Sometimes I get to the coffee pot a little late in the morning, so I heat a cup of it in the microwave for a little over a minute. Then I put in the splenda, and often the coffee will start to bubble right away. What's going on in my coffee cup?

I have seen situations where water heated for several minutes in the microwave-- to the boiling point --will bubble vigorously when some sugar is added. This *seems* like it could be an example of "superheated" water, which lacks a "seed," so to speak, for transitioning to boiling. You might try using other substances, to see if the effect is the same.

"The FDA has received reports of serious skin burns or scalding
injuries around people's hands and faces as a result of hot water
erupting out of a cup after it had been over-heated in a microwave
oven. Over-heating of water in a cup can result in superheated water
(past its boiling temperature) without appearing to boil.

This type of phenomena 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."

From:
http://1.usa.gov/dpHbS7

See also:
http://www.snopes.com/science/microwave.asp

Thanks for your answer. Oddly, sugar won't cause the coffee to boil under the same conditions, just splenda. I'll try adding other substances, too. Cheers.

Laura,

Are you referring to an actual flash-boil, or just bubbling?

What Windell described was a flash-boil, which, while it happens every so often, shouldn't happen much, if at all, with coffee, due to the impurities in the liquid, and is much more explosive.

A fizzy-type of bubbling, however, can be caused from any number of things. Splenda, as an artificial sweetener, has a different crystalline structure than cane sugar, and, as such, has a different surface area, trapped air, etc.

Quote by: OohSciency

Quote by: squall_line

Laura,

Are you referring to an actual flash-boil, or just bubbling?

What Windell described was a flash-boil, which, while it happens every so often, shouldn't happen much, if at all, with coffee, due to the impurities in the liquid, and is much more explosive.

A fizzy-type of bubbling, however, can be caused from any number of things. Splenda, as an artificial sweetener, has a different crystalline structure than cane sugar, and, as such, has a different surface area, trapped air, etc.

Sorry for the late response, but I wanted to kindly thank everyone on here for their scientific explanations. I actually found myself experiencing the same thing when I re-heated coffee with artificial sweetener in it -- Equal specifically! Very really understood why it bubbled up so strangely, but I guess the chemical compounds explain a lot. Go science!

Now, I'm curious -- does one think that various types of water filters could (naturally) filter out impurities that could heighten the bubbling? Thanks, all! =)

Actually, I think I may have answered my own question with this :
http://www.differencebetween.net/object/comparisons-of-food-items/difference-between-equal-and-splenda/

I have seen this happen as well. I'm not sure if it's because splenda is not a natural substance?
To prevent getting burned by bubbling water...sometimes it can catapult right out of the cup, try putting something in the plain water. If I am making tea in the microwave, I add a tea bag to the water first and then microwave.