Michael Kupetz (1), Thomas Becker (1), Bertram Sacher (1); (1) Chair of Brewing and Beverage Technology, Technische Universität München, Freising, Germany

Technical Session 12: Filtration
Tuesday, August 16  •  8:15–9:30 a.m.
Plaza Building, Concourse Level, Governor’s Square 14

Membrane filtration is a widely used method for beer clarification. Although this filtration type is used very successfully in various breweries, repeatedly problems in filter performance, pressure increase or membrane cleaning can be observed. The origin of procedural problems can often be found in the composition of unfiltered beer. These filtration-inhibiting substances originate in raw materials like barley malt, as well as yeasts and other microorganisms. Especially beta-glucans and arabinoxylans are involved in these fouling processes. The negative impact of increasing concentration and molar mass are well known from the literature. Nevertheless, a detailed description of membrane fouling and the resulting reduction in filter flow could not be found. For this reason, the development of an imaging technique for determination of membrane fouling caused by beta-glucans, arabinoxylans and volatiles are the focus of this study. The main advantage of this method is a deeper insight into type and structure of fouling layer on the membrane surface. Imaging was performed using confocal laser scanning microscopy. Membranes were stained with Calcofluor, a specific fluorescent dye for beta-glucans, Nile red, a specific fluorescent dye for fatty acid residues and a fluorescence antibody dye for arabinoxylan detection. Filtrations were performed with an automatic laboratory filter system using polyethersulfone and cellulose-nitrate membranes. Furthermore, structure and molar mass (MW) of polysaccharides were characterized by means of asymmetrical field-flow fractionation. Initially, development of methodology took place with the help of model beer solutions. Afterward, the method was validated with beer samples. The combination of these measuring methods resulted in conclusions about polysaccharide retention on polymer membranes depending on particle structure, size and concentration. It could be shown that filtration properties of polysaccharides were mainly influenced by their structural characteristics (spherical/random coil/rods). Cereal polyethersulfone glucans (0-600 mg/L) were able to pass through the membrane pores due to their random coiled structure (RMS plot ?? = 0.55, MW = 262 kDa), resulting in a cover layer of maximum 10%. Dosage of volatile components (ethyl decanoate and decyl acetate) to beta-glucan solutions resulted in a drop in filter performance (flow 200 mg/L = 7.8 g/cm2 × bar × min –> 3.0 g/cm2 × bar × min) and a layer formation up to 95%. Furthermore, significant differences in type of added volatiles were found for filtration behavior and covering layer. In addition to hydrophilic or hydrophobic interactions of beer ingredients with membrane material, influences on agglomeration behavior of beta-glucans was observed. Arabinoxylan had an impact on both, filtration performance as well as layer formation. Transfer of method to beer samples permits targeted conclusions about layer formation and shares of beer ingredients participating in filter blockage. A covering layer for both volatiles and beta-glucans could be measured between 10 and 99%.

Michael Kupetz graduated from the Technical University of Munich in 2011 as a degreed engineer for brewing science and beverage technology. In 2012 he started as a scientific assistant on his doctoral thesis at the Chair of Brewing Science and Beverage Technology (head of the chair: Prof. Thomas Becker). His research project is the “Comparative Identification of Inhibitory Substances in the Membrane and Diatomaceous Earth Filtration of Beer.” Furthermore, he is engaged in the development of new analytical methods in the brewing sector, with a main focus on polysaccharides from malt and yeast.