Why does milk overflow when boiled but not water?

[aapar]

hi dear frns!
why milks boil n overflow although this phenomenon is not seen in case in water?

 

[mathman]

Layman's guess: The solids in milk (fat, protein) give the bubbles more stability.

 

[sponsoredwalk]

Here is a pretty interesting answer to a pretty interesting question:

Milk is not a simple liquid — it contains tiny globules of fat and casein which are not dissolved but suspended in water. On heating milk, there occurs a separation of constituents and some elements like cream, being lighter, float up.

After some time, a membrane-like film containing cream and casein is formed. When milk begins to boil, the heat energy is used for the conversion of water into steam.

As a result, the pressure below the film increases suddenly and the rising bubbles of steam makes the milk overflow. On heating water, no such film is formed and the bubbles of steam formed by boiling escape easily without any resistance. Hence, water does not overflow
on boiling.

— Arun Syamal, Mumbai
http://timesofindia.indiatimes.com/...ed-but-water-does-not/articleshow/1973641.cms

Avoid milk or other liquid overflow: When boiling milk or other liquids, put a metal spoon in the pot. The metal deflects heat and will prevent the milk or other liquids from over flowing, saving you from sticky clean ups ...
http://www.sizzlingpots.com/toolbox/tips/168-prevent-milk-overflows.html