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Draught beer (also called draft beer or tap beer) has several related though slightly different understandings. The majority of references to draught beer are of filtered beer that has been served from a pressurised container, such as a keg or a widget can. A wider meaning of beer that is served from a keg (or tap), but not from a can, bottle or cask, is also used. A more traditional definition is beer that is served from a large container, which could be either a keg or a cask. The different understandings may at times overlap and cause confusion. Some traditionalists object to the more modern use of the word when applied to canned beer. The slight usage differences of the term is due to the history and development of beer dispensing.
History of draught
Until Joseph Bramah invented the beer engine in 1785, beer was served direct from the cask and carried to the customer. The old English word for carry was dragen from the German tragen, which developed into a series of related words including drag, draw and draught. By extension the word for carrying or drawing a beer came to mean the serving of the beer, and in some senses the act of drinking or a drink of beer itself regardless of serving method. By the time Bramah's beer pumps became popular the use of the word draught to mean the act of serving beer was well established and transferred easily to beer served via the hand pumps.
By the early 20th century draught beer was starting to be served from pressurised containers, and artificial carbonation was introduced in Britain in 1936 with Watney’s experimental pasteurised beer Red Barrel. Though this method of serving beer did not take hold in Britain until the late 1950s, it did become the favoured method in the rest of Europe where it is known by such terms as en pression. The method of serving beer under pressure then spread to the rest of the world, and by the early 1970s draught beer was almost exclusively beer served under pressure.
Shortly after the British consumer organisation CAMRA was founded in 1971 to protect unpressurised beer, they devised the term Real Ale to differentiate beer served from the cask from beer served under pressure. By 2004 the term Real Ale had been expanded to include bottle conditioned beer, while the term Cask Ale had become the accepted global term to indicate a beer not served under pressure.
Keg dispense
In modern beer dispensing, a metal keg is pressurised with carbon dioxide (CO2) gas or nitrogen (N2) gas or a combination of both. Pressure in the keg drives the beer to the dispensing tap, or faucet.
Pressurised CO2 in the keg's headspace maintains carbonation in the beer. The CO2 pressure varies depending on the amount of CO2 already in the beer and the keg storage temperature. Occasionally the CO2 gas is blended with Nitrogen gas. CO2 / Nitrogen blends are used to allow a higher operating pressure in complex dispense systems.
Nitrogen is used under high pressure when dispensing dry stouts (such as Guinness) and other creamy beers because it displaces CO2 to form a rich tight head and a less carbonated taste. This makes the beer feel smooth on the palate and gives a foamy appearance. Premixed bottled gas for creamy beers is usually 75% Nitrogen and 25% CO2. This premixed gas which only works well with creamy beers is often referred to as Guinness Gas, Beer Gas, or Aligal. Using "Beer Gas" with more common ale and lager styles can cause the last 5% to 10% of the beer in each keg to taste very flat and lifeless.
Country differences
Draught beer is usually unpasteurised in America. It is intended to be kept refrigerated between 2°C (35°F) and 4°C (40°F), and consumed quickly after being "tapped". Above 6°C (44°F), a beer may within two days turn sour and cloudy. Below 6°C (44°F), a keg of draft beer should last 20-30 days before it loses its fresh taste and aroma.
In the UK draught beer is nearly always pasteurised. The term keg beer would imply the beer is pasteurised. Some of the newer microbreweries may offer a nitro keg stout which is filtered but not pasteurised, but the older established breweries do pasteurise.
Smooth flow
Smooth flow (also known as cream flow or just smooth) is the name brewers give to beers pressurised with nitrogen; either from a can or bottle with a widget, or from a pressurised keg.
Canned and bottled draught
Recently the words "draft" and "draught" have been used as marketing terms to describe canned or bottled beers, implying that they taste and appear as beers from a keg. Two examples are Miller Genuine Draft, which is a cold-filtered pale lager, and Guinness stout in patented "Draught-flow" cans and bottles. Guinness is an example of beers that use nitrogen widgets to create a smooth beer with a large foamy head.
See also
"Draught beer"