Filter Media Used in Beer Making
The material out of which the filter is made is what defines the beer clarity. This is also known as the filter aid. When the beer liquid is lautering, the grain and husk residue acts as a filter aid. When the sweet wort seeps through the grain bed, trapping the particles in the matrix, this is another instance of filter aid. The exact same principle applies to hop backs.
Diatomaceous Earth / DE / Kieselguhr: Diatomaceous earth has many uses besides being used as a filtration medium, like in gardens and as an additive in polishing materials.
Organic DE can be found in many products around the world. It is a natural sedimentary material comprised of the calcified skeletons of ancient sea plankton that have turned into silica.
Perlite: This material is similar in composition to DE. Its source material is volcanic rock that has turned into aluminum silicate.
Plate / Frame Filters:
These filters consist of plates wrapped in a cloth material. Hollow frames containing filter aid are proximal to the plates. Frames and plates are alternated for the entire length of the filtration process. The beer liquid is passed through the frames, and the particles are trapped. This is an extremely efficacious and cost-effective method of beer filtration.
The beer liquid in passed through highly compressed pads containing DE. Opaque beer flows in the one side of the compressed pad and the clear, filtered beer exits on the other side. Sheet filters contain less surface area compared to powder filters. It is for this reason that they are used as a secondary filtration method to “polish” the beer.
By using hollow mesh screen filters positioned vertically and horizontally along the central shaft of a cylindrical vessel, the DE can be pumped into the vessel in a process called pre-coating. The DE is caught by the mesh screens and then trap the particles when the beer liquid is circulated through. Fresh DE must be continuously introduced into the filtration process to ensure the screens don’t clog up with the beer solids.
Candle filters work in a similar way to screen filters. Instead of screens, candle filters have round hollow tubes containing narrow, open slots. The operation of both screen and candle filters are nearly identical, however, the increased surface area offered by the candle filters permits faster filtration and uses less filter aid. Candle filters trap most large particles, such as yeast and other inclusions. This is also a very successful method of beer filtration.
Constructed from polymer materials, membrane filters capture particles and produce extremely fine filtered liquids. They clog (blind) very quickly.
These are better than membrane filters as they pump the beer liquid across the surface area quickly, which leaves the surface relatively clog-freed. The downside to this convenience is they are expensive and complicated to operate.