Sugar + pop = fizz, but not salt.

Factual Questions
1

If you take a glass of Coke, or any other carbonated soft drink, and dump in a spoonful of sugar, it will instantly begin foaming vigorously. I had always attributed this to the addional solute replacing some of the dissolved CO2 and forcing it out of solultion. I don’t know if it’s a matter of causing the solution to go past saturation or what, but this was always my personally accepted explanation.

However, if you put a similar amount of salt into a container of Coke, there is no fizzing. In fact, almost nothing happens. So it would seem to me that the solubility explanation doesn’t make sense. What else is going on here?

What mechanism is responsible for the soda fizzing when sugar is added, and why doesn’t salt have the same reaction? What about other solutes?

Is it a chemical reaction, perhaps involving the acids in Coke? I don’t know the reactions of all other sparkling drinks. I know that other colas do it, but i’m curious about, say, sparkling water

Also, curiously, adding a pinch of salt to beer gives it a nice, foamy head. Salt in coke…nothing. Salt in beer…foam. What gives?

2

I always thought it foamed because of additional points of nucleation. Perhaps the surface structure differences between salt and sugar account for the different behaviour.

3

The Master (Briefly) Weighs In. Nucleation sites, he says.

What sort of salt did you use when you tried this in the soda? I used to be enthralled with a perfectly infantile play-with-your-food trick in college, involving soda and table salt. And the soda foamed a-plenty.