Why does a pot of ramen boil over more easily than plain water?

When water boils, bubbles of steam form at the bottom of the pot and rise. In plain water, each bubble pops as soon as it reaches the surface, and only the steam escapes. Water on its own can't keep a thin film going for long.

Adding noodles changes that. Starch on the surface of wheat noodles dissolves into the hot water, making it slightly sticky, and this starch coats the bubbles and strengthens their film. New bubbles keep piling on top of the ones that haven't popped, so a heap of foam creeps up the side of the pot. Milk boiling over works in a similar way, except that milk proteins form the film.

People say that laying a wooden spoon across the pot keeps it from boiling over. It does help. Dry wood doesn't conduct heat well, so it stays cooler than the foam, and its surface is full of tiny pores. When foam touches the cool spoon, the steam inside the bubbles cools back into water, and the porous surface disrupts the film, so the bubbles pop.

But the effect doesn't last long. Once the spoon heats up and gets soaked with starchy foam, it no longer pops bubbles well. That's why some people say they tried it and it didn't work. Metal spoons are said to work for an even shorter time because they heat up quickly.

If you lower the heat a little when the foam starts rising, fewer new bubbles form and the foam soon settles. A lid traps heat inside and makes the foam rise faster, so after adding the noodles it's better to leave the lid slightly open.

Using plenty of water and a wide pot also helps. More water dilutes the starch, and in a wide pot the foam spreads sideways before it can pile up, giving it more room to pop. Stirring once with a spoon or blowing gently on the rising foam also makes it go down, because your breath cools the steam inside the bubbles.