The well-remembered beer was pretty popular in the Cleveland area, being brewed here.
According to the Encyclopedia of Cleveland History, P.O.C. stood for "Pilsner of Cleveland" since it was brewed by the Pilsener Brewing Company located near the intersection of Clark Avenue and W. 65th. But in the ad above from the April 23, 1954 Lorain Journal, P.O.C. could also stand for other things, depending on the ad campaign, such as "Premium of Course." Over the years, I also heard of other answers to the P.O.C. mystery: Pride of Cleveland, Pilsner On Call, etc.
The Encyclopedia of Cleveland History entry notes that in 1963, the brewery was purchased by the Duquesne Brewing Company, so P.O.C. was re-imagined to stand for "Pleasure on Call."
The brew has made a few comebacks, most recently in 2016 as a craft pilsener by Double Wing Brewing Company.
Here is the link to the page on its website for P. O. C. Pilsener.
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I hope that the latest version of P.O.C. is successful. It's pretty tough to get beer drinkers to switch brands (unless they are influenced by so-called influencers).
I know my taste in beer has evolved since the mid-1970s. When I was old enough to drink, my inaugural beer-drinking choice was 3.2% Miller. In college, my favorites were Genesee Cream Ale and later, Rolling Rock. (I can't forget Old Dutch, since my parents used to bring me a six-pack when they visited me in the dorm at Ohio State.)
After college, I haven't had too much beer in the last 40+ years; when I do, it's usually a brand with nostalgic appeal, like Carling's Black Label or Hamm's (which is in my fridge right now). But I will have the occasional Guinness on St. Patrick's Day. In fact, I made Slow Cooker Guinness Beef Stew last years for my work's St. Paddy Day luncheon and it was a hit. Of course, we had to limit servings, since each bowl of stew had some brew in it.
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P.O.C. Beer has been served up on this blog a few times. This post featured a 1949 hockey-themed ad; and this 1954 ad include an appearance by Pilsner Pete.