A Westerns staple is the saloon, where men went to meet, gamble, and drink. For the most part, the movie booze was fake—tea or colored water stood in for whiskey and beer, while a whipped, refined sugar was used to create the foam head. Producers didn’t use the real thing for fear that the actors would get drunk over a span of several takes.
But it appears that the beer on Gunsmoke was the real deal. James Arness was quoted as saying that low-alcohol beer was used to maintain at least some sobriety on the set.