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​14. A study of the functionality of hop epsilon-resins as a novel brewing product

Cynthia Almaguer, TU-München, Germany

 

ABSTRACT: 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 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. Hitherto, research has primarily focused on studying the impact on beer properties of the major hop bitter acids (alpha- and beta-acids) extracted from 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. It has been established that the hard resin is mainly composed by oxidation products insoluble in hexane. However, to date, the brewing value of these products and their contribution to beer quality has not been determined. In this study, through the development of novel fractionation techniques, it was possible to further purify the hard resin extract. From this purification process the delta-resin and epsilon-resin were obtained, and from each resin, it was possible to further extract it to retrieve 11 fractions. It is the purpose of this work to determine which of and to what extent the fractions found in the hard resins contribute to beer quality. It is known that certain hop compounds possess antimicrobial activity. To the brewer, this is of great value since by addition of selected hop compounds, these antimicrobial properties can be exploited to enhance the microbiological stability of beer. Therefore, the minimum inhibitory concentration as well as the bitter intensity of the 11 fractions were independently determined and correlated. The fractions that proved to be active were further purified, and the obtained pure compounds or subfractions were tested for activity. As a result, inhibitory and taste active hop compounds or subfractions present in the hard resin could be identified. It was seen that the epsilon-resin was more active than the delta-resin. For this reason, the functionality of the total epsilon-resin as a brewing product was examined, and finally, the epsilon-resin contribution to the microbiological stability of beer was assessed. To achieve all this, brewing trials were conducted in which hop pellets were replaced with an epsilon-resin rich extract. In these laboratory scale experiments, it was possible to determine that independent of the addition point, the epsilon-resin contributes to the microbiological stability of beer. In the different sensory evaluations of the fresh beers, it was shown that addition of this resin had a positive impact on all taste relevant attributes. Although in terms of microbial stability the addition point had no influence, from the sensory point of view, the beer in which the resin was added upon boiling was generally preferred. As a result of this study, novel hop products that positively contribute to beer taste and stability were proposed.