The Oxford Companion to Beer definition of
Aluminum Kegs are containers once widely used for transporting, storing, and serving beer. The use of aluminum as a material for beer barrels started after the end of Prohibition in the United States in 1933. In older days, most barrels had been handmade of hardwood and hoops and then lined with pitch. The coopers who made the barrels were employed by the breweries, but when Prohibition closed the breweries, it also effectively eliminated the profession of the cooper. When brewing became legal again, there was simply not enough cooperage available to handle the volume of fresh beer that needed to be packaged in a hurry. Industrially made replacements were the only answer. Cast-iron containers were tried, as were those made of stainless steel and aluminum. Compared with wood, metal barrels were easy to sterilize and needed less maintenance, and the beer inside was less likely to spoil. They also could withstand high pressure for carbon dioxide, nitrogen, or a combination of both, which made them suitable for holding virtually any kind of beer. Aluminum also had a few advantages not shared by other metals. It was fairly low cost in relation to its strength, and it was comparatively light weight. Unfortunately, aluminum is also easier to recycle than steel, which made aluminum barrels a favorite target for keg thieves and unscrupulous scrap metal dealers. Aluminum is also susceptible to corrosion by both beer and caustic soda, the principal cleaning agent used in breweries. Aluminum kegs therefore required epoxy linings. As a result of these deficiencies, aluminum kegs are now rarely seen, having been replaced by stainless steel.
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