduate at Cornell University. Because there was funding for collaborative research between the Food Science and the Chemistry departments to work with a local brewery, Ithaca Beer Company, he and classmates toured the brewery. He was immediately struck by the inherent inefficiency of industry-scale dry hopping.
[Spoiler alert: Hauser’s research led Josh Chapman at Black Narrows Brewing in Chincoteague Island, Virginia, to brew a beer using spent hops.]
“I spent the next term probing this question with a group of students who were similarly intrigued,” he writes via email. “At the end of the term, I was not fully satisfied with the scope of our results, and pitched the idea of using supercritical CO2 for the recovery of bitter acids to Dr. Syed Rizvi, which would be the basis of my undergraduate honors thesis. Still not satisfied, I applied to Tom Shellhammer’s lab at Oregon State University for my master’s degree, which seemed an ideal place to get to the bottom of my question on whether spent dry hops can be reused.”
That’s where he conducted the research cited here, and continues to do research as he works toward earning his master’s degree.
He adds: “On a more personal level, my attraction to the food science world is not necessarily a pursuit of flavor for the sake of flavor, but rather an interest in what we in the food industry can do to make our processes more efficient from an environmental perspective while preserving quality or perhaps finding new flavors.
“The sustainability challenges facing the food and beverage industries are formidable, and so any way that we can change processes or create new ones to lessen our footprint, whether it is by valorizing byproducts such as spent hops or otherwise, should be looked into. 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 presented the results of his research at both the Young Scientists Symposium and Brewing Summit 2018. Here’s the elevator version:
– Hauser, and others as OSU, examined multiple lots of Amarillo, Cascade and Centennial hops. The Amarillo hops were kilned under many different conditions, and the Cascades and Centennials had several different harvest maturities.
– Overall, spent pellets retained 77 percent of alpha acids.
– Overall, spent pellets retained 51 percent of total oil.
Bottom line: Dry hopping is a very ineffective process and spent dry hops are a rich source of alpha acids and hop oil.
How might brewers tap into this source?
“Unfortunately, I have not yet tried this, although I am hoping to run an experiment on this subject in the next few months,” he answers. “The data suggests that spent hops have more hydrocarbon character, with a greater prevalence of hydrocarbons relative to oxygenated compounds, which may lead to more herbal/grassy notes relative to citrus or fruity aromas. However, it is hard to speculate what the result would be in an actual beer application. As with most new uses/technologies in food, the best way to work spent hops into a product is likely trial and error.”
There’s a lot to consider. First, dry hopping efficiency is different at each brewery. And, as Hauser wrote, a larger percentage of oxygenated compounds such geraniol (and also geranyl acetate and geranial, which are sometimes also transformed into other compounds during fermentation) and linalool are transferred during dry hopping than hydrocarbons such as myrcene, humulene, and caryophyllene.
Put another way, the profile the second time around won’t be the same as the first. Extraction is going to be different with T-90 pellets (different still with other pellets), Cryo Hops, and T35 Lupulin Powder. And the results are variety dependent. Amarillo retained 57 percent of oil, Cascade 42 percent, and Centennial 51 percent. Oh, one more thing. Small breweries don’t have the tools to assay spent hop oil profiles.
Beyond that, dry hops are no longer dry when brewers are done with them. “Gloopy mess” is the technical term one brewer used when we were discussing this. Depending when they are added in the process, the spent hops may contain yeast.
Nonetheless, looking at what might otherwise be wasted, a bit of effort sorting this out seems appropriate. “Hops reuse is largely a question of scale and timing,” Hauser writes. “If a brewer knew the composition of volatiles and bittering components in their spent hops, and the timing worked, they could theoretically divert spent hops into the brew kettle or maturation tank for reuse.
“Of course, there are a lot of ifs that need to be addressed in that statement, namely the potential variation in the composition of spent dry hops, and the fact that they would likely need to be stabilized or stored in some way. It is also possible that if brewers need to freeze the spent material, for example, the energy consumption involved in freezing and storing the hops may outweigh the resources that are conserved by reuse itself.”
Now, indulge my interest in what makes young scientists tick. Hauser writes:
“Two important takeaways from my relatively brief experience as a researcher are that success is based mainly on how hard you work, and that novel questions require novel answers. Research on hops, beer, and food in general is time consuming, and also time sensitive. Whether its long hours in the pilot plant producing experimental dry-hopped beers with exactly four days of beer-hop contact, or pulling all nighters checking the moisture content of hop kiln beds, the complex nature of the biological systems that are our food means that the study of food can be all-consuming at times.
“No matter how great your idea is or how clever you are, research rarely goes according to initial planning, and obstacles such as spending weeks troubleshooting gas chromatographs or trying to clean shellac out of you supercritical CO2 extractor are to be expected. Sometimes, an assay simply won’t work with your application of it, regardless of how long you spent trying to use it. However, it all seems worth the effort when stakeholders in industry express interest in what I have to say, and what I have found.”