In Medieval Europe, Monks and Nobility were the only brewers.
Lagering Cellars in the Monasteries were locked, as the Monks guarded
the secrets to their craft. The monks carried keys to these lagering
cellars on their cinch – or belts. It was this key from which the
"Church Key" opener gets its name

(alleged) Source: Anheuser-Busch Knowledge Base; Internal Dbase -via wikipedia