Part of the show How Acupuncture Works
Some people object to a big head on their pint of beer because they argue it takes up space in the glass. But if you are a fan of a big head then this new device will interest you. Before the beer is poured a piston is pushed into the glass and the beer-delivery nozzle is poked through a hole in the middle. As the glass fills the piston is pushed up in the air. When the glass is nearly full the barman stops pouring and pulls the piston up and out. The low pressure momentarily generated above the beer as the piston is withdrawn pulls gas out of the liquid to form a big frothy head.