Presenter: Frank-Juergen Methner, Berlin Institute of Technology, Institute of Biotechnology, Chair of Brewing Sciences, Berlin, Germany. Coauthor(s): Thomas Kunz, Berlin Institute of Technology, Institute of Biotechnology, Chair of Brewing Sciences, Berlin, Germany.
Filtration trials with kieselguhr, CMF, and other filter aids have shown a different influence on the haze formation and oxidative stability of beer. Our recent studies have shown that in stabilized beer the chill haze formation is correlated with oxidative processes and reaction products originating from the Fenton-Haber-Weiss reaction (Fe3+, Cu+, OH·) system after the consumption of the endogenous antioxidant potential (EAP). These reaction products start interacting and generate metal ion complexes with oxidized, haze-active polyphenol-protein complexes. These complexes are significant for their visible chill haze formation. The formation is dependant on temperature, because of the low bonding forces. Based on the stronger bonding forces of specific metal ions in beer at lower pH values a higher haze formation can be observed. This phenomenon can be explained by more bonding sites that stabilize the generated chill haze. However, the EAP consumption proceeds slower, because there is a lower concentration of iron ions available for the acceleration of oxidative processes and the radical generation caused by the Fenton-Haber-Weiss reaction system. This results in a higher oxidative stability, but later and stronger chill haze formation. Contradictory to that, 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. The results show that a lower availability of iron ions generally leads to a higher oxidative stability. Based on the described reaction mechanism the metal ion insertion during filtration has an important influence on the oxidative beer stability and haze formation. A high metal ion insertion with kieselguhr filtration leads to an acceleration of oxidative processes by the Fenton-Haber-Weiss system and results in a faster consumption of the antioxidative potential. Depending on the metallic ion content a stronger chill haze formation by oxidation and the formation of metal complexes with oxidized haze active polyphenol-proteins can be observed in beer stabilized with PVPP. In comparison to the kieselguhr filtration combined with PVPP stabilization, a new filter aid (polystyrene combined with PVPP) without metal ion insertion was used for beer filtration. The results clearly demonstrate higher oxidative beer stability and lower radical generation mainly caused by lower metallic ion content. Additionally, significant higher colloidal beer stability could be observed. It has been shown that this research work can provide useful knowledge about the increase in oxidative beer stability using a new filter aid and avoiding the undesired haze fermentation in beer and other beverages.
Frank-Juergen Methner studied brewing science at Berlin Institute of Technology (TU Berlin) from 1975 to 1981. After his studies, he worked as an operations supervisor at the Schlösser Brauerei. From 1982 to 1986 he as a scientific assistant with teaching duties at the Research Institute for Brewing and Malting Technology of the VLB. His Ph.D. thesis was on "Aroma Formation of Berliner Weissbier with special focus on Acids and Esters." For 18 years, starting in 1987, Frank-Juergen held a leading position as a director at the Bitburger Brauerei, Bitburg, Germany, with responsibilities in fields such as technology and quality assurance. Beginning with the winter semester of 2004/2005, he took over the Chair of Brewing Science at the Berlin Institute of Technology.