Spoilage. One factor that can change the charge of the casein proteins is acidity. ... Eventually, the milk becomes acidic and develops a sour smell, and the casein proteins clump together in large curds. The effect of acidity on the milk proteins is accentuated by heat, which is often why your milk curdles when heated.

Why does milk curdle when heated?

Milk is a mixture (called an emulsion) of butterfat, proteins, and water. When milk is boiled, the three components of the emulsion break apart: the milk proteins coagulate and separate from the water, producing what is commonly known as curdled milk.

What to do if milk curdles while boiling?

If the milk curdles when boiling, the first thing to do is to strain it and remove all the excess water. But before that make sure you boil it for some extra time. You can also wash this in water to remove any smell that irritates you and then squeeze out all the water.