Finishing and Stability Session
Thomas Kunz, Technische Universität Berlin, Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany
Co-author(s): Kristian Schubert, Jörg Kaspar, and Frank-Jürgen
Methner, Technische Universität Berlin, Department of Biotechnology,
Chair of Brewing Sciences, Berlin, Germany
ABSTRACT: It is generally known that metallic ions like
iron or copper have an impact on oxidative beer stability. Metallic ions
can activate oxygen by electron transfer and have an influence on
radical generation due to their catalytic effect on the
Fenton-Haber-Weiss system. Our prior studies proved that after
consumption of the endogenous antioxidant potential the reaction
products of the Fenton system (Fe3+, Cu+, OH*
radicals) interact and generate metal ion complexes with oxidized, haze
active polyphenol-protein complexes, which are significant for visible
chill haze formation. The aim was to investigate the influences of
kieselguhr (KG), membrane, and Crosspure (CP) on iron content, radical
generation, chill haze formation, and oxidative stability. Another focus
was the new filter aid Divergan HM (DG HM), which can be used to reduce
metallic ions during filtration, to get a deeper view of the specific
properties and the possible procedures in application. Besides a
turbidity meter, AAS to analyze iron and EPR spectroscopy to determine
the influence on radical generation and oxidative stability were used.
The lowest iron content and influence on oxidative beer stability
resulted from CP, followed by membrane filtration. With a clear
distance, KG showed the strongest acceleration in radical generation and
the most negative effect on oxidative stability mainly caused by iron
entry. In comparison to KG filtration with comparable PVPP stabilization
CP showed a lower increase in chill haze formation under storage
conditions. DG HM was characterized by a fast reaction rate and
sufficient properties to reduce iron during filtration, but this kind of
reactions is directly connected to an increase in pH resulting in a
negative effect on oxidative beer stability. Additional trials
demonstrated that the aggradation of Divergan HM with acids could be a
useful process to eliminate the influence on beer pH. The combination of
organic acids like lactic and citric acids with DG HM showed the most
positive effect on oxidative and colloidal beer stability. Besides
slight oxygen entry during KG filtration the most negative effect on
oxidative beer stability results from iron entry. In contrast, CP
filtration led to a slight decrease in iron, which can be explained by
the discharge of iron ions involved in polyphenol-protein complexes. The
significantly lower iron content was jointly responsible for lower
chill haze formation during storage. DG HM only has advantages for
oxidative and colloidal beer stability if the negative effect on pH can
be compensated for with by acid aggradations. Additionally, the fast
reaction rate of DG HM can improve its application in the brewing
process. Our recommendation is to use DG HM with organic acids in a
continuous dose during filtration. An alternative procedure would be the
addition of a DG HM citric/lactic acid solution in combination with the
continuous KG dose.
After qualifying as a certified technician
in preservation engineering (1991–1993), Thomas Kunz completed his
basic studies in chemistry at the University of Applied Sciences, Isny
(1994–1995), and his basic studies in food chemistry at Wuppertal
University (1995–1998), before studying food technology at the
University of Applied Sciences, Trier (1998–2002). After graduating, he
worked as a chartered engineer in the area of ESR spectroscopy at the
Institute of Bio Physics at Saarland University (2002–2004). Since
January 2005, he has been employed as a Ph.D. student at the Research
Institute of Brewing Sciences, Berlin Institute of Technology
(Technische Universität Berlin). His main research focus lies in
analyzing radical reaction mechanisms in beer and other beverages using
ESR spectroscopy.
