Filtered beer has been deliberately cleaned of significant contact with yeast through filtration. The process of filtering removes carbonation so that the beer requires force carbonation. Mechanical filtering and pasteurisation of bottled beer started at the end of the 19th century. Beer in which yeast is no longer in suspension is known as bright beer. Beers may also become "bright" by waiting for the yeast to drop of its own accord, clearing with finings or by draining the beer off the yeast.
Non-filtered beers include the cask ales of the UK. In the UK a beer which has been filtered in the brewery is known as "brewery conditioned".
Beer is mechanically filtered by flowing the beer through layers of filter material; the two main techniques being 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 tight enough to strain colour and body from the beer. Normally used filtration ratings are divided into rough, fine and 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 are removed during the filtration process. 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.
Pre-made filters have two sides: one with loose holes, and the other with tight holes. Flow goes from the side with loose holes to the side with the tight holes, with the intent that large particles get stuck in the large holes while leaving enough room around the particles and filter medium for smaller particles to go through and get stuck in tighter holes.
Sheets are sold in nominal ratings, and typically 90% of particles larger than the nominal rating are caught by the sheet. For sterile filtration, a typical size is 1 micrometre or less.
Filters that use a powder medium are considerably more complicated to operate, but can filter much more beer before needing to be regenerated. Common media include diatomaceous earth, or kieselguhr, and perlite.
Though all filtering is done cold, the term cold filtering is used for a filtering process in which the beer is chilled so the protein molecules clump together and so are easier to filter out. Breweries tend to differentiate cold filtered beers from those that have been heat pasteurised.
When a beer has been left to allow the yeast to settle at the bottom of the vessel in which it is held (usually a conditioning or lagering tank), it has "dropped bright". Finings can be introduced during the production of beer in order to induce it to drop bright more readily.
Home Brewed Beer
Beer filtration is also common on a small scale. It is not uncommon for homebrewers (those who brew their own beer at home, often in small batches around 5 gallons) to filter their own beer. While they lack the sophisticated equipment of large-scale breweries, they can achieve satisfactory results using plate filters or small scale 10" filters. Most homebrewers filter their beer down to 5 microns to remove the majority of yeast and sediment. Brewers may filter their beer down to 1.0 or 0.5 microns, but anything smaller creates the risk of removing flavor and beneficial compounds.
- ^ A history of beer and brewing - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=QqnvNsgas20C&pg=PA670&dq=Filtering+beer&as_brr=3&client=firefox-a. Retrieved 2009-07-13.
- ^ Clear Beer Through Finings Technology, Ian L Ward, brewerssupplygroup.com. Retrieved 13 July 2009.
- ^ A history of beer and brewing - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=QqnvNsgas20C&pg=PA670&dq=%22brewery+conditioned%22. Retrieved 2009-07-13.
- ^ Handbook of Brewing: Processes ... - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=L8RwjqUKLygC&pg=PT257&dq=cake+filtration+brewing&as_brr=3&client=firefox-a. Retrieved 2009-07-13.
- ^ "Beer Conditioning". www.toonale.co.uk. http://www.toonale.co.uk/conditioning.htm. Retrieved 2009-07-13.
- ^ "Beer Maturation: Secondary and Cold Storage". www.beer-brewing.com. http://www.beer-brewing.com/beer-brewing/beer_conditioning/beer_maturation.htm. Retrieved 2009-07-13.
- ^ Malting and Brewing Science: Hopped ... - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=ciA6-YMTI-UC&pg=PA688&dq=brewery+conditioned+beer&as_brr=3&client=firefox-a. Retrieved 2009-07-13.
- ^ The Little Black Book of Beer: The ... - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=RQyJLxdFgp8C&pg=PA48&dq=%22cold+filtering%22&as_brr=3&client=firefox-a. Retrieved 2009-07-13.
- ^ Garrett Oliver, The Brewmaster's Table, page 19.
- ^ Pennsylvania Breweries - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=-Wd-9CLcJ88C&pg=PA255&dq=%22cold+filtering%22&as_brr=3&client=firefox-a. Retrieved 2009-07-13.
- ^ The Biotechnology of Malting and Brewing - Google Books. books.google.co.uk. http://books.google.co.uk/books?id=TQuwGXt2NYAC&pg=PA138&dq=conditioning+tank+beer&client=firefox-a. Retrieved 2009-07-13.
- ^ "Homebrew Filtration F.A.Q.". www.homebrewfilers.com. http://www.homebrewfilters.com/Store/F.A.Q..html. Retrieved 2010-11-22.
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