''SO YOU mean I can drink this beer for free?'' asks a man at the bar. He's wearing a smart shirt and slacks with short pockets. The thought of paying nothing for a pot unnerves him.

He's doing hazy sums in his head. Right now at the bar you may pay as much or as little as you please for a beer that ordinarily costs $4 a pot. Every cent, though, goes to charity: say, Christmas presents for indigenous kids in Port Augusta or a remedial bike for four-year-old Piper from Kalorama with cerebral palsy, whose smiling photo sits atop the bar.

Every evening at 5pm the Bridge Hotel Richmond puts on the Karma Keg. Credit:Craig Sillitoe

It's 5pm Friday at the Bridge Hotel, Richmond, and the ''karma keg'' is on tap.

Consider it a moral test: what to pay when you may pay nothing at all? DJ Ollie Holmes, 20, puts $25 into the money jug on the bar for his round of seven pots - about $3.55 a beer. ''I should have put in $50 but I will next round, I reckon,'' he says. ''I'm not one to take freebies, you put in what you get out.''