In 1691, an article in the London Gazette mentioned John Lofting, who held a patent for a fire engine: "The said patentee has also projected a very useful engine for starting of beer, and other liquors which will draw from 20 to 30 barrels an hour, which are completely fixed with brass joints and screws at reasonable rates".
In the early 20th century, serving draught beer from pressurised containers began. Artificial carbonation was introduced in the United Kingdom in 1936, with Watney’s experimental pasteurised beer Red Barrel. Though this method of serving beer did not take hold in the U.K. 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; by the early 1970s, draught beer was almost exclusively beer served under pressure.
Shortly after a British consumer organisation called the Campaign for Real Ale (CAMRA) was founded, in 1971, to protect unpressurised beer, the group devised the term real ale to differentiate between beer served from the cask and 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 beer is a term for beer which is served from a pressurized keg. While often considered synonymous to draught beer, keg beer refers specifically to beer served under pressure, while draught beer may refer to any beer served from a larger container, including both keg beer and cask ale. Keg beer is often filtered and/or pasteurized, both of which are processes that render the yeast inactive, increasing the shelf life of the product at the expense of flavor.
In brewing parlance, a keg is different from a cask. A cask has a tap hole near the edge of the top, and a spile hole on the side used for conditioning the unfiltered and unpasteurised beer. A keg has a single opening in the centre of the top to which a flow pipe is attached. Kegs are artificially pressurised after fermentation with carbon dioxide or a mixture of carbon dioxide and nitrogen gas.
Keg has become a term of contempt used by some since the 1960s as pasteurised draught beers were replacing traditional cask beers. The quality of the kegging process was not as good then as it is today, and sometimes the keg beers are referred to as Plastic Beer. Some people believed that chemicals (adjuncts) were used to create a foam head. These perceptions exist to this day.
Despite this consumer concern, keg beer was replacing traditional cask ale in all parts of the UK, primarily because it requires less care to handle. Since the mid-1970s, the Campaign for Real Ale (CAMRA) has been conducting a successful consumer campaign which focused attention on those consumers who preferred traditional cask beer. As well as this CAMRA has lobbied the British Parliament successfully to ensure support for cask ale. New, small microbreweries have sprung up to serve those consumers who prefer traditional cask beer. Today many pubs in the UK will serve both keg and cask beer.
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.
In the UK, the term keg beer would imply the beer is pasteurised, in contrast to unpasturised cask beer. Some of the newer microbreweries may offer a nitro keg stout which is filtered but not pasteurised, but the older established breweries do pasteurise.
Different beers also require different equipment for dispensing. For a detailed listing of brands and their respective keg taps and couplers, please see the Beer Brand / Keg Taps Couplers Listing
In some countries such as Japan, the term "draft" applied to canned or bottled beer indicates that the beer is not pasteurised (though it may be filtered), giving it a fresher taste but shorter shelf life than conventional packaged beers.