Chillproofing is a term used when a beer undergoes a process to protect its clarity or brightness when it is cooled to very low temperatures approaching 0°C (32°F). With most beers, chillproofing is a very important part of the modern brewing process. The earliest use of a form of chillproofing occurred in the mid-19th century with the brewing of lighter lager beers. The original pilsner beers were stored in caves packed with ice, which helped to chillproof the beer through cold aging. Traditionally beers are chillproofed by being stored at 0°C or below for long periods of many weeks or months. During this time protein and polyphenols derived from malt in the beer coagulate to form larger molecules, which can then be removed by filtration. In the days before beer filtration, the beer was aged long enough for the particles to simply settle out. Most filtered beers are clear and bright when bottled or kegged, but without chillproofing the protein–polyphenol coagulation occurs in the package, and the beer becomes hazy within several weeks. In modern beer production, processing aids are used to shorten the chillproofing process from weeks or months to only a few days. Proteolytic enzymes, which break down larger protein molecules, were some of the first chillproofing aids. Nowadays protein and polyphenol adsorbing materials are often used. Beer that is clear (bright) at ambient temperature but that becomes cloudy when cooled is said to have a “chill haze.” Beer with a chill haze will become clear again when it returns to room temperature.
