Dowbrigade

Scientists have shown that the bubbles in a pint of Guinness
really do move down instead of up.

To mark St Patrick’s Day, a team of Scottish and US researchers has
produced video evidence to show the bubbles being dragged to the bottom
of the glass.

An earlier study concluded that the phenomenon may only have been an
optical illusion.
Close examination reveals that as the pint settles, bubbles touching
the walls of the glass experience drag that prevents them floating up.

Bubbles in the centre of the glass, however, are free to rise. A circular
flow is created, causing bubbles at the the edge to be pushed downwards
on the inside surface of the glass.

The effect occurs in any liquid, say the scientists, but the contrast
between the dark stout and its creamy bubbles makes it easier to spot
in Guinness.

The Scottish scientists worked in collaboration with colleagues led by
Professor Dick Zare at the University of Stanford in California.

from Ananova