PORTLAND — The Shipyard Brewing Co. has formed a partnership with Miller Brewing Co. that will pay off Shipyard’s debts, double its production and continue its rapid growth, officials said Thursday.

American Specialty & Craft Beer, a Miller subsidiary dedicated to forming alliances with microbreweries, is buying a 50 percent stake in Shipyard, said Fred Forsley, Shipyard’s president.

With the capital infusion, the state’s largest brewery will boost its annual production capacity from 54,000 barrels to 108,000 barrels, allowing a push into the New York market, Forsley said.

Forsley and master brewer Alan Pugsley will maintain control of the company and production of its brews, which include Shipyard Export Ale, Blue Fin Stout, Moose Brown Ale and Longfellow Winter Ale.

“We have control over how Shipyard Ale and our other beers are brewed,” Forsley said. “It’s not a sellout.”

Scott Barnum, general manager of the Miller subsidiary, said his operation will act as a buffer to make sure Miller does not interfere or “Miller-ize” the company.

“We would be committing hari-kari if we messed with the product,” Barnum said.

Officials declined to say how much the deal was worth. But Forsley said he needed a $1 million investment to boost production and another $1 million investment for improvements to the company’s property.

Under the arrangement, Shipyard will be able to rely on Miller’s specialty beers subsidiary for marketing advice, technical expertise and economies of scale in such areas as bottle purchases.

The deal will allow Shipyard to boost its work force of about 50, Forsley said. Shipyard’s Kennebunkport Brewing Co. and Federal Jack’s brew pub in Kennebunk are not part of the deal, he said.

For its part, Miller gets its foot in the door on a segment of the beer industry that is seeing growth in a flat market.

Craft-brewed beer accounted for 1.3 percent of overall beer consumption in America last year, but it’s expected to reach up to 5 percent this year, said Jim Neighbors from the Institute for Brewing Studies in Boulder, Colo.

Some in the industry have predicted that craft-brewed beer could ultimately reach 10 percent of the market.

State reports indicate microbrewed beer already accounts for at least 4 percent of the beer market in Maine, said David Geary, who started the state’s microbrew revolution with his Geary’s Pale Ale.

There are now 16 breweries in Maine, including the likes of Shipyard, Geary’s, Casco Bay, Sea Dog, Carrabassett Valley, Sunday River, Black Bear and Lake St. George, Geary noted.

Nationally, microbreweries and brew pubs are opening at the rate of five per week, Neighbors said.

Shipyard, which started in 1992, grew swiftly into the state’s largest brewery with an anticipated production of 30,000 barrels this year, pushing it out of the microbrewery category.

“They’re experiencing unbelievable growth,” said Neighbors.

The major brewers have taken note, starting up specialty beers of their own, like Miller’s Red Dog and Anheuser Busch’s Red Wolf. Anheuser Busch also bought a stake in Red Hook in Oregon, which is opening a brewery in Portsmouth, N.H.

Miller’s original involvement with microbreweries started eight years ago with the purchase of Jacob Leinenkugel Brewing Co. in Chippewa Falls, Wis., Barnum said Thursday.