When milk is boiled for the second time, it can create a bursting or foaming sound due to a phenomenon called the "Milk Boiling Effect." This effect occurs because milk contains proteins, primarily casein, which can form a thin film or layer on the surface of the milk when it is heated.
During the first boiling, some of the proteins in the milk may form a layer on the bottom of the pan, sticking to the surface. When the milk is cooled down and then reheated for a second time, these proteins can create a barrier that traps steam beneath the surface.
As the temperature rises and the trapped steam builds pressure, it eventually ruptures the protein barrier, causing a sudden release of steam. This release of steam leads to the bursting or foaming sound you may observe when boiling milk for the second time.
It's important to note that the milk boiling effect can be reduced or avoided by taking certain precautions:
Stirring: Continuously stirring the milk while heating can help distribute the heat more evenly and prevent the formation of a thick protein layer on the bottom.
Lower heat: Using a lower heat setting when reheating milk can reduce the chances of the milk boiling over or creating the bursting sound.
Covering the pan: Placing a lid on the pan while reheating the milk can help contain the steam and minimize the milk boiling effect.
By employing these precautions, you can minimize the likelihood of the bursting sound and potential mess when boiling milk for the second time.