The Freshening Power of Centennial Hops

ABSTRACT

The addition of hops to fermented beer in the presence of yeast may result in a secondary fermentation commonly referred to as “after-fermentation,” “dry-hop creep,” “ABV creep,” and “the freshening power of the hop” (FPH). The effect is most likely caused by glycolytic enzyme(s) in hops converting residual nonfermentable polysaccharides from malt into simple sugars that are then fermented by yeast. The FPH must be considered because the ethanol increase can exceed ±0.3% ABV tolerance set out in the U.S. Code of Federal Regulations. Furthermore, with unpasteurized and unfiltered beers, the commensurate rise in carbonation levels may lead to high pressures and potential consumer hazard. Development of a quantitative measurement system for FPH will be a critical component in an ongoing challenge in the industry to consistently ‘brew to final gravity’ while minimizing handling and blending prior to packaging and to ensure ABV compliance. The research presented herein was carried out to characterize the FPH of Centennial hops, identify key factors involved, compare the magnitude of hop-induced secondary fermentation in common dry-hopping processes, and provide a roadmap to develop a quantitative protocol to predict FPH potential in any given sample of hops. In this paper, we review the current understanding of FPH and present a relatively simple and affordable method to measure FPH impact to better understand and control ABV, CO₂ output, and diacetyl in beers that are dry-hopped in the presence of live yeast and brewed to final gravity.

KEYWORDS:

• ABV creep
• dry-hop
• dry-hop creep
• FPH
• freshening power of hops
• hop diastase
• Humulus lupulus
• secondary fermentation

Conflict of interest

Authors J. A. Kirkendall and L. R. Chadwick were employed by Bell's Brewery during the experimentation and manuscript preparation. C. A. Mitchell declares no conflict of interest.

Acknowledgments

The authors have engaged in countless discussions on this topic with brewing scientists, microbiologists, enzymologists, pharmacognosists, and brewers from Kalamazoo, throughout the United States and overseas. As of this writing, such discussions continue to provide further insight; we are still in awe and disbelief that only two papers have ever addressed this topic. We specifically acknowledge insights and/or support from the Technical Brewing team at Bell's (Tim Lozen, Matt Brower, and Andy Farrell) who dug deep into production data and characterized the “real-world” situation for us; Andrea Baillo, who provided the insight that VDK production occurs hand-in-hand with FPH; Todd Barkman (Western Michigan University), who provide the notion that tannin is “too blunt of an instrument” to shed light on this system; Jeff Pregenzer (freelance consultant) who provided the connection between FPH and diabetes research into amylase and glucosidase inhibitors; Jason Perkins, Zach Bodah, Tom Shellhammer, and Kaylyn Kirkpatrick for cluing us in to the work of Janicki et al.,^[17] the phrase “hop diastase,” and ultimately the “lost” work of Brown and Morris.^[16] We are extremely grateful to Mary Jane Maurice and her team at MaltEurop North America for valiant attempts to measure hop amylase activity for us using malt amylase assay(s). We further express our gratitude to Google (books.google.com) and the UC Davis Library for making available the ability to scour an enormous wealth of out-of-copyright brewing knowledge with unprecedented ease and to all the others whose insightful contributions have been overlooked. Thanks also to Rupert Baker and the Royal Society for providing us with a scan of the unabridged original publication of Brown and Morris^[16] from the Transactions of the Institute of Brewing. Finally, we want to express our personal gratitude to the Bell family for continuing a centuries-old tradition of breweries sponsoring basic research.