Patents: Stout foam

26 February 1994

The Whitbread brewery in London and Heineken’s technical division in
Amsterdam have joined forces to patent (PCT 93/15973) a solution to the
age-old problem of how to make canned stout pour like draught stout.

The draught drink, once poured, sports a close-knit creamy head, but
this vital element is missing in a glass of the canned version. So Whitbread
and Heineken plan a new type of can, with a cup-shaped plastic pod sealed
to the bottom of the ring-pull lid. The pod has a small perforation in the
bottom and a short tube attached to it.

At the factory, the can is filled with stout, and a small dose of liquid
nitrogen or solid carbon dioxide is dropped in just prior to sealing. The
gas evaporates to build up a pressure of several atmospheres inside the

When the can is opened, the bulk of the excess pressure is released
into the atmosphere. But the pressure in the plastic pod stays high. The
trapped gas jets down the tube and out of a small hole, into the main reservoir
of stout. This shock causes mechanical shear in the stout, making it release
small bubbles of gas that create foam.

When the stout is poured into a glass, the foam rises to the top to
give a milky head.