Graduate Thesis Or Dissertation
 

The Influence of Regional Identity and Harvest Timing on Hop Dextrin-Reducing Enzyme Activity

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/x920g5783

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  • The hydrolyzation of dextrins in beer caused by hop-related enzymes added during dry-hopping creates challenges for brewers interested to make hop-forward beer styles like India Pale Ales (IPAs). The fermentation of newly liberated fermentable sugars slows production and leads to over attenuation, higher alcohol and carbonation, and, potentially, buttery off-flavors from increased diacetyl concentrations. As such, brewers have widely encouraged research into the factors that influence so-called “hop creep.” While several studies have investigated how growing conditions (terroir) and harvest timing (maturity) impact the chemical and sensorial properties of hops, there is limited information assessing how those factors influence the dextrin-reducing enzyme activity of hops. The first manuscript analyzed how hop variety and growing conditions influence hop creep potential. Cascade and Mosaic® hops from 35 fields located in two states (Washington and Oregon) were collected over two harvest years (2020 and 2021), along with information regarding weather, climate, soil type, and farm management decisions (fertilizer, herbicide, fungicide, and insecticide use). Data from 25 soil, 14 management, 13 climate, and 27 chemistry variables were compared against the hops’ dextrin reducing enzymatic potential from a bench-top dry-hopping assay. Hop variety explained the most sizeable portion of the variability in enzyme activity between samples (two sample t-test p-value = 1.18 × 10 -14) with Cascade hops being approximately 60% higher on average than Mosaic® hops regardless of growing region or harvest year. ANOVA performed on the farm-related variables also showed statistically significant interactions with enzymatic activity (p-values of 7.82 × 10-9 for Cascade and < 2 × 10-16 for Mosaic®), though there was little clarity with respect to the specific “terroir” variables that might relate to hop creep. The second manuscript analyzed how harvest timing decisions influence the hop creep potential of the Citra® cultivar, as well as other chemical and sensorial characteristics. Citra® hops were harvested weekly at seven different time points throughout each hop picking season over two or three consecutive harvest years from three fields in Yakima Valley, WA. For each time point, field, and year, the dextrin-reducing enzyme activity of hops was measured using a bench-top dry hopping assay. A selection of relevant hop quality chemical and sensorial measurements were also taken, such as total essential oil content, hop acids concentration, hop storage index, volatile profile by GC-FID, and check-all-that-apply (CATA) sensory analysis. Dextrin-reducing enzyme activity for the Citra® hops decreased as much as 66% as time-on-bine increased, regardless of field location or harvest year. This finding suggests that leaving hops on the bine longer could reduce the impact of hop creep in the brewer. However, sensorial analysis mitigated the impact of this conclusion as Citra® hops underwent a rapid change from early-harvested hops exhibiting green vegetable-like characteristics such as “grassy,” “green pepper,” and “melon,” to late-harvested hops displaying pungent “onion,” “garlic,” and “sweaty” aromas. Citra® hops harvested near the middle of the picking season had the best combination of the chemical, biochemical, and sensorial traits most sought by brewers. These studies add to the increasingly convincing body of scientific evidence that variations in regional growing conditions and harvest timing decisions are important indicators of hop quality. Further research is needed to better understand causal interactions between farm, soil, climate, and management practices and dry-hop-induced dextrin-reducing enzymatic activity. Hop growers and brewers may use the information presented herein to make more informed decisions regarding the best practices for growing and brewing with the highest quality hops.
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