But the real advantage for Pretty Things is the creative flexibility that comes with having few sunk costs. Conventional breweries need to make a regular income to cover loans, pay investors, and meet insurance premiums—which, at least until the upfront costs are covered, means brewing beers that will sell widely. That's partly why new breweries start with crowd-pleasers like IPAs and brown ales, and only later venture into palate-challengers like sour ales and imperial stouts.

"We're able to be crazy creative," Martha said. "We brew for our own entertainment." Indeed, few breweries are as proudly idiosyncratic as Pretty Things. They draw their own labels and promote their new beers with home videos posted to YouTube. Like other gypsy brewers, they eschew standard styles in favor of deeply personal tastes; Babayaga, which Dann described as a "woodland stout" and is brewed with malts roasted with rosemary, "was meant to taste like an old lady made it in a shack in Eastern Europe."

It's a similar story for Mikkel Borg Bjergsø, who started brewing under the Mikkeller label in 2007 and has become one of Europe's best-known craft brewers. He said he chose the gypsy brewer route specifically because he wanted the freedom to tap different breweries with different areas of expertise. "I get to choose the breweries I want to work with," he said. "Different breweries have different advantages"—everything from the characteristics of their water supply to the training of their brewers. In less than four years, he's collaborated with a veritable who's who of world-class breweries, including Belgium's De Proef, Norway's Nøgne Ø, Scotland's BrewDog, and Indiana's Three Floyds.

It's also been a way for Bjergsø to break into the U.S. market. Not only do the beers he makes stateside not need to clear customs, but by working with domestic breweries, he's built up an impressive list of contacts among brewers, distributors, and importers, all people who can help him get his beers into the hands of American consumers.

There are, of course, downsides to gypsy brewing. For one thing, the concept is still foreign to most consumers, even many beer geeks. Dann Paquette said a lot of people think Pretty Things is a contract brewery—that is to say, a brand that pays someone else to actually make the beer. "Everything about the beer comes from us," he said. "The brewery just provides the equipment."

Gypsy brewers also have to work around their hosts' schedule. "There aren't many brewhouses these days that are sitting around with excess capacity," said Brian Strumke, the owner, brewer, and sole employee of Stillwater Artisanal Ales.

Strumke brews most of his beer at a facility outside Baltimore, but he frequents breweries in Belgium as well. By both choice and necessity, he said, "my business model is to be wide and shallow," producing a wide range of styles in small quantities. Microscopic, at times: as part of Baltimore Beer Week, Strumke recently debuted Requisite, an "imperialistic" stout available for a single night at a single bar.