M-30: Characterization of horizontal layers of the lautering filter cake

J. ENGSTLE (1), M. Kuhn (2), P. Först (2); (1) Technische Universität München, München, Germany; (2) Technische Universität München, Freising, Germany

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Lautering is still a kind of “black box” operation in the brewing process. The separation of soluble and insoluble parts of the mash is still not completely understood. By sedimentation of insoluble components, a cake layer is formed on the filter medium. Due to different particle sizes and density differences the cake consists of horizontal layers of varying characteristics. This cake is used for the following solid-liquid separation by filtration as a filter cake. Filter cake formation, porosity, composition and the role of these cake layers for the filtration step have been not analyzed enough, so lautering is often considered the brewhouse’s bottle neck. For the formation of lautering filter cakes a laboratory-scale lauter tun was used. The cakes were fragmented in horizontal layers by a cutting device. Layer porosity was measured gravimetrically. Filter cake resistance of single layers was detected by filtration with constant pressure. Laser diffraction spectroscopy and sieving were used to determine particle size distributions in different layers of the cake. X-ray microtomography allowed a three-dimensional analysis of the cake structure. The behavior of the cake layers under compression was observed by a compression cell. Statements found in various references that the flow rate-limiting layer is the upper most layer, consisting of fine, jellylike particles, could be acknowledged. Filter cake resistance is multiple times higher in these layers than in the lower layers, consisting of coarser particles. X-ray microtomography shows this arrangement in different layers. Cake porosity decreases with the height above the filter media. For analyzing porosity a chord-length distribution was calculated. According to the decreasing porosity the pore size decreases also with increasing height, until no porosity or pore size is measurable. Blocking layers between coarser layers also were measured. A correlation between these blocking layers in the depth of the cake and the amount of fine particles in these specific layers could not be observed. Nonetheless, particle shape could be related to the blocking property of this layer.

Jörg Engstle studied at the Technical University of Munich. He graduated with a degree in brewing and beverage technology. Jörg is currently a Ph.D. student at the Chair of Process Engineering of Disperse Systems in Weihenstephan, Germany.

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