Minnesota's booming craft beer industry has created a huge demand for hops, an ingredient that provides the suds with bitter, citric, and zesty flavors and aromas.

A small but growing number of Minnesota farmers are answering the call.

"There was never a market here for Minnesota-grown hops until the craft brewing industry took off," said John Brach, owner of Stone Hill Farm near Stillwater and president of the Minnesota Hop Growers Association. "We are really just an offshoot of that economic engine."

Right now, only about 30 people are growing hops in the state, nearly all of them on 1 acre or less. Yet Minnesota growers are producing hops on a total of 73 acres this year, up from 26 acres in 2015, Brach said.

"We're getting more and more hops into the pipeline each year," he said.

One team of Minnesota entrepreneurs that planted its first 20 plants four years ago will grow 40,000 this year; it's building a production facility as well.

"We're trying to take an industry of local hops that is very, very small, and mature it to a place where it produces enough hops to supply livelihoods," said Eric Sannerud, co-founder of Mighty Axe Hops in Ham Lake.

Sannerud and his partner, Ben Boo, hatched a plan to grow hops as students at the University of Minnesota and have been experimenting with different varieties on 3 acres of Sannerud's grandfather's farm, selling them to local brewers.

Earlier this month, they announced an expansion to grow hops on 80 acres in Benton County northeast of St. Cloud, and they are planting the first 40 acres there this summer. They also have received financing and additional investment to build a state-of-the-art production facility with equipment to harvest, dry and pelletize the crop.

"It's been a wild ride," Sannerud said.

Hops, harvested from mid-August to September, are actually the cone-shaped flowers of female hop plants that grow on long vines, called bines. Sannerud and Boo walked their 3-acre site last week, pointing to pine poles 18 feet tall connected at the top with wire cables, from which long ropes or strings are strung and anchored to the ground in a V-shape. At this time of year the bines can grow a foot or more each day, Boo said, and they will eventually reach the top and form a canopy as the hop cones begin forming and growing.

Minnesota hops production pales in comparison with the epicenter of U.S. production in Washington state, where more than three dozen varieties are being cultivated on about 37,500 acres this year, according to federal estimates.

Brach, of the growers' association, said there's a "pecking order" in the industry, with the freshest and best hops sold to the largest national customers. "Whatever is left over is what's available to smaller brewers that can't sign the big contracts," he said.

Niko Tonks, head brewer for Fair State Brewing Cooperative in northeast Minneapolis, said that he buys whatever he can from Mighty Axe Hops in the fall when the cones are fresh but that he needs to rely on distant sources for dried hops during the rest of the year.

"People look to us as a local product, and it's incumbent on us to support other local enterprises," he said. "It's something we think is important."

Tonks said that he sometimes makes beer with one variety of hops but that he often uses a combination of two, three or four varieties.

"They provide bitterness, which counterbalances the natural sweetness of barley malt," he said. "And we get aromas and flavors from hops that vary from citrus to pine to tropical fruits to fresh and grassy. It's really all over the place."

Angela Orshinsky, assistant professor of plant pathology at the University of Minnesota, said hop plants have natural enemies such as aphids and mites. But the biggest challenge to growing hops in the Midwest is disease: powdery mildew and especially downy mildew, which can destroy crops.

Growers need to spray hops with fungicides every seven to 14 days to manage the mildew, Orshinsky said, so she is working on developing new hop varieties that would be more resistant to the mildew. The disease is less of a problem in the more arid hop farms in Washington, Idaho and Oregon, she said.

Breeding varieties more suitable to Minnesota's climate is a long-term effort, Orshinsky said, so she also is pursuing a separate track. "We're also researching ways of managing fungicides that have less environmental effects and also have less impact on the pocketbook," she said.

Getting started with a hops enterprise is expensive and labor-intensive, said Annette Vetse, co-owner of Gerhard Hops in Pine City. The perennial plants produce nothing the first year and only about 50 percent of their potential during the second year, so it takes three years to achieve full production. And every hop yard, no matter how large or small, requires painstaking work each spring, she said, including running new lines up and down the trellises.

"You also have to manually go out and train each plant to work its way up the string," Vetse said. "If you don't, then they'll snake all over the ground and then you've got a mess that's not worth anything."

Gerhard Hops began with a few plants in 2012 and will harvest 5 acres this year, she said. Vetse, her husband and two of his brothers own the farm, she said, and last fall they purchased another 40 acres that they will plant in phases during the next few years. All four co-owners have day jobs, she said, and tend to the hops mainly on weekends.

"Right now, we're not making a living off this, but the intention is that we will eventually, as the plants mature," she said.

Brach of the growers' association said it costs about $10,000 per acre to establish a hop yard, including a trellis structure, plants and an irrigation system.

Successful growers can sell the hops for between $10,000 and $20,000 per acre each year, he said, depending on variety and quality, before paying expenses. "The rule of thumb is that it takes about five years before you start seeing a return on your investment," Brach said.

With upward of 100 craft breweries in the state, he said, there's lots of room for more hop farmers to enter the market. The biggest obstacle to faster growth is the lack of production facilities like the one Mighty Axe Hops is building, because then the industry could serve the craft brewers year-round.

Sannerud expects that more hop farmers will emerge as the industry proves itself commercially. Despite the disease pressure and other risks, Sannerud said he's glad at least that hops are not attractive to critters like deer and rabbits that bother so many Minnesota gardeners.

"Mammals don't really like hops," he said. "They don't taste good until they're in a beer."

Tom Meersman • 612-673-7388