Kyle Sherrer of Millstone Cellars in Maryland visits Black Locust Hops in Baltimore County. He has used hops as an ingredient in his hard cider. (Jeff Benzon)

In late July, Kyle Sherrer and his father, Curt, the founders of Baltimore County’s Millstone Cellars, visited a nearby hop farm. At Black Locust Hops, they walked among trellises of bines — the vinelike creepers on which the pine-cone-shaped flowers grow — and crushed hops between their fingers, smelling the citrusy aromas that the ingredient often lends to India pale ales and other beers.

Soon after, some of the harvest found its way into barrels of Millstone’s Hopvine cider, not kegs of IPA. With two years of commercial cider and mead production behind them, the Sherrers introduced the batch during a mid-October tasting dinner at Pizzeria Paradiso in Georgetown. They plan to distribute bottles throughout Maryland and the District this winter.

The apple, it seems, has learned to love the hop — and not only hops but bourbon barrels and beer yeasts. As the American cider industry goes through a seemingly endless growth spurt — shipments during the first quarter of 2013 were nearly double those of the same period in 2012, according to the Beer Institute — it is diversifying, too, with artisans sometimes borrowing flavors and techniques from their craft-brewer cousins.

“If you look at what’s popular, it’s really running the gamut,” Kyle Sherrer says. “There are the purists on one end, just caring about the apples. But then there are a lot of cidermakers, younger ones in particular, who are taking cues from craft beer.”

In part, this blurring of boundaries can be attributed to the involvement of former home-brewers and beer professionals. Consider Greg Hall, the longtime Goose Island brew master who has launched Michigan’s Virtue Cider and who says he is in talks to sell his products in Maryland and Washington in early 2014.

While Hall, who riffs on the ciders of England, France and Spain, is something of a traditionalist, he also makes a bourbon-barrel-aged cider that he calls “uniquely American,” an apple-y counterpart to Goose Island’s Bourbon County Stout. Hall’s background also manifests itself more subtly, in an emphasis on the scientific aspects of fermentation. He says, for example, that he just hired Mary Pellettieri, a yeast and quality-control expert who helped develop some of the Goose Island beers that feature Brettanomyces, a rustic yeast that Hall uses in his ciders.

“We look at cider and say, ‘Boy, what are the different variables we can control?’ ” Hall says. He attributes the rise of hopped ciders and other innovations to this decidedly un-European spirit of experimentation: “They’ve been making cider next to hop fields in England for, you know, a thousand years or so, and I don’t think anybody has ever thought to put hops in cider over there.”

But Stephen Wood, of New Hampshire’s Farnum Hill Ciders, sees good reason for this conservatism: “In England, they always say you should never let a brewer make cider.” Brewing, he says, is like cooking, with the quality of the result depending largely on technique and creativity; cider, in contrast, is all about the apples, which are akin to a winemaker’s grapes.

Still, with many small cidermakers, one gets the sense that winelike refinement is less of an objective than a certain no-holds-barred playfulness, in which there is much to love.

There would be something almost Grinchlike, for instance, in frowning upon what home-brewer Devin Britton and seventh-generation apple grower Albert Wilklow are doing in Upstate New York with their young Bad Seed Cider Co., whose bottles are available primarily at New York City farmers markets. Britton says many of his ciders are based on his old home-brew recipes: “I more or less just said, ‘All right, let’s make them with cider and see what happens.’ ”

The result: Bad Seed’s Belgian Witte Reserve, fermented with orange peel, coriander, hops and Belgian beer yeast, smells like bright citrus and champagne and is eminently gulpable — tart, fruity and refreshing. Whiskey enthusiasts, however, might prefer Bad Seed’s straightforwardly oaky and caramelly Bourbon Barrel Reserve.

In case you aren’t passing through New York anytime soon, beery ciders are available closer to the Capitol. In addition to Millstone, tiny Blue Bee Cider of Richmond makes a cider with Cascade hops, and Anthem Hops cider — the piney, grapefruit-y creation of Oregon’s Wandering Aengus Ciderworks — is sold at craft-beer bars such as Meridian Pint.

National brands have gotten into the game, albeit with mixed results. Fox Barrel Wit Pear Cider, a concept similar to Bad Seed’s Belgian Witte, is sweet and lifeless. But Crispin’s the Saint, fermented with a Belgian Trappist ale yeast and maple syrup, stands out with pleasant fruity aromas and a smooth, slick texture that fades into nuanced notes of real maple.

The imprimatur of MillerCoors, which owns the Fox Barrel and Crispin brands, might lead some to view hops and beer yeasts as cider-world gimmickry. But there’s a more optimistic way to interpret the conglomerate’s products: as part of a spectrum that encompasses both the country’s second-largest beer company and tiny Bad Seed Cider, both purists like Stephen Wood and the sort of cidermakers who stroll through hop fields.

“At the end of the day,” Millstone’s Kyle Sherrer says, “everyone is taking their own approach to what American cider can be.”

Fromson is the author of the e-book “Finding Shakespeare,” published in August by the Atavist, and a Web copy editor at the New Yorker. He writes Beer monthly.