W. T. Lee and M. G. Devereux [1] review the bubble formation processes in carbonated drinks, like fizzy pop or champagne and compare this with heavy stout drinks. Stout beers have lots of dissolved nitrogen and this makes the physics slightly different to the carbonated drinks. Specifically, although the same mechanisms apply the time scales are very different. Stouts will not spontaneously form a head of foam. This means that a widget or similar needs to be added to cans in order to aid the nucleation of gas bubbles.
In the paper both the mathematical and experimental issues are discussed. I recommend you use the paper as a conversation starter next time you are wasted on stout at your local ale house.
Bottoms up!
References
[1] W. T. Lee and M. G. Devereux. Foaming in stout beers. arXiv:1105.2263v1 [physics.chem-ph]
“It has been shown theoretically and experimentally that stout beers do foam by the same mechanism as carbonated drinks, but that this occurs at rate too slow to generate a head in a feasible time”
And there was me thinking that the traditional Irish way of pulling the pints 5 minutes in advance was some weird marketing ploy or just the landlord keeping himself occupied.
Problem is its 11:25 and now I really want a Guinness.