This week I take a close look at the effects of Dry Hop Creep in highly hopped beer styles like IPAs and what can be done to limit the problem.
For some time now, brewers of IPAs using very high levels of dry hopping have been aware of stability issues with their finished beer including diacetyl, over attenuation and even carbonation issues.
However not until 2018 were researchers able to explain the problem in some detail. Oregon State University published a paper in the Journal of Agriculture and Food Chemistry and also presentations were made by Caolan Vaughan at Brewcon 2018 in Sydney and another was done at the Oregon Beer Summit.
The term “Hop Creep” or “Dry Hop Creep” was coined to describe the problem which occurs when high levels of dry hops are used. Ironically, the problem was described by Brown and Morris way back in 1893 including the cause, but that knowledge was largely lost over the last 126 years.
What is Hop Creep
At its core, hop creep is continued fermentation in the bottle or keg after the finished beer has been packaged for distribution. Symptoms include overcarbonation of bottles and kegs, over-attenuation of packaged beer, and diacetyl off flavors. It can occur in any unpasteurized or unfiltered packaged beer. Warm storage of the packaged beer can make the situation worse.
The root cause of hop creep is high levels of dry hopping. Hops actually contain trace amounts of both alpha and beta amylase as well as limit dextrinase enzymes. After dry hopping these enzymes can continue to convert a small amount of starch into sugars even at room temperature. If yeast is still present the sugars will ferment, lowering the final gravity of the beer and also creating carbonation.
The net effect can be as much as a 1-2 Plato drop in final gravity over a period of 40 days, which leads to a 5% increase in carbonation levels and 1.3% increase in alcohol (Kirkpatrick and Shellhammer). There tests were done at 20 C, and higher storage temperatures can result in even more attenuation. This means the bottles and kegs will be overcarbonated, and the increased attenuation can also affect the malt-hop balance and body of the finished beer – big problems for commercial breweries.
In addition the fermentation will raise the diacetyl levels of the beer, and there will likely not be enough yeast to clean that diacetyl up resulting in a buttery off flavor in the finished beer.
Preventing Hop Creep
There are a variety of techniques that may reduce the effects of hop creep though they may not completely eliminate it. Some of these also have limited hard experimental data behind them:
- Filter or Pasteurize the Finished Beer – Really the only way to completely eliminate hop creep, filtering or pasteurizing will remove live yeast from the equation, stopping further fermentation.
- Reduce Dry Hop Levels – Shift some dry hops to the whirlpool (before fermentation) where they are less likely to create enzyme problems.
- Cold Store you Beer – Hop creep is temperature dependent, and if you can ensure that the finished beer is stored cold, it will significantly reduce the enzyme and fermentation activity.
- Design “Creep” into the Recipe/Process – Some brewers purposely under-attenuate and also under-carbonate their beers, assuming hop creep will occur in finished bottles/kegs. While this won’t solve potential diacetyl issues, it can help with over-carbonated/over-attenuated beers. It can be difficult to determine how much “creep” to expect however.
- Dry Hop Earlier – Though not much reasearch has been done on this, some brewers believe dry hopping closer to fermentation will give the hop enzymes and yeast time to act before the beer is packaged, reducing the scope of the hop creep problem.
- Use Sulfites/Sulfates to Reduce Yeast Activity – While not an option for naturally conditioned bottles, you can consider adding potassium metabisulfite (and possibly potassium sorbate) to kegs to inhibit further fermentation. These additives are widely used in the wine/mead industry as a preservative and also to inhibit further fermentation.
I hope you enjoyed this week’s article on hop creep. Thank you for joining me this week on the BeersSmith blog – please subscribe to the newsletter or listen to my video podcast for more great material on homebrewing.