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Beer Conditioning
Beer Clarification
Following fermentation, beer is quite turbid due to the presence of yeast, protein/polyphenol complexes, and other insoluble material, all of which are responsible for haze formation in beer. Extended lagering periods at low temperatures, the addition of finings to the beer, and centrifugation are some of the techniques that brewers use to reduce these substances. Each of these processes is described in the following sections.
Lagering
Lagering is one method to achieve beer stability and involves holding the beer in shallow vessels at temperatures between -1 and 2ºC. The cold temperatures reduce fermentation byproducts by reducing their solubility and encouraging precipitation of yeasts and other haze-loading material. Natural sedimentation yields beer that is slightly turbid. Even though sedimentation is a simple technique employed by many brewers, it requires a long storage period; however, tanks may be under counter-pressure to expedite sedimentation. Another drawback is that the sludge in the tank bottom can warm up, allowing yeast autolysis and producing off-flavors in the beer. The sludge also contains a considerable amount of beer, which could otherwise be recovered with filtration and/or centrifugation processes. In addition, the sludge must be removed from the tank manually, which increases operating costs and prevents utilizing the tank in a closed system. In reference to ales, this process is often referred to as cold conditioning.
Fining
Although good clarity can be obtained from simple sedimentation by prolonged storage at low temperatures, better results can be obtained in less time by adding fining agents either during transfer from the fermenter or during storage. Finings are available in several forms to improve clarity and improve physical stability. Isinglass and wood chips can be used to improve clarity by precipitating negatively charged yeast cells. The use of finings is not universal. They find their widest employment in the United Kingdom, but there is renewed interest in North America.
Centrifugation
Centrifuging is a popular method of reducing the solids content of beers, and takes the place of lagering or fining. Lagering requires a long residence time in tanks, and thus high capital expenditures for storage capacity. Finings will produce relatively bright beer, but some yeasts do not always respond to fining action, and the finings themselves tend to create tank residues.
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