microwaving milk

[slinkycat]

Not sure if this question should be here or in science! My son has just warmed up some milk in the microwave in a mug, to just below boiling point, it didn't overflow, but when he took it out and put a teaspoon in to stir it, it frothed up and bubbled over the mug, he says it has happened before, and seeing that I was browsing on here, he was wondering if any of you could explain why that would happen? By the way he didn't add sugar or anything to it, Thanks!

[Mortartube]

As I understand it. There can be pockets of heat in microwaved liquids, so the temperature is not even throughout the milk. When you put in a teaspoon you release one or more localised hotspots which may be at boiling point and they bubble to the surface causing an overflow.

[slinkycat]

Thanks for that Mortartube, sounds logical to me, I'll tell my lad to use less milk or a bigger mug!

[Ice.Maiden]

Don't suppose he's too young noknow, or he surely wouldn't be up at almost quarter to midnight.

[heathfield]

It's caused by ''superheating'' the liquid to above its normal boiling temperature, and can be very dangerous.
Read about it here.

[slinkycat]

That link makes scary reading Heathfield, will show it to my lad , who is 18 by the way no.knowledge!

[Jugglering]

Just a note... Heathfield is quite correct re the superheating stuff.... it is scary ! Do not do this unless you have permission or authorisation first, please !