THOMAS KUNZ (1), Stefanie Karrasch (2), Patricia Diniz (1), Frank-Jürgen Methner (1)
(1) Berlin Institute of Technology (TU Berlin), Department of
Biotechnology, Chair of Brewing Sciences, Berlin, Germany; (2)
University Hannover, Hannover, Germany
Our recent studies prove that the chill haze formation in stabilized
beers is correlated to oxidative processes and generated reaction
products of the Fenton-/Haber-Weiss reaction system after the
consumption of the endogenous antioxidant potential (EAP). Our
investigations clearly show that after the achievement of the EAP-zero
value the reaction products of the Fenton-/Haber-Weiss system, such as
Fe3+, Cu+, and OH•– radicals, start
interacting and generating metal ion complexes with oxidized,
haze-active polyphenol-protein-complexes. These complexes are
significant for the visible chill haze formation and the formation
depends on the temperature because of the low bonding forces.
Experiments which have been carried out under addition of metal ions
with specific oxidation steps such as Fe3+, Fe2+,
and others to beer within different pH ranges clearly show an increase
in haze, caused by these complexes. When facing different pH areas, the
highest haze formation was observed to be around the pH value of 3.5. It
seems that based on the stronger bonding forces of specific metal ions
in beer at a lower pH value a higher haze formation can be observed.
This phenomenon can be explained by more bonding sites which are
stabilizing the generated chill haze. However, the EAP consumption
proceeds more slowly, because there is a lower concentration of iron
ions available for the acceleration of oxidative processes and the
radical generation by the Fenton-/Haber-Weiss reaction system. This
results in a higher oxidative stability but later and stronger chill
haze formation. Contradictory experiments at higher pH areas resulted in
an earlier but lower haze formation due to the weaker bonding power in
the metal complexes with haze-active polyphenol-protein complexes and in
a significantly faster consumption of the EAP. Furthermore, experiments
with and without oxygen addition allow the conclusion that the oxygen
content is the most important factor for the formation of oxidized
polyphenol-protein complexes and their further complexation with
specific metal ions. In both cases (with and without oxygen addition),
the metal ions are responsible for a higher haze generation by metal ion
protein-polyphenol complexes. In separated chill haze from beer, an
agglomeration of stabilized organic radicals also could be detected by
EPR-spectroscopy. During the progress of beer aging, the oxidized
polyphenol-protein-metal ion complexes, including the stable organic
radicals, can react in radical reactions and form covalent bonds, one
way for converting chill haze to permanent haze. Additional filtration
trials with kieselguhr, CMF, and other filter aids show a clear
influence of different metal ion insertion on the haze formation and
oxidative beer stability. It has been shown that this research work can
give useful further knowledge about avoiding the undesired haze
formation in beer and other beverages.
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 starting to study 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 Biophysics
at Saarland University (2002–2004). Since 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.
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