The Beer Keg
At parties there is often a keg of beer. Kegs are popular because they can hold a lot of beer in one spot. Some people claim that tap beer tastes better than any other kind of beer. Most restaurants and bars have several different kinds of beer on tap, although their extraction methods work a little differently.
A keg mixes science with pleasure. Physics actually plays a huge role in the process. Kegs actually began to be used thousands of years ago by the Romans. Wooden casks were used then, but the science of storing beer has advanced far beyond that now.
The Aluminum Casing
Most beer kegs are constructed of aluminum or steel casing. They are designed to hold the beer at a constant pH balance of around 3.5, and are tested for durability to see if they can withstand being dropped or mishandled without breaking. The beer goes into the bottom of the container, and a section is made at the top for the CO2 and nitrogen. Usually the floor of the keg where the beer is stored is raised slightly, to keep the beer from getting trapped at the bottom when the keg is nearly empty, wasting the drink.
CO2 and Nitrogen
The beer kegs are pressurized with CO2 and nitrogen. Sometimes nitrogen is used, and sometimes CO2. Usually, however, a combination of the two is used. This keeps the beer at the right pH balance, and makes the tap work when pushed into the metal.
Modern Keg Standards
Modern kegs are usually constructed from an aluminum alloy. They have to withstand rough handling and maintain the pressure necessary to dispense the beer. Most kegs have a spot designated on the top for placing the tap into. Usually the bottom of the keg is "dimpled" (meaning that it is slightly dome shaped), so that more of the beer is extracted. Different kinds of beer use different materials to be pressurized. Guinness beers use nitrogen for a creamier beer.
Using the Tap
To use a tap, the tap is stuck into the designated spot on the keg. The tap is secured, and then pumped a few times to get the beer flowing out the spout. Once this happens, sometimes the beer flows out without any help and sometimes a handle has to be used to get it out.
Dispensing the Beer
The beer comes out of the spout attached to the dispenser, which is attached to the keg. The pressure of the CO2 inside the keg keeps the beer coming out at a high pressured rate. This makes it possible to extract all of the beer from the keg without having to tip it over.
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