Why Does Pasta Water Foam Up?

If you guessed B. Starch helps stabilize bubbles at the surface, you got it! 🎉

You’ve probably had it happen before: you’re boiling pasta, turn away for a minute, and suddenly a layer of white foam is creeping toward the top of the pot.

But why does pasta water foam so much more than regular boiling water?

It has a lot to do with the starch released by the pasta as it cooks.

Where Does the Foam Come From?

As pasta cooks, some of its starch moves from the pasta into the surrounding water.

Meanwhile, boiling water is constantly producing bubbles of water vapor. In plain water, those bubbles usually reach the surface, burst, and disappear fairly quickly.

Once starch is in the mix, those bubbles can become more stable. Instead of immediately bursting, they can collect at the surface and form the familiar layer of foam you see on top of pasta water.

Why Does It Sometimes Spill Over?

As more bubbles accumulate, the foam can rise higher and higher in the pot.

If the boil is vigorous enough—or there isn’t much extra room in the pot—the foam can eventually climb right over the edge.

That’s why a pot of pasta can seem perfectly fine one moment and suddenly need your attention the next.

How to Help Keep Pasta Water From Boiling Over

You can’t stop pasta from releasing starch, but you can help keep the foam under control:

Use a larger pot to give the foam more room to rise.
Lower the heat once the water returns to a boil. You only need a steady boil—not the most aggressive boil possible.
Stir occasionally, especially shortly after adding the pasta.
Keep an eye on the pot during the first few minutes, when foaming can be more noticeable.