Microwaved coffee can explode in your face

I received this urban legend in an email from my grandmother. She's a sharp old lady, so I can't believe that she fell for it and forwarded it to me.

The email claimed that if a liquid heated in the microwave did not boil, that it was because it had heated faster than the "bubbles" could release heat, and that therefore there is a stored up amount of heat waiting to be suddenly released in a burst of "bubbles" if your disturb the surface of the liquid. It contained several examples of people who had been horribly scalded by trying to stir microwaved liquids immediately after taking them out. One version even recommends that you leave a spoon in the cup in the microwave to solve the problem. (I assume you all know what happens when you put metal in a microwave).

Obviously false- laughably so. Microwaves don't heat from the bottom like a pot on the stove, and this is why liquids don't boil quite like on a stove. more can evaporate from the top without disturbance because microwaves heat more evenly.
As for the "bubbles" theory- give me strength. I can't believe what a moron the initiator of this myth was. The "bubbles" aren't a heat release per se. They are the escape of material which has been heated to a gaseous state. When it reaches a given temperature, it turns to gas and escapes. Period. There can be no super-condensed bubbles waiting to explode from a still cup of microwaved liquid.

Erm...I hate to be the voice of dissent here..but....

This would indicate your info might not be correct...

Even Snopes confirmed the phenomenon.

Thought I've never witnessed it happening with the microwave, I've been dumb enough to add boiling water to a not-so-sturdy china mug and have it "explode".

And wasted good coffee, too. Hmph.

Edited for spelling errors caused by a distinct lack of...you guessed it. Coffee!

[edit on 17-8-2005 by Tinkleflower]

Yeah, the bit about leaving a spoon in the cup is bad advice. No metal in a microwave.

But the phenomenon is real. Seen it on Mythbusters and news shows.

Just don't use perfectly smooth glass containers to heat water.

It's the imperfections in older glass (or other materials) that starts teh formation of bubbles and release of steam.

That energy is still in non-boiling water that's over the boiling point. It just needs a catylst, like a spoon. then poof! It's all steam in your face.

I'm officially freaked out by your superpowers, Rant.

I posted here, and then skipped off into Ye Olde Kitchen (to make coffee)....

I did my usual routine. Boiled kettle (sidebar: why the flying heck don't they sell electric kettles in this country?!?!?!??! Hmph). Made toast. Got sidetracked (like I do).

Poured water into awaiting mug (Macy's, not expensive, pretty picture of tulips. At least there used to be....).

My.
Cup.
Just.
Exploded.

I cannot believe this.

Rant - much as I wub you this is just unacceptable from a Mod.

If you're gonna put me under The Fluence, at least let me enjoy my Sanka first, huh? I just wish I had a camera to show you the mess

Originally posted by Tinkleflower
My.
Cup.
Just.
Exploded.

I cannot believe this.

That's amazing! Hope you're okay though!

I've got a GE electric "kettle" actually. And it's amazing!!! Clear plastic, low wide base. Boils a cup worth in about 1.5 minutes.

Sorry for your loss.

Oooooooooooh you have a leccy kettle?!?!??! That gives me hope!

I might once again be able to forego the decrepid gas stove and return to my previous state of Electrikettled bliss. This makes me a happy little flower indeed.

(I'm ok; the mug didn't fare so well, and I'm still skeered by your almighty superpowers though... )

Just to clarify- I am aware that rapid temperature variations can shatter a mug- that part is obvious- no argument there.

But are you guys saying that water can be hot enough to generate steam, yet not steam, and only when disturbed will suddenly release a large burst of steam into your face? I have a very hard time believing this. Somebody is going to have to clue me in on exactly how you prevent a liquid which has passed its volatile temperature from becoming gas until you touch it.

I know that i have warmed water for coffee in the microwave, and when I added the coffee powder, it bubled out of the cup pretty hard , and splatered all over my hands... does that count has an explosion ?

Not as dramatic as the email suggested, but yes, that seems to count.

I can't emphasize just how shocked I am to find a grain of truth to what seemed utterly impossible as far as my elementary understanding of the principles at work was concerned.

Well...I'm always glad to help...if i have to get my hands splaterred with burning coffee to do so... 8)

hmm,

I was just making a cup of instant.
It' never exploded on me, but I have had it fizz over in my cup
just as I added the sugar..I always wrote it off, as the sugar lowering the boiling point of the water, just enough to make it boil for a few seconds..

I have no idea how it explodes.

When it's happened to me (ahem. As today would show. Hmph), it's been..

Water, added to instant coffee (which is probably a sign that I deserved it anyway) usually with milk or cream at the bottom first.

No sugar.

Originally posted by The Vagabond
Just to clarify- I am aware that rapid temperature variations can shatter a mug- that part is obvious- no argument there.

Yes, and I think that's what happened to to Tinkle earlier since she poured boiling water on cold cream...

But are you guys saying that water can be hot enough to generate steam, yet not steam, and only when disturbed will suddenly release a large burst of steam into your face? I have a very hard time believing this. Somebody is going to have to clue me in on exactly how you prevent a liquid which has passed its volatile temperature from becoming gas until you touch it.

Yes, that's exactly what I'm saying. It's odd, but happens. Only in perfectly smooth (usually glass) containers when used in the microwave.

My understanding is that some imperfection, anywhere is all that's required to start bubbling and the steam. No imperfections (hard to find) will not.

From Tinkle's Snope's link:

The Food and Drug Administration (FDA) has advised consumers:
This type of phenomenon occurs if water is heated in a clean cup. If foreign materials such as instant coffee or sugar are added before heating, the risk is greatly reduced. If superheating has occurred, a slight disturbance or movement such as picking up the cup, or pouring in a spoon full of instant coffee, may result in a violent eruption with the boiling water exploding out of the cup.

The show's I've seen (I was serious, both experiments and news shows with victims) tended to say it happened to people using the old style perfectly straight glass measuring cups to boil water. Even the slightest curve in a regular cup will avoid this.

But this is why (for example) adding salt to water on the stove makes it boil faster. Not the salt. It's the imperfections/movement. I heard a very detailed explanation on the physics of superheated water molecules with nowhere to go (no motion), but I couldn't do it justice. But that's the idea.

gotcha,

The crystals of salt, or sugar, offer the imperfections on which the
bubbles form....
I need to try this at Macdonalds, I will split the proceeds from the lawsuit, with you Rant..

The bubbles need something to form on (notice how they form on the sides and bottoms of a container, but not spontaneously in the middle.).
This is because of minor imperfections (or crud) on the surface of the container.
The effect is best achieved in glass containers that are un-damaged and have just had an acid-distilled water rinse to remove all the crud.

As the temperature rises the bubbles cannot form so the water eventually super-heats. When something breaks the surface is disturbs everything allowing bubbles to form on the stuff added. This massive release of steam pushes the liquid above it up and (sometimes out of) the container.

I've seen videos of it happening and, sand crystals used to speed up the boiling too so I can confirm it happens.

First off, as if another voice were needed for confirmation, I remember hearing about this a long time ago. Took me forever to not worry about reheating coffee in the microwave--and now that little neurosis is back again, thank you very much .

I figured I'd throw something into the ring as well here as showing how funky liquids and temperature can be. I wouldn't have the slightest idea of where to look this up at, so please forgive the lack of sources.

When I was taking chemistry in college a couple of years ago, there was one lab we had that had to have been one of the most interesting concepts I'd ever heard of. We took one liquid--acetic acid I believe--that had a freezing point a little higher than regular water, and kept it in an ice bath and as still as possible. Even the breeze from the A/C could've screwed it up if I remember right. But you sit there with a thermometer in it, and watch the temperature drop past it's freezing point while it's still obviously a liquid. Once it gets down as low as it'll go, you give it a slight shake and you can actually watch it turn to ice.

The science behind that much isn't that spectacular; in order to form into a solid, the molecules need to be lined up perfectly to get the crystalline structure. As a liquid, they generally are just floating around at random, and even though the temperature's down they won't lock into place. A little shake knocks everything into place, and you've got ice at the same temperature you just had a liquid.

Anyways, probably not terribly relevant, just though I'd throw it out there. If anyone can give me a suggestion as to where to look, I'd be glad to try and find something to back it up.

A similar thing to the above happens when you "super saturate" something.
As you heat up something like water keep dissolving in sugar until no more will go.
Once no more will dissolve then stop and let it cool. None should come out. Then drop something small in (or bump it hard) and all the extra should precipitate out.

i can just add to all the other confirmations here;
i saw it happen on mythbusters, with my own two eyes :p

and yes, it does sound incredible and unbelievable, but it is true.

It is a totally real hpenomenon but some of the explanations are a bit misleading.

The bubbles that form in boiling water dont have anything to do with "releasing heat" and the like.

What actually happens is when you get a reasonably pure source of water (ie it has very little air and minerals dissolved in it) the water can become superheated. This means that its temperature is greather than 100oC but it is not vapourising.

As a microwave can excite water molecules very quickly this means that superheating can occur. When sugar/coffee/spoon are added they act as acatalyst for the vapourisation and the water instantly boils, occasionally bursting out of the cup.

WHat was incorrect in the original email was that this cannot happen in a cup of coffee as coffee is already a solution and anything but a pure water sample. As I said above though, it could happen while making coffee if the water is first boiled in the microwave and then instant coffee added.

P.S. what some other posters are describing when they talk about adding hot water to a cold cup and seeing it shatter is temperature shock. This can be seen over and over again in a chemistry lab where exo- or endo-thermic reactions can change temperature at a very fast rate and shatter even a pyrex beaker.