# A nice, safe cup of tea

As I was making tea this morning, I was reminded that many people on the internet think I’m an idiot. I’d like to defend myself.

I heat the water I use for brewing tea in a microwave oven. This is, according to the internet, a terribly dangerous practice, as I could very easily end up with superheated water that will suddenly boil over and scald me. That I’ve never had such an accident in maybe 20 years of making tea this way is a strong hint that I’m doing it safely, but it isn’t proof. Maybe I’ve just been lucky the roughly 6,000 times I’ve done it.

So let’s do some calculations. The thermal mug I currently drink from has a 20-oz capacity, so I heat up about 600 ml of water in a Pyrex measuring cup. I put the measuring cup in a 1200-watt microwave and set the timer for 3:10. That works out to

$\left(1200\phantom{\rule{thickmathspace}{0ex}}\text{J/s}\right)\left(190\phantom{\rule{thickmathspace}{0ex}}\text{s}\right)=228,000\phantom{\rule{thickmathspace}{0ex}}\text{J}$

of energy being put into the water (J = joules). This is an overestimate, as it doesn’t account for the heating of the glass cup.

The water coming out of my kitchen faucet tends to be 50–55°F. Let’s call it 12°C, so bringing this water to the boiling point requires

$\left(88\phantom{\rule{thickmathspace}{0ex}}\text{K}\right)\left(600\phantom{\rule{thickmathspace}{0ex}}\text{g}\right)\left(1\phantom{\rule{thickmathspace}{0ex}}\text{cal/g-K}\right)\left(4.184\phantom{\rule{thickmathspace}{0ex}}\text{J/cal}\right)=220,900\phantom{\rule{thickmathspace}{0ex}}\text{J}$

The energy I’m putting into the system is, at most, about what it takes to bring the water to a boil. So I’m not creating superheated water.

What about hot spots? If I’m not heating the water uniformly, I could still be superheating some portion of it, right? I suppose, but like all microwave ovens, mine has a turntable, so no part of the measuring cup stays in the same place. Not even the center, because I don’t put the cup in the middle of the turntable.

Now, I don’t want to be irresponsible here and suggest you all go out and start microwaving water with no concern for the risks. But there is a way to do it safely, and I’d like to be given some credit for knowing how.