Why did my Tea Boil Over?

Factual Questions
1

Something weird just happened, and it’s the second time this week. WTHeck?

OK, so here’s the normal procedure:

Fill mug with “Hot” water from Cooler (Our water filter/cooler/dispenser/doodad has both hot and cold spigots. The hot is really just very warm.) and add tea bag.

Place in microwave and run on “high” 30 seconds.

Pull out and allow to steep 3 minutes while walking back to desk.

The 30 seconds in the microwave are just enough to bring it to a full rolling boil, and this occurred as usual in these cases.

Now, the past two days I’ve had a very sore throat, so I added cold water to the mug after it had steeped, just a bit to keep it from burning my sensitive throat.

And both times, when I added the cold water, the tea suddenly and violently boiled over the sides of the cup.

The tea had already been boiling, (stopped as soon as the microwave turned off, and showed no movement as I carried it across the room) so it’s not a matter of superheated water suddenly getting a nucleation site.

The cooler doodad receives water from the wall, runs it through an RO filter, and then cools it in a tank, or heats it in a coil, so I would think it gets plenty of opportunity to out-gas, and anyway our local water supply comes from an open reservoir, not underground wells.

The dispenser has no aerator on it (the water stream is smooth and clear, not white and bubbly.)

So what just happened here? :confused:

2

Well, this was my guess, and it’s probably still the best explanation for what’s going on. I’m wondering – when you microwave the tea – are you doing it with the teabag in the mug? I’m wondering if the teabag is getting hot enough to keep heating the tea after you remove it from the microwave.

3

Yes, the bag is in there, another point against sudden nucleation.

4

The water is horrified by, and registering its deep disapproval of, this barbaric way of making tea.

njtt (a British person)

5

Dude, I’m in the pseudo-kitchen at work; it’s pulverised tea in a dip bag. No amount of chadao is going to make it “good” tea.

TruCelt (an Irish-American person)

6

Superheated water

7

^

Yeah, I’ve experienced the same thing by using the microwave to boil a cup of water then adding instant coffee to it.

8

That’s a very different situation. In the OP’s case, the water was boiling already, so it could not have been superheated.

9

have you measured the temperature of the water?

10

If the boiling water had sugar added to it this would raise the boing point of the water, if cold clear water were added without sugar it may suddenly reduce the boiling point of the sugar water to a temp lower than it’s present temp.

11

Ditto. Or you can try [Wikipedia](http:// Superheating - Wikipedia)'s explanation.

12

True. But the amount the boiling point would have been raised is minuscule. Even if it was 50% sucrose, that would only change the boiling temp 2 degrees C. I’m not sure that would have caused it to boil over again, but who knows. I’m assuming it’s some sort of superheating thing at work here.

13

If the sugar had not been stirred in a possible hot spot may exist in the bottom of the cup? Possibly the concentration of sugar gradually disapated into the surrounding water causing it not to boil until sudenly agitated. Kind of like pooring water into hot oil.

14

I just tried it with two heaping spoonfulls of sugar not stirred in and no boil over, I tried it with plain water and no boil over. Interesting challenge.

15

This happened with me once when I was trying to make garlic butter.

Normally, I just put some butter and then garlic powder with salt in a coffee cup and MW for about 60secs.

Well, the time it overflowed on me I did all that except I forgot to add the salt. So I pulled the cup out of the MW and immediately added salt with explosive reults. It did not help matters that I was about six beers in at the time. :smack:

16

When I was young, we were so poor my dad paid me 5 cents to go to bed without my tea. In the morning he charged me 5 cents for breakfast.

17

You’ll be happy to know, I think, that I find this amusing but suspect I’m missing something.

(an American person)

(I always sorta thought thought njtt is from New Jersey until he said bollocks in another thread.)

18

Ummm, Huh?

If I read it correctly he put hot water with a tea bag in it in the microwave, then added cold water and got a reaction.

What’s the major difference between that scenario and mine?

19

Apologies for being away all weekend!

Superheating occurs when the water has no nucleating particles to help start the boiling process. Your case fits that scenario because there was nothing in the water until you added the coffee powder. In my case, the tea bag was in the cup and the water was at a rolling boil when I removed it from the microwave.

HoneyBadger - Great guess, but there was no sugar involved.

20

Apologies for being away all weekend!

Superheating occurs when the water has no nucleating particles to help start the boiling process. Your case fits that scenario because there was nothing in the water until you added the coffee powder. In my case, the tea bag was in the cup and the water was at a rolling boil when I removed it from the microwave.*

HoneyBadger - Great guess, but there was no sugar involved. I wonder how much adding the tannins etc. of tea does raise the boiling point of water? Even still, in order for this to be the explanation, the hot water would have to be heating the cold over it’s boiling point before mixing with it.

*This has raised another question for me though; I wonder if adding cold RO water could start superheated water overflowing before it cooled it down?