California Common beer is a style of beer brewed with lager yeasts but at ale fermentation temperatures. It has its origins as Steam Beer. Steam Beer is a trademark of Anchor Steam Beer brewery of San Francisco.
No one can say exactly where the name Steam beer came from. Perhaps the name Steam is derived from the 19th century when steam seems to have been a nickname for beer brewed on the West Coast. Or, it may be that the name derives from the sound of steam escaping from a tapped keg! No one can say for certain why the word steam came to be associated with this particular beer, however most would agree that the term originated on the West Coast.
At the time, brewing was done under primitive conditions. Ice was hard to find and probably non-existent for brewers. Resourceful California brewers used lager yeast but at higher ale temperatures. Why is this important?
Final flavors of beer are influenced by the strain of yeast and the fermentation temperature. Lager yeast is best used at temperatures from 55°F down to 32 °F. Classic lagering of beers takes place over a period of time from weeks to many months at a temperature of 45°F. Lager yeasts are bottom fermenting, which is to say that they will flocculate and settle to the bottom of the fermenting vessel.
Ale yeast is best used at temperatures from 55°F UP to 75°F. Fermentation by ale yeasts produces a beer that has a distinctive ale flavor. Ale yeasts are Top-fermenting, that is they flocculate on top of the fermenting beer. Steam Beer uses bottom fermenting lager yeasts at ale temperatures, which results in a very distinctive flavor profile that includes both ale and lager characteristics.
Today, California Common Beer is recognized as a unique America Amber beer style.