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Tea Physics

jj

Penultimate Amazing
J
Joined
Oct 11, 2001
Messages
21,382
I used to wierd out folks at work by taking my teacup, filling it with hot water from the "hot" water dispenser (about 180), then putting it in the microwave, and heating it until it just started to bubble.

Then I'd take it out (quite superheated) and toss in some loose tea, and have it start to boil away on the countertop.

Nice little Mr. Wizard trick. Made better green tea, faster, too. Didn't have to wait forever for the leaves to sink.
 
The physics that people REALLY care about all happens in kitchens- who needs cyclotrons?
 
Just out of curiosity- has anyone used a microwave at really high altitude? Winter Park CO is probably my record. It seemed to me that it got the water a lot hotter than a stove.
 
jj said:
I used to wierd out folks at work by taking my teacup, filling it with hot water from the "hot" water dispenser (about 180), then putting it in the microwave, and heating it until it just started to bubble.

Then I'd take it out (quite superheated) and toss in some loose tea, and have it start to boil away on the countertop.

Nice little Mr. Wizard trick. Made better green tea, faster, too. Didn't have to wait forever for the leaves to sink.
Click to expand...

You've obviously got a deft hand at this by now, and probably already know this, but I have to say: be careful. If you get a really, really clean container, you can superheat it enough to where it will blow into steam when you disturb it.

H.
 
Whenever I have made tea using microwave heated water and a tea-bag, I find the tea tastes unpleasant. The water/tea combination foams in an unsavoury manner and a somewhat salty flavour ruins the tea.

These days I stick to water boiled in a kettle on a gas stove and we brew loose leaves in a teapot. When it comes to tea, it seems I am a technophobe. :)
 
Re: Re: Tea Physics

Houngan said:


You've obviously got a deft hand at this by now, and probably already know this, but I have to say: be careful. If you get a really, really clean container, you can superheat it enough to where it will blow into steam when you disturb it.

H.
Click to expand...

Oh, yes, I'm quite aware of that. I tended to drop in the tea from a distance, well, that and the fact that my tea cup was never THAT clean :)
 
I've had this happen warming a cup of coffee. Take it out of the microwave, add sugar and foom! It boils over.
 
Soapy Sam said:
Just out of curiosity- has anyone used a microwave at really high altitude? Winter Park CO is probably my record. It seemed to me that it got the water a lot hotter than a stove.
Click to expand...

Surely some mistake:

Water boils at a lower temperature with increasing altitude (mountain climbers know this) and a microwave oven is merely heating water. Once it is boiling it can't get any hotter. It must be your imagination?

A little trick I used to do at school to prove this was to take a large syringe (20ml is ideal), fill it with about 5 ml of hot water then block the end and pull the plunger OUT, not in. This reduces the pressure around the water as though suddenly taken up to a few thousand feet asl and the water will start to boil within the syringe.
 
peptoabysmal said:
I've had this happen warming a cup of coffee. Take it out of the microwave, add sugar and foom! It boils over.
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Why would that happen btw?

Also I have tried to microwave an egg (as opposed on paoching/frying/boiling but no matter how carefull I was the egg would always explode all over the microwave.
 
Jon_in_london said:


Why would that happen btw?
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It has to do with bubbles, I seem to remember: surface tension initially retards bubble formation, which means no vaporization, which means the water gets hotter than 100 C. Introduce an irregularity (a spoon, say) to mess with the surface tension; bubbles will form suddenly as the water releases its extra heat.

Somebody tell me if I got this right!
 
ed- I expressed myself ambiguously. You are, of course, right about boiling point decreasing with pressure and inversely with altitude. My observation was that AT the same altitude a microwave oven seemed to get water hotter than a pan on the stove. I suspect the kind of superheat effect jj is describing takes place, at <100C, but higher than the boiling point of an open pan.
I never tested this with a thermometer, but it certainly seemed to get tea water hotter.
Of course a pressure cooker is the answer.
 
Jon_in_london said:

Also I have tried to microwave an egg (as opposed on paoching/frying/boiling but no matter how carefull I was the egg would always explode all over the microwave.
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Assuming that you've taken the egg out of its shell (!) you have to prick the yolk. Otherwise the membrane lets the pressure build up to the point where it goes pop. This doesn't make for good fried eggs, so it's best to aim for scrambled.
 
Kiri said:



It has to do with bubbles, I seem to remember: surface tension initially retards bubble formation, which means no vaporization, which means the water gets hotter than 100 C. Introduce an irregularity (a spoon, say) to mess with the surface tension; bubbles will form suddenly as the water releases its extra heat.

Somebody tell me if I got this right!
Click to expand...

There are several things going on to cause this. First, when you heat in a microwave you are usually using a container that is very smooth (relative to a saucepan), and thus it is hard for bubbles to form (they form around an irregularity). Without bubbles, the water will superheat (heat above 100C), as you say.

Second, when you heat in a microwave you are heating the water directly, and the container is cooler than the water, which lowers the chances of a bubble forming on the container at 100C, initiating boiling. Whereas on your range the saucepan is applying the heat to the water, and thus is hotter than 100C, at least in areas, by the time the water is 100C. Thus when a bubble forms around an irregularity, it is likely to be at 100C or greater, and initiate a boil.

Dumping sugar (or tea leaves, as in jj's example) in a superheated mug of microwaved water causes an instant boil (or even an explosion) because bubbles form around the sugar, and the entire cup boils at the same time.
 
spoonhandler said:
Whenever I have made tea using microwave heated water and a tea-bag, I find the tea tastes unpleasant. The water/tea combination foams in an unsavoury manner and a somewhat salty flavour ruins the tea.

These days I stick to water boiled in a kettle on a gas stove and we brew loose leaves in a teapot. When it comes to tea, it seems I am a technophobe. :)
Click to expand...

Double blind!:p
 
speaking of tea and surface tension, somewhere on a NASA web site I saw a Quicktime movie of astronauts on the International Space Station making a floating droplet of tea about 2 cm in diameter and then picking it up with chopsticks and eating it.

However, Eddie the Shipboard Computer did not chime in to say that they are stupid monkeys who don't know any better.
 
At extreme altitude, water boils at insanely low temperatures. A few friends of mine and I climbed Manaslu, one of the 8000m peaks, in Nepal. (Elevation 26,758ft) We could stick our hands in the water we boiled for some (extremely sketchy) tea near the summit- it was warm, but not very. We all got quite a bang out of it. This could have been due to hypoxia, however. :D Oxygen starvation-my anti-drug! Whee!
 
On the general subject of microwave silliness. When I first bought one, I experimented by putting many things in it. (No poodles).
Lightbulbs are good.
Paraffin wax is impressive. Absolutely nothing happens (no double bonds?) unless you use a syringe and inject some water into the wax. Then you have an inside out lava lamp.

Nb. Microwaves can get many household substances (like sugar) dangerously hot. If experimenting, protect skin and eyes and have a basin of ice cubes or cold water ready to stick burned fingers in.
 
spoonhandler said:
Whenever I have made tea using microwave heated water and a tea-bag, I find the tea tastes unpleasant. The water/tea combination foams in an unsavoury manner and a somewhat salty flavour ruins the tea.

These days I stick to water boiled in a kettle on a gas stove and we brew loose leaves in a teapot. When it comes to tea, it seems I am a technophobe. :)
Click to expand...


I find that teas tastes terrible too when I use a microwave to heat water.

Being British it is a kin to blasphemy not to bring water to a boil before using it for tea. :D
 
HEATING WATER in MICROWAVE (not a joke) PLEASE READ

jj said:
I used to wierd out folks at work by taking my teacup, filling it with hot water from the "hot" water dispenser (about 180), then putting it in the microwave, and heating it until it just started to bubble.

Then I'd take it out (quite superheated) and toss in some loose tea, and have it start to boil away on the countertop.

Nice little Mr. Wizard trick. Made better green tea, faster, too. Didn't have to wait forever for the leaves to sink.
Click to expand...

just got a similiar email to that which is contained within the following page:

http://www.snopes.com/science/microwav.htm#htw

A safety message.
Click to expand...
 
Hot tea is always a good Brownian Motion producer.

Just the thing while working on your prototype Infinite Improbability Drive.
 
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