How Beer Kegs Work

Types of Kegs
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When a pub orders up its draught beer supply, usually what's delivered is a truckload of standard kegs known as "half barrels." The half-barrel is also the garden-variety keg commonly nestled in a big bucket of ice at a frat party. It's called a half-barrel because the "barrel" is a legal unit of measure used for import and export statistics. In the U.S., a barrel, by definition, is 31 gallons (117 liters) of fermented beverage. So, as you might have guessed, a half-barrel holds half that amount -- somewhere between 14 and 16 gallons (53-60 liters), or by a more agreeable measure, 124 pints (117 metric pints). This is slightly larger than the 50 liter (13 gallon) standard European keg. Fill either kind of keg with beer, and you've got an object weighing about 160 pounds (73 kilograms). By contrast, an empty half keg is a lonesome but hardly insubstantial object that weighs approximately 30 pounds (14 kilograms) [source: Wayland Works].

If you're at a smaller party where people aren't jumping naked into the pool and spraying shaving cream all over somebody's car, then you might encounter a more civilized vessel -- the quarter keg, aka the "pony keg." It's called a pony because, like ponies, the quarter keg is small -- but it can still hold 90 pounds (41 kilograms) of beer. [sources: Wayland Works, Word Detective].

For the sedate dinner party, there's the refined and aerodynamic "torpedo keg" (or the "sixth barrel") which holds a little more than 5 gallons (19 liters). And for an evening with friends, there's the very restrained "mini-keg," affectionately known as "bubba," which provides a pleasant 10 and a half pints (10 metric pints) with which to while away the football game. Last but hardly least is the Beer Ball, a plastic number cradling 5 gallons (19 liters) in its svelte interior [source: Micromatic].

There are other, more arcane vessels lurking in the margins of beer culture. The Cornelius, or "corny" keg, is the basic soda canister that servers are always changing at fast-food joints. Capable of holding 5 gallons (19 liters) of liquid, the corny keg was long ago identified by home-brewers as the ideal vessel for their purposes. [source: Brew Ware].

All kegs, no matter their size or style, must deal with the same vital issue: how to get the beer out. On the next page we'll talk about the complex challenges this seemingly simple problem presents.