system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does coke foam so much in a coke float?
gpt
CO2 isn't a stable suspension in atmospheric pressure, but needs sharp edges or rough surfaces to come out, called nucleation points. The net amount of foam in a soda's based on how many bubbles are created versus how fast the bubbles dissipate.

The ice cream is mainly crystalline in structure, which provides a large amount of nucleation points. Along with this the ice cream that mixes with the coke makes it thicker, which means that the bubbles will be more durable and longer lasting than they would be in just coke.

So ice cream both makes the bubbles come out a lot faster, and makes them dissipate slower, making the foam rate high.