Dry Hop Creep, Over-Carbonation and Diacetyl in Beer

by Brad Smith on March 31, 2019 · 2 comments

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.

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{ 2 comments… read them below or add one }

Ted Bybel April 1, 2019 at 10:17 am

You wrote:

“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.”

Thanks for the data re: “hop creep.” It at least partially explains some issues I’ve noticed in some of my beers in the last year or so, but it also brought to mind some questions as well as possible solutions.

First question: I’m presently brewing an experimental ‘Dry PA’, hoping to get the final gravity below 1 P/0.998 SG by using Omega Yeast’s new strain OYL-501 “Gulo” which claims to attenuate to 85-90%. They advertise that the strain tests positive for var. diastaticus, so given enough time that alone should get FG down to 1.003~1.005. Additionally I’ve added amylase enzyme to the mash as well as amyloglucosidase to the mash (both denatured by mash out and the boil) and a small amount of amyloglucosidase to primary fermentation to drive the conversion of dextrines and other unconverted starches. OG of the mash was 1.055, so the final goal is a very dry, light bodied beer in the 6.5%-7.5% ABV range. Hops were Nelson Sauvin and Hallertau Blanc.

The fermentation has been robust but not out-of-control, maintaining a center core temperature of 68F (the recommended low optimum for the yeast) and SG dropped over 30 points in the first two days. My concern is with your statement about trace amounts of alpha and beta amylase being present in hops, and how that can persist in subsequent batches. The last time I brewed with a fast fermenting, highly attentive yeast was with a Nottingham strain which finished out well below 1.008 SG. It was meant to be a quick, quaffable, lightly hopped summer beer but turned into a phenolic shipwreck instead. The next several batches of beer I brewed had symptoms of diacetyl. I suspected pedio despite solid cleaning protocols, but ended up ditching the plastic fermenters and replacing with stainless steel. I also quit doing a dedicated secondary fermentation and instead now do a single stage ferment ~21 days with a trub dump after the first day or two followed by another around the time when I would have previously done a transfer to secondary. This has seemed to mitigate some of the issues associated with diacetyl (or pedio) which you described as possible consequences of hop creep or possible carryover of diastaticus strains. I’m sure the investment in stainless steel has been a driving factor.

The second question I have with regards to the blog post is how much of the trace alpha and beta amylase/limit dextrinase enzymes issue could be eliminated or at least reduced by substituting the dry hops charge with either distilled hop oils or a steeped hop tea? That is to say, are the enzymes primarily contained in the vegetal hop material as opposed to the oil distillates? Even if they are not, wouldn’t the heat of processing an oil or steeping a tea be sufficient to denature the enzymes? The concern here would be whether the time/temperature would be sufficient to eliminate the limit dextrinase enzymes.

One the one hand, normal pasteurization is one method suggested in the blog post, but I wonder whether it would be enough (unless it was a “flash” pasteurization). This concern relates back to my first concern: how can I eliminate var. diastaticus or limit dextrinase enzymes in my equipment from carrying over into subsequent batches utilizing standard sanitizing techniques, absent any ability to sterilize or autoclave my equipment?

After more than 25 years of brewing, I’m still trying to perfect my processes and procedures. They keep evolving and improving, though Beer Nirvana is an elusive goal. With your continued help, I may eventually get there.

Brew On!

Brad Smith April 1, 2019 at 11:04 am

Not sure I can answer all the questions but I believe some people have been experimenting with Cryo-Hops (aka Luplin powder) to reduce hop creep and believe it may help. In addition distilled hop oils don’t contain the enzymes as far as I know so those may also be good options.

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