Beer clarification by microfiltration - product quality control and fractionation of particles and macromolecules

Beer clarification by microfiltration demands a finely balanced retention o f colloidal particulates (yeast cells, chill haze flocs, etc.) and transmis sion of soluble macromolecules including carbohydrates, proteins, flavour, and colour compounds which give the "whole some" quality of a beer. The req uired porous transmission of these macromolecular species led to an unavoid able, complex and dynamic in-pore membrane fouling in terms of fouling cons tituents, formation, structure and kinetics, which are the main obstacles i n obtaining an economically viable flux and consistency in permeate quality . This experimental study was carried out with the aims of understanding the dynamic inter-relation between flux, fouling and system selectivity during a cross-flow beer microfiltration process so that an effective operating st rategy for flux optimisation could be formulated in conjunction with the pa rallel objective of good product (permeate) quality control. Tubular cerami c membranes (Ceramem) with nominal pore diameters of 0.2, 0.5, and 1.3 mum were used. Simultaneous measurement of flux and permeate qualities, such as specific gravity and chill haze level enabled identification of the effect of anti-fouling techniques, such as backflushing on transmission of essent ial beer components and on the filtered beer quality. The experimental evid ence lead to an understanding that the drastic flux enhancement achieved by employing backflushing at reversed membrane morphology was associated with enhanced solute transmission which could, without careful control, upset a balanced transmission of essential beer components and the retention of un wanted "chill haze" components. Further operating parameters and varying sy stem configurations were investigated over their effect on both flux perfor mance and system selectivity. These include membrane pore size, filtration temperature, and the addition of an amorphous silica particles as coagulati on agent for hydrophilic proteins. (C) 2001 Elsevier Science B.V. All right s reserved.