Why did Microwave burn the stem of squash

February 3, 2006 12:25 PM

Microwave Puzzle - I cook a chunk of winter squash daily, for putting into rice and vegetables. last week I cooked a chunk with a woody stem maybe 3/4 " long, 1/3 " across, same amount of time as usual. (three minutes). the squash cooked fine, but by the end of the time, smoke was coming out of the microwave. I stopped it, half of the stem end was black, burned. I've cooked pieces with stems before, what happened?

My theory is that it has something to do with the length/width ratio of the stem? This actually had embers inside when I knocked it off. I don't get it - you can put paper in the microvave, what was different in this case.

posted by judybxxx to science & nature (7 comments total)

Do you have a rotating platter in your microwave? The electromagnetic field inside has hot and cold spots repeated in a regular, but complex, pattern. Rotating reduces the chance that something will sit in a single hot spot for too long.

That, and microwaves are magic, so all bets are off really.
posted by odinsdream at 12:27 PM on February 3, 2006

[...] something to do with the length/width ratio of the stem
Very possible, although, I think the curve of the stem might be a bigger culprit (reflecting the waves into the stem and stuff). Have you tried nuking a grape split in transverse halves? Takes only a couple of seconds there.
posted by pantsrobot at 12:37 PM on February 3, 2006

Without having more details it's going to be very difficult to say. Was the stem over the centre of the plate? Had the rotating platter stopped rotating? If so then a hotspot could have formed inside the stem, causing the burning. If the 'meat' of the squash had been in this spot then it would be unlikely to heat up enough to burn.

The wavelength of the microwaves in a microwave oven is about 12cm so I doubt that the size or the lenght/width ratio of the stem had any significant effect.
posted by alby at 1:34 PM on February 3, 2006

No rotating platter in the oven, I have no idea of the exact placement, so I guess there was a hot spot, and I need to watch it? and watch for stems? oh well, not a big deal. It would be nice to know what to watch out for.
posted by judybxxx at 1:44 PM on February 3, 2006

If there's no rotating platter, your microwave probably has a "mode stirrer" which looks kind of like a metal fan that may or may not actually be visible. Moving that shuffles all the hot/cold spots around the box.

Most likely, the stem just absorbs a lot of energy and can't conduct it away very quickly because it's woody and so the temperature rises rapidly.

If you want to map any hotspots that may or may not be present, you can do it by placing a sheet of damp paper in there for a few seconds and looking for dry patches. If you wanna be ultra-fancy, use thermal fax paper and have a print-out of the result...
posted by polyglot at 6:24 PM on February 3, 2006

Could the stem have been more dried out than usual?
posted by degnarra at 7:56 PM on February 3, 2006

There may have been a metallic fragment that had grown into the stem somehow...
posted by Roger Dodger at 11:13 AM on February 4, 2006