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====The Freshening Power of the Hop (Hop Creep)====
Also known as "dry hop creep", it was first discovered in 1893 by Brown and Morris that dry hopping increases the ABV of beers and dries them out. It was proposed that the likely cause is the release of glycolytic enzymes that break down starches into sugars which viable yeast can then ferment. Brewers normally aim to control the final alcohol percentage in a beer through brewhouse operations rather than postfermentation dilutions with lower/higher alcohol beers or water. This approach to brewing is called "brewing to final gravity." Due to the need to have a predictable ABV for government regulatory reasons, unexpected fermentation is, therefore, a concern for many breweries <ref name="Kirkendall_2018">[https://www.tandfonline.com/doi/abs/10.1080/03610470.2018.1469081?journalCode=ujbc20 The Freshening Power of Centennial Hops. Jacob A. Kirkendall, Carter A. Mitchell & Lucas R. Chadwick. 2018. DOI: https://doi.org/10.1080/03610470.2018.1469081.]</ref>. Hop creep can also result in additional attenuation and higher carbonation after packaging, as well as diacetyl production.
Historically, there have been two studies published on the phenomenon of hops releasing glycolytic enzymes that break down starches during dry hopping: [http://barclayperkins.blogspot.com/2018/03/why-dry-hop.html Brown and Morris (1893)] and [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1941.tb06070.x Janicki et al. (1941)]. More recently, several researchers and brewers have revisited this phenomenon. Brown and Morris (1893) discovered that hops could break down maltodextrin, but failed to identify the enzymes from the hop plant material and hypothesized (probably incorrectly) that tannins were inhibiting the enzymes. Janicki et al. (1941) came to similar conclusions regarding the enzymes and tannin inhibitors, and they also concluded that the enzyme activity was independent of hop variety, geography, age, storage conditions, pH values between 4.1 and 4.8, and that one or more additional unknown factors were at play <ref name="Kirkendall_2018" />.
Kirkpatrick and Shellhammer (2018) found that the enzymes responsible for the conversion of dextrins into sugars include amyloglucosidase (removes glucose from non-reducing ends of α-1,4 and branching α-1,6 linkages, with a preference for α-1,4 linkages and longer chain oligosaccharides), α-amylase (hydrolyzes randomly along glucopolysaccharides to produce maltose, maltotriose, maltopentaose, and maltohexaose products from amylose as well as maltose, glucose, and branched dextrins from amylopectin), β-amylase (saccharifiying enzyme, cleaving maltose in small amounts from nonreducing ends of glucopolysaccharides, and to a minor extent, maltotriose), and limit dextrinase (debranches limit dextrins at α-1,6 linkages, producing linear α-1,4 chains which can further be degraded by the combined action of amylases). They were able to successfully extract them from Cascade pellet hops using commercially available assays (enzyme specific para-nitrophenyl blocked oligosaccharide substrates). The amount of α and β-amylase found in Cascade hops was well below that of malted barley, but within the range reported in other plant leaves. These enzymes are denatured by high temperatures, and as such would be denatured when boiling hops. They reported a similar increase in ABV of 1.3% after 40 days when dry hopping a beer with Cascade hops (and a decrease of 1.9°P) at a rate of 10 g/L. They also found that the hops contained glucose and a small amount of fructose, which accounted for a sugar increase of 0.02−0.03 °P per gram of hops. More studies on whether or not the amount of dry hopping has a large effect needs to be done, and whether or not warmer temperatures speed up the enzymatic breakdown of dextrins, and the authors hypothesized that the rate of dextrin break down could be slowed by dry hopping at lower temperatures <ref name="Kirkpatrick_2018">[https://pubs.acs.org/doi/pdf/10.1021/acs.jafc.8b03563 Evidence of Dextrin Hydrolyzing Enzymes in Cascade Hops (Humulus lupulus). Kaylyn R. Kirkpatrick and Thomas H. Shellhammer. 2018. DOI: DOI: 10.1021/acs.jafc.8b03563.]</ref>.
The exposure time of the beer to the dry hop material played a significant role in the breakdown of dextrins. Most of the breakdown of dextrins occurs within 5 days (+0.7% ABV), but continued slowly up until at least 40 days (+1.3%). They also tested removing the hops via centrifuge and storing the beer at 10°C or 20°C. Their results suggested that the effect of the enzymatic breakdown of dextrins by hops appears to only be active when in contact with the hops and that once the beer is removed then this breakdown of dextrins stops. The authors suggest that to avoid as much breakdown of starches and over-attenuation from dry hops as possible, brewers can limit the amount of time sits on the hops and reduce the temperature, however, it is also important to consider how this might impact the product's flavor and careful measures should be taken to balance the over-attenuation problem and overall beer quality <ref name="Kirkpatrick_2018" />. After removing the beer from the hops, a second diacetyl rest has been suggested as a way to clean up any diacetyl or off-flavors that the yeast produces from the additional fermentation during dry hopping <ref>[https://www.rockstarbrewer.com/how-dry-hop-creep-causes-diacetyl-in-beer-and-how-brewers-can-minimise-the-risk/ STEVE 'HENDO' HENDERSON. How “Dry Hop Creep” Causes Diacetyl In Beer and How Brewers Can Minimise The Risk. Rockstar Brewer Academy website. 09/03/2018. Retrieved 10/05/2018.]</ref>. Other recommended solutions to avoiding hop creep is crashing out the yeast before dry hopping.
See also: