Curdling of Milk

What happens when we add few drops of lime juice when the milk is about to boil over? It curldes, isn’t it? Why does this happen?

Milk is a colloid. It is a lyophobic colloid to be more specific. See, colloids are of two types, the lyophilic ones and the lyophobic ones. The lyophilic ones are those from which the dispersed phase (solute) and the dispersion medium (solvent) can be separated and also can be re-mixed into the original colloid. The lyophobic ones on the other hand can be separated by creating an imbalance in its pH but can’t be re-mixed into the original colloid. Once it is separated, it is separated. There is no going back.

When we add lemon juice to the hot milk it decreases the pH of milk and the dissolved particles (or the compounds that milk is made of) come out of the solvent in chunks. If we try mixing these chunks back with the solvent we will not be able to do so.