Kegs are durable, portable, and ready for any occasion.

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Whether it's standing proudly at the center of a party or hiding discretely in the back room of a pub, the keg is the vessel of choice for beer. That's why more than 60 million gallons of beer are sold in kegs every year. After all, what better way could there be to move that precious liquid around than in a big, round barrel that can be rolled, stacked and tapped? No need to worry about bottle caps or broken glass; the keg is incredibly durable, requires no cap and is completely recyclable [source: Beer Institute].

But what's going on inside a keg? While beer bottles are transparent, kegs reveal nothing of the complex and uneasy chemical truce that's been established in their dark interiors, nor of the technology that makes them work. When we press on the tap of a keg at a party, or when we order up a pint at the bar, we take it for granted that beer will flow forth with just the right proportions of foam, carbonation, coolness and flavor. But the truth is that a great deal of thought has gone into achieving that perfect balance.

A keg is a fancy version of your basic barrel. In the factory, a sheet of stainless steel is rolled into a cylinder and welded together. Then, at the cylinder's midpoint, a set of ribs is pressed into it for added rigidity. Next, top and bottom steel plates are stamped out and likewise welded into place. The steel in question, a particular alloy of chromium, nickel, manganese and several other elements, is used because it welds cleanly leaving a smooth joint -- this is very important for a food-grade container because you don't want any rough surfaces where bacteria can set up shop. [source: nickelinstitute.org]

The airtightness of a keg is incredibly important -- it's what keeps the beer from becoming flat and flavorless. Still, the beer has to come out somewhere, and that's why there's a spear. The spear is a long metal tube that reaches almost to the bottom of the keg. Despite its warlike name, the spear is basically a big metal straw through which beer can travel up from the bottom of the keg and out through the tap at the top [source: nickelinstitute.org].

Just what are taps, and why do English and American brews refuse to come out of the same ones? We'll get to that in a bit. Right now, let's find out why all kegs are not created equal.