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.