Program Book - Master Brewers Association of the Americas

their maturation capacity and to save both energy costs and the
environment by making cold maturation obsolete.
P-199
The influence of the Fenton- and Haber-Weiss-reaction system
on haze formation in stabilized beer
THOMAS KUNZ (1), Stefanie Karrasch (2), Frank-Juergen Methner
(1)
(1) TU Berlin/VLB Berlin, Berlin, Germany; (2) TU Braunschweig,
Braunschweig, Germany
During the last 40 years various working groups have described
generally accepted models for haze formation mechanisms in beer.
The interactions between polyphenols and proteins have been
identified as the main reaction system. Based on this cognition the
brewers utilize PVPP and silica gel to stabilize beer. Nevertheless
chill haze or permanent haze formation can be observed in
beer after a certain storage time. It is also well known that the
presence of oxygen, higher temperatures, light, metallic ions and
mechanical influences accelerate haze formation during storage,
but the responsible reaction mechanism could not be determined
satisfactorily up to now. Also the described approach according to
an oxidation reaction which activates the polyphenols by generating
ortho-chinons, which are able to react with other beer ingredients, is
not able to explain haze formation in stabilized beer completely. Our
investigations on detached haze by solid measurements using ESR
at 77 K have approved ESR signals in haze, which cannot be found in
filtrate. The different ESR-signals are caused by stabilized organic
radicals and ions like Fe 3+ . These results indicate an interrelation
with the Fenton reaction system, resulting in iron-(III)-ions and
hydroxyethyl radicals. The application of several analytical methods
(ICP-OES, ESR, gel electrophoresis) helped to characterize the
composition of chill haze and permanent haze during storage.
Based on the additional comparison of the development of the
endogenous antioxidative potential (EAP) and haze formation
during shelf life, an important coherence in the haze formation
of stabilized beer could be observed. The analytical methods have
clearly demonstrated that oxidative processes are the major cause
for colloidal haze formation in stabilized beer. On the basis of the
former postulated haze theories, a mechanism was mapped out, in
which the reaction products of the Fenton and Haber-Weiss-reaction
system in beer play a central role in the formation of haze during
the beer aging. After consumption of the EAP, the reactive hydroxyl
radicals and secondary radicals are generated by the catalysis of
iron and copper ions. At the same time the formation of iron-(III)
and copper-(I)-ions, as well as oxidation of beer ingredients and
formation of stabilized organic radicals occurs. Due to the complex
formation among oxidized polyphenol-protein-complexes and iron-
(III) as well as copper-(I)-ions the development of chill haze can
be observed. During the progress of beer aging the oxidized ironpolyphenol-protein-complexes,
which include the stable organic
radicals, react with each other by attendance of radical reactions
and formation of covalent bonds. This process describes the
conversion of chill haze to permanent haze. Based on the results the
effectiveness of influencing factors on haze formation in stabilized
beer can be better understood, and the arrangements to increase
colloidal beer stability can be optimized.
After qualifying as a certified technician in preservation engineering
(1991–1993), Thomas Kunz completed his basic studies in chemistry
at Isny University of Applied Sciences (1994–1995) and his basic
studies in food chemistry at Wuppertal University (1995–1998)
before starting to study food technology at Trier University of Applied
Sciences (1998–2002). After graduating, he worked as an engineer
(Dipl.-Ing. FH) in the area of ESR spectroscopy at the Institute of
164
Biophysics at Saarland University (2002–2004). Since January
2005, he has been employed as a Ph.D. student at the Research
Institute for the Technology of Brewing and Malting at VLB/
Technical University of Berlin under the supervision of Professor
Methner. His main research focus is analysis of radical reaction
mechanisms in beer and other beverages using ESR spectroscopy.
P-200
Colloidal stability—The effect of excess stabilization
MORITZ PÖSCHL (1)
(1) TU Munich, Lehrstuhl für Technologie der Brauerei II, Germany
Preservation of colloidal stability in bottom fermented and
filtered beers can be regarded as one of the biggest challenges
breweries have to meet in the current beer markets, which exhibit
an ever increasing tendency toward globalization combined
with rising consumer-expectancy of the clarity and quality of
beer. One focal point of the current research is the improvement
of the predictability of haze formation before filtration and
stabilization to enable more specific beer stabilization and prevent
excess stabilization. This in turn would lead to reduced costs
for stabilization agents and the preservation of health-relevant
substances such as polyphenols. The aim of this study is to highlight
the effect of excess stabilization on the composition and quality
of the resulting beers. In this context unstabilized beer has been
compared to PVPP-stabilized (50 g/hl) beer and to double stabilized
beer (PVPP 50 g/hl, Xerogel 100 g/hl), each beer deriving from
the same batch (Pilsner type). Analyses included monitoring of the
phenolic spectrum and protein fractions as well as measurement
of the reducing power, foam stability and colloidal stability. PVPP
stabilization resulted in an obvious decrease in total polyphenols,
flavanoids and haze relevant flavan-3-ols (measured by HPLC) but
did not influence the concentrations of phenolic acids. Stabilization
with silica gel induced a significant decrease in tannin-precipitable
proteins; the reduction of total nitrogen was quite low. The
measurement of the reducing power, using two electrochemical
methods, brought out a significant deterioration of antioxidative
capacity stabilizing with PVPP compared to the unstabilized beer.
Foam stability was slightly worse after stabilizing with silica gel. The
force test (0°C/40°C) in the unstabilized beer showed an increase
in haze of 2 EBC already after 2 warm days; the stabilized samples
can be regarded as excessive stabilized, showing an increase in haze
lower than 0.2 EBC even after 16 warm days. It has been shown that
stabilization should be done in a more specific and selective way to
produce higher quality beer combined with lower costs.
Moritz Pöschl was born in Munich in 1978. After studying brewing
and beverage technology at the Technical University Munich, he
is now (since 2004) a scientific assistant at the Chair for Brewing
Technology II. The focal points of his research are the enhancement of
stabilization in a technological/natural way and the improvement of
the predictability of colloidal stability.