By Jim Busch (Brewing Techniques)
Clear beer is primarily achieved by removing yeast and minimizing the production of haze-producing compounds during the brew session. When these preventive measures can’t do the job, filtration remains a good option.
The most common ways to achieve a clear pint include using natural sedimentation/cold conditioning, the addition of finings, and filtration/centrifugation. Although natural sedimentation and the use of finings are simple and attractive methods of obtaining brilliant beer, sometimes filtration makes perfect sense. This article explores the natural and process-oriented solutions to beer haze and ventures into that sometimes taboo realm — filtration.
In some cases, filtration is virtually required for the beer to be completely authentic in presentation; Kristall Weiss, German Altbiers, and Kölsch are all good examples of beers that benefit from filtration. Other beers should never be filtered (cask ales and Hefeweizens, for example). Sometimes a brewer needs to filter to “clean up” the taste of a young beer that must be served in a short time. Other times a brewer may find that the yeast refuses to drop out of suspension, no matter what natural methods are used. And then there’s the case of the beer that is to be entered into a homebrew competition, where clarity may provide the winning edge. For these reasons and no doubt others, a filter is a great tool to have available, even if you don’t intend to filter routinely.
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Success in filtering beer requires awareness of the different sized particles that exist in and make up beer. Knowledge of these particles enables brewers to make intelligent decisions about which ones to remove and which ones to keep.
The main constituents of concern in beer are yeast, proteins, polyphenols (tannins), and hops. The cloudiness that results from suspended yeast is separate from the haze that results from the interaction of proteins and polyphenols. As is common in brewing, however, the two cannot be completely separated.
The aim of filtration is to remove the vast majority of the yeast and at the same time retain enough of the proteins to keep from negatively affecting head retention. Although the point of filtration or clarification is not to remove hops, hops do adhere to yeast cells; therefore, removing the yeast can sometimes lead to a small reduction in the overall hoppiness of a beer (but not the overall bitterness of the beer — bitterness is a result of iso-alpha-acids that survive filtration).
Yeast: Yeast cell sizes tend to fall in the 5–10 micron range, which is why a rough or polish filtration is usually done at 5 microns. This is the general size of diatomaceous earth (DE, or Kieselguhr) filters often found in microbreweries. It is also a common size in plate and frame filters, which use disposable filter pads. In professional breweries, the DE or pad is selected based on the tightness of its filter media. The choice here leads to the overall degree of filtration.
Filtration below 0.5 microns is called sterile filtration; beers filtered to this level are generally microbiologically stable, but may lack fullness or mouthfeel and often exhibit poor head retention because too many proteins were removed in the process.
Haze producers: Beer haze is often discussed as a matter of colloidal stability. According to the American Heritage Dictionary, colloid is defined as “a suspension of finely divided particles in a continuous medium …” and “the particulate matter so suspended.” Colloidal stability refers to the absence of the two main classes of haze in a finished beer, which Manfred Moll categorized as follows:
· Chill haze — turbidity that forms when beer is cooled to 32 °F (0 °C) and redissolves when the beer is reheated to 68 °F (20 °C) or higher. Particulate size is between 0.1 and 1.0 micron.
· Permanent haze — haze that is present in beer at 68 °F (20 °C) or higher. Particulate size is between 1–10 microns.
Haze is formed when high molecular weight proteins combine with polyphenols (tannins) to form insoluble colloidal haze in the form of a protein–tannin complex. To combat haze, brewers remove or minimize the quantity of either high molecular weight proteins or polyphenols, thereby preventing the formation of the complex.
The quantity of haze-causing proteins and polyphenols can be controlled in the brewhouse through procedures that minimize the carryover of large proteins and polyphenols. Haze-causing fractions can be minimized by using well-modified malts and proper protein rests in mash programs, proper control of pH during mashing and sparging, optimized hot break formation in the kettle through vigorous boiling, and proper separation of wort from coagulated break material in the kettle. Kettle coagulants such as Irish moss also help to reduce the quantity of haze-forming compounds that carry over into the fermentor. Haze can also be controlled by the addition of additives after fermentation, such as Polyclar (PVPP), silica gel, or the enzyme papain (a papaya-derived enzyme available at homebrew supply stores and health food or nutrition stores).
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Preventing Haze Formation in Beer Starts in the Brewhouse |
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The key to preventing haze formation in beer is to minimize the carryover of large proteins and polyphenols into the finished beer. If you need clear beer, you can start in the brewhouse: (1) Use well-modified malts and proper protein rests in mash programs. (2) Control pH during mashing and sparging. (3) Optimize hot break formation in the kettle through vigorous boiling. (4) Make sure to get good separation of wort from coagulated break material in the kettle. Other options: · Use kettle coagulants such as Irish moss to reduce the quantity of haze-forming compounds that carry over into the fermentor. · Use postfermentation additives, such as Polyclar (PVPP), silica gel, or the enzyme papain. |
Although filtration can do an adequate job of removing much of the permanent haze, it can remove little of the chill haze. Haze can also form in packaged beers through oxidation reactions in the finished beer and bacterial infections — yet another reminder to be careful to keep beer in its reduced (as opposed to oxidized) state throughout the brewing process.
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When all else fails to clear your beer, or when you need the cleanest flavor possible, a filter can be used to produce a polished to brilliant beer.
Hardware considerations: A filter should meet the following criteria:
(1) It should be relatively easy to use.
(2) It should be relatively easy to clean.
(3) It should achieve the desired level of clarity while leaving a good beer head.
(4) It should admit no oxygen.
(5) It should be affordable.
One type of filter that meets these goals is the cylindrical cartridge filter. These filters are often sold in hardware stores as “whole house” filters. They consist of a 12in. tall housing 5⅛ in. across. This size of housing fits a standard cylindrical 10 in. long X 2¾ in. o.d. filter. The filter cartridge has top and bottom O rings for a tight fit. Fluid is pushed in one side of the top fitting, is forced through the filter media, and then exits the other side of the top fitting. This type of filter is sold by The Filter Store Plus (Rush, New York) and others. The key to this filter’s effectiveness is the particular type of filter cartridge that is used. These filters are fabricated of pleated polypropylene and are listed according to both efficiency and micron size. The type I like to use is the 99.9% efficient 5-micron unit. The lower the efficiency rating, the higher the probability that some beer will get by unfiltered. The importance of high efficiency ratings is the main reason not to use any of the common industrial filters sold in hardware stores. Other reasons include cleanability (many inexpensive ones cannot be cleaned after yeast has been impregnated in them) and the desirability of food-grade (FDA-approved) construction.
Some filters include carbon in their media; these filters would be useful only if you want to have home-brewed “clear beer,” because they tend to strip beer of much of its character (clear beers like Zima are in fact manufactured using carbon filters). A good high-quality pleated filter cartridge costs about $35 and will filter at least 200 gallons of beer. (I have probably filtered more than 300 gallons through one of mine.)
Getting started: Before filtering kegged beer, it is helpful to cold condition the beer between 32 °F (0 °C) and 40 °F (4 °C) for several days to a week or more. Cold conditioning helps to sediment yeast and haze products that will easily drop out of solution. The beer can be carbonated during this period and the final carbonation adjusted after filtration, or the beer can be filtered and then carbonated. Filtering still beer is usually easier because it requires less attention to the back pressure that otherwise must be maintained on the receiving keg.
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Step-by-Step Cartridge Filtration |
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1. Cold condition beer. 2. Sanitize the cartridge and equipment. 3. Connect CO2 tank and regulator to unfiltered beer keg via the CO2 IN line. 4. Purge air from unfiltered keg and serving keg using CO2 cylinder; pressurize serving keg to 10 psi. 5. Connect bleed valve to CO2 OUT fitting on serving keg. 6. Connect filter cartridge to keg with unfiltered beer via the keg’s BEER OUT line. 7. Fill filter cartridge with beer. Bleed off air if desired. 8. Connect receiving keg to filter via its BEER OUT line. 9. Open bleed valve to allow beer to flow through system to serving keg. 10. Adjust flow rate if desired via CO2 regulator. 11. Disconnect everything and enjoy your clear beer. |
Filters must be sanitized before use. To do this I usually disassemble the filter and soak the tubing, the filter housing, and the filter in a sanitizer. I then reassemble the parts and backflush the filter with hot water, forcing the water in through the BEER OUT side. It’s a good idea to taste and smell the water exiting the filter; when it has no trace of sanitizer it is ready to use.
Step-by-step filtration: The flow rate of beer across the filter can be controlled simply by adjusting the carbon dioxide pressure at the regulator, connected through the CO2 IN line of a standard Cornelius keg. The BEER OUT line is connected to the filter, and the output of the filter will be connected to the BEER OUT fitting of the receiving keg.
To begin filtering, I like to have a bleed valve connected to the CO2 OUT fitting on the receiving keg. This valve lets me control the flow rate independently of the regulator, and if the beer is carbonated it allows most of the carbonation level to be maintained. It also reduces fobbing in the receiving keg.
Once the filter is connected to the keg containing unfiltered beer, the filter cartridge can be filled with beer. The filter cartridge can be bled off if desired; this can be useful if you want to purge any air that may be in the filter. The receiving keg is then connected through the BEER OUT line, and the bleed valve is opened to allow the beer to flow through the system.
It is always a good idea to fill the receiving keg through the BEER OUT line so that the keg fills from the long liquid tube — from the bottom of the keg up — to minimize agitation and possible aeration of the beer. Before filling, always purge the air from the receiving keg by filling it with carbon dioxide. Once the receiving keg is sanitized and purged with carbon dioxide, pressurize it to 10 psi. Filtering requires that the filter elements fit tightly and maintain a good seal. A tight seal means that the flow across the filter cartridge will be even and laminar and also ensures that no oxygen is introduced into the beer in transit. You can monitor the effectiveness of the filter by disconnecting the BEER OUT line of the receiving keg and filling a glass of beer by hand. This can be made even simpler by placing a “T” in the beer line after the filter and before the receiving keg. The “T” then connects to a shutoff/sample valve. I usually sample at the start of the filtering and again if the flow rate seems too slow. A slow flow rate could indicate that the bleed valve on the receiving keg is closed too much or that the filter is overloaded with yeast. If the filter gets stuck, it must be backflushed to purge the yeast. Once the filtering is complete, back-flush the filter and store it in a mild sanitizer/caustic. I keep mine in a sealable plastic bag in the refrigerator with some weak B-Brite.
Although crystal clear homebrew is not required for a tasty pint, it is sometimes beneficial to remove the yeast to clean up the appearance and taste of a beer. Clear beer is the conquest of both haze compounds and yeast, each of which should be dealt with separately. Haze can be reduced significantly through brewhouse procedures. Cloudiness resulting from yeast could be due to the strain of yeast, the health of the yeast, and the amount of yeast pitched.
Although home brewers have a variety of filter types from which to choose, the cartridge filter offers a cost-effective and efficient solution to producing brilliant beer.
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