Powder Filter Aids
Types of Filter Aids
There are two types of filter aids used in conjunction with powder filters, which are diatomaceous earth and perlite.
The most popular powder used for filtration is diatomaceous earth (DE), which consists of skeletal remains of single-celled plants called "diatoms" that contain silicon dioxide. The three classifications of diatomaceous earth are natural, calcined, and flux-calcined. The natural product is referred to as "diatomaceous earth" and the name "kieselguhr" is used only for the calcined grades of diatomaceous earth.
Perlite is alumino-silicate rock that has been expanded by heat treatment and later crushed and graded.
Safety and Disposal
Diatomaceous earth is very dangerous when inhaled; it can lead to irritation of the lungs and even long-term lung damage. It is considered carcinogenic to human beings and can also cause silicosis, a progressive and sometimes fatal lung disease, following long exposure to silica dust.
Powder Aid Filtration Process
Smaller breweries will usually empty the filter aid from the bags directly into the slurry tank adjacent to the filters. Larger breweries rely on dry-conveying the filter aid to the tank using screw or pneumatic systems.
In order to form a stable filter bed structure, it is first necessary to pre-coat the cloth or wire mesh screen with a number of DE layers of sequentially finer grades. The pre-coat is built up by circulating the beer through the powder filter and dosing it with DE until the emerging liquid is clear. This signals that the support mesh is fully bridged over or coated with DE.
Beer filtration is started when the pre-coats are established and the re-circulating liquid is clear. To prevent clogging of small pores of the filter and to achieve extended filter runs; filter aid is continually metered into the unfiltered beer as "body feed."
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