Why is it that every time you cook pasta, nothing happens for the longest stretch and then, exactly when you turn your back to sneak a little snack or wash a dirty spoon, a volcano erupts through the lid and across the stove? I was sick of it. So one day I borrowed a concept I learned for lentils, and I added a splash of oil to the pasta water. And ever since, not a spill.
Adding oil while cooking starchy foods isn’t new. Many cooks in South Asian countries add a spoonful of oil when cooking lentils or rice to prevent liquid from boiling over. Plain boiling water—like when you put the kettle on for tea—bubbles ferociously, but those bubbles are actually pretty weak. As they butt up against each other, they break almost as quickly as they form.
Yet when you boil certain foods like pasta, rice, or beans, some of their starches and proteins dissolve in the water, causing it to thicken and form a thin film on the surface. This time, as the water boils and the bubbles form, they stick around, their walls strong and gummy from all those dissolved starches. As the water continues to boil, the bubbles band together, building up and up and up, until finally (like when you’re washing the spoon, for example) everything whooshes over.
Oil prevents this. Add even just a spoonful, and the action of boiling smashes it into hundreds of microscopic droplets. These tiny oil soldiers sneak between those pesky bubbles, making them too slick to stick together. And by lowering the surface tension of the water, the oil makes the starchy bubbles pop and fizzle before they have a chance to grow and overflow the pot.
There are other ways to prevent pasta water volcanoes. My husband claims he’s never had this problem because he cooks pasta in a giant, uncovered pot, which supposedly keeps the bubbles in check. I gave him a little spiel about energy efficiency and latent heat (yes, I’m lots of fun), then proceeded to ask my coworkers if they’ve seen similar success, but senior cooking editor Emma Laperruque told me, “I cook pasta uncovered, and it often boils over.” Others balance a wooden spoon on top of the pot, to absorb excess heat and provide a surface for the bubbles to break against (chance of success: low). You can stir the pasta frequently (this one works, actually). Or you can pull the pot halfway off the burner (see above re: energy efficiency). But none work as effectively for me as the splash of oil.
And no, the oil doesn’t “prevent the sauce from sticking to the pasta,” or whatever that old fear is. Think about it: Your sauce probably includes oil or butter already. Any residual oil on the pasta is simply emulsified into the sauce. So risk the wrath of a thousand nonnas and add a bit of oil to your pot of pasta water. Your clean stove will thank you kindly.
