Technical Session 04: Hops II Session
Cynthia Almaguer, TU-München, Germany
Co-author(s): Martina Gastl, Michael Dresel, Thomas Hofmann, and Thomas Becker, 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.
In 2008, Cynthia Almaguer completed her B.S. degree
in biochemical engineering at Jacobs University Bremen. She then started
her graduate studies in a collaborative project between the Institute
of Brewing and Beverage Technology (Thomas Becker), TUM-Weihenstephan,
and the Department of Food and Nutritional Sciences (Elke Arendt),
University College Cork. Her research project aims to understand and
reveal the contributions of hop hard resins in beer. A significant
portion of her research activities are directed toward the investigation
of the taste as well as the antimicrobial properties of hops.
