I was wondering when I boil water in a pot it only shakes too much while boiling. But I could not figure out why tea rises in the pot when we boil it. It is also a liquid but it starts rising up till it jumps out of the pot and tries to kill the flame.
I think this happens due to change in the adhesive properties of the water due to addition of milk, sugar and tea leaves to it. Am I right? if not what the reason behind it?
Best Answer
The phenomenon at play here is foaming. Due to the heat the water will start to boil. In normal water this will result in small bubbles that pop quickly. When you add milk, you create a mixture which has the ability to foam due to proteins and surfactants present in the milk. This foam will rise up the pan and eventually boil over.
A common misconception is the explanation for example on this website (which is about pasta, but the story in terms of physics/chemistry is the same) where they say that the surface tension of water is increased due to starches. This is plain wrong. You cannot increase the surface tension of water by adding stuff, you can only decrease it (see e.g this book by Israelachvilli).