# What causes the milk to suddenly rise up & spill out if not stopped?

Well, when milk is heated in a container its temperature starts rising & water vapor bubbles rise up through it. This initially causes a little and slowly rise in level of milk. But after certain time, a point reaches when milk level starts rising rapidly & spills out if not stopped. I have observed that higher the rate of heating milk, faster this point reaches & more rapidly milk rises to spill out.

My question is that what causes the milk to rise rapidly & spill out at a certain point of time while being heated? Is it due to rapid heat transfer or boiling of water or due to fatty foams or films become impermissible to rising vapor bubbles in bulk at a certain point while heating?

I found some answers here: How can a wooden spoon be used to prevent water from over boiling? None answered my question.

I will really appreciate any explanation answering this question.

Milk is an emulsion of butterfat in water, having emulsifying agent as casein protein, usually there is a sheet of negative charges around fat droplets in milk emulsion, when milk is heated the charges on surfaces of droplets gets disturbed (due to collisions) causing the fats to coagulate and precipitate down the vessel causing water content in milk to rise up while fats to remain down. the same notion goes when you add some acidic substance like squeezing lemons over milk the electrolytic nature of acids causes the negative charges on surface of droplets to get neutralized by $$H_+$$ ions of acid (however fats don't adsorb negative anions of acid as it shows preferential adsorption), causing fats to coagulate, same principal for centrifugation when you get butter out of milk ,in this case also the negative charges over fat droplets get disturbed and fats coagulate