Filtered beer

Filtered beer refers to any ale, lager, or fermented malt beverage in which the sediment left over from the brewing process has been removed. Ancient techniques included the use of straw mats, cloth, or straws, and frequently left some sediment in the drink. Modern filtration, introduced at the end of the 19th century, uses a mechanical process that can remove all sediment, including yeast, from the beer. Such beer is known as bright beer and requires force carbonation before bottling or serving from a keg. In the United Kingdom a beer which has been filtered in the brewery is known as "brewery-conditioned," as opposed to unfiltered cask ales

Beer is mechanically filtered by flowing the beer through layers of filter material; the two main techniques are surface filtration and cake filtration. Filters range from rough filters that remove much of the yeast and any solids (e.g. hops, grain particles) left in the beer, to filters fine enough to strain colour and body from the beer. The normal filtration ratings are defined as rough, fine or sterile. Rough filtration leaves some cloudiness in the beer, but it is noticeably clearer than unfiltered beer. Fine filtration yields a beer which is nearly transparent and not cloudy, although observation of the scattering of light through the beer will reveal the presence of some small particles. Finally, as its name implies, sterile filtration is fine enough that almost all microorganisms in the beer have been removed. Beer which has been filtered is usually held in "bright tanks" at the brewery before bottling or additional treatment.

A beer which is filtered is stable, so all conditioning has stopped - as such it is termed "brewery-conditioned". Beers which are in contact with the yeast are known as bottle-conditioned or cask-conditioned.

Sheet filters use pre-made media and are relatively straightforward. The sheets are manufactured to allow only particles smaller than a given size through, and the brewer is free to choose how finely to filter the beer. The sheets are placed into the filtering frame, sterilized (with hot water, for example) and then used to filter the beer. The sheets can be flushed if the filter becomes blocked, and usually the sheets are disposable and are replaced between filtration sessions. Often the sheets contain powdered filtration media to aid in filtration.

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Wikipedia