Conditioning, Clarification, Stabilization
Stabilization
In addition to clarification (i.e., removing yeast), beer must display physical stability with respect to haze, i.e., the beers must be bright and remain so from the brewery to the consumer. Clarity is one of the most appealing characteristics of beer that drives consumption of products such as lagers and Pilsners. Consumers often perceive haziness as a defect and a potential health threat, and avoid hazy beers as a result. However, there are some exceptions to this rule. German and Belgium wheat (white) beers are designed to be hazy beers, and in their case, this is a highly desirable characteristic. The expansion of craft and organic beers is associated with a lack of filtration and chemical stabilization, which, in turn, results in hazy beers.
Colloidal Stabilization Treatments
The most effective beer treatment with respect to haze stability is the cold storage of the beer for about seven days at -1 to -2 degrees C (30–28°F). As the haze is a product of protein and polyphenols, removing or reducing the concentration of either component from beer will prevent haze formation. Several techniques, referred to as “chillproofing” are used for reducing chill haze. Most treatments and agents are oriented to remove proteins and/or polyphenols from beer. It is not necessary to remove all of the haze components, but just enough to ensure stability.
Removal of Polyphenols
Polyvinylpolypyrrolidone. Polyvinylpolypyrrolidone (PVPP) selectively binds to polyphenols responsible for chill and permanent haze. Part of PVPP’s success as a beer stabilizer stems from the fact that it mimics the action of proteins by combining with polyphenols at a greater magnitude than proteins (O’Reilly, 1994). Polyvinylpolypyrrolidone is popular with many continental European lager brewers because it is in compliance with Germany’s Reinheitsgebot and because it doesn’t remove foam-positive proteins like other fining agents.
Removal of Proteins
Silica Gels. Silica gels are effective chill-proofers in that they remove high-molecular weight proteins responsible for haze formation without detriment to foam stability. The several types of silica gels are differentiated by surface area, porosity, and water content. Silica gels are broadly classified according to their water content as xerogels or hydrogels.
Tannic Acid. Tannic acid is traditionally used to remove haze-forming protein and is still employed in Germany. The advantage of this method is that tannic acid does not affect those proteinaceous compounds that contribute to foam. It also has a secondary effect as an oxidizing agent. It is usually purchased as a powder, mixed with de-aerated water, and added to the beer en route to the conditioning tanks.
Hydrolysable Tannins. Hydrolysable tannins are also used to precipitate proteins. Beers treated with hydrolysable tannins show excellent colloidal stability as well as acceptable clarity values (Ryder et al., 2006). Hydrolysable tannins are added to the beer during conditioning, or following conditioning as the beer is transferred to the diatomaceous filter (Delcour et al., 1988).
Proteolytic Enzymes. Proteolytic enzymes are prepared from papain or pepsin and act on proteins by degrading them to smaller molecules. They do not increase the volume of solids, and thus do not create filtration problems and beer losses. Papain and pepsin are not specific to haze proteins, so mid-sized proteins (i.e., polypeptides), are often reduced, which affects beer foam.
Bentonite. Bentonite, an insoluble alumino-silicate, can also be used as a protein adsorbent, but it is beset with many disadvantages. For one, it is nonspecific, adsorbing all groups of proteins and thereby impairing foam stability, though this effect is of much less concern with bentonite than with papain (Munroe, 1995b). Bentonite also requires lengthy cold storage for settling time.
Removal of Polyphenols and Proteins
Composite stabilizers are products that combine both polyphenol and protein stabilization efficacy are also widely available and include mixtures of PVPP and silica gel (e.g., Polyclar™ Plus 730).
Measuring Haze
In brewing, a haze meter is a convenient, often handheld device used for quantitative measurement of beer’s haziness. Beer haze, scientifically termed turbidity, should be consistent between each commercial batch, as well as within the consumer base’s preference and expectations. Turbidity is caused by the individual particles of a substance within a fluid causing the fluid to range from mostly clear to hazy, or opaque. A haze meter measures the extent to which the turbid particles within a fluid scatter incident light, and outputs this measurement in a quantitative unit, the Formazin Turbidity Unit (FTU).
Brewhouse Techniques for Stabilizing Beer
It should be noted that neither, stabilization or clarification or for that matter filtration are end-all measures for correcting mistakes made in the production process. Therefore, from the very beginning, it is necessary to perform stringent quality control paying attention from the selection of raw materials all the way through to conditioning, filtration, and packaging. Some of the techniques that a brewer can employ to achieve colloidal stability are as follows:
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