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Q & A: bubbles in almost boiling milk

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Most recent answer: 07/15/2016
Q:
In a milk boiler, the vessel containing milk is surrounded by a layer of water. When the water boils, it does not appear that the milk is boiling also; however, a top layer of bubbles form in the milk.is the milk actually boiling? Is this process sufficient to kill the germs in milk?
- Rajiv (age 61)
A:

As we've discussed elsewhere, the dissolved sugars and salts in milk raise its boiling point slightly above that of water. You might want to look at these old answers: https://van.physics.illinois.edu/qa/listing.php?id=1451. Still, even when it's not quite boiling, water molecules will evaporate quickly from the top of the hot milk. There's probably a thin layer of fat and maybe protein on the surface of the milk. The evaporated water molecules form bubbles under this layer. In pure water they would just head away into the atmosphere.

Mike W.


(published on 07/15/2016)

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