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Contributions of Hop Hard Resins to Beer Quality
C. Almaguer, M. Gastl, E. K. Arendt, Th. Becker

The brewing value of hops (Humulus lupulus) is primarily attributed to the flavor- and bitter-active compounds found in the resins. These resins are synthesized and accumulated in the lupulin glands of the female hop cones. Early work on the fractionation of hop resins, based on the solubility of resins in various organic solvents, classified them into soft resins and hard resins. The hard resin is mainly composed by oxidation products insoluble in hexane. Hitherto, research has primarily focused on studying the impact on beer properties of the major hop bitter acids (α- and β-acids) present in the soft resin. Therefore, little information is available on the functionality of the hard resin and for years it has been considered of no brewing value. Further the exact role of the hard resins in the brewing process is not well understood. For these reasons, a detailed study of the hard resins contributions to beer quality was performed. Brewing trials were conducted in which hop pellets were replaced with resin rich extracts. Thereby it was possible to establish the brewing potential of the hop hard resin. There is evidence to suggest that further degradation products were formed upon vigorous boiling of the hard resin. It is believed that upon extended storage periods these ultimate oxidation products are also formed. From the analytical data it was established that the hard resins positively contribute to the foam stabilizing properties. Furthermore, in the different sensory evaluations of the fresh beers, the hard resins proved to impact all analyzed attributes. With increasing hard resin concentrations, higher bitter intensities were recorded. The perceived bitterness of the hard resin beers suggested that the hard resins have a high bittering potential. Finally, at high hard resin concentrations a pleasant bitterness was produced and the overall flavor stability of the beers was high.

Descriptors: hops, hard resins, soft resins, bitterness, flavor stability

BrewingScience - Monatsschrift fr Brauwissenschaft, 65 (July/August 2012), pp. 118-129