The smell of a popping fliptop

[LordEoin]

I notice that when I open a fliptop I get a burst of chocolate&vanilla smell, kinda like a cup of cocoa or a bowl of cocoa pops.
This seems to be regardless of what kind of beer is in the bottle, same for a stout, bitter, lager.
Anyone have any idea why the CO2 'pop' has this delicious sweet chocolatey smell?
And has anyone else noticed it, or is it just me?

[Ciderhead]

Strange fettish
I tend to point the fecker away from my face in case it's lively.

[johnrm]

Was it porter? ;-)

[LordEoin]

all kinds.