Beer Department: What the Heck is Dry Hop Creep

Okay everyone, in an effort raise awareness on a serious brewing issue that’s becoming more and more widespread, we’re going to have to head down the rabbit hole of beer geekiness. To those who are unprepared for such nerdy travels, you might want to turn back now. But for the rest of you, those of you seeking far more knowledge about beer that will ever be useful in any practical sense, please join me on this beer-soaked journey. In fact, grab a beer before you continue reading!

Quick refresher: Dry hopping is the process of submerging hops in a finished beer, after the boil, in order to impart more hop aroma. Dry hopping has been popular for some time but has proven especially popular among this new wave of hazy, juicy,  unfiltered New England style IPAs that are prized for their aromatics. Some breweries even boast of double and triple dry hopping for massive aroma boosts.

Quick refresher #2: Certain enzymes in malted grain are responsible for converting long chain complex sugars into simple sugars that can be eaten by yeast and converted into alcohol (fermentation). These enzymes typically don’t convert all the complex sugars into simple fermentable sugars. Therefore, nearly all beers have at least some residual sugar in the finished beer.

So why did we need these refreshers and what do they have to do with one another? Well, the brewing community and scientists are rediscovering a brewing problem that used to be fairly common knowledge in the beer world. This problem is called “dry hop creep” and was recorded in brewing journals dating as far back as 1893. What brewers knew then and we’re re-learning now is that it appears as though the same enzymes that are in malted grain that convert complex sugars into fermentable sugars can also exist in hops. So when these enzymes in the hops are introduced to a finished beer via dry hopping, they begin converting the residual sugar in the beer into fermentable sugars. Having fermentable sugars in beer never caused a problem before recently because most beers were filtered and had no remaining yeast left behind. With the modern proliferation of unfiltered beers, however, the enzymatic power of hops are creating fermentable sugars that the leftover yeast in the can, bottle, or keg can begin fermenting.

Why worry about secondary fermentation? If one fermentation cycle is good, two must be great, right? Wrong. This phenomenon of dry hop creep creating secondary fermentations creates a truckload of problems for brewers, distributors, retailers and, most importantly, the consumer. A beer that might fall prey to dry hop creep is impossible to detect at the brewery. While it is theoretically possible for any unfiltered, dry hopped beer to experience dry hop creep and the subsequent unwanted secondary fermentation, most simply won’t because enzymes and yeast are fickle and all the stars have to align against us in order for dry hop creep to happen. A dry hopped, unfiltered beer will only exhibit symptoms of dry hop creep weeks after it has left the brewery. Sensory symptoms of these dry hop creep induced secondary fermentations include elevated alcohol levels, elevated acidity, and too much carbonation as well as a lack of sugar that will make the elevated acid even more apparent.

While these symptoms are problematic since they fundamentally change the beer in ways the brewers never intended and can’t control or predict, there are more troubling problems that can arise. Alcoholic fermentation also creates carbon dioxide, meaning that a secondary fermentation will fill the bottle or can with additional CO2 which may raise the internal pressure to such high levels that the container bursts. We call this a “bottle bomb” and people can be seriously injured by glass, aluminum, or corks. The other major problem we face from dry hop creep is the unchecked creation of diacetyl. Diacetyl is a natural intermediary byproduct produced by yeast during fermentation. The yeast typically scrubs all the diacetyl out of the beer during a rest, but it may not have the chance to do that to a packaged beer that’s kept cold because the cold inhibits some yeast activity. While the presence of diacetyl in small concentrations is acceptable in some English ale styles, it is a major fault in most other styles. Diacetyl tastes like movie theater butter and is extremely off-putting if you encounter it.

So what can we do about this newly re-awakened scourge of dry hop creep? Brewers and scientists are working hard to understand the intricacies of how it works and (ostensibly) developing ways to head it off at the pass, possibly through creative filtering techniques or the introduction of a preservative like potassium sorbate that will kill all the yeast it encounters. Until they publish the fruits of their findings, the best thing we can all do is to be vigilant about the sensory symptoms and the taste of diacetyl that I outlined above. If you ever taste a beer that seems off, please bring it to the attention of wherever you bought it. It is in the best interest of both the retailer and the consumer to pass all available feedback on to the brewery so that they can make corrections as needed. Stay vigilant, love beer, and beware the dry hop creep! Cheers!

Eric, Eastgate

Certified Cicerone®