O-47. Influence of special malt and coloring agents on the oxidative beer stability and aging components

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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