Cooking is all fun and games until the water in your pot boils over and your cooktop becomes a sticky mess. Not surprisingly, this leaves many home cooks like you and me wondering if there was some secret way to keep the water in our pots from boiling over.
I was researching this topic on the Internet and kept coming across the usual superstitions (like how adding salt to your pot keeps the water from boiling over), until I stumbled upon a trick that seemed so simple and so effective, I found it hard to believe.
After testing this trick out for a week, I can confirm to you that it actually works. And I’ve been using it ever since.
In this post, I’m going to tell you all about it.
To keep the water in your pot from boiling over, put a wooden spoon across it. As the spoon isn’t submerged in the water and wood is a poor heat conductor, the spoon will stay drier and cooler than the pot. When water bubbles come in contact with the spoon, they’ll burst because of its dry, cool, and rough surface.
This trick works primarily when boiling starchy foods. Here’s the scientific reason why.
Why a Wooden Spoon Keeps Water From Boiling Over
Starch is a carbohydrate that’s naturally present in vegetables, like potatoes, beans, lentils, peas, chickpeas, and corn, as well as in grains and flour products, like rice and pasta noodles.
Starch dissolves in water and swells up in the presence of heat. When you add starchy foods to a pot of boiling water, the water strips away some of the starch granules on the food’s surface. These starch granules dissolve and swell, causing the formation of bubbles.
The bubbles form because the starch granules absorb increasing amounts of water until they finally burst, sending starch molecules into the water which results in white foam.
This is also the reason why your cooking water turns white when you make pasta.
There’s one last piece to the puzzle I need to show you before you understand why a wooden spoon keeps water from boiling over.
When you bring a pot of water to a boil, the water boils in continuous cycles called convection currents.
Here’s an illustration of how these convection currents look like:
In physics, density is a measure of an object’s mass per one unit of volume. Submerged in water, less dense objects will float and denser objects will sink.
When the temperature of water rises, its density decreases. Which is why the water molecules that sit the closest to the bottom of your pot will heat up and become less dense.
As the molecules on the bottom heat up and lose density, they will rise up to the surface and get replaced by denser and cooler water molecules.
This happens again, and again, and again in cycles—until you remove the pot from the heat.
No matter if you knew this before coming to this post or not, you’ve probably noticed it already because the bubbles in a pot of boiling water will form in cycles. When too many bubbles grow too big too quickly and lump too much together, the water will boil over.
Think of it as a self-reinforcing loop. Starch bubbles heat up, swell up, and burst, heating up other starch granules and turning them into bubbles in the process. The bubbles become structurally stronger and create multiple layers of foam.
As the cooking water becomes starchier and thicker, the bubbles on the surface prevent steam from escaping from the bottom of the pot, causing the liquid and bubbles in the pot to rise.
Putting the lid on won’t help. If you do it, the water will only boil over faster because the steam is going to have a harder time to escape.
Putting a wooden spoon over the pot works because the foam will eventually meet the spoon as the foam bubbles up. The spoon sucks up the thermal energy from the bubbles so that they don’t grow too large, lump too much together, or grow structurally stronger.
“That makes lots of opportunities for bubbles to start absorbing and wicking into the wood. This stretches the bubble,” Scott Beaver, Doctor of Chemical Engineering and creator of Learn Science with Dr. Scott, tells North Carolina TV station WRAL.
“The stretching force to pull the bubble apart becomes greater than the force of surface tension to hold the bubble together. So the bubble collapses.” When this happens over and over, the foam goes down.
Try this trick out for yourselves and let me know how it worked out for you.
Don’t Cook All of Your Food in a Rolling Boil
When you set the heat on your cooktop to high and place a pot of water on the burner, the water will eventually reach a rolling boil.
A rolling boil is when the water in your pot reaches a temperature of 212°F (100°C), also known as the boiling point of water, and bubbles start forming and bursting vigorously as a result.
It’s also when starchy water can boil over the easiest because the internal temperature and convection currents of the water create the perfect conditions for it to happen.
Contrary to what some folks think, you don’t really need to cook most of your soups and stews on high (or even medium-high). Bring the water to a boil, then turn down the heat to medium or medium-high. By doing so, you reduce the risk of your cooking water boiling over.
You should only cook pasta in a rolling boil. Since pasta noodles rehydrate and cook fast—and adding cold or room-temperature ingredients to a pot of water causes it to drop temperature—you want your pot to recover quickly. This makes timing easier.
Does Adding Salt Keep the Water From Boiling Over?
Adding salt to a pot of boiling water won’t keep the water from boiling over.
While it’s true that salt dissolved in water raises its boiling point to a temperature above 212°F (100°C), the quantity of salt that you use when cooking isn’t big enough to make much of a difference.
Now you know why putting a wooden spoon over a pot of starchy water will keep it from boiling over. Just remember that, sooner or later, it’s a good idea to turn the heat down 🙂 .
The next time you cook pasta noodles or make lentil soup, try putting a wooden spoon over the pot and share how it worked out for you in the comments below.