Alt refers to an old-school, top-fermented style of brewing ale rather than a relatively modern bottom-fermented lager. Altbier is especially associated with the city of Dusseldorf. Alts are a bit difficult to explain to the uninitiated - kind of like a hoppy Oktoberfest? A very malty pale ale? You'll just have to try a glass of coppery-brown, rich, caramelly, and bitter ale to get the idea.
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