Big-headed beer

Brandbrew of Luxembourg wants to put bigger heads on beer (GB 2368335). Before the drink is poured, a piston is plunged down into the beer glass. Then the beer-delivery nozzle is poked through a hole in the middle of the piston, filling the glass and pushing the piston up as it does so. When the glass is nearly full, the barman stops pouring and pulls the piston up and out. The low pressure this creates above the beer drags any gas out of the drink to create a mass of bubbles and a frothy head.