An important characteristic quality of beer is its brightness and its product durability. The beer of retail quality will be filtered after maturation , where a certain sedimentation of haze particles has taken place. Filtration belongs to the oldest technical treatment. It is just a separation of solid substances in a suspension. The suspension, consisting of a discontinuous phase, runs through a porous filter aid. While this process the solid particles (substrate) are sedimented by the filter aid and the filtered liquid (filtrate) leaves the filter aid in a clear
condition. It is distinguisched between surface- and depth-filtration. Cake filtration with a continious kieselguhr dosage belongs to the surface-filtration, but trub particles are also separated in the deeper regions of the cake. The pressure differential is the outer force which keeps the fluid on the run against the resistance of the filter, filter-aids and separated substrate.

Theory of Filtration (Poiseuille, Ergun, formation of the Filtercake)