ATLAS TWP, MI -- When Sean Trowbridge breaks the seal on the latched door to a walk-in freezer storing bags of varying sizes, a hoppy blast slaps you in the nostrils.

(Take a look at three beers using hops from Top Hops in their brews)

The aroma is wheaty, flowery and distinct to Top Hops Farm in Atlas Township, a commercial hops farm that's looking to grow in 2015 and build relationships with local brewers and capitalizing on the industry's growth in the state.

"My parents and I we were kind of interested in trying to find something that would work here on the farm, as far as farming produce," he said of the 55 acres purchased a few years back by his father Mark Trowbridge, a retired engineer.

"With the way the craft beer industry had been going, we'd already been growing crops for a couple of years and we just visited some other hop farms in Michigan to get an idea of what it's really like," said Sean.

"We started out with a few plants next to the corn crib out here," Mark Trowbridge said. "Sean went out and bought some rhizomes off of Craigslist and put them in. They actually took off and grew quite well. I think that helped to motivate us to take the next step."

Sean Trowbridge said he grew 10 to 15 plants on the side, eventually moving to a trial yard of around 200 "When we were really serious about looking at commercial production" and planted five and a half acres in spring 2013.

Witnessing the craft beer industry flourish, he said, "We decided we'd commit to putting in a commercial amount of hops that would be substantial enough that the brewers could use it and that there could be a supply year-round and not just a couple brews."

The craft brew industry saw $14.3 billion in sales nationwide in 2013, up 20 percent from the previous year, according to figures from the Brewers Association, a Boulder, Colo.-based membership organization started in 1978.

The state of Michigan had 131 craft breweries in 2013, the fifth-most in the nation, producing nearly 583,000 barrels of craft beer that equaled $1.005 billion in economic impact.

Jason Moon, public information manager for the Department of Licensing and Regulatory Affairs, said there are 133 licensed micro brewers in the state in 2014, as well as 43 pending applications.

In terms of production, Moon said micro brewers are allowed to produce up to 60,000 barrels of beer in one year for consumption on-site, for take-out or sale to a licensed wholesaler.

Micro brewers can also sell directly to retail licensees if they produce less than 1,000 barrels each year and don't have a sales territory granted to a wholesaler for that specific area. Moon said micro brewers are not required to have an additional license.

Hops production remains a small industry in Michigan, compared to other states such as Washington, Oregon and Idaho. Nevertheless, Michigan has become the fourth-largest grower in the country.

Approximately 39,272 acres of hops were produced in the U.S. in 2014, according to the Hop Growers of America, with 29,021 acres, or nearly 74 percent of that amount in Washington state alone.

Rob Sirrine, a community food systems educator with Michigan State University Extension, said there are now more than 400 acres of hops in Michigan, exceeding the largest production numbers in the state since the 1880s.

"It's been growing pretty substantially," he said, with some of the larger farms including Empire Hops Farm in Northwest Michigan and Hop Heads Farms outside of Kalamazoo.

The industry may also receive a bump with a House Bill 5275 working its way through the state Legislature. The bill would provide a tax credit to brewers using at least 20 percent hops and 40 percent other ingredients grown in the state.

"You compare that to Washington and they're monsters out there, but people are starting to take notice, actually (of Michigan)," said Sirrine.

Starting with five and a half acres of the three standard Cs of hops -- Centennial, Chinook and Cascade varieties - Sean Trowbridge said Top Hops broke ground on the crop in fall 2012, and put plants in the ground by spring 2013.

"The safe bet starting out was to get some of the C hops that are just really common in the American IPAs and American pale ales," he said. "It's what a lot of growers planted, so that's what a lot of growers that are just getting into it are continuing to plant because they hear they do well here in Michigan."

But placing the plants in the ground and hoping they will grow is just a small step in the process. The family had to purchase equipment, set up the process and hire employees to help out during the fall harvest.

"It was huge (in terms of investment)," said Sean Trowbridge, while noting the harvest takes patience in the first few years. "Hops aren't mature from their first year into the second year to the third year you're starting to see a mature crop of hops, so you put the investment in and it takes quite a while to see the return."

The farm yielded 6,300 pounds of hops in 2014 following an extensive process. The perennial plants shoot up each year in the spring, Sean said, with an 18-foot trellis made of Michigan white pine wood and steel wiring from a Flint business holding up Coir yarn made of coconut husks.

"One plant at a time you wrap the vines up the strings. It is labor-intensive," he said. "Once that's done, you really just maintain your fertilizer and pest maintenance in your hop yard."

Spider mites and aphids are the main pests, along with weeds. The farm uses a synthetic fertilizer through a drip line irrigation system hovering over the plants.

"We're not an organic farm, but we're certified an environmentally friendly farm through the state, the NRCS (Natural Resources Conservation Service) program, so we definitely make an extra added effort to make sure we're not polluting the grounds," said Sean Trowbridge. "We're not having off-target drift from our spray when we spray. We have buffer strips in place around riparian zones and areas of wetlands."

Near the end of June, Trowbridge said, the plants start to cone out "based on a photo period that triggers a response in the plant for flowering and it is daylight oriented."

"They start to flower out and by mid-August to late August, they have full cones formed and you start checking the hops to see their doneness," he said, including sending portions of the green hop to laboratories to check on their acidity and moisture content.

Sean said the main location used for that portion of the process is KAR Laboratories, a Kalamazoo-based environmental testing lab.

Once the hops are deemed ready, which Trowbridge said can be a head-scratching process at times because they want to remove them at their peak to ensure the most taste and freshness, a crew is assembled to cut down the plants at the top and bottom, and place them in a harvest wagon.

The plants are then brought into their barn and laid on a tarp before being fed into the Wolf 140 machine that carries the hops on a conveyor belt, with picking fingers stripping everything from the hop vine, Trowbridge said. The vine and coir go into a chopper motor and spit out as waste and hops separated.

While it depends on the variety of plant and its health, Trowbridge said up to two pounds can be harvested from each plant before they are packaged into a variety of weights -- from one-pound pouches to provide during business meetings with those interested in the product to dozens of pounds of pelletized hops for beer production that can be stored longer.

"When we set the business up we realized that 99 percent of brewers only used pelletized hops," he said. The farm does offer some fresh, wet hops from the field to box they can get out in five to 10 hours. "Their brew systems aren't set up for whole cone and wet hops are a relatively young thing."

Sirrine commented "More and more folks are trying to do harvest ales" that use fresh hops, but it's not a very large market, Sirrine said.

"They're a seasonal thing and you take them to the brewers and put them in," he said of the hops. "There's a short window. By December, the flavor of those beers in the bottles has started to change."

Top Hops Farm provide hops for brewers in other places around the state, but the majority are in the southeastern Michigan area, including Redwood Lodge in Mundy Township, 51 North Brewing in Lake Orion, Fenton Winery & Brewery, Rivers Edge Brewing in Milford, Eternity Brewing in Howell, Sherwood Brewing in Shelby Township, Falling Down Beer Company and Kuhnhenn Brewing in Warren.

Bill Gravanis, owner of Red Baron Taproom & Grill in Burton, recently purchased a total of 20 pounds -- including Cascade and Chinook -- to use for brewing in an IPA over the next couple weeks.

"So far, they've been good," he said of the hops bought from the farm, adding "Anything I can get locally produced, especially hops, is a plus."

In trying to keep up with the changes and growth in the industry, the farm planted an additional five acres in 2014, with hop varieties including Mt. Rainier, Tahoma and Cascade. "There are a lot more beers out there that don't use Cascade, Chinook and Centennial," Trowbridge said.

He welcomes anyone who wants to enter the business, including Martin Hops Farm in Durand that farms few acres of hops on their property, But he cautions people who may see it as a quick production that it's a lot of work.

"It's very expensive to start up, the profit margins are fairly slim, so if you're only producing a small amount of hops, it's probably going to be difficult to get any money out of it with all the money that's put in," he said.

Sirrine said start-up for a hops farm can run $15,000 per acre along with $4,000-$6,000 for operational costs, not including the cost for land or equipment. A five-acre farm could cost between $250,000 and $500,000.

Mark Trowbridge said 2015 should be the turning point in terms of seeing a return on their investment. "We're trying to cut back on any expansion funds or anything like that. We're pretty much tapped out, so we're just trying to get through next year."

Sean Trowbridge said when they first began selling hops there was a hurdle with brewers in the state.

"It was still early in Michigan hops and up until the last couple of years they've been having people come up and say 'hey, I grow these hops in my backyard, buy these hops," he said. "I think the brewers have probably been off put for a while saying no you probably don't have hops."

Sean said it took some time for them to realize "This guy's got a commercial hop farm. He's got adequate quantities; he's got quality control things in place. This is a viable option for me to use local hops and it's going to be a good quality product."