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#1
Old 02-06-2012, 11:20 PM
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How can you safely boil water in a microwave

In order to avoid superheated water that can explode, what can a person do to prevent that from happening (aside from boiling water in a tea kettle on the stove instead of the microwave)?

Snopes says putting some kind of impurity like a wooden stirrer or plastic piece of silverware in the cup will prevent it from happening by allowing bubbles to form.

http://snopes.com/science/microwave.asp

Would using a wooden cup instead of a glass cup prevent this from happening, or is that overkill? Will something as simple as a chopstick in the water pretty much prevent this from happening?
#2
Old 02-06-2012, 11:47 PM
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I use a teakettle myself but I've heard the chopstick thing works (as does regular stopping and stirring).
#3
Old 02-06-2012, 11:57 PM
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A Staff Report
#4
Old 02-07-2012, 12:37 AM
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The staff report is correct;

superheated microwaved water that will "explode" will only happen with a near perfectly smooth glass container. So give it a "rough" surface on which ready-to-boil water can nucleate and you're set.

This can be -

a stirrer
a wooden spoon
a glass rod
or even just stirring the damn thing

That said, a consumer bowl that would be smooth enough to allow superheating - that to me sounds pretty damn improbable. All of the glass cookware I've ever used has enough rough imperfections to allow boiling and freezing.

Hell, I'm a chemist, and even most common lab glassware isn't smooth enough to give superheating or supercooling phenomena. When I saw the "supercooled liquid" demo years back in chem lab the professor had to use a specially polished piece of equipment that he used for nothing else.
#5
Old 02-07-2012, 01:44 AM
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I don't know, GameHat. I have several styles of tea cups/mugs that can become superheated. It's never happened to the point of being dangerous, but it's not uncommon to have perfectly still water start boiling only after I put in a tea bag.

For the OP: I wouldn't worry. If you insist on being careful, my recommendation is a toothpick. They fit in any size cup, are cheap and disposable and will prevent any problems.
#6
Old 02-07-2012, 04:41 AM
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I routinely boil water in a glass bowl in the microwave, and have never seen this happen.

I think my reasons for this may be one or more of the follows (some of which have already been mentioned above):

-- Glass 2qt Pyrex bowl (but nearly full).
-- Stir water before starting (but not several times during). I guess this means there is some residual turbulence in the water the whole time?
-- And this: This oven has a turntable. I think there's a certain amount of vibration coming from that. I imagine that would prevent super-heating.
#7
Old 02-07-2012, 04:48 AM
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Mythbusters clip - they had to use distilled water for it to work.
#8
Old 02-07-2012, 04:56 AM
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Happened to me with a cup of black coffee.

Didn't boil until I took a sip. All the lining of my mouth under my tongue came off in one piece.

Didn't do that again.
#9
Old 02-07-2012, 08:29 AM
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I am a chemist. Happens with a beaker over a Bunsen burner too. We use a glass stirring rod a glass bead, ceramic chip, whatever. At home recently I had to boil water for medical reasons. No it wasn't a baby. I used a glass marble. Just don't use a metal utensil.
#10
Old 02-07-2012, 10:06 AM
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cookware or mugs often have imperfections or scratches and that make it less likely. a microwave with a rotating platform causes vibration and makes it less likely. though not frequent, i have seen it happen in home situations.

laboratories use boiling chips, marbles, glass stirring rods. chips and marbles are a swallow hazard so a stirring rod or a chopstick would work fine.

if you don't have something in the water during heating then at least before touching the bowl put something long (chopstick, fork) into the liquid, holding that from the far end.
#11
Old 02-07-2012, 10:55 AM
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Quote:
Originally Posted by Wesley Clark View Post
In order to avoid superheated water that can explode, what can a person do to prevent that from happening ...
Don't nuke for too long...? A standard-size coffee mug filled with lukewarm water is hot enough for tea or instant soup in a minute or so, and maybe two minutes if the water runs really cold from the tap.

So, don't set the microwave for eight minutes for one cuppa and you should be OK.

For the Dopers who have seen it in home settings ... what were the circumstances? Were you hanging out with my former roommate, who once put a small plate of leftovers in the microwave and hit FIVE MINUTES.

Last edited by purplehorseshoe; 02-07-2012 at 10:56 AM. Reason: don't put metal forks into the microwave whether or not they're in a cup of water
#12
Old 02-07-2012, 12:02 PM
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I am childishly entertained by dropping the teabag into superheated water in my cup and watching it suddenly bubble up. I have the timing down for the oven at work -- hot water from the watercooler + 1 minute 45 seconds in the microwave.
#13
Old 02-07-2012, 12:35 PM
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Run it from a tap with an aerator. Or pour it quickly into the cup so that many air bubbles are created. Superheating usually happens when you first boil the water, thus driving out all the air bubbles that provide nucleation sites and prevent superheating. Then you get distracted and forget about the cup of water in the microwave. An hour later you remember, but the water is now cold, so you reheat it. Now the water is prone to superheating. Another way is reheating coffee that has gone cold. You can test for superheating by using a long handled spoon (keeping your hand back from the cup) to drop in a few grains of sugar or salt.

Last edited by Kevbo; 02-07-2012 at 12:37 PM.
#14
Old 02-07-2012, 12:42 PM
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I often heat water in a Pyrex measuring cup, and I've twice had a cup of water explode when I was taking it out of the microwave. I'm now suspicious of heated liquid that isn't actively boiling. Our new microwave has a turntable, though, so maybe I'll never see this again.
#15
Old 02-07-2012, 12:50 PM
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Quote:
Originally Posted by purplehorseshoe View Post
For the Dopers who have seen it in home settings ... what were the circumstances?
Nothing special. Water comes out of my kitchen sink (with an aerator, without any special filtration) into a mug. Mug goes into the microwave (which has a turntable) for 2.5 minutes. Mug comes out onto the counter right in front of the microwave. The water in the cup appears still; you might not even think it was all that hot. But when I put a tea bag in, it boils for about five seconds or so. There are no explosions, splashing, etc. but the water was clearly superheated.

At the relatives I visit for Christmas, their microwave has a hot water setting. If I add an extra 30 seconds, I'll get the same effect more often than not.
#16
Old 02-07-2012, 04:07 PM
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Quote:
That said, a consumer bowl that would be smooth enough to allow superheating - that to me sounds pretty damn improbable. All of the glass cookware I've ever used has enough rough imperfections to allow boiling and freezing.

Hell, I'm a chemist, and even most common lab glassware isn't smooth enough to give superheating or supercooling phenomena. When I saw the "supercooled liquid" demo years back in chem lab the professor had to use a specially polished piece of equipment that he used for nothing else.
I've seen it happen with my mug up at the office, which always has a little tea and honey residue and calcium build-up, using tap water. Granted, it doesn't usually happen (I've only seen it once), but it can. Yeah, I was pretty surprised, too.

And a minute or two might be long enough to make tea in some microwaves, but the (admittedly old) one here takes 3:17 to boil, starting from room temperature.
#17
Old 02-07-2012, 06:52 PM
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I've had it happen heating water in an ordinary coffee mug. I put it in for extra time because I wanted it to be boiling when done, since I was then going to pour it into a boullion mixture. When I removed it and put it on the counter, it started hissing and spraying furiously, though it didn't burst or explode.
#18
Old 02-07-2012, 07:08 PM
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I've had at least 2 superheated water 'explosions' that drained most of the water from the cup and caused minor burns. Several other minor ones which made nice bubbles.
#19
Old 02-07-2012, 07:13 PM
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Quote:
Originally Posted by purplehorseshoe View Post
For the Dopers who have seen it in home settings ... what were the circumstances? Were you hanging out with my former roommate, who once put a small plate of leftovers in the microwave and hit FIVE MINUTES.
Insulated plastic coffee mug. Blew up when I finally added the instant coffee. I was maybe 13 at the time and was making coffee for mom; I didn't really know the right time for nuking stuff and surely overdid it. Mostly first-degree burns over my hand, with small patches going to second-degree.
#20
Old 02-07-2012, 07:29 PM
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Quote:
Originally Posted by Kevbo View Post
... Another way is reheating coffee that has gone cold...
I thought coffee, not being pure water, would not allow this to happen at all.
#21
Old 02-07-2012, 07:46 PM
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Originally Posted by purplehorseshoe View Post
I thought coffee, not being pure water, would not allow this to happen at all.
if the coffee is all dissolved at a normal concentration then it is much like water in relation to boiling.
#22
Old 02-07-2012, 11:16 PM
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Originally Posted by dracoi View Post
I don't know, GameHat. I have several styles of tea cups/mugs that can become superheated. It's never happened to the point of being dangerous, but it's not uncommon to have perfectly still water start boiling only after I put in a tea bag.
I'll back off a bit on my claim that the glass or ceramic needs to be really smooth and polished. There's enough claims here where I'm beginning to think that it's not so uncommon. I honestly wasn't aware that consumer glass/ceramic could do this. Lesson learned
#23
Old 02-07-2012, 11:23 PM
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What, this is a thing? Not an urban legend?

I boil water in the microwave ALL THE TIME. I use a plastic microwave teapot I bought. It used to whistle, doesn't any more, and I use the "beverage" setting on my microwave for the appropriate amount (up to 2 cups).

If they didn't want me to boil water in the microwave they shouldn't have a "beverage" setting.

I did once explode a very nice ceramic cup, and that was kinda scary. Peeled the paint right off of it.

Last edited by Hilarity N. Suze; 02-07-2012 at 11:24 PM.
#24
Old 02-08-2012, 01:46 AM
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Quote:
Originally Posted by Hilarity N. Suze View Post
What, this is a thing? Not an urban legend?

I boil water in the microwave ALL THE TIME. I use a plastic microwave teapot I bought. It used to whistle, doesn't any more, and I use the "beverage" setting on my microwave for the appropriate amount (up to 2 cups).

If they didn't want me to boil water in the microwave they shouldn't have a "beverage" setting.

I did once explode a very nice ceramic cup, and that was kinda scary. Peeled the paint right off of it.
It is rare and requires water that is very high purity in a container that is very smooth and flawless, but yeah it can happen. Someone above said he had the water explode in his face and lost a lot of skin in his mouth from it.

Last edited by Wesley Clark; 02-08-2012 at 01:46 AM.
#25
Old 02-08-2012, 02:06 AM
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Originally Posted by Wesley Clark View Post
Someone above said he had the water explode in his face and lost a lot of skin in his mouth from it.
It wasn't water, it was reheated coffee. Now I know what dragons feel like - no wonder they're grumpy.
#26
Old 02-08-2012, 06:51 PM
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I'll back off a bit on my claim that the glass or ceramic needs to be really smooth and polished. There's enough claims here where I'm beginning to think that it's not so uncommon. I honestly wasn't aware that consumer glass/ceramic could do this. Lesson learned
That probably is required, to do it consistently. You probably don't want to try a few hundred times for a class demonstration.

Supercooling seems to be somewhat easier-- Some brands of bottled water will do it every time, if you keep them in the freezer.
#27
Old 02-08-2012, 07:34 PM
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Quote:
Originally Posted by Chronos View Post

Supercooling seems to be somewhat easier-- Some brands of bottled water will do it every time, if you keep them in the freezer.
Bottled coke will do it to. I love opening a bottle and having it flash freeze on me. The trick seems to be having the freezer set at its lowest temp and keep the drink from being moved while it's in the freezer.

At least that's how it works for me.
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