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Yesterday the wife and I decided to boil some potatoes in a normal non-stick pan.

We added salt, potatoes and boiling water. We put this on an electric hob, with no lid at maximum heat (marked at 6, which is ~10 times hotter than our 5 setting. The remaining settings are each, from experience decrease in operating temperature linearly ). They come to the boil and then the lid is added.

Almost immediately they boil over, spilling water across the hob. Remove pan from heat, remove lid, put pan back on heat turn down to setting 3 and wait. Once at the lower temperature, replace lid. Pan boils over.

I know the basic mechanism behind boiling over. Some agent increases the surface tension of the bubbles meaning many bubbles form causing the boil over. In third person my guess is that the agent was starch. I don't know what factor the lid plays, as occasionally the pan boils over without the lid on.

Is there anything I can do? Are the pans not clean enough? Not enough/too much salt? Wrong type of salt?

I've heard of the wooden spoon trick, but I actually want to tackle the root cause. Plus most of my spoons are silicone, and the trick doesn't work with them.

So what can I do too prevent boiling over?

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1  
highly related (if not duplicitive) : cooking.stackexchange.com/q/7909/67 –  Joe Aug 14 at 15:37
    
Water boils and turns into steam. As more water boils more and more steam is produced and the pressure builds up. When there is enough pressure, the lid lifts ever so slightly letting the steam out. When this hot steam hits the rather cold air outside some of it turns back into water. To continue boiling under these conditions turn the temperature of the hob lower and have it boil more slowly or even simmer or get one of those lids that has an opening you can open and close by turning the lid handle clockwise. –  unmircea Aug 14 at 18:49

6 Answers 6

You are doing precisely the opposite of 'normal' procedure, which is to put the lid on the pan until the water starts boiling, then remove the lid (either partially or completely) to prevent boiling over. A reduction in the hob temperature will also probably be necessary, and is in any case desirable - mercilessly boiling any vegetable is rarely a good thing.

With the lid off, heat is lost at the top of the pan at a rate which is usually sufficient to prevent boiling over. With the lid on, much of the heat is retained, which A) helps the water come up to a boil quicker and B) causes it to boil over much more easily.

See this answer for more information.

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I never did understand why more people didn't just reduce the temperature ... once it's boiling, there's no need to keep the heat on high. –  Joe Aug 14 at 15:34
    
@pureferret I agree with this answer that the root cause is that you are using way too much heat. If your second-highest setting is too low to cook the food through (which I doubt - I sometimes bring potatoes to a boil, then remove them from the plate and they cook through nevertheless), try a combination of cooking in a Dutch oven (which you heat on the high setting) and cooking less food at once. But seriously, if your second highest setting cannot keep at least 85 Celsius in a normal sized pot of potatoes, you will spare yourself much kitchen grief if you replace it. –  rumtscho Aug 14 at 18:09

Besides temperature adjustments or stirring, in the case of boiling starches in water (pasta, potatoes, etc.), you can add a little bit of oil to mess with the formation of the bubbles. This won't help if you've got a rolling boil, but will give you a better safety margin when you're closer to a simmer.

Place any wooden-handled utensil into or across the top of the pot. It doesn't necessarily have to be a spoon, just something wood (metal or plastic won't pop the bubbles as they're too smooth; placing it across the top might not pop them in time, but if the utensil isn't heat-safe, it's a last resort.

You can also try a splatter screen across the top of the pot (again, to break the bubbles).

For milk, there's a device that you place in the bottom of the pot to help dissipate large bubbles called a milk watcher. I've never used one myelf, but there's an answer to a similar question suggesting it works for pasta, too.

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Other answers have suggested taking off the lid when your pot boils, lowering the temperature, stirring, the wooden spoon trick, and adding fat (oil). These are all helpful suggestions, but one special case comes to mind that's worth mentioning. That case would be cooking rice in an inexpensive rice cooker, of the type that's vented through the lid and has no real temperature control. They look like this:

picture of rice cooker

If the contents of the bowl produce a lot of bubbles, they can block the vent. When the vent is blocked:

  • Air doesn't escape as quickly, so there's more pressure and less cooling;
  • Lack of temperature control combined with the above means the bowl gets hotter;
  • Hotter bowl creates more bubbles.

End result can be a pretty big mess as the bubbles start to leak out through the lid and around the rim. You can get a surprisingly big puddle on your countertop this way, and water overflowing on an electric appliance is never a good idea.

But with the rice cooker, you can't really take the lid off or it won't cook right. So you can't use the spoon trick or stir to break up the bubbles, either. And there's no way to control the temperature on these models. The one thing that does help is adding fat, but sometimes you don't want to add fat or it's not helping enough.

So, what can you do to stop this other than cook several smaller batches or buy a bigger/more expensive rice cooker?

The answer is simple: rinse your rice thoroughly. This is specifically a problem with white rice because of all the loose starch that's formed during the milling process, when the bran and germ (the parts that remain in brown rice) are removed. Depending on the type of white rice, more or less starch might be created; depending on the brand, more or less might remain on the packaged product. This loose starch essentially turns the water in the cooker into a thin paste, which bubbles like crazy. If the rice is starchy enough you can even have issues with the cooker half full (or less).

If you prefer the texture of the un-rinsed white rice, you could try only rinsing it a little; otherwise, you want to rinse until the water runs reasonably clear.

Of course, you wouldn't want to rinse arborio rice for a risotto, but if you're making risotto in a rice cooker I think we have bigger problems that need to be addressed...

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When a liquid is boiling, putting more heat energy into it doesn't make it get hotter: it just makes it boil (i.e., turn to a gas) faster. Putting the lid on means that heat leaves the pan more slowly, which has the same effect of putting heat in more quickly: it makes the pan boil faster.

The fastest way to get the water boiling is on high heat with the lid on. (Actually, if you have an electric kettle, it's usually faster to boil the water in that and then transfer it to the pan.) Once the pan of water is boiling, turn the heat down and, if necessary, take the lid off or partly off. Turn the heat down as far as you can while still keeping the water boiling (i.e., with bubbles of steam forming throughout the water, not just at the bottom). Anything higher than that is just wasting energy, filling your kitchen with steam and encouraging your pan to boil over. Be careful with electric hobs, which often respond rather slowly to changes in setting: it might take quite some time for the hob to react to you turning the heat down from high so you might want to turn it down a bit before the water comes to a boil.

Pans of starchy food do tend to boil over even on relatively low heat if you have a lid on. Rinsing the food before boiling this helps, as does putting a little oil in the water – a teaspoon or so is usually fine.

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2  
Worth noting that while you can't make the boiling liquid hotter, you can definitely make the container hotter, which can help keep the liquid above boiling temperature as you add cooler ingredients. (Not to mention things stuck to the bottom of the pot - you can heat those up real good!) –  AirThomas Aug 14 at 18:16

This work very well for most foods. Grease a 1 to 2 inch ring around the top inside lip of the pot with either oleo, butter, crisco etc. I always use this when cooking rice, oatmeal, grits, potatoes etc. This causes the bubbles or liquid to fold back into the pot. However nothing will work unless you reduce the heat to the correct level. Any thing above the boiling point of the contents will wildly escape as steam. The temperature will not rise above this point. Never remove the cap from a boiling car radiator. This reduces the boiling point from some point well above 212 degrees to 212 degrees. The excess heat erupts from the radiator resulting in severe burns. This is the same principle as cooking on too high of a heat setting. The heat has just gotta go.

Been there done that.

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