Beer kegs - what they are and what they do

A keg is a cylindrical container, usually constructed of aluminium, steel or wood. It is commonly used to store, transport, and serve draught beer. Other alcoholic or non-alcoholic drinks, carbonated or non-carbonated, may be housed in a keg as well. Such liquids are generally kept under pressure.


Beer kegs are made of stainless steel or aluminium. A beer keg has a single opening at one end. A tube (called a "spear") extends from the opening to the other end. There is a self-closing valve that is opened by the coupling fitting which is attached when the keg is tapped. There is also an opening at the top of the spear that allows gas (usually carbon dioxide) to drive the beer out of the keg. The coupling fitting has one or two valves that control the flow of beer out of the keg and gas into the keg.

Keg sizes and capacity

Historically a beer barrel was a standard size of 50 gallons, opposed to a wine barrel at 32 gallons, or an oil barrel at 42 gallons. Over the years barrel sizes have evolved and breweries use different sized containers. Even when the content capacity of two kegs are equal the keg shape and keg tap system may differ heavily. Most U.S. brewers sell beer in 1/2 barrels between 14 and 16 gallons, 1/4 barrels between 7 and 8 gallons, and 1/6 barrels between 5 and 6 gallons.

In European countries the most common keg size is 50 liters - this includes the UK with its non-metric keg system where the standard keg of 11 imperial gallons is almost exactly the size of 50 liters in the metric system. The German DIN 6647-1 and DIN 6647-2 have also defined Kegs in the sizes of 30 and 20 liters. A newer Euro regulation defines 50, 30, 25 and 20 liters where the Keg shape is usually thicker but less tall than the German keg specifications.

Keg types

There are other types of beer kegs around, aside from the most common 50 liters capacity. These include:

• Cornelius keg - originally used by the soft drink industry, now commonly used to store and dispense beer, especially homebrewed beer.
• Mini keg - is a 5 liter keg produced for retail sales. Mini kegs are typically not returned to the manufacturer for cleaning and refilling. The kegs, being made of aluminum, may be recycled.
• quarter barrel / pony keg - is a beer keg containing approximately 7.75 U.S. gallons (29.33 liters) of liquid. It is half the size of the standard beer keg and equivalent to a quarter of a barrel
• sixth barrel keg - becoming the choice for many establishments and breweries that wish to use kegs smaller than a half barrel, the sixth barrel kegs are the same size and volume as a Cornelius keg

Tapping a keg

A beer tap is a valve / tap, for controlling the release of beer. While in other contexts a "tap" may be a "faucet", "valve" or "spigot", the use of "tap" for beer is almost universal.

There are two different types of tapping equipment that are available for kegs, party pumps and gas taps.
Party pumps utilize outside air, which introduces bacteria inside the keg and will certainly introduce oxygen, which will cause the beer to oxidize. Kegs operating a party pump should be used within 18–24 hours otherwise the beer may become unpalatable.
Gas pumps normally use CO2 (carbon dioxide), but certain brewers require a mix of other gases (Guinness requires 25% CO2 and 75% nitrogen). Gas pumps can preserve a keg up to 120 days with proper refrigeration.

Kegerator - keeping the keg refrigerated

The term Kegerator is a rather new word in the English language - a combination of the words "keg" and "refrigerator". A kegerator can be a specialized appliance built solely for the purpose of dispensing beer in an intimate setting. Another type of kegerator is the refrigerator or freezer that has been modified to accommodate kegs, and dispense their liquid contents. The most efficient aspect of owning a kegerator is that it extends the life of your beer and allows for purchase and dispensing in mass quantity. Beer stored in a kegerator is preserved for as long as 6 months.