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.
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