Presenter: Thomas Kunz, Technische Universität Berlin,
Department of Food Technology and Food Chemistry, Chair
of Brewing Science, Berlin, Germany
Coauthors: Till Stoffregen, Cecilia Cruz Palma, Chaochao Xu,
and Frank-Jürgen Methner, Technische Universität Berlin,
Department of Food Technology and Food Chemistry, Chair
of Brewing Science, Berlin, Germany
The effects of special malt and coloring agents on oxidative
beer stability and flavor during storage are controversially
discussed in the literature. The Maillard reaction products
generated by high temperatures during kilning or roasting
of malt and then further by boiling processes are jointly
responsible for the characteristic color and flavor of the final
beer. Due to their complexity, these products can participate in
numerous reactions during brewing and beer storage. Thanks
to our previous investigations using roasted/color malt or the
addition of caramel color and roasted malt beer in the brewing
process, it was possible explain the contradictory interpretation
of the influence of specific intermediate Maillard reaction
products with a reductone/endiol structure on reduction power
and pro-oxidative activities. Novel investigations using ESR
spectroscopy (EAP and T values) and different methods for
the determination of reduction power or potential (Chapon,
MEBAK) demonstrate the correlation of two significant key
factors in special malt and coloring agents that are responsible
for the effects on oxidative beer stability. One is the extremely
high iron entry caused by the significant iron release from malt
during the kilning and roasting process. The second factor
arose from the strong reduction properties of specific Maillard
reaction products with a reductone/endiol structure that can
rapidly reduce oxidized metallic ions such as Fe+3 to Fe+2. Both
factors are responsible for an acceleration of oxygen activation
and intensification of the Fenton-Haber-Weiss reaction system.
Consequently, an acceleration of oxidative processes and a
stronger radical generation of very reactive radicals (OH·) can
be observed in the wort and beer matrix. This fact results in
a faster consumption rate of specific antioxidative substances
such as SO2 and, thus, lower oxidative beer stability indicated
by the decrease of the EAP value and a stronger increase in
specific aging compounds during storage, especially typical
oxidation indicators like 3-/2-methylbutanal, phenylethanal,
etc.) analyzed via GC-MS. Altogether the results present the
influence of the reduction power and pro-oxidative effects of
special malt and coloring agents like caramel color, roasted
malt beer in the wort, and beer matrices. Additionally, the
study gives advice on how to reduce or respectively avoid the
pro-oxidative effects through optimized handling during the
brewing process or the use of alternative coloration substances
to adjust beer color.
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 Bio
Physics 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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