Various approved additives are frequently used during the post-fermentation steps.These include agents to improve flavor, color, appearance, and stability. Hop extracts are sometimes added late in the process to provide additional hop flavor. Another important additive is pro-teolytic enzymes, which are used as "chill-proofing" agents. These enzymes hydrolyze proteins that would otherwise precipitate and form complexes with tannins and other polyphenolic compounds at low temperatures and give a cloudy or hazy appearance when the beer is chilled. Hydrolysis of these proteins prevents this "haze" or cloudiness.
Several commercially available types of enzymes are used. Papain, obtained from papaya, is commonly used, as are fungal- and bacterial-derived proteinases. The main requirements are that the enzyme be rather specific for haze-forming proteins (and not the foam-forming proteins), and that they are inactivated by a subsequent heating step, so residual activity in the finished beer is absent. Although widely used in the United States, chill-proofing enzymes are not allowed in many European countries.
Non-enzymatic, chill-proofing agents are also used, including tannic acid, bentonite, silica gels, and PVPP. Again, the use of these agents is permitted in some countries, and prohibited in others. In the United States, regulations regarding permitted additives and process aids are described in the U.S. Code of Federal Regulations, Title 21, Part 173. Other general regulations on beer manufacturing are contained in Title 27, Part 25.
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