tation, yeast is produced in excess. A part of this yeast is reused for a new hatch of wort, the remainder being discharged or treated as a by-product. The production yeast is typically reused several times (perhaps up to ten generations).Yeast TreatmentThe yeast treatment involves the following functions:• Yeast propagation, i.e. production of new yeast•Pitching of yeast to wort•Storage of production yeast•Storage and discharge of surplus and spent yeastStorageThe beer is stored for a certain period following primary fermentation.The objective of storage is to obtain:•Settling of yeast and other precipitates•Maturation•Stabilisation•CO2 saturationAfter storage, the beer is ready for filtration.CentrifugingFor beer with a very high yeast cell count, a centrifuge may he necessary for pre-clarification prior to filtration in order avoid blockage of the filters. Installation of a centrifuge may further reduce the consumption of kieselguhr, the filtration medium.CoolingThe cooling of beer prior to filtration is important in regard to shelf life, since a forced precipitation of haze particles takes place at this stage rather than hater in the bottles. Cooling must be controlled very carefully to ensure a constant beer temperature of approximately -10C to -l.5C.FiltrationThe purpose of filtration is to obtain the specified low level of initial haze in the beer and to facilitate prolonged shelf life.Filtration typically takes place in a kieselguhr (diatomaceous earth) filter. Perlites (volcanic residues) are sometimes used instead of kieselguhr. Diatomaceous earth performs the filtration, with the filter itself acting as support for the filter cake.The small diatoms form a rigid but porous filter cake which sieves out particulate matter as it passes through the filter. To prevent “blinding” of the filter, and to achieve extended filter runs, kieselguhr is continuously dosed into the u...
