By James Marson

GRIMBERGEN, Belgium--The boss of beer giant Carlsberg A/S had a question before he picked the site for a pricey new microbrewery at the 900-year-old abbey here: Where did the last one stand before French revolutionaries torched it?

Those are the kind of questions that matter these days to executives at big brewers like Carlsberg CEO Cees 't Hart, who are responding to beer drinkers' thirst for exclusivity.

Grimbergen Abbey on Thursday relaunched a brewery inside its walls for the first time in more than 200 years. The resurrection has furnished its sponsor, Carlsberg, with its own kind of holy grail: unique and authentic brews.

The facility will produce beers inspired by ingredient lists found in ancient manuscripts in the abbey library -- the kind of niche brews that have helped upstart competitors take chunks out of Carlsberg's mainstay market of mass-produced lagers.

The Danish beermaker has spent millions of euros on the project, making it one of the company's most expensive per hectoliter produced, says its chief commercial officer, João Abecasis. One reason was the age of the building site and efforts to respect traditions.

Global brewing conglomerates including Dutch Heineken N.V. and AB InBev, the Belgian brewer of Budweiser, have snapped up craft rivals in recent years to try to boost growth as beer drinkers turn away from bland lagers.

"It's very important for our growth, now and in the future," Mr. 't Hart said at the launch at the abbey Thursday. "It's a fantastic story. It's appealing to everybody that likes beer."

Centuries ago, monks were the original craft brewers, using local ingredients to create small batches of singular beers. But the number of monks to beer the brew has dwindled. Global brands have stepped in, hoping to cash in on demand for specialty brews like abbey beers, which have become a commercial hit for big brewers.

The brewery at Grimbergen Abbey, on the northern outskirts of Brussels, has burned down three times since it was founded in 1128 by Norbertine priests. Beer likely tasted very different then and was often preferred to water for sanitary reasons, says Father Karel Stautemas, a 57-year-old former accountant who takes care of the abbey's finances, as well as its beer. A cow bone, used in the brewing process to purify the water, was discovered during construction and dated to before the French Revolution, he says.

When priests returned in the early 19th century, they didn't restart brewing. But in 1958 a Belgian brewer offered to pay royalties to the abbey to produce beers under its name. The relationship was common at the time as monasteries struggled with aging communities and weakening finances. Abbey beers, including InBev's Leffe, are produced at commercial facilities that have little in common with houses of worship, leading to criticism that they are inauthentic.

Several Trappist abbeys where monks still oversee production created a label in 1998 with strict rules in order to demonstrate their authenticity, including that the beer should be brewed inside the abbey walls and any profits should be spent on the community or charity. Father Karel says he checks in every day on the three brewers from Carlsberg who work in the new brewery.

In 2016, Father Karel says, he told Mr. 't Hart of his idea to restart brewing, and he says the chief executive was enthused. Carlsberg had already launched other microbreweries with adjoining bars in France, Norway and Sweden that focused on the historical connections of its brands, said Mr. Abecasis, the chief commercial officer.

Sales of beers branded Grimbergen grew 35% in the three years before the coronavirus pandemic. Craft and specialty brands, which make up one-tenth of Carlsberg's portfolio, managed to inch up 1% last year.

The abbey brewery will initially produce three beers, blending tradition with exotic twists. One uses smoked malt of the kind popular in medieval times. Another combines hops from Belgium and Australia.

The beers will be sold in kegs and bottles to Carlsberg's main European markets. The brewery will continue to experiment with new flavors that will be tested at the bar and restaurant at the abbey, which has doubled in size and has a window into the facility, so visitors can see the brewing process.

"A cathedral of beer," says Father Karel.

The priests, who rise to pray at 7 a.m. and then breakfast in silence, have blessed the brewery. They have final say over the beers, Carlsberg executives say. In their white habits, the priests stand out as they glide through the glitzy bar and brewery with its modern equipment.

The royalties from Carlsberg help pay for the upkeep of the abbey's buildings and the priests' pastoral and charitable work, says Father Karel.

How much does Carlsberg pay the abbey? Father Karel leans forward and, after a pause, whispers: "That's a commercial secret."

In the brewery, a skateboard leans against the wall under a simple wooden cross.

Not mine, says the abbot, Erik de Sutter. "I am not so sporty," adds the 57-year-old.

It belongs to Marc-Antoine Sochon, the 28-year-old Carlsberg brewer who has overseen this project.

In the brewery on Wednesday, Father Karel ribbed Mr. Sochon about his first strands of graying hair. Mr. Sochon spoke of good-natured squabbles over beer with Father Karel, who is not a fan of sweeter tastes.

"We usually find a compromise," says Mr. Sochon.

Father Karel chides a visitor who asks whether the abbey's 15 priests still drink beer. "What do you think?" he says.

Not every day, of course, he quickly adds, but usually on Sunday evenings.

"We have a full panel of tasters right here," says Mr. Sochon.

Write to James Marson at james.marson@wsj.com

(END) Dow Jones Newswires

05-31-21 1605ET