Keg Beer
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A typical half-barrel with single opening in the centre of the top end Keg beer is a term for beer which is served from a pressurized keg. While often considered synonymous to draught beer, keg beerrefers 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.[citation needed]
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[citation needed] 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.