Boozier Beer and Exploding Bottles

Zymology by | Aug 2019 | Issue #134

The Curious Case of Mystery Fermentation

Nobody thought the explosion of dry-hopped beer was going to be literal. But research into the secret double lives of the aromatic green flowers combined with the growing experience of brewers shows that heavily dry-hopping at the end of the brewing process can restart fermentation, potentially pumping up alcohol content and carbon dioxide levels in a phenomenon known as hop creep.

“In the worst-case scenario, the refermentation of dry-hopped beer can over-pressurize glass bottles, and no brewer wants an exploding beer on the shelf or in their customer’s hands,” says Kaylyn Kirkpatrick, a brewing extension associate at Cornell University’s College of Agriculture and Life Sciences.

Maine’s Allagash Brewing Company has been bottle conditioning beers, mostly those brewed in the Belgian tradition, for more than 20 years.

But it wasn’t until relatively recently when brewmaster Jason Perkins started to dabble in dry-hopping that he noticed a “really weird trend” happening in bottles supposed to be ready to sell. Bottles of Allagash’s Hoppy Table Beer appeared to be undergoing new fermentation in the glass containers, which was increasing alcohol and carbonation to higher levels than he expected.

Perkins and others at Allagash suspected that the Comet and Azacca used in dry hopping the beer had something to do with the problem, and ran some basic tests on a beer they were pretty sure was stable. They added 10 grams of Cascade hop pellets per liter and three types of yeast (Allagash house yeast, Chimay yeast, and Chico yeast) to some Coors Banquet they had and were fascinated to watch a “tremendous” drop in malt extract. Then they dug through the professional literature and found some old articles noting the issue. Even so, Perkins felt he needed to speak to a hop chemistry expert to tell him he wasn’t crazy.

That someone was Dr. Tom Shellhammer, Nor’Wester Professor of Fermentation Science at Oregon State University. Shellhammer and Kirkpatrick repeated Perkins’ rough experiment in the laboratory with more rigorous analysis.

Their results, published recently in the Journal of Agricultural and Food Chemistry, show that enzymes present in Cascade hops can actually break down the normally unfermentable residual dextrins in malt that are left over after the initial brewing process, converting them into glucose molecules. Starved yeast remaining in the beer will greedily feast on this sugar, producing more carbon dioxide and alcohol as byproducts.

“In some cases, brewers don’t know when [fermentation is] going to stop,” Shellhamer says, adding that if dry-hopped beers are packaged too soon, the additional fizz could result in gushers or, in the worst case, even explosive bottles or cans that could be a danger to drinkers and bartenders. And while a little extra booze may not seem like a problem, even a small percent increase could cause a regulatory compliance headache for brewers by bumping the alcohol over the number listed on their labels. At the very least, both of these factors could affect quality control, resulting in a beer that noticeably differs from the product that a brewer intended to make.

“Because hop enzymes have the potential to significantly change beer fermentability and flavor, it will be important for brewers to anticipate their activity when formulating recipes,” Kirkpatrick explains.

She adds that brewers will need to be particularly careful with IPAs, especially since double or triple dry-hopped hazy IPAs have taken the craft brewing world by storm. “I believe that we weren’t really aware of this phenomenon until now because of the relatively recent popularity of IPAs,” says Kirkpatrick. “Many of these popular styles, like the New England IPA, get a heavy dose of dry hops which still contain active enzymes, unlike hops added during the boil.”

Mike Pawley is the production manager for Commonwealth Brewing Company in Virginia, a brewery that makes a lot of sought-after hazy IPAs. He says that hop creep is definitely something they consider during their dry-hopping process as it can have an effect on the finished product. “It’s pretty much the number one talking point in the more intellectual side of the industry,” he says, mentioning that the variety of hops used seems to be a factor as well. Some of the bigger offenders are Fuggle, Cluster, Nugget, and Perle while others like Amarillo vary by year. “You can do the same process with the same hops, [and] sometimes it happens and sometimes it doesn’t.”

Shellhammer notes that one of the ways to control hop creep includes pasteurizing beer after the dry-hopping process. But for brewers who might balk at this idea due to the trendiness of unpasteurized brews, he suggests waiting a few days before packaging anything that has been recently and heavily dry-hopped.

While hazy IPAs are often better fresh as the desirable fruity characteristics of the hops are more evident, Commonwealth founder and head brewer Jeramy Biggie agrees that the brewery still has time to let the hop creep die down before packaging. “We’ve rarely had a creep issue so extreme that it affected the freshness of a beer,” he says.

For Perkins, the most important thing is to get the word out. In 2017, he gave a presentation at the Craft Brewers Conference in Washington, DC about hop creep and while some in attendance had already noticed anomalies without connecting the dots, others still didn’t believe it was possible.

“Most of the danger right now with this phenomenon is that people don’t know about it,” he says. “It’s really just about educating people that this is something that hops can do.”