Lager ((ドイツ語:storeroom or warehouse)) is a type of beer that is conditioned at low temperatures,〔Briggs, D.E.; Boulton, C.A.; Brookes, P. A.; and Stevens, R. ''Brewing'', 2004, CRC. ISBN 0-8493-2547-1 p. 5.〕 normally in cold storage at the brewery, before being delivered to the consumer. It may be pale, golden, amber, or dark.
Although the defining feature of lager beer is its maturation in cold storage, it is also distinguished by the use of bottom-fermenting lager yeast. While it is possible to use lager yeast in a warm fermentation process such as with American steam beer, the lack of a cold storage maturation phase precludes such beer from being classified as lager beer. On the other hand, German Altbier and Kölsch use traditional top-fermenting yeast and temperatures, but with a cold storage finishing stage; its classification as ''obergäriges lagerbier'' (top-fermented lager beer) may be controversial.
Until the 19th century, the German word ' referred to all types of bottom-fermented, cool-conditioned beer, in normal strengths. In Germany today however, the term is mainly reserved for the prevalent lager beer styles of southern Germany. In common parlance, these beers are distinguished by their colors, and referred to as a (Bavarian) "Helles" (pale), or a "Dunkel" (dark), though both words may be used as adjectives to describe other types of beer. The popular Pilsner style, which is more heavily hopped, although it is also a pale lager, is most often known as simply "Pilsner" or "Pils", and generally is called neither a "Lagerbier" nor a "Helles". Numerous other types of lager beer styles are produced, such as Bock, Märzen, and Schwarzbier.
In the United Kingdom, the term ''lager'' commonly refers specifically to pale lagers, many of which are derived from the Pilsner style. Worldwide, pale lager is the most widely consumed and commercially available style of beer. It is often known primarily by its brand name, and labeled simply as "beer". Well-known brands include Budweiser, Stella Artois, Beck's, Brahma, Corona, Snow, Tsingtao, Heineken, Carling, Foster's, and Baltika.
==History of lager brewing==
While cold storage of beer, "lagering", in caves for example, was a common practice throughout the medieval period, bottom-fermenting yeast seems to have emerged as a hybridization in the early fifteenth century. In 2011, a team of researchers claimed to have discovered that ''Saccharomyces eubayanus'' is responsible for creating the hybrid yeast used to make lager.
Based on the numbers of breweries, lager brewing became the main form of brewing in Bohemia between 1860 and 1870, as shown in the following table:〔Pasteur, Louis, ''Studies in Fermentation'', 1879. English translation reprinted 2005 Beerbooks.com ISBN 0-9662084-2-0 p10. Citing ''Moniteur de la Brasserie'', 23 April 1871.〕
The rise of lager was entwined with the development of refrigeration, as refrigeration made it possible to brew lager year-round (brewing in the summer had previously been banned in many locations across Germany), and efficient refrigeration also made it possible to brew lager in more places and keep it cold until serving. The first large-scale refrigerated lagering tanks were developed for Gabriel Sedelmayr's Spaten Brewery in Munich by Carl von Linde in 1870.〔
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