The science of tapping beer cans
I'm linking to a Danish page here, sorry to those of you who do not quite master that language yet.
It concerns the age old question of whether you prevent a shaken beer can from spilling when you open it, if you tap the can on the top first. A lot of people do this, but does it have any effect?
Klaus Seiersen -- incidently an old drinking buddy of mine from the physics department -- did an experiment with 30 cans and didn't see any correlation with tapping and amount spilled.
You spill your beer when it foams out of the can, and the foam is caused by the CO2 in the beer. When you shake the can, the CO2 gets mixed with the beer, and the beer foams. To prevent this, all you have to do is to wait until the CO2 settles in the top of the can again...