The Freshening Power of Centennial Hops

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.