Don’t assume the brewery on the label made the beer in the bottle.

Contract brewing is a common practice in the beer world, from craft outfits like Gritty McDuff’s, whose 12-ounce beers are brewed and bottled by Shipyard, to giants like Pabst, who pays Miller to brew Pabst Blue Ribbon.

For brewers who want to avoid the expenses of upgrading to larger brewing systems and hiring more employees, it’s an attractive deal.

For John Patrick Mullen, owner of Belfast Bay Brewing, it meant an end to 10-hour days to produce 60 cases of beer, not enough to keep up with demand.

He said the worst part was bottling. “We had a small capping-bottling machine, and it was just awful,” Mullen said. “I couldn’t hire anyone to do the work.”

In Portland, Shipyard had upgraded its equipment and wasn’t selling enough beer to keep its fermenters full and its bottling line running constantly. Mullen said he brought his two best beers, Lobster Red Ale and McGovern’s Oatmeal Stout, to Shipyard brew master Alan Pugsley, who reformulated his recipes to brew in larger volumes.

At the time, Mullen was struggling to sell his beer outside Maine. Now, it’s sold in 13 states and his role is solely marketing his brews down the East Coast and as far west as Chicago.

In the 1980s, craft beer fans criticized the Boston Beer Company for contract brewing Samuel Adams Boston Lager at several breweries across the country. Many argued that paying someone else to make your beer, even by your own recipes, was inauthentic.

It’s more accepted now as breweries see fast-paced growth that many can’t keep up with. The Brooklyn Brewery, a prestigious brand based in New York City, has most of its beer made by the Matt Brewing Company, best known for the Saranac line of beers.

The Boston Beer Company now owns its breweries, including one in Cincinnati that used to contract-brew its beer.

Luke Livingston, president and owner of Baxter Brewing Co. in the Bates Mill in Lewiston, said that from the beginning it was important to make his own beer.

“When I first wrote my business plan, the thought of contract brewing was a last resort for me,” Livingston said. “It was sort of, ‘Well, if I don’t have any other choice, it would be better than nothing.’”

Shipyard brew master Alan Pugsley said that about 15 percent of the brewing company’s production is contract work for other brands. In Maine, that includes Gritty’s, Belfast Bay, Peak Organic and some brewing for Atlantic Brewing Co.

The brewery also works for several out-of-state brands, including the Woodstock Inn Brewery in New Hampshire, Davidson Brothers in Glens Falls, N.Y., and St. John Brewers in the Virgin Islands.

Gritty’s co-founder Ed Stebbins said having Shipyard brew his beer was a perfect arrangement. After all, Pugsley helped Stebbins and Gritty’s co-founder Richard Pfeffer start the Portland brew pub back in 1988. Pugsley designed some of Gritty’s most enduring recipes, including Pub Style Ale, Best Bitter and Black Fly Stout.

“We have a great relationship,” Stebbins said of Pugsley. “I am the luckiest guy in the world in that I get to brew my beer two blocks away from my brew pub using the same water, the same yeast, same everything.”

To many Gritty’s customers, it’s no surprise. Jacob Gilbert of Livermore, who has his own mug at the Auburn pub, said Gritty’s is his favorite watering hole, though he’s a fan of most Maine beers. He said he knew Gritty’s bottles were made by Shipyard.

“I like Shipyard. Geary’s, Gritty’s, Sebago, Allagash,” he said, listing off some of Maine’s largest breweries. Gilbert said he and his brother, Caleb Gilbert of Buckfield, go to beer festivals in Maine and Massachusetts and are familiar Maine’s brewing scene.

Steve Gorrill, who runs the Sheepscot Valley Brewing Company in Whitefield, had much of his beer brewed by Sebago Brewing for years. Sebago was brewing his flagship Pemaquid Ale in 22-ounce bottles and and in kegs.

“I did it not really to get bigger,” Gorrill said. “I did it so I didn’t have to work 70 hours a week.”

In the past year, growth at Sebago Brewing meant it had to use all of its equipment for its own beer. Gorrill pursued a contract-brewing relationship with Geary’s but decided against it.

Gorrill still does good business with growlers, half-gallon bottles for which his customers drive to his small farmhouse brewery to buy refills. He hasn’t ruled out another contract brewing deal in the future.

For now, Gorrill would rather stay small than work extra hours. His brewery is open for growler refills for about 90 minutes a week, usually on Friday evenings.

Mullen still brews small amounts of Belfast Bay beers in his brew house. According to MaineBiz, Mullen brewed three 31-gallon barrels of his brewery’s 1,020 barrel output in 2009. Under Maine state liquor law, his brewing allows him to distribute his product around Maine.

He said he’s glad that when he sells beer in another state, he doesn’t have to worry whether he can produce enough to fill the orders. “We call up Alan and say, ‘This is what we need.’ I make sure the trucks go down and make sure they’re ready and they just load the trucks.”