Those particular leaves were Labrador tea. Nearby were sacks of mugwort, yarrow and bee balm, all of which Mr. Hunt uses to make a little-known style of beer called gruit, brewed in a centuries-old tradition, without hops. Today's craft brewers are hops-mad. Most use the plant with expressionistic abandon in ever-bitterer brews: dry-hopped, fresh-hopped and continuously hopped double, triple and imperial IPAs. Eschewing hops is rebellious (in fact, technically illegal—by government definition, a "malt beverage" must include some hops, so even Mr. Hunt uses a little). But in beer's seven-millennia history, it's nothing new.

Brewers only began using hops regularly 700 or so years ago, when they discovered that the thumb-size cones of resinous leaves would help keep beer fresher longer. Before that, beers were flavored with dozens of different herbs and spices—medicinal, symbolic or just plain potent. In 1699, diarist John Evelyn wrote that a dose of borage would "cheer the hard student." Henbane, once a popular addition, is hallucinogenic, and in some doses, lethal. Hops, a sedative related to cannabis, would have seemed tame by comparison—one reason, some argue, that promoting temperance through hopped beer was a Protestant cause; Martin Luther drank it at Worms.

"Is this reactionary?" Mr. Hunt asked. "Yes. All the beers in this country use just one species of plant: hops. What if there were a hundred species? Where could this go?" Working in the gruit style, brewers like Mr. Hunt can blend flavors untasted for centuries and also tell stories untold until now. MateVeza's Morpho uses floral hibiscus and minty bay leaf to transport drinkers to the South American jungle; Cambridge Brewing Company's Weekapaug Gruit, made with locally plucked bog myrtle, says there is more to Massachusetts swamps than cranberries. While other beers use hops trucked in from time zones away, Moonlight's Working for Tips thinks local: Its redwood twigs come from a tree in the brewery's front yard.

These beers take some explaining—one reason they can be hard to find. "It's easier to do in a brewpub, when you can interact with people about it," said Dave McLean, owner of San Francisco's Magnolia Gastropub and Brewery. Take a beer like his sweet gale–, yarrow– and wild rosemary–flavored Weekapaug Gruit (like the brewer at Cambridge, Mr. McLean is a fan of the band Phish, and the song Weekapaug Groove): It's unique, but not aggressively so. When introducing unfamiliar flavors, a delicate touch is best. Revolution needn't shout. Mr. Hunt jokes about "roasted-chicken gruits," too heavy on the rosemary. "My intention is to make a delicious beverage. I don't want a beer to taste like a Christmas tree," he said—even if, one day, he might brew a gruit made with one.