The beers in this category are:
The area around Düsseldorf is one of the oldest inhabited areas in the world. In fact, Neanderthal man was found in one of the suburbs of Düsseldorf, about 10 miles east of the center of the city. While the Neanderthals weren't making the Altbier style arguably one of the oldest continuously brewed beer styles in the world. Before lagers were first brewed in the 1600s in Bavaria, the Altbier was simply known as "bier". It has only acquired the name "alt" since the 1800s when the style was threatened by the new lagers which are now the most popular beer in the world.
The history of California Common is a bit more ambiguous. The only beer which survives from the 19th century San Frisco area is Anchor Steam. No one really knows how close this beer is to the original "steam beers" brewed in San Francisco, but it has become the model for most modern versions. Because of the lack of refrigeration in any form, brewers in the San Frisco area had to rely on coolships with a large surface area to dissipate the heat of fermenatation. A lager yeast is used but at warmer than normal temperatures for typical lager fermentation. The word "steam beer" was probably derived from the German style, also called "steam beer" or Dampfbier. Dampfbier was fermented at warm temperatures with a Weizen yeast which produced unusualy active fermentations, which appeared to be boiling or "steaming". A couple of other possibilities for the name came from the idea that the high amount of carbonation in the style caused the kegs to whistle when tapped. Or, that the coolships gave off clouds of steam.
The Amber Hybrid category of beers is definitely one that all brewers should try.
References: Information for this page was adapted from the 2008 BJCP Style Guidelines, the page on Altbiers from The German Beer Institute, The German Beer Portal for North America, Brewing Classic Styles, 80 Winning Recipes Anyone Can Brew, by Jamil Zainasheff and John J. Palmer, and the article in Home Brewing Wiki about Steam Beer.
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