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Anne Marie Helmenstine, Ph.D.

The Myth About Superheating Water in the Microwave

By September 25, 2013

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Have you ever experienced the phenomenon of superheating water in the microwave? Superheating is what happens when water is heated past its boiling point, yet doesn't form the bubbles we associate with boiling. Superheated water is dangerous because it looks like it's cooler than boiling, yet may actually be several degrees hotter! Also, when the superheated water is disturbed, as by bumping the container, stirring the water or adding something to it, the water may suddenly boil or vaporize into burning steam.

Minimize the Risk of Superheating

You can lessen the chance of superheating your water by using the minimum cooking time for water or by providing starting bubbles that will allow the water to boil more freely. These bubbles can be introduced by something as simple as using aerated water from the tap. Glassware that is slightly rough or scratched is less likely to superheat water, too.

The Myth About Superheating Water

Some people believe only pure water will superheat. This is not true. Water with impurities, such as tap water, can superheat. It is simply less likely to superheat because tap water usually comes straight from the tap and contains a lot of air. Tap water that has been sitting on the counter for a while can superheat. Many homogenous liquids can superheat, including coffee and tea. Similarly, it is untrue that you can only superheat water in a microwave. It is true that it's easiest to superheat water in a microwave, particularly one that does not rotate the food, but you can superheat water on the stove or other heat source.

Share Your Experience

Have you experienced superheating? Feel free to share your experience, particularly if you superheated a liquid other than pure water.


March 4, 2012 at 12:51 pm
(1) Lorelei Osborne says:

I am so glad to see this post today.

I actually superheated coffee just moments ago. It was the first time that anything like this had ever happened to me. My coffee maker is fairly cheap, and doesn’t actually make good hot coffee. So I will often microwave it for 30 seconds to a minute to make sure that its hot enough for my sugar to melt it in afterward.

Today, I took the coffee, freshly brewed, and did what I normally do. I sat the hot mug gently on the counter. It was still. I then dipped in a bamboo skewer (what I typically use to stir my coffee) and wham! It bubbled uncontrollably and exploded out from the mug. Luckily I was standing far enough back that it didn’t get on me anywhere but my hand on a couple of small places. But still, it was frightening.

The reason I was looking for an article like this is because my boyfriend (who was in the room at the time of the incident, but not paying attention to it) didn’t believe me when I told him what had happened. He thought that I was just being clumsy and spilled it. He believed that only distilled or pure water could be superheated.

Now, with your help, I feel that I can successfully prove what happened today. So thank you!

June 7, 2012 at 1:33 pm
(2) isBubba says:

I just experienced super heating of water. It was tap water … aerated … in a large mug, for tea. The microwave was one that rotates the contents, and not too smoothly at that. I did heat it several times in a row since it did not boil … I thought it was just not heating well in the cheap oven.

When it finally appeared to be hot, putting off a wee bit of steam, I took it out. I set it in a saucer, and proceeded to put the tea bag in. When it touched the water, the water started boiling violently as if spattered directly on a red hot stove top.

Just goes to show most of the “rules” didn’t apply in this case … just the over-heating.

July 5, 2012 at 1:37 am
(3) John M says:

I actually attempted to superheat water in the microwave. After several attempts, the water boiled at 94.9 celcius. So I switched containers and got liquid water up to 105.0 celcius. At that point, I put a long handled fork in the water, and the water splashed violently all over the microwave. The water was superheated and reacted violently with the introduction of a nucleation site. It did clean the microwave quite nicely, but that is definitely not the safest way to clean it.

July 13, 2012 at 3:29 pm
(4) steve r says:

I for one do not have to attempt this experiment since it is untrue. It is a proven FACT that water starts to boil at 212 degrees. This is when it changes state and turns to steam. Any additional heat that is added is carried away in the steam. Water will not exceed 212 degrees under atmospheric pressure therefore will not superheat (as you call it) in a microwave as described.

September 13, 2012 at 6:13 pm
(5) don says:

I know water can explode from a cup as the burns on my hand are real and painful. I had about 12 oz of premade coffee that had cooled down but still fairly warm. I always set the timer for 2 minutes when heating room temp liquid. I forgot adjust duration down. After two minutes, I looked at cup and clearly saw no boiling. I had a towel in my hand that I used to grab the cup. The instant the cup moved, nearly the entire glass of coffee blew out and all over including my hand. I immediately placed my hand in ice water but it still killed nearly all the skin on the back of my hand and left a decent sized scar.

It can happen but seems to be a rare occurrence. I am surely more careful pulling hot items from the microwave.

October 10, 2012 at 9:16 am
(6) Michelle says:

I remember the first time I superheated water. … I was about 12 and looking for an easy way to make Jello. I tried several times to heat the water to boiling in the microwave and it just wouldn’t work! So, I decided to see if the gelatin would dissolve in whatever temperature I had reached. BIG MISTAKE! Sticky redness all over the place! Over 80% of the water immediately jumped out of the cup.

I have been playing with superheated water the last couple of days – trying to find the point where my daughter can see the reaction without it bursting into her face. It looks like with my current microwave and hot water heater setting, 1 minute and 18 seconds will be perfect.

October 10, 2012 at 7:48 pm
(7) mike says:

Nice person that she is, my wife heated tap water for my morning tea. I stayed in bed a while before going to the microwave. She said I would probably need to reheat the water. I hit the ‘add 30 seconds’ and it didn’t boil so I hit it again, then again. Still no boiling! While I was looking thru the door there was an explosion. The door blew open and hit me in the mouth. Six stitches and a repaired broken tooth later I can attest to the reality and power of this dangerous phenomenon. Don’t try this at home, or anywhere else for that matter.

October 16, 2012 at 3:59 pm
(8) cjs says:

Happened at the office twice in a commercial microwave with no turntable using an uncovered new glass Pyrex measuring cup with filtered hot tap water.

Very similar to mike above, I began with preheated water. After the initial minute and a half the water wasn’t boiling so I added 20-30 seconds 2 or 3 times more.

The first time it happened inside the microwave but I didn’t see it so I wasn’t sure what happened. I cleaned up and tried again.

The second time it happened upon removal. The water EXPLODED and seemed to go everywhere — on me, a coworker, and the 9′ high ceiling tiles. Fortunately, neither me nor the co-worker got burned.

I googled exploding water and for 3rd attempt I put a plastic knife in the water while heating and it boiled normally in less than a minute.

@steve r – you don’t have a clue, that’s a FACT

October 25, 2012 at 6:50 pm
(9) sibyl says:

Steve -

Water boils at 100 CELSIUS, and 212 FAHRENHEIT. Two different measuring systems. One is the metric system, and the other is US Customary. They use Celsius in Europe and Canada, and everywhere else besides uuuuhh-merica.

It is true. Try it. ;)

November 21, 2012 at 3:21 am
(10) Donovan says:

Water does not always boil at 100 degrees Celsius, this is the boiling point ar sea level or 1 bar atmospheric pressure. Boiling point on Everest for instance is 69 degrees Celsius. As for super heated fluids, I don’t know, never experienced it.

December 15, 2012 at 12:49 am
(11) John M says:

Steve, normally that is true, at atmospheric pressure at sea level, water will boil at 100C, or 212F. But superheating does happen. This wikipedia article describes how water can be heated up to 374C, or 705F.

Since making that post, I’ve been able to heat liquid water up to 120C, or 248F, using nothing more than bottled water, a brand new measuring cup, and a microwave. This isn’t a safe experiment to try, and I haven’t tried it in a number of months because water heated to that temperature will instantly cause 3rd degree burns. It is definitely not a myth.

March 4, 2013 at 10:14 am
(12) Dianne A says:

I made jello last night the way I always do. I was heating 2 c. of tap water in a 4 c pyrex measuring cup. The *fourth* batch took more time to boil. I was standing around waiting for it when the microwave door flew open – kinda like Mike described,above – and 1 and 1/2 c. of water went everywhere! Only 1/2 stayed in the measuring cup. I have no way to reproduce this phenomenon since it happened only once. I did the exact same thing for the prior 3 batches. And I’ve done it dozens of times in the past with no problems.

March 8, 2013 at 8:15 pm
(13) chiu says:

I think Steve should come back and own up that he was a pre-teenager when he wrote that comment so that he does not have to feel silly for the rest of his life

August 24, 2013 at 10:31 pm
(14) vince says:

I could not believe what had happened to me as I was unaware that it was possible for water to behave like this…
I was making mac n cheese on the stove. I filled the pot 2/3 the way with water and put on full flame/heat and then went to play on the computer while it heated to a boil. Of course I forgot about it and about 15 minutes later I walk into the kitchen to see the water not boiling and the flame still on high. Im thinking there is something wrong here. So I cautiously examine the water/pot closely. I touched the handle and all of a sudden… BOOM!! It goes straight to a roaring boil and explodes all over my kitchen. Almost all of the water was shot out of the pot all over the place. Thankfully I reacted quickly, jumped back and didnt get burned. I couldnt explain what just happened. Like I said I wasnt aware this could happen so of course I blamed it on the most logical thing… ghosts! haha. Anyways, I just wanted to share my story.

October 1, 2013 at 6:38 pm
(15) Water Damage says:

I am very impatient and often preheat water in the micro prior to using it to cook noodles I was never aware of the superheat phenomenon and will be changing my cooking practices!

October 3, 2013 at 10:30 am
(16) James Milne says:

I apparently superheated two cups water about an hour ago. While heating water to use in a coffee press I also did other little tasks around the kitchen. Then I’d remember the water and restart the microwave. Apparently I’d brought it to a boil a couple of times so that it effectively became near “distilled”. The final time I set the microwave for four minutes and near the end of the cycle watched through the glass in the door. I was about to open the door when there was a metallic “bang” and the glass momentarily clouded up. I opened the door and found the measuring cup nearly empty and the rotating dish and floor of the microwave awash in hot water.
At least the inside of my microwave has had a needed sterilizing rinse.

October 5, 2013 at 3:13 pm
(17) Dee says:

Today I was heating white vinegar in a glass cup to clean my microwave. I was standing in front of the microwave when it “exploded” and blew the door open. At least half the vinegar blew out of the microwave on to my shirt and the stove below.

January 4, 2014 at 3:42 pm
(18) thebasedgod says:

Steve – Remember a thermometer measures KINETIC energy, because temperature is the average kinetic energy. If you take some sort of gas, and heat it to plasma, and then continue heating it, it will still accept heat but its average kinetic energy will reach it’s peak, yet it will constantly gain energy as the potential energy will constantly grow.

January 10, 2014 at 11:52 pm
(19) Lula Singletary says:

After two weeks my hands are just healed from the first step of making vanilla pudding in the microwave. I have made hundreds of batches of vanilla pudding (for banana pudding), but then I paid strict attention to timing. This time the mixture of cornstarch, sugar and milk seemed too thin and I continued cooking it to allow it to thicken. I did notice that it was not boiling up or rising in the large Pyrex container. I was watching to prevent boiling over, but was somewhat distracted. When I removed the mixture and put the whisk in it readying to incorporate the eggs, my mixture flew everywhere including on my hands. Fortunately I was at the sink and ran extremely cold water over both hands, nevertheless I had severe burns. Burnjel and vitamin E oil has both hands back to normal. I believe this mixture caused a more severe burn than water would have. I highly recommend strict timing or a pause, allowing some cooling before putting a utensil in the mixture.

January 11, 2014 at 12:28 am
(20) Lula Singletary says:

You asked for response from overheating other than water.

My severe burns were caused from an overheated pudding mixture in the microwave. I deliberately continued to cook the pudding to thicken it. I was aware of superheated liquids but in this case was distracted. When I inserted the whisk, six cups of superheated mixture, milk, sugar and cornstarch, went everywhere including both hands and wrists. Fortunately I was at the sink and immediately ran extremely cold water over my hands for a long time. After two weeks and daily use of Vitamin E Oil 100 iu and BurnJel my hands are almost normal. The skin is a little thinner. I will continue to use the microwave for making puddings but will respect the cooking time, or pause the process until the temperature of the product drops.

February 11, 2014 at 1:16 am
(21) Trish says:

I was on my third round of heating water in a glass measuring cup (with vinegar mixed in) to clean my microwave. This works great to steam clean a microwave by the way. I had burned a lean cuisine previously and was trying to get the burned smell out of my microwave. The water was going through it’s third round of six minutes when the microwave door flew open with a loud sound and the water came flowing out of the microwave when I opened the door. The water was under the glass turning plate and my container was almost empty of its water and white vinegar mix. What a surprise!

March 15, 2014 at 3:26 am
(22) Bill says:

I just experienced this twice in the last week. I place an espresso cup full of tap water in the microwave to heat the cup before I draw my espresso. The first time it exploded it was before the one minute timer finished and the microwave was still working. I suspected the water somehow got trapped under the cup and and expanded rapidly throwing the cup upward and POW!
This time however after the timer stopped I reached in and grabbed the cup pulled it out and the water just exploded upward in my face. Fortunately the water cooled enough between the cup and my face was only hot not scolding. All of the water exploded out of the cup and I was just holding an empty with water all over the place.
Often I would only heat the water for 30 seconds and when placing the espresso spoon in to heat it as well before drawing the coffee I would see the water boil around the spoon violently for a couple of seconds.
Increasing the time to one minute makes the water superheated without boiling and this seems to create the explosion.

March 18, 2014 at 10:38 pm
(23) tehmina says:

Dear all

Thanks for sharing your experiences, recently my (AGE 60) got burnt with microwave wrong usage. Actually she boiled egg in microwave by putting the egg in water and leave it on a timer of 3 Minutes. When she opened the door a big Blast happened and all the egg along with water went on her face. Luckily she was wearing her spectacles that time but the blast sound was so big that her spectacles also went of her face and all her forehead and nose got badly burnt. We went to hospital and doc has given her antibiotics and gel as well but now she got severe swelling all over her eyes and cheek bones all the skin is gone from forehead. In simple words we can’t recognize her. Tomorrow we are taking her to skin specialist. But please can anyone tell me about any medicine or can share their experience that how she can get healed quickly as she is diabetic and cardiac patient also she live in Pakistan and the temperature is tooo much high in summer and summer is very near. I will really appreciate your help as i want that NO scar will be left on her face …I love my mum soooo much and tears are coming from my eyes while writing all this. Please any medication or treatment anyone can tell me. As I am in UK and i can send her medicines from here.
Waiting for the kind reply my personal mail id is ( t_1505@yahoo.com) waiting to hear from all of you and also please pray fro my mum’s health GOD bless you all and your parents amen

March 19, 2014 at 9:37 pm
(24) JANET MYERS says:

This happened to me last night ~ I was boiling 2 cups of tap water in a Pyrex measuring cup for time I usually do….was standing in front of the microwave trying to watch through door to see if boiling yet and THE WHOLE THING EXPLODED ~ BLEW OPEN THE DOOR OF THE MICROWAVE AND BOILING WATER BLEW OUT EVERYWHERE!! Scared the crap out of me!! Not good…IT CAN HAPPEN. :(

April 18, 2014 at 11:45 pm
(25) baba says:

Just happened to me and it destroyed my microwave!

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