TLDR; Hop creep is a phenomenon in which dry hopped beer continues to ferment, resulting in over attenuation. Here are a few key points from recent research on hop creep.

• Bacteria and fungi associated with pellet hops produced amylases but did not produce hop creep

• There is Genetic potential of hops to produce endogenous amylase enzymes.

• Genes that appear to encode amylase found in Citra® hop cultivar.

• Significant impact on beer's aroma profile due to yeast-hop interactions and amylase activity

Brewers have long been aware of a phenomenon known as "hop creep" - an over attenuation caused by diastatic enzymes present in dry hopped beer which continue fermentation even after bottling or kegging, resulting in a sweet, sticky mess on tap lines or bottles that don't carbonate properly. Recently, researchers have conducted a search for the sources of these diastatic enzymes driving this process, uncovering some interesting findings along the way.

In study one, microbial cultivation and assays of amylase enzyme activity were used to isolate and identify microbes from pellet hops that are potential sources of amylases associated with but exogenous to hops (Humulus lupulus). Bacteria and fungi associated with pellet hops produced amylases but did not produce hop creep in assays using finished beer and fermenting wort with added microbes. However, Cannabis sativa flower was found to produce over attenuation of fermenting wort equivalent to that seen with hops!

Comparative bioinformatic analysis revealed the genetic potential of H. lupulus to produce endogenous amylase enzymes, as well as sequence similarity between amylases annotated in the C. sativa proteome and previously unidentified genes in H. lupulus - 13 genes likely encoding amylases were identified! PCR and sequencing further confirmed the occurrence of genes encoding α-amylase and β-amylase in the Citra® hop cultivar - providing evidence for a genetic basis for hop creep!

This research provides brewers new knowledge about controlling hop creep produced by endogenous amylases present within Humulus lupulus - enabling them to better understand this phenomenon while developing new approaches for controlling it.

The second study investigated impacts of part of the enzymatic content of hop (α-amylase and β-amylase) on yeast metabolism, and its potential for impacting aroma profile production during secondary fermentation. This has become a current trend in craft breweries as they frequently carry out heavy dry-hopping by increasing the hopping rate - which sometimes leads to uncontrolled and aberrant aroma profile production.

To assess this phenomenon, spectrophotometric methods were used to determine amylase activity within hop; liquid chromatographic methods (HPLC-ELSD) showed modification of the beer sugar profile through production of glucose and maltose as well as degradation of higher degree polymerization sugars; and gas chromatographic techniques (GC-ECD/FID) used vicinal diketones (diacetyl/pentanedione) as a marker of secondary fermentation. Finally, principal component analysis (PCA) demonstrated how this yeast-hop interaction significantly impacted beer’s aroma profile.

So what can be done?

The Brewers Association technical brief included the following information about a few possible (and practical) solutions.

Methods for controlling hop creep, to either accentuate or reduce it, involve manipulating wort composition, yeast strain selection and suspended cell concentration during dry-hopping, and dry-hop form, timing, contact time and temperature.

Arnbjørn Stokholm and Thomas H. Shellhammer Oregon State University, Corvallis, Oregon, 2020

Hop creep research is still top of mind for many, and with more information, better solutions will become available to control it.

Sources:

https://cdn.brewersassociation.org/wp-content/uploads/2020/05/Hop-Creep-%E2%80%93-Technical-Brief.pdf

Matthew T. Cottrell (2022) A Search for Diastatic Enzymes Endogenous to Humulus lupulus and Produced by Microbes Associated with Pellet Hops Driving “Hop Creep” of Dry Hopped Beer, Journal of the American Society of Brewing Chemists, DOI: 10.1080/03610470.2022.2084327

Trancoso I, de Souza GAR, dos Santos PR, dos Santos KD, de Miranda RMdSN, da Silva ALPM, Santos DZ, García-Tejero IF, Campostrini E. Cannabis sativa L.: Crop Management and Abiotic Factors That Affect Phytocannabinoid Production. Agronomy. 2022; 12(7):1492. https://doi.org/10.3390/agronomy12071492

Pierre-Yves Werrie, Sylvie Deckers & Marie-Laure Fauconnier (2022) Brief Insight into the Underestimated Role of Hop Amylases on Beer Aroma Profiles, Journal of the American Society of Brewing Chemists, 80:1, 66-74, DOI: 10.1080/03610470.2021.1937453