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Beer Filtration
Using Filter Aids
Background
Yeast, protein, and carbohydrate particles must be removed from the beer to achieve the necessary clarity. As the first step in filtration, powder filters are used in conjunction with a filter aid for removing these suspended particles. The filter aid is injected at the point where the beer stream, together with the yeast and other suspended solids, forms an incompressible mass referred to as the "filter-cake." The porous bed creates a surface that traps suspended solids, removing them from the beer. Filter aid, referred to as "body-feed," is continually added into the flow of beer to maintain the permeability of the cake. Not all of the particles will be trapped at the surface; some, especially the finer material, will pass into the filter cake and be trapped – a process referred to as "depth filtration." Depth filtration is not as effective as surface filtration, but is still a significant mechanism of filtration by filter aids. Powder filtration is generally regarded as providing the most economical form of filtration. The cost of filter aids is quite low, and long filtration cycles at high flow rates are possible.
Body Feed
Beer filtration is started when the precoats are established and the recirculating liquid is clear. To prevent clogging of small pores of the filter and to achieve extended filter runs; the filter aid is continually metered into the unfiltered beer as "body feed." In all cases, it is prudent to start the filtration cycle with a high dosing rate and decrease it as the differential pressure decreases across the filter bed. Underdosing of body feed will cause premature fouling of the filter, leading to a short filter cycle.
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