There are a couple of reasons why water in a pot will boil over and they have to do with two things: heat and proteins. When you put pasta in boiling water and let it continue boiling over high heat, you may notice that after a while the water boils up and over the edges of the pot in a big foamy mess. This is because the pasta has created a "foaming boil" instead of retaining a "rolling boil."
When plain water boils by itself, the bubbles rise from the surface area of the boiling pot and then break at the surface of the water. This is because water doesn't have enough surface tension to hold back the explosive force of the bubble coming to the surface. However, when you add pasta to the water, organic material in the form of proteins and starches come off the pasta and mix with the water. The starches increase the surface tension of the water, making the surface bubbles stretchy and pliable. This stretching increases the amount of time it takes for a bubble to burst.
The resulting cascading effect causes a "foaming boil" whereby bubbles stack under more bubbles that take too long to burst. Eventually, the stack of foam rises above the lip of the pot and over the edge.
To avoid boil over, add a little canola oil to the water. The oil molecules interfere with the surface tension of the starchy bubbles and they break faster. The only problem with this method is that the oil will coat the pasta and whichever sauce you use will not stick.
· 10 years ago