Hop creep is a term that has been recently popping up in commercial craft brewing circles to describe increased attenuation following dry-hopping. Reports in brewing literature indicate that a small handful of craft breweries may have been aware of this general phenomenon for the past few years, but most were not. The industry’s understanding of what was happening was changed in 2017 by research conducted at Allagash Brewing that followed their very first dry-hopped beer, Hoppy Table Beer, brewed in May of 2016. Allagash closely follows the progress of carbonation and attenuation in their quality-control (QC) lab because they bottle condition almost all of their beers. Because of their diligent practices, they were able to flag that something was amiss with their first foray into dry hopping.
What they observed were increases in carbonation and decreases in real extract that exceeded their experienced expectations. After 3 weeks, the carbonation level in bottles of Hoppy Table Beer were over 4.5 volumes, or more than 1.5 volumes greater than their 3.0 volume target. On the surface, this looks similar to beer that contains Brettanomyces, but that was not the case here.
The QC group at Allagash embarked on a series of experiments to determine the root cause of this phenomenon and ended up using dry-hopped Coors Banquet beer as a model system. Their model system behaved like their Hoppy Table Beer when yeast was present and became dryer and more carbonated after being dry hopped; samples without yeast did not demonstrate the same behavior. Allagash collaborated with Dr. Tom Shellhammer’s research group at Oregon State University (OSU) to further the investigation. Shellhammer’s team began by repeating the trial using dry hopped Coors and were able to repeat Allagash’s experiment.
After digging deeper into the potential causes of the phenomenon, the OSU team found the smoking gun; hops contain several amylolytic enzymes, including amyloglucosidase (AMG). When AMG is added to wort or beer, limit dextrins (those carbohydrates left behind after alpha and beta amylases hydrolyze amylopectin) are broken down into the fermentable sugar glucose. What Allagash and OSU observed in the model system with Coors Banquet, hops, and yeast was glucose production and subsequent fermentation by yeast as a direct result of AMG degrading limit dextrins in the beer. This is what brewers call hop creep, a phenomenon last reported in the brewing literature by Janicki and others in 1941 and, nearly 50 years earlier in 1893, by Brown and Morris.
The odd thing about this topic is that dry hopping bottle-conditioned beers is not a new thing for craft brewers, and reports of hop diastases are certainly not new. But over-carbonation in dry-hopped, bottle-conditioned beers does seem new. Take Sierra Nevada as an example; their Bigfoot Barleywine and Celebration Ale are both generously dry-hopped, contain plenty of chewy dextrins, are bottle-conditioned, and neither are known for their extreme levels of carbonation after cellaring (contrast this to Orval that is bottle-conditioned with Brettanomyces). Hop creep has turned into a very hot hop topic and it will be interesting to learn more about this as brewing scientists uncover more findings. Practical brewers anecdotally know that this phenomenon is not associated with all hops, and there does not seem to be any obvious association with specific varieties or hop growing regions. In other words there is still a lot of mystery in this occurrence.
What makes hop creep a very big deal is its potential to cause package explosions at home or in the market. It’s bad enough for commercial brewers that hop creep results in over-carbonated beer and increases a beer’s ABV beyond what the label states, but the liability concerns surrounding package failures is huge. Homebrewers definitely need to be mindful of hop creep by paying attention to changes in carbonation levels in bottle-conditioned beers and staying abreast of this topic as research continues peeling back the layers of this interesting topic.