Filtered beer has been deliberately cleaned of significant contact with yeast through filtration. The process of filtering removes carbonation and renders the beer technically unstable so it needs force carbonation to keep it "alive".[1] Mechanical filtering and even pasteurisation of bottled beer started at the end of the 19th century, though the first beer known to have been mechanically filtered and force carbonated for the keg to be served as a draught keg beer was Watneys Red Barrel in 1931.[2]
Beer in which yeast is no longer in suspension is known as bright beer, though not all bright beer is mechanically filtered. Beers may also become "bright" by passively waiting for the yeast to drop of its own accord (dropping bright or lagering), clearing with finings, or by draining the beer off the yeast.[3]
Filtration is a normal process for most beers, other than the cask ales of the UK. In the UK a beer which has been filtered in the brewery is known as "brewery conditioned".[4] Bottle conditioned beers may have been filtered before being reseeded with yeast.
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Filtration
Beer is mechanically filtered by flowing the beer through layers of filter material; the two main techniques being surface filtration and cake filtration.[5] 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.[6][7][8]
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.
Cold filtering
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.[9] Breweries tend to differentiate cold filtered beers from those that have been heat pasteurised.[10][11]
Bright beer
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), [12] it has "dropped bright". Finings can be introduced during the production of beer in order to induce it to drop bright more readily.
References
- ^ "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.
- ^ "Watneys Red Barrel". www.retrowow.co.uk. http://www.retrowow.co.uk/retro_britain/keg_bitter/watneys_red_barrel.html. 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.
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