Nucleation. Carbon Dioxide. Ice cream float. And why you should pour soda into ice cream (and not the other way round).
Why do the bubbles in an ice cream float form and stay foamy longer than if it was just a glass of soda without ice cream?
It’s got everything to do with of the fats, proteins, and air in the ice cream, and the behavior of the carbon dioxide in the soda.
Soft drinks (or soda) are made by pressurizing carbon dioxide (CO2). When we open a bottle or can of soda, the pressure quickly drops and the CO2 escapes as little bubbles (read more about this at the 1-Minute NomNom “Why sodalicious?“).
This escape is quickened when the number of nucleation sites is increased. Nucleation is the “process in which a change of state … occurs in a substance around certain focal points… [such as] the appearance of gas bubbles in a liquid“. These focal points are known as nucleation sites. When we place anything into soda such as ice cubes and lemon slices, they become and increase the number of nucleation sites.
An extreme example of this is is Mentos sweets in diet soda (see video above). The sweets’ rough surface provides so many additional microscopic nucleation sites for the carbon dioxide to form and escape, that the effect looks and feels like an explosive eruption!
That is what happens – albeit less explosively – when we put ice cream and soda together. The ice cream provides nucleation sites, creating many fizzy bubbles.
In addition, ice cream contains a lot of air from all the churning when mixing the ingredients. This provides even more nucleation sites for even more fizzy bubbles (we’ve known this since we were kids: remember what happened when we blew bubbles through our straws into the soda?).
As the bubbles rise through the ice cream float, the carbon dioxide bubbles are coated with the fats and proteins in the ice cream. This coating slows down the rate of bursting. As a result, the foam of bubbles dissipates slowly (compare how similar this is to the foam in beer in the 1-Minute NomNom “How a bubbly beer-sonality is foamed“)!
Understanding the phenomena gives us an idea why we should add ice cream to soda and not the other way around:
“If you add soda to your ice cream, you will get a much grander eruption than if you add ice cream to your soda. This is because if you pour the soda into the glass first, a lot of the carbon dioxide will have formed bubbles and popped by the time you add the ice cream. If you add the ice cream to the glass first, there will actually be more bubbles when you add the soda.” (Source: Lucky Peach)
Try it the next time you make an ice cream float!
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photos: in order – depositphotos/kung_mangkorn; norgallery; bhofack2