PORTLAND, Maine — Tom Bull’s got a bunch of hops in his company’s refrigerator – which makes sense, as the company is Bull Jagger Brewing Co.

The thing is, the hops aren’t his.

They belong to Maine Beer Co., a neighbor in the same building that needed some extra space. But when Bull needs a forklift to load something heavy, he just helps himself to Maine Beer’s. And New England Distilling, a relatively new neighborhood denizen, has got Bull’s grain mill — at least on loan.

For years, economists and economic development specialists have talked about the importance of growing sector “clusters,” with similar businesses growing up around each other a la Silicon Valley, the Research Triangle or Massachusetts’ Route 128 corridor.

In Maine, that’s often proven to be a tough go. The state has a variety of businesses but they tend to be spread out all over the state — a semiconductor company here, a boat builder there, a big biotech company around the corner.

But on its own, driven by market forces and business decisions, Portland has a brewery/distillery cluster off Riverside Street in an industrial area on the fringe of the city. The breweries and distillery share equipment and expertise.

And businesses — particularly the new ones — are benefiting from some of the classic features of a cluster.

“I think it’s been crucial,” said Bull. “It’s been extremely helpful to have them around, and to be able to pick each other’s brains. If we’re up against a problem, they’re right here.”

First there was the D.L. Geary Brewing Co., incorporated in 1983 by David and Karen Geary as one of the first microbreweries not only in the neighborhood but in Maine and even New England.

“We were it — we were it in New England,” said David Geary. “We didn’t get to borrow from anybody.”

Geary’s, which specializes in English-style beers, started brewing in the neighborhood in 1986 in 5,000 square feet of space. The business has expanded several times and Geary now jokes it’s a 22,000-square-foot brewer in 18,000 square feet of space.

In 1995, Allagash Brewing Co.‘s Rob Tod started making his Belgian ales in the same industrial park.

Maine Beer Co. has been in at 1 Industrial Way for about three years, said co-owner David Kleban, across the street from Allagash and in the same building as Bull Jagger, which moved in about a year ago.

Rising Tide Brewing Co. had been in the same building but moved recently to the East Bayside neighborhood of Portland, an industrial area tucked between the base of Munjoy Hill, Interstate 295 and the Franklin Arterial.

Another brewing/distilling cluster is growing there. Bunker Brewing and Urban Farm Fermentory both are close by and a new distilling company has just signed a lease, said Nathan Sanborn, owner/brewer at Rising Tide.

There are a few reasons the clusters are growing in such a way, said the business owners. A big one is zoning. Both of those areas are zoned industrial, and that’s what breweries need. The other is the space is fairly inexpensive and the right size enough to work for the small breweries, now being referred to popularly as “nano-breweries.”

“It’s a great incubator space. The rent is cheap, relatively speaking; the community is here, with all of the brewers,” said Bull, “and then our distributor is also right here — Mariner Beverages.”

But there are other reasons that have to do entirely with having a community of similar businesses around.

Kleban said when he and his brother first started Maine Beer, they were walking across the street to seek advice from Allagash regularly. Kleban and his brother were experienced brewers but were able to learn a lot about selling to the public, production-scale work and other areas of knowledge necessary for a successful business. Kleban said the folks at Allagash would open up their equipment, showing him how a solenoid valve was wired or how other equipment worked.

“If you’re starting a small brewery and you haven’t been in the commercial brewing world for a lot of years, you have a lot to learn,” said Kleban.

Deedee Germain, who handles marketing and communications for Allagash, said her company is happy to see the other companies doing well and feels that a rising tide lifts all boats.

“When Rob [Tod] was starting, there weren’t a ton of other brewers around; we had to go it alone a lot,” said Germain. “There’s merit to that, but we learned a lot and we’re happy to try to help out when we can and pass on our knowledge, all the lessons we learned.”

Allagash is in 20,000 square feet of space and has 46 employees.

Bull tells a story about how he was in the middle of brewing a batch of beer when his pump died. He started asking around about where to buy a new one, and Allagash sent over one of its engineers to fix the pump.

Sanborn, from Rising Tide, said he had brewed a special barrel-aged beer one time and he needed to do a cell count to figure out how much yeast was still in the beer and how much he should add for fermentation. Allagash used its lab to help him out, said Sanborn.

“I would have had to buy a microscope and a hemocytometer and do it myself. That’s something we’re building toward, but this was fairly early on, and it was helpful,” said Sanborn.

He said he needed to move as his business was beginning to grow. Rising Tide recently installed a larger brewing operation and Sanborn has his first part-time employee starting soon, with a full-time worker on the horizon.

And the move downtown will make his company more accessible to the population at large, said Sanborn. Even so, he said, it was a difficult choice to make.

“The community was fantastic,” said Sanborn.

Another benefit of the “Brewer’s Row” cluster off Riverside is that people tend to take tours of breweries and those businesses can suggest they hit the other breweries in the neighborhood, said Ned Wight, owner of New England Distilling.

Wight is making gin and rum and developing some whiskeys.

In one tight area, visitors can tour a lager brewery, a maker of traditional British ales, a Belgian brewery and an American ale maker — not to mention the distillery, noted Wight.

That variety is part of why the cluster works, several of the brewers said.

“We feel there’s so much market share, so much to be had, and everyone’s kind of an artisan who’s after great beer,” said Kleban. “As long as all the great beer’s different, there’s plenty of room for all of us, in terms of growth.”

Added Bull, “Yes, we’re all competition, but we’re all each other’s biggest fans — it’s amazing.”

Geary noted that there is an active brewers guild the companies belong to which tends to socialize members and lead them toward cooperation and encouragement. And, said Wight, the industry tends to attract folks who are so inclined.

“In general, the folks that are drawn to producing beer and spirits, and I’m sure wine, are generally pretty laid-back, pretty nice people. It’s a great bunch of folks to hang out with,” said Wight. “They tend to be very passionate people about what they’re doing.”

Brewer’s Row, off Riverside Street

D.L. Geary Brewing Co., 38 Evergreen Drive

Allagash Brewing Co., 50 Industrial Way

Maine Beer Co., 1 Industrial Way, No. 3

Bull Jagger Brewing Co., 1 Industrial Way, No. 8

New England Distillery, 26 Evergreen Drive

East Bayside Brewers

Rising Tide Brewing Co., 103 Fox St.

Bunker Brewing, 122 Anderson St.

Urban Farm Fermentory, 200 Anderson St.