Looking to get my tea fix of the night, I didn’t have the patience to watch the water boil, so I just microwaved the water for three minutes and dumped sugar and a tea-bag in it.
Two things happened;
- The water started foaming. (A subject I’ve found discussed on here earlier)
- The bag refused to sink for the next five minutes, no matter my prodding or persuasion skills. I submerged the tea-bag to be sure it wasn’t just trapped oxygen, but still nothing.
What gives?
As the temperature is increased in the microwave oven dissolved gases (air) becomes less soluble. The water probably did not boil and subsequently precipitate out the gases, but became supersaturated with gas (gas wants to get out but it kinetically restricted*). Adding the teabag provided sites for nucleation and precipitation out of the air - that is it sped up the formation of bubbles by giving the dissolved air a surface to form on. This, in turn, provided bouyancy to the teabag, since it had lots of little bubbles impregnated in it.
Also a reason not to drop sugar into superheated water - it can result in bumping (sudden release of gas from the hot liquid) - which can burn.
*insert joke here