The Bitter Qualities of Reduced and Nonreduced Iso-α-acids

Abstract

The temporal and qualitative bitterness of reduced and nonreduced iso-α-acids were measured in this study. A trained panel using a time-intensity protocol determined the temporal attributes of these compounds added to an unhopped lager beer. Principal components analysis and analysis of variance were applied at equibitter concentrations to determine differences among compounds (α = 0.10). Qualitative characteristics of the hop compounds, quinine sulfate, and caffeine were evaluated at equibitter concentrations using a free-choice profiling sensory protocol and were statistically separated through the application of generalized procrustes analysis (GPA). Caffeine and quinine were significantly harsher and less vegetative than the hop compounds. To further understand the differences among hop acids, the nonhop compounds were removed, and the qualitative data were reevaluated by GPA. Overall, tetrahydro-iso-α-acids were the most different in both temporal and qualitative aspects, with a longer duration and greater overall impact, and were described as harsher and more medicinal than the other hop acids. Hexahydro-iso-α-acids and iso-α-acids did not diverge significantly in time-dependant aspects but were qualitatively different, with hexahydro-iso-α-acids being more medicinal and metallic. Rho-iso-α-acids and iso-α-acids were similar temporally, except that rho had a greater initial intensity, whereas, qualitatively, rho-iso-α-acids and iso-α-acids were smoother and more vegetative than tetrahydro-iso-α-acids and hexahydro-iso-α-acids.