Caramthros
3 HN mentions · mentioned in 3 months, 2020–2022
1:41 · 2.4M views · Oct 19, 2007
A short clip of the Mythbusters demonstrating superheated water in a microwave, which can erupt violently when disturbed.
HN cites it as the standard demonstration of superheated water, in threads about microwaving water and tea.
3 comments from Hacker News
I thought one of the reasons not to use a microwave is that it's way to easy for the water to get superheated. Especially in a ceramic mug that is smooth on the inside, with no nucleation sites for the water to form steam it can get way over boiling point fairly easily. Then when you put something in (like a teabag or sugar) you're dropping a ton of nucleation sites in and the water will flash to steam, occasionally exploding the mug. But maybe that's just an urban legend. /shruggie Mythbusters took a look: this video Could you use a small saucepan and bring water to the desired temperature if you don't want to use a microwave or teapot? Maybe a small coffee maker without any coffee in it, just to get the water up to the temperature you want.
It's something to be aware of, but in practice it's very difficult to superheat water at home. For superheating to occur, you need very pure water in a smooth container with no imperfections. Tap water in most places cannot be superheated because it contains too many minerals, and most ceramic cups aren't smooth enough to prevent boiling. If you're making tea, an easy way to prevent superheating is to drop the bag in the water before you heat it. Another way is to put a wooden stirrer in the cup. There's a mythbuster video here where they show water being superheated: this video , but note that they use distilled water (which nobody drinks) in a Pyrex container (which nobody uses). And they actually use a mug of tap water as a control.
I seem to remember as well that the coffee was reported as instantly boiling when sugar was added. If that's the case (and no reason to disbelieve the plaintiff), that's a superheated liquid. In other words, it is a liquid above its own boiling point and waiting for a cavitation event (something for bubbles to hold on to) to instantly boil. And this seems to coincide with the coffee explosion and burns from the plantiff. Mythbusters video of an example of superheated water: this video