Chris Lohring surveyed America’s beer scene in 2010 and decided to play the contrarian. Rather than mimic the popular and potent stouts and India pale ales, he would specialize in low-alcohol, high-taste “session beers,” as he called them.

To lenders, though, the business plan held as much appeal as flat beer. So Mr. Lohring kept costs low by using established breweries in Maine, Massachusetts and Connecticut to produce and package crisp pilsners and rustic farmhouse ales under his Notch Brewing label.

Contract brewing, as it is known, was perfect for a start-up like his, requiring no expensive infrastructure. “There’s nothing riskier than building a plant before the brand and the beers have been proven,” said Mr. Lohring, who in 1993 helped found Tremont Brewery in Boston.

Craft brewing’s decade-long global surge has been partly fueled by contract, or “gypsy,” brewers, rootless beer makers whose recipes are realized on other breweries’ equipment. Early trendsetters like Evil Twin Brewing and Mikkeller of Copenhagen and Stillwater Artisanal of Baltimore built themselves into international brands through sales in bars, supermarkets and beer stores.