A charge modified cellulose filter mass, designated Cuno ZP820, has been developed to replace the cotton/asbestos Enzinger pulp pad used for sterile filtration of beer. The Enzinger pulp pad is prepared by hydropulping the filtration material and processing the pulp through several washing stages. A 4% makeup is added to compensate for losses. The pulp is finally pressed through a mould into pads which weigh 15 lbs and have a diameter of 20.25 ins. The pads are mounted into the filter in much the same way as a sheet filter. After a series of filtration runs with in situ backwashes, the pads are removed and reprocessed through the washing and pressing operations. The new filtration material had to be equilibrated with beer. This was done by repeated filtration, washing and repressing, replacing a few more of the old asbestos pads each time a new set of Cuno SP820 pads had reached equilibrium with the beer. The predicted schedule of operation called for less repulping and washing of the Cuno ZP820 material than the old asbestos material. Prior to change over 17.6 barrel/pad of Coors Beer and 52.5 barrles/pad of Light Beer were filtered between repulping of the pads. Initial trials with the new filter material resulted in only 14.4 barrels/pad for the Coors Beer and 23.9 barrles/pad for the Light beer. Success of the conversion of the sterile filters depended on the filtration efficiency of diatomaceous earth filters which should have passed a turbidity of no more than 5.0 mg/l silica. This was not the case. Optimising the D.E. filters to pass less than 5 mg/l silica resulted in greatly improved run lengths on the pulp filters: 40 barrel/pad for Coors Beer and 92.3 barrel/pad for Light Beer. Although the usage of diatomaceous earth was increased, the changeover to Cuno ZP820 generated overall cost savings: beer left in lines and filters was reduced by 24% as a result of increased run length; pulp makeup (in compensation for washing losses) was reduced; and reduction in manpower for replacing and washing the pulp pads.
Keywords: beer cellulose filter filtration pulp