Though Prague has become a hot spot for beer tourism, visitors can end up disappointed by the lack of options in the city’s pubs. Many bars in town are locked into exclusive agreements with large breweries, which often install and control the taps. (Obzerstvi’s standard offer is Staropramen, a mass-produced brew from Prague that is part of the giant Anheuser-Busch InBev.) But recently, a few pubs like Obzerstvi have begun selling rare craft beers on a so-called ctvrta pipa, or fourth pipe, a new term for an independent tap on which pubs can offer a greater variety of brews.

“First it was fourth pipe, then there was one pub with seven taps, then it went to 13 or 14,” said Jan Kocka, one of the owners of the cult brewery Pivovar Kocour Varnsdorf, in northern Bohemia, whose beers are often available at the British-style pub Tlusta Koala in central Prague. “So fourth pipe really just became the word for rotating beers.”

This fall I spent several days touring the city’s ctvrta pipa pubs, from Obzerstvi in the south to bars on the semi-industrial north and many stops in between. Along the way, I heard several fanciful variations on the origin of the term fourth pipe. None was particularly convincing, but one version that at least sounded plausible  in part because it was so simple  came from Jirka Stehlicek, the owner of a tram-themed pub called Prvni Pivni Tramway.

“The fourth-pipe term really started with us,” said Mr. Stehlicek, speaking over a pint at a brewers’ awards ceremony last month. “We originally had three taps that stayed the same, and the fourth was just whatever else we could get. And it took off from there.”

Earlier this year Mr. Stehlicek joined with the owners of four other pubs, including Mr. Holcak, to form the Aliance P.I.V. (www.aliancepiv.cz), a group whose aim is to spread the word about quality beer by grooming more knowledgeable bartenders and providing more informative beer lists in the pubs. “We want to educate people,” Mr. Stehlicek said. “We want beer drinkers to know how their beer is made, what are the ingredients, as well as what kinds of Czech craft beers are now available.”