Physics about Guinness

This time we get to the physics of a kind of Irish beer, Guinness, which catches eyes for the bubbles and colors forming in it.

Look closely at a pint of Guinness and tell me: do the bubbles go up, or do the bubbles go down? Why is the head coloured the way it is? Is foam a gas, liquid or solid? An Irish physicist discusses.
....
The paper referenced in this discussion is "Waves in Guinness" by Marguerite Robinson, A. C. Fowler, A. J. Alexander, and S. B. G. O'Brien [DOI: 10.1063/1.2929369; free PDF]. And yes, it is rather intense reading, unless you are a fluid physicist or an astronomer. [http://www.guardian.co.uk/science/punctuated-equilibrium/2011/aug/02/1]