What causes water to boil over?
What are the mechanics of water boiling over? How can you stop it from happening? Is it more likely to happen with certain ingredients? Which? How does the amount of water effect the likelihood of water boiling over? What role does burner temperature have? Will it only occur during a rolling boil?
This is brought up by this comment by MeltedPez in one of the cooking pasta questions:
The only other argument for using more water is that less water is more likely to cause the pot to boil over. Basically the starch in the pasta makes it easier for the water to form bubbles that collect and spill over when not paying attention. I've found that with a very low pasta to water ratio can end in a messy kitchen.
This seems very counter intuitive to me initially, as I feel less water should make it harder to boil over the edges.
Best Answer
Adding a starchy substance such as rice or noodles to boiling water increases the surface tension of the water. When it's just plain water boiling the surface tension of the water can't hold back the force of the steam rising and the bubbles burst. Starches increase this surface tension making the bubbles more elastic/pliable (essentially creating a foam), thus requiring more force for them to burst. This makes the bubbles last longer which allows them to build up and eventually boil over.
It's more likely to occur with anything starchy like rice and pasta.
A lower temperature should help to control a boil over as it will allow the water to cool somewhat and slow the boil.
I'd assume that, from your quoted text, that if you use less water you're still imparting the same amount of starch making a thicker solution. More water would dilute this and bring it closer to normal water. In my own experience, small amounts of water allow lots of bubbles to form but nothing really boils over, it just splatters a bit. But reducing temperature and tilting the lid to let some air in has helped me in the past.
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Quick Answer about "What causes water to boil over?"
With the combined influences of heat and water, the starch thickens as it rises to the surface, creating an active agent at the top of the water which blocks air from escaping. Because it contains more air, the volume of water then expands, rising to the point of boiling over.How do you keep water from boiling over?
It's simple, but can help postpone a surprise stovetop mess in the heat of the moment. All you need is your trusty wooden mixing spoon. If you lay a wooden spoon across the top of the pot of boiling water, the water will not boil over.What happens when water boils over?
When water is boiled, the heat energy is transferred to the molecules of water, which begin to move more quickly. Eventually, the molecules have too much energy to stay connected as a liquid. When this occurs, they form gaseous molecules of water vapor, which float to the surface as bubbles and travel into the air.Why does water boil over when adding salt?
The salt does not instantly dissolve so the surface of the crystals suddenly provides a lot of nucleation sites for the water to form vapour - hence the surge as it boils from these surfaces. The white is due to turbulence from the boiling just like waterfalls look white.More answers regarding what causes water to boil over?
Answer 2
Add a pea sized dab of butter or margarine next time.
Answer 3
A small amount of salt will raise the boiling point of water, giving a bit more leeway.
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