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Beer Conditioning
Beer Maturation
Maturation of "green beer" involves four general schemes: traditional lagering, bottle conditioning, casking, and accelerated lagering.
Lagering beer involves secondary fermentation of remaining fermentable extract at a reduced rate controlled by low temperatures and low yeast count. The low temperatures also aid in settling the remaining yeast and precipitating haze-forming material (protein/polyphenol complexes). The evolution of carbon dioxide during secondary fermentation not only carbonates the beer, it reduces byproducts (including sulfur compounds and other volatiles). Bottle conditioning involves secondary fermentation and clarification in the bottle induced by adding yeast and sugar to the beer. Cask-conditioned beers involve secondary fermentation and clarification in the cask induced by adding yeast, sugars, hops, and finings. In accelerated lagering the beer is fully attenuated, virtually free of yeast, and stored at higher temperatures. Unlike beers that have undergone traditional or accelerated lagering, beers conditioned in a bottle or cask are neither filtered nor pasteurized.
Beer Bottle Conditioning
The practice of using priming sugars for beer bottle conditioning has been refined by British brewers and is still followed by some craft brewers as well as a few larger British brewers. Belgian brewers are also known for using this method to add unique flavors. Bottle conditioning usually involves a short time in the conditioning tanks to improve overall stability and flavor before adding priming sugars. Some brewers allow some yeast to pass through for secondary fermentation, while others prefer to completely remove the primary fermentation yeast and repitch with ale or lager yeast. Some brewers use lager yeast because it generally has a smaller cell mass, is less likely to leave an autolyzed flavor, and flocculates and settles better than ale yeast. Thompson reports pitching rates between 0.75 and 3.0 million cells/ml (46). After a brief conditioning period, the beer may be filtered before being sent to tanks with stirring agitators, where the priming sugar (e.g., glucose, dextrose, or invert sugar) is added. The beer is then bottled for secondary fermentation, which takes between 10 and 14 days. After secondary fermentation, the bottled beer is moved to cold storage (5–15ºC) to protect the flavor and to expedite yeast sedimentation.
Beer Casking
Casking beer has its origins in the British Isles and is most widely used to make pale ales (bitters), porters, and stouts. Beer is racked either directly from fermenting vessels into casks when fermentation is judged sufficiently complete (a residual extract of 0.75 to 2ºP) or when the correct charge of yeast is present (0.25 to 4.00 million cells/ml) (27/19). If too little yeast is present in the beer, secondary fermentation is too slow and insufficient carbon dioxide is dissolved in the beer. However, if too much yeast is suspended in the beer, secondary fermentation may to violent.
Traditional Beer Lagering
Lagering beer was developed in Germany for bottom-fermented lagers, and it involved a long, cold storage between 1 and 3 months in conditioning tanks. Today the trend is for shorter storage times of between 2 and 3 weeks at higher temperatures, to free up tanks. However, the shorter lagering programs can result in beer with higher levels of yeast and haze, requiring subsequent clarification steps.
Accelerated Beer Lagering
Traditionally, lagering served four purposes: extract reduction, clarification, carbonation, and flavor maturation. However, given the capital-intensive nature of storage, many brewers have reduced the storage time and downsized the required plant facilities. Today, with better equipment obviating the need for secondary fermentation, the wort is usually fully attenuated during primary fermentation, thereby eliminating the need for traditional lagering. The beer is usually conditioned between 2 and 5 days at temperatures ranging between -1 and 2ºC before filtration.
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