Applications of High-Performance Liquid Chromatography in the Control of Beer Bitterness. I. McMurrough, K. Cleary, and F. Murray, Research and Development Department, Arthur Guinness Son & Co. Ltd., Dublin, Ireland. J. Am. Soc. Brew. Chem. 44:0101, 1986.

Isocratic high-performance liquid chromatography (HPLC) on reverse-phase columns was used to measure α- and β-acids in hops and hop products and also to measure iso-α-acids in stout worts and beers. For fresh hops and for hexane extracts of hops, the contents of α-acids measured by HPLC were similar to the lead conductance values, but for aged hops marked differences were found. The effects of different conditions on isomerization of α-acids in hop extracts boiled in different production-scale and laboratory-scale vessels were also studied. Decreases in α-acids were shown to follow first-order reaction kinetics, and the rates were influenced by temperature, pH, and the concentrations of divalent cations. Utilization of α-acids was higher in a production-scale superbarometric kettle at elevated temperatures than when worts were boiled at 100° C, cohumulone always being utilized preferentially. A rapid spectrophotometric method did not give an accurate measure of utilization because of variations in the amounts of non-iso- α-acid bittering substances present in iso-octane extracts of worts and beers. Tasting trials, however, indicated that the results of the rapid spectrophotometric method related to palate bitterness better than did measurements of iso- α-acids.

Keywords: α-Acids, β-Acids, High-performance liquid chromatography, Iso-α-acids, Isomerization, Utilization