Beer is a most popular fermented alcoholic beverage which is made from barley. Its fermentatıon occur in two type as top and bottom fermentations. Traditionally, there are two types of beer yeast, based on their physical behavior: ale yeast the top fermenting type, Saccharomyces cerevisiae and lager yeast the bottom fermenting type, Saccharomyces carlsbergensis.Top fermenting yeast flocculate and rise to the top of the fermenting wort producing a stable yeast head, while bottom-fermenting yeast flocculate and settle on the bottom of the fermenter.
However, some modern ale strains are selected for use in cylinder or conical fermenters because they are poor head formers, the yeast crop being harvested from the base of the fermenter.The factors that affect fermentation conditions are time, wort temperature, volume, fermenter design, pressure, agitation, and currents in the wort. Extended lagering periods and the addition of flocculation aids both greatly reduce yeast and haze loadings. Centrifuges are mainly used in the preliminary reduction of suspended particles, primarily in yeast before sending to the conditioning tanks. Although these methods are very effective in prefiltering the beer, a final filtration is needed to remove residual yeast, other turbidity-causing materials, and microorganisms in order to achieve colloidal and microbiological stability.If there is a significant quantity of suspended material to be removed, powder filters using diatomaceous earth or perlite must be employed. Although powder filters can produce beer of acceptable brilliance after a single filtration, a two-stage filtration