Why does a wooden spoon stop water from boiling over in a pot?
The short answer
Placing a wooden spoon across the top of a pot of boiling starchy foods, like pasta or potatoes, prevents spills by disrupting the bubbles as they rise. The wood's lower temperature and rough surface bursts the bubbles, keeping the foam from building up and spilling over.
The long answer
It's pasta night. You've got a mouthwatering sauce simmering, noodles cooking in a boiling pot, glass of wine in hand. Ahh, it's the simple pleasures.
Then all of a sudden, disaster strikes! The pasta pot seems to erupt and spill water over the sides in a big foamy mess.
The reason pasta water tends to boil over is due to surface tension. Water alone has a high surface tension which prevents bubbles from forming. But when you're boiling a starchy food like pasta or potatoes, the starch molecules reduce the surface tension and cause bubbles to be more elastic and less prone to breaking. As more of these bubbles accumulate, they create a layer that traps steam from escaping the pot, which can eventually cause the water to boil over.
All of this could have been prevented with a simple kitchen trick: Place a wooden spoon on top of the pot and no water will boil over.
Here are the two main reasons why a wooden spoon stops water from boiling over in a pot.
Reason #1: Wood is cooler in temperature.
Wood doesn't conduct heat well. So when you place the spoon on top of a pot of boiling water, it'll remain cooler than the pot and the water. As a pasta water bubble hits the wooden spoon, the steam trapped in that bubble condenses back into liquid because the spoon is less than 100°C (212°F). This difference in temperature continues to break bubbles as they reach the spoon, helping it prevent spillage.
Reason #2: Wood has a rough surface.
While your spoon feels smooth, the surface of the wood is actually quite rough when you zoom in.
Here's a microscopic look at wood (200 µm is 0.2mm). "Puidu pind 2" by Kent Gregor Mahla, Maido Merisalu is licensed under CC BY 4.0.
The roughness of wood increases its surface area, so when a pasta water bubble hits the wood, it stretches. The stretching force becomes greater than the surface tension holding the bubble together and it pops.
When does the wooden spoon trick not work?
As the wooden spoon gets hotter and wetter resting on your pot, it will become less effective at preventing a boil-over event. You're better off using a bigger pot or reducing the heat a touch, chef.
I wish you a peaceful pasta night in your near future. Here's your pasta gift from me for reaching the end of this article.
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Sources
Ahn, K. (2014, June 10). Why Does a Wooden Spoon Stop Pasta from Boiling Over?. WonderHowTo. https://food-hacks.wonderhowto.com/how-to/why-does-wooden-spoon-stop-pasta-from-boiling-over-0151541/
Anas, B. (2022, August 14). Why putting a wooden spoon on a pot prevents water from boiling over. Simplemost. https://www.simplemost.com/why-wooden-spoon-stops-pot-boiling-over/
Fun Loving People. (2023, April 9). Secrets Behind Pasta’s Boiling Froth. Fun Loving People. https://www.flp.co.za/secrets-behind-pastas-boiling-froth/
Grey, S. (2020, October 8). Why Does Pasta Foam? A Quick Guide. Grow Your Pantry. https://growyourpantry.com/blogs/pasta/why-does-pasta-foam-a-quick-guide
Spivack, E. (2024, February 20). Molecular chemistry debunks a misguided pasta cooking technique. Inverse. https://www.inverse.com/science/cook-oil-pasta-myth