  Stout beers show the counter-intuitive phenomena of sinking bubbles while the
beer is settling. Previous research suggests that this phenomena is due the
small size of the bubbles in these beers and the presence of a circulatory
current, directed downwards near the side of the wall and upwards in the
interior of the glass. The mechanism by which such a circulation is established
and the conditions under which it will occur has not been clarified. In this
paper, we demonstrate using simulations and experiment that the flow in a glass
of stout depends on the shape of the glass. If it narrows downwards (as the
traditional stout glass, the pint, does), the flow is directed downwards near
the wall and upwards in the interior and sinking bubbles will be observed. If
the container widens downwards, the flow is opposite to that described above
and only rising bubbles will be seen.
