Open Access Thesis
Master of Science (MS)
Humulus lupulus, a climbing perennial vine, is grown and used extensively in the brewing industry as a natural preservative and to impart the bitter flavor and aroma typically found in beer. The flowering cones of the female H. lupulus plant are of particular importance as they contain the main flavoring compounds, especially the organic compounds known as -acids: humulone, cohumulone, and adhumulone. There are several known methods for the extraction of the -acids described here, with the highest yield of 37% on the lab scale from organic solvent extractions. During the brewing process, these chemicals undergo an isomerization reaction into the iso--acids: isohumulone, isocohumulone, and isoadhumulone. This reaction is first-order and proceeds slow enough that it can be monitored by nuclear magnetic resonance (NMR) spectroscopy. From this, the rate constant, k, at 80 °C was determined to be 2.9x10-3 s-1, although this value is over 200 times the rate reported in literature. More research is necessary to fully understand the reason for the elevated rate.
Fink, William, "A preliminary investigation of the chemistry of hops: Methods for extraction and alpha-acid isomerization kinetics" (2017). Master's Theses and Doctoral Dissertations. 753.