The 21st Amendment to the consitution is the one that repealed the 18th Amendment--Prohibition--thus ending the Great Experiment in 1933. Another part of the amendment gives the states a lot of latitude to regulate the alcohol business as they see fit, explaining why laws about the sale of beer vary so much more than laws on the sale of pop or coffee. Hence the name of the 21st Amendment Brewery in San Francisco. The brewhouse and restaurant are on 2nd St., between the downtown section and AT&T Park, where the Giants play baseball.
On to the beer! 21st Amendment ales have entered a lot of markets with their 12-oz cans. All the canned beers they sell under their name are brewed under contract at Cold Spring Brewing in Minnesota. Contract brewing has been a perjorative in some purist circles, but as Maureen Ogle points out in Ambitious Brew, her history of brewing in America, many successful craft brewers used contract arrangements to become successful, like Koch's Samuel Adams. My server told me the Cold Spring folks also fill 21st Amendment's barrel and half barrel kegs for the draft trade. The brewing equipment on the premises in San Francisco is in use, but only for mega-kegs (400 gallons or so) used right there on the premises.
The restaurant was crowded on a sunny Sunday afternoon after a ball game; on days like that you can bet the bartender is happy the kegs won't run out anytime soon.