I’ve noticed - when you’re making a mixed drink, whiskey foams more (and the foam lasts longer) than any other spirit I’ve used.
Example:
Take one shot each of:
Rum
Vodka
Gin
Whiskey
Pour one shot of each in a pint glass.
Then add 1 can of cola (I know, this doesn’t really go with the gin, but humor me. You can substitute a can or equivalent of tonic, but then it wouldn’t be scientific.)
The whiskey drink will foam much more than the others and the foam seems to be “stickier.” Why?
It’s not actually the whiskey, but the cola that’s foaming. There must be more nucleation sites in the whiskey than in the other spirits, but I couldn’t tell you why. I’m at work so I can’t test this (the bastards) so you’ll just have to take my word on it.
Aren’t the other spirits you are using clear? Could you do a control where you use a dark rum?
It is (if a real effect – I refuse to waste any of my whiskies in a “mix with cola” situation) most likely due to the additional impurities in a dark liquor giving more structure to the foam.
I too have noticed the same phenomenon when it comes to mixed drinks. Foaming is an issue that effects full scale chemical production as well. The same dynamics happen in your kitchen as they do in a chemical plant.
Foaming happens when there is a mixture of solid particles suspended in the vapor phase. There are chemical streams which are known to be common foamers, such as amines (nitrogen containing compounds).
Whiskey probably either has more solids in it than the other spirits, or a type of solid that foams when mixed with cola. My best guess would be an organic base that comes from the barrel in which it is aged. Whiskey always has the "woodiest" flavor of the aforementioned spirits, which most likely means that it has the most of these compounds.
