F. J. METHNER (1); (1) Berlin Institute of Technology, Berlin, Germany
Finishing and Stability
Saturday, June 7 - 8:00 a.m.-9:45 a.m.
Level 4, Grand Ballroom
Oxidative processes play an important role in flavor and haze stability. Beer off-flavors caused by oxidation have been attributed to the formation of specific aging compounds. The mechanisms may differ, but they are mainly caused by oxygen activation and the formation of reactive oxygen radicals (ROS) resulting from the Fenton and Haber-Weiss reaction in beer and other beverages. Therefore, in addition to the presence of oxygen, the intake of pro-oxidative catalytic Fe2+ and Cu2+ ions is the main reason for the acceleration of oxidation processes. Haze formation in bottled beer also is significantly influenced by oxidative processes and the complex formation of polyphenols and proteins with oxidized metal ions. Consequently, to improve haze and oxidative stability several technological aspects have to be taken into consideration. Primarily, oxygen ingress has to be avoided, as well as excessive heat load during beer processing. On the other hand, it is also possible to reduce the intake of iron and copper during beer production. One possibility is the complexation of transition metals to reduce their catalytic properties in oxidation reactions. In different practical trials it has been shown that the reduction of metal ions by incremental hop dosage during wort boiling led to reduced oxidation processes. Another important point seems to be the improvement of beer filtration. In the case of membrane filtration or use of an alternative (e.g., iron-free filtration aids are used instead of kieselguhr), an improvement in flavor stability is observable. Furthermore, haze stability could also be improved by this procedure. The use of tannins for stabilization in different brewing steps, like wort boiling or filtration, is able to improve haze and flavor stability by withdrawal of haze-active protein fractions and binding of metal ions in complexes. In this way the generation of radicals could be reduced, which could result in a better colloidally and oxidatively stable beer. By binding metal ions in complexes and removal, the generation of radicals can be reduced, resulting in better stability. The heat intake during kilning of malt, as well high thermal ingress of thermal load during wort boiling, causes increased levels of specific intermediate Maillard reaction products with reductone/endiol structures. It could be shown that these reductones unfortunately cause a fast reduction of oxidized Fe3+, resulting in accelerated oxygen activation by electron transfer and formation of pro-oxidative radicals. This kind of reaction is the reason for increased levels of radicals, which reduce flavor as well as haze stability when using roasted or dark malt types. The presented results are a practical aid for brewers to minimize oxidation and haze formation processes with a minimum of effort.
Frank J. Methner studied brewing science at Berlin University of Technology (TU Berlin) from 1975 to 1981. After these studies he worked as an operating supervisor at the Schlösser Brauerei. From 1982 to 1986 Frank was a scientific assistant with teaching duties at the Research Institute for Brewing and Malting Technology of VLB in Berlin. He has also conducted research projects and Ph.D. thesis on “Aroma Formation of Berliner Weissbier with Special Focus on Acids and Esters.” For 18 years, starting in 1987, he 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 TU Berlin.