Even if you thought you chose a pot large enough to keep your pasta water contained, it might still end up boiling over. This, as Gizmodo explains, is because starch molecules from the pasta seep into the water and make the bubbles extra sturdy. Those bubbles form a thick layer of foam across the surface of the pot, preventing steam from escaping and eventually causing a small eruption of water all over your stove.
An oft-mentioned hack for avoiding this is to balance a wooden spoon across the top of the pot. Somehow, its thin handle keeps the froth from reaching unmanageable heights. Unsurprisingly, there’s a little science behind this phenomenon.
As Simplemost reports, it mainly has to do with two of wood’s most notable qualities: It’s good at absorbing water, and it’s bad at conducting heat.
“If the bubbles touch the colder and dryer wood, these [starch] molecules break their chain and the bubble bursts, which releases the steam from inside the bubble,” Michelle Dickinson, a biomedical and materials engineer and the author of The Kitchen Science Cookbook, told Simplemost.
In other words, the surface tension keeping each bubble intact is no match for the wood; and when the bubbles touching the spoon burst, that action will also cause the bubbles touching those bubbles to burst. Because a wooden spoon is much more absorbent and heat-resistant than, say, a metal spoon, it’ll help keep foam at bay for longer than a metal utensil would.
That said, even a wooden spoon may eventually get so warm and water-logged that it’ll stop interfering with the rise of the foam. Other ways to prevent boil-over include turning the heat down so it’s just above a boil or choosing a truly massive pot. Or, instead of a wooden spoon over the surface, you could always try a two-by-four.