Depth filtration removes particles from beer within the depth structure of the filter medium itself. The particles are either mechanically trapped in the pores or absorbed on the surface of the internal pores of the filtration medium. The filter media can be pre-made sheet filters or fine powder made of, for example, diatomaceous earth (DE), also known as kieselguhr, which is introduced into the beer and re-circulated past screens to form a filtration bed.
Surface filtration can be either absolute or nominal with a minimal depth capacity. Surface filtration consists of a thin membrane or a thin membrane covered with polypropylene or polyethersulfone in which particles are trapped in pores in the filter medium.
Singel- or Double-pass Filtration
The beer can undergo a single- or a double-pass filtration process. The double-pass filtration consists of two steps: a primary (rough) filtration, and a secondary (polish) filtration.
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