Why does milk expand and spills over when boiled?

Water when boiled will not spill over where as milk even at low temperature expand and spills over.

Milk mostly consists of water, proteins, lactose and some fats. The fat of milk is a mixture of fatty organic substances with less density. The fat in the milk which is in a form of solid is spread in the milk in the form of tiny globules. When we heat the milk in a vessel, the fatty globules of less density rise to the top at a temperature of 45°C, which is their melting point and forms a layer and cover the surface like a blanket and prevent any loss of water in the milk or any other substance by evaporation.

The steam bubbles that forms in the milk accumulates under this layer formed by the fatty globules increase in number combine and create a pressure which raises the layer and makes some of the milk to spill over the layer formed can be broken by stirring with a spoon which releases the pressure and spilling over of milk can be prevented.

Lakshmi Emani

Published date : 12 Oct 2012 04:34PM