Draught Beer - Keg Beer

Keg beer is a term for beer which is served from a pressurized keg. Keg beer is often filtered and/or pasteurised, both of which are processes that render the yeast inactive.

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, particularly in Britain, since the 1960s when pasteurised draught beers started replacing traditional cask beers.

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 1971, the Campaign for Real Ale (CAMRA) has been conducting a 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.

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 tap.

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 (artificially) 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 other beer styles can cause the last 5% to 10% of the beer in each keg to taste very flat and lifeless.