Millions of gallons of beer stuck in stadiums, concert halls, restaurants and bars are fast going stale, leaving the beer industry with a tricky problem: What to do with all that booze nobody will ever drink?

The coronavirus pandemic forced U.S. bars to close ahead of two of the country’s biggest drinking occasions: St Patrick’s Day and the “March Madness” basketball tournament. Beer intended for those events is now spoiling in locked establishments, and brewers are trying to get it back so kegs can be refilled before lockdowns...