Why does milk rise and overflow when it boils? Is it just the heat, or is there a secret behind it? 🤔

 

Milk often boils over because of a complex interaction between heat and the milk's own composition; it's not simply a case of it "boiling and steaming."

Initially, as milk heats up, a very thin layer of fats and proteins (especially casein) forms on its surface. This layer appears as a thin film or covering over the milk's surface.

This film becomes a significant problem: it traps the steam that forms at the bottom when the milk reaches boiling point. Instead of easily rising to the surface and being released, the steam remains trapped beneath this layer.

 

As heating continues, steam production increases rapidly, and pressure begins to build up under this thin film. The problem is that this layer doesn't allow for expansion or easy steam release, so it becomes like a balloon that expands from within.

At a certain point, the pressure overcomes the strength of the layer, causing the milk to suddenly and rapidly rise, overflowing the container and creating the familiar mess.

Simply put: Milk doesn't boil over just because of heat, but because of a layer that blocks the steam until the pressure becomes too high and it suddenly escapes.