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In recent years, proprietary hops (Citra, Simcoe, and Mosaic) become the most sought-after hops among brewers due to their excellent aroma. However, they are restricted to the owners unless other growers purchase the costly licensing agreements. Many public hops are available to the growers without any additional costs, but their aroma is difficult to match to the proprietary hops. Although proprietary and public hop varieties are unique in their aroma profiles, all hops varieties contain similar volatile compounds, merely differ in the quantity of different individual compounds. The main objective of this thesis was to investigate the feasibility of matching the aroma of proprietary hops by blending a number of public hops. The aroma profiles of hops were detected by flavor-detection methods including Gas chromatogram-flame ionization detector (GC-FID), Gas chromatography-mass spectrometry (GC-MS), Headspace solid-phase microextraction/gas chromatogram–mass spectrometry (HS-SPME/GC-MS), and sensory evaluation. The modeling was achieved by applying a mathematical optimization technique – quadratic programming. For matching proprietary hop aroma, public hop pellets or hop oils were mixed with different percentages in models (e.g., proprietary hop A= x% public hop B + y% public hop C + z% public hop D). The aroma of Citra pellets was closely mimicked by 25.2 % Eureka, 33.2 % Centennial, and 36.7 % Triple Pearl. The aroma of Simcoe pellets was closely mimicked by 10.0 % Cascade, 50.0 % Us Goldings, 71.1 % Centennial, and 10.4 % Triple Pearl. The aroma of Mosaic pellets was closely mimicked by 6.5 % Eureka, 84.8 % Centennial, and 3.0 % Triple Pearl. In addition, it nearly mimicked the Citra oil with 35.2% Brewers Gold, 5.2 % Cashmere, 32 % Centennial, and 35.7 % Triple Pearl. The obtained aroma of models was validated in the beers with both the high similarity of aroma profiles (R2 > 0.90) and sensory evaluation. This research provided a novel idea on the application of mathematical optimization and flavor-detection technologies for modeling the aroma of hops. The success of this project can increase the usage of public hops and extend such an application to other flavor developments.
Advisor: Changmou Xu