MBAA TQ https://doi.org/10.1094/TQ-57-3-1002-01 | 
VIEW ARTICLE
James Bruner (1,2), Joseph Williams (1,3), and Glen Fox (1,4). 1. Food Science and Technology Department, University of California, Davis, CA 95616, U.S.A. 2. 1221 Robert Mondavi Institute South, University of California, Davis, CA 95616, U.S.A. 3. 1107 Robert Mondavi Institute Brewery Winery Facility, University of California, Davis, CA 95616, U.S.A. 4. 2158 Robert Mondavi Institute North, University of California, Davis, CA 95616, U.S.A.
Abstract
Dry hopping beer to add aroma is a long-standing practice, and recently brewers have been adding greater quantities in an effort to get even more hop aroma. This has led to a seemingly new phenomenon termed “hop creep,” in which the dry hop addition leads to additional attenuation and lower final gravity than expected. Studies have shown this to be caused by endogenous starch-degrading enzymes in hops hydrolyzing unfermentable dextrins into fermentable sugars. This study describes two experiments: first, a study to confirm refermentation in finished beer was possible with added hops, and second, developing a forced fermentation method to speed up the process for assessing the degree of refermentation. In our study, laboratory-scale dry hopping was carried out by adding 10 g/L of pelletized T90 hops to both a commercially available ale and lager, in the presence of yeast, over the course of 30 days. Extract and alcohol measurements were made using an Alcolyzer at 1, 2, 4, 10, and 30 days during the trial in order to confirm refermentation. Four different hop cultivars were used, using one variety from each of the four categories established previously by an Oregon State study, ranking hops based on starch-degrading potential. Refermentation due to dry hopping in the presence of yeast was confirmed, with alcohol increasing as much as 1.06% v/v for the lager and 0.88% v/v for the ale over the course of the 30 days. However, the verification of the hierarchical classification by cultivar was inconclusive, because observed results in this study showed similar potential across all hop varieties. Further studies should be done to address these observations, the enzymatic potential of other advanced hop products, and the implications this information has on production brewing. Additionally, five different experimental brews with variable malt profiles and yeast selections were performed and forced fermentations done with and without hops. Each forced fermentation with hops showed a significant reduction in residual sugar and increase in alcohol when compared with the non-hopped sample. A simple method is proposed to determine the effect of dry hopping on secondary fermentation.
Keywords: dry hopping, hops, enzymes, hop creep, laboratory method, forced fermentation
