Why does coke foam so much in a coke float?

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Why does coke foam so much in a coke float?

In: Chemistry

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.

In a related tangent, why does root beer have far more foam than, say, a Pepsi when pouring it into a glass?

Coke has air trapped in it.

Ice-cream is actually a collection of *very* small solid bits.

The air in Coke likes to gather around very small solid bits. When enough air is gathered around a small solid bit, the air escapes the Coke as a small bubble.

Ice cream melts in Coke and becomes a liquid that is much thicker than the Coke.

Thicker liquids are better at holding on to small bubbles than thinner liquids like Coke.

The thick-liquid ice cream re-traps the newly escaped small bubbles and makes foam… a lot like dish-soap, except much better tasting.