If you grew up in the 70s or 80s , there was one rule:
No metal in the microwave!
None. Nada. Don't do it, ever, under any conditions. If you put metal in the microwave, it would spark and explode. That was how science worked back then.
So you can imagine the surprise that Gen Xers and millennials who might have been browsing Reddit this week are feeling.
A Reddit user recently shared a confusing warning label on their microwave, seemingly encouraging them to leave a (presumably) metal spoon in any liquids while heating.
The illustrated sticker shows two cups of liquid. The plain cup — with only liquid inside — has an X crossing it out, as if to indicate you're not supposed to microwave a plain container of liquid. The allowed version, confusingly, has a spoon sticking out of it as the liquid bubbles! Last time I checked, most spoons are metal.
So what exactly is going on here?
from mildlyinteresting
Is the microwave manufacturer actually... encouraging us to microwave metal?
Some users were baffled and began questioning their entire existence:
"We grew up in the 70s being told to never put metal in a microwave. Hard to learn that," wrote u/dustin91.
"Growing up in the '70s, we were drilled to never put metal in the microwave. It's tough to shake that mindset," said u/GoodnessEmma_.
In fact, the OP was not the first person to be confused by this sticker on their microwave. Posts just like this one are surprisingly common.
from mildlyinteresting
Luckily, there's a simple explanation for this counterintuitive sticker: Sometimes, under certain circumstances, putting metal in the microwave is perfectly OK.
But before you go microwaving your whole silverware drawer, let's hear out the scientific explanation.
"[The] electromagnetic activity [in a microwave] can do a number on metal. The oscillation of the microwaves can produce a concentrated electric field at corners or an edge of a metallic object, ionizing the surrounding air," which creates popping, sparking, and arcs of electricity. That's according to a post on MIT's "Ask an Engineer."
However, when a metal object in the microwave is thick and or smooth, with no sharp edges, there's little risk of a fire breaking out.
A YouTuber named ElectroBOOM actually (and bravely) tested different metals in the microwave.
Smooth, thick metals (like spoons) did fine, even when he used two spoons close together or touching. Things with sharp edges (thin strips of foil, a fork) did not, and sparked or caught fire quickly.
It makes sense the more you think about it.
A lot of foods (like Hot Pockets) come with a metal or foil-lined tray to encourage heating. Your microwave may even have a metal shelf inside!
The confounding sticker suggests leaving a spoon in any liquids to prevent superheating — which can cause scalding hot water or other liquids to explode.
In some cases, microwaving a liquid can cause it to heat beyond its boiling point — without actually boiling. (This is especially likely if you were to heat a liquid without any "impurities," like distilled water.) When superheated liquid is disturbed (by sticking a spoon in, adding a sugar cube, or just sloshing it around) it can explode and scald you.
Mythbusters tested this scary idea many years ago — and confirmed that it can happen!
Leaving a spoon in the water creates "nucleation points," or opportunities for bubbles to form, rise to the surface, and release heat — which is how normal boiling is supposed to work.
It doesn't HAVE to be a metal spoon, of course. A wooden spoon or chopstick will have the same effect.
So now we know that some metal in the microwave is OK. But there are enough caveats that you really ought to know what you're doing before you try it.
Having done the research, I can see now why our parents and teachers figured it was just safer to tell us to never put any metal in the microwave under any circumstance.
We believed a lot of stuff we were told as kids in the 70s, 80s, and 90s. Black belts in karate had to register their hands with the police as deadly weapons. People put razor blades in Halloween candy and apples all the time. We were very likely to encounter quicksand at some point. Acid rain would kill you. Fruit could grow in your stomach if you swallowed seeds. Alligators lived in the sewers.
Frankly, "never microwave any metal" was the least crazy thing we were told back then. The truth is a little more complicated, but it kept us safe at the time, right?
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