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Cask ale or cask-conditioned beer is unfiltered and unpasteurised beer which is conditioned (including secondary fermentation) and served from a cask without additional nitrogen or carbon dioxide pressure. Cask ale is also sometimes referred to as real ale in the United Kingdom, a term coined by the Campaign for Real Ale, often now extended to cover bottle-conditioned beer as well.〔 == The history of cask and keg beer == Cask means container. The Histories of Herodotus, written in 424 BC, refers to "casks of palm-wood filled with wine" being moved by boat to Babylon, though clay vessels would also have been used. Stout wooden barrels held together with an iron hoop were developed by the north European Celts during the Iron Age for storing goods. Over the centuries other methods have been developed for preserving and storing beer but this method is still used, particularly in Britain. Bottled beers were commonplace by the 17th century for the well off who wished to drink outside of public inns, or who wanted to take a beer with them when fishing. Such as the famous story of Alexander Nowell, the Dean of St Paul's, who, in 1568, left his bottled beer by the river bank, and upon returning a few days later discovered the bottle opened with a bang and that the contents were very tasty. But while the middle and upper classes could indulge themselves with such expensive luxuries, the ordinary folk continued to drink their beer served direct from the cask. India Pale Ale (IPA), the famous ale that was shipped to India was delivered in casks, and only transferred to the bottle for the civilian middle classes; the troops drank their beer the same way they drank it back home, from flagons filled direct from the cask. But as beer developed and became paler and lower in alcohol, so it became more difficult to keep it fresh tasting in the cask, especially in countries with warmer climates. By the late 19th century commercial refrigeration and Louis Pasteur's flash heating method of sterilisation prolonged the life of beer. In Britain's cooler climate these methods did not catch on at this time. Not all beer in mainland Europe is pasteurised; there are plenty of examples of unfiltered, unpasteurised beers, but these will commonly be served from a chilled container under pressure: a keg. Traditionally draught beer came from wooden barrels, also called casks. In the 1950s these began to be replaced by metal casks of stainless steel or aluminium, mainly for quality reasons as they could be sterilised and the beer was therefore less likely to spoil, but also for economic reasons. An additional benefit of the switch to metal casks was that staling from oxygen in the air could be reduced. Subsequently, in the early 1960s a form of metal cask, known as a keg, was introduced which allowed for more efficient cleaning and filling in the brewery. The essential differences between a traditional cask and a keg are that the latter has a centrally located downtube and a valve that allows beer in and gas out when filling and vice versa when beer is dispensed. Also kegs have a simple concave bottom whilst the barrel or cask design allowed sediment to be retained in the cask. This aspect of keg design meant that all the beer in the keg was dispensed which therefore required that the beer be processed by filtration, fining or centrifuging, or some combination of these, to prevent sediment formation. Lastly, kegs have straight sides unlike the traditional barrel or cask shape. In order to get the beer out of a keg and into a customer's glass, it can be forced out with gas pressure, although if air or gas at low pressure is admitted to the top of the keg it can also be dispensed using a traditional hand pump at the bar. By the early 1970s most beer in Britain was keg beer, filtered, pasteurised and artificially carbonated, and most British brewers used carbon dioxide for dispensing keg beers. This led to beers containing more dissolved gas in the glass than the traditional ale and to a consumer demand for a return to these ales. By contrast, in Ireland, where stout was dominant, the use of a mixture of carbon dioxide and nitrogen for dispensing prevented the beer from becoming over-carbonated. Rare examples of natural beers could still be found in the farmhouse beers of Northern Europe and the maize beers of South America for example, in essence the last great stronghold of natural beer was about to be wiped out. In 1971 the Campaign for Real Ale (CAMRA) was founded in Britain to save what they came to term "real ale". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cask ale」の詳細全文を読む スポンサード リンク
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