But the abbey only has a limited brewing capacity, and was not able to cope with the beer's sudden popularity.

"Our shop is closed because all our beer has been sold out," said a message on the abbey's answering machine, which it calls the "beer phone".

And the abbey has no intention of boosting its capacity to satisfy market demand.

"We are not brewers, we are monks. We brew beer to be able to afford being monks," the father abbot said on the abbey's Web site.

Monk Mark Bode told De Morgen daily: "Outsiders don't understand why we are not raising production. But for us life in the abbey comes first, not the brewery."