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December 24, 2013 1:04 PM   Subscribe

In an attempt to be all healthy and virtuous, I tried to make kale chips in the microwave. I nuked a small plate of plain, unadorned kale. The kale WENT UP LIKE A FREAKING FIREWORK (sparks, flames, scary noises). Multiple times (hey, I learn by doing). WHY?!

Kale chips are one of the few veggies my little bastard children will eat, so when The Internets told me they could be prepared in the microwave, I was SUPER-excited. However, when I attempted to do so, my kale violently BURST INTO SPARKS/FLAMES, scaring the bejesus out of me. Why did my kale do this? If I ever muster up the courage to try again, how can I avoid the same terrifying consequences?

- The kale was prewashed, prebagged stuff from Trader Joe's. I did not put anything on it.
- The microwave is standard-issue above-the-stove Kenmore one. It is used frequently and has never misbehaved.
- The kale was on an uncoated paper plate. I have microwaved stuff on these plates before, sans incident.
- I tried microwaving multiple batches of kale, multiple times. Each microwaving resulted in sparks/flames within 45 seconds. The sparks seemed to originate from the stem area.
- I didn't invent the microwave method: multiple food blogs advocate this method.

If you'll excuse me, I'll be hiding in the cupboard and shaking while I await your replies...
posted by julthumbscrew to Food & Drink (16 answers total) 9 users marked this as a favorite
I have seen broccoli do this as well, so maybe it is some mysterious aspect of brassicas? I would trust your own experience in this instead of the blogs and use the oven from now on.

OH BUT I would also try again with the stem bits trimmed away as much as possible. FOR SCIENCE!
posted by elizardbits at 1:13 PM on December 24, 2013

This has happened to me with carrots before.

It could be the result of the concentration of trace minerals found in the kale itself. Kale is notoriously high in things like iron, magnesium and other 'metals' that may produce a reaction when microwaved.

The microwave could also be drying the kale out so quickly that it charrs and sparks.
posted by stubbehtail at 1:14 PM on December 24, 2013

Erm.. get it on video?

Top comment at America's Test Kitchen, here, had the same thing happen.

I love this recipe–so quick and yummy!–but three times I had flames and sparks erupt from my plate. I’ve had this with other green veggies on occasion, such as heating broccoli, so I’m guessing it has something to do with minerals/metals in the foods, such as iron and magnesium.

Her guess is as good as mine. ATK does recommend a particular variety of kale, a coating of oil, and kosher salt. ATK is not usually pro-microwave, so if they recommend a microwave technique, it's worth paying attention to.
posted by Sunburnt at 1:14 PM on December 24, 2013


It turns out that dense vegetables such as green beans, carrots, kale, and green peppers have a higher amount of minerals than other food items, including iron, magnesium and selenium. According to the Canadian Food Inspection Agency, cooking these vegetables in a microwave can actually create sparks; the minerals act like tiny pieces of metal and create arcing effects in a microwave. "The sparks result as the microwaves reflect or bounce off the metal. The arcing does not harm the food but it does prevent it from heating thoroughly." So if you'd like to try this method of cooking kale, we suggest you keep a close eye on the food while you're cooking and stop the cooking if the arcing becomes serious - too much can damage the oven.
posted by catalytics at 1:15 PM on December 24, 2013 [10 favorites]

I don't think it's the mineral content; I've done this on purpose with grapes (cut a grape in half but make sure the halves are connected by a little bridge of skin, place face down on a plate, microwave and watch the AMAZING ARCS). I think it has something to do with ionization of water, but I don't know exactly how. Was your kale wet?
posted by KathrynT at 1:50 PM on December 24, 2013 [1 favorite]

Metals on your dish? Twist tie? I once nuked some cheese with just the teeny weeniest bit of tin foil attached (whoops!) and the thing sparked like crazy.
posted by St. Peepsburg at 2:39 PM on December 24, 2013

I once posted an AskMe about beef liver doing this (which is too aggravating to link on my phone) and the consensus was it was the iron content. So since kale is also high in iron I would think that's the culprit. I agree, it's terrifying. ZZZZZZZZZT!
posted by HotToddy at 3:22 PM on December 24, 2013

Best answer: Microwave ovens are designed to heat food by transferring energy primarily to water molecules. As you dry out the food, there is less and less water to absorb the energy so the energy becomes concentrated on what little water is left, possibly getting hot enough to cause flames. The stem area, since it is thicker, is the last place to give up its water and concentrates all of the energy.

A microwave oven is not the best device for drying foods. Better to use a regular oven.
posted by JackFlash at 3:56 PM on December 24, 2013

Best answer: It wouldn't be the mineral content. If it were, kale would serve as a useful substitute for iron ore. Looking it up, kale has 0.9 mg iron per 100 grams (depending on the field). And that iron is probably tied up in iron sulphate or something, rather than in the form of metallic fibers.

I'd guess kale and other veggies are weakly conductive - they're spongy sacks of saltwater, after a fashion, as are we, and we can conduct electricity if we put our minds to it.

It may have something to do with the shape - kale and broccoli fork off into a bunch of locally pointy bits, and
electric field lines on charged conductors* have a stronger field strength near locally pointy bits. (A fork is going to spark in a microwave sooner than a spoon will.)
posted by sebastienbailard at 4:37 PM on December 24, 2013 [3 favorites]

Best answer: You might try bruising the kale a bit first, at least, that's how I make kale chips in the microwave: I roughly chop or tear the leaves then grab a piece of coconut oil, which melts in my palm, and roll the leaf pieces between my hands. Perhaps it's the oil or the mechanical action that makes my kale non-sparky? Next time I'm going to try the kale naked and see if I can get arcs!
posted by anadem at 5:47 PM on December 24, 2013

Best answer: The sparks seemed to originate from the stem area.

My guess is that the sparks and flames are coming from the cut ends of veins in the stem which extend up into the quite veiny leaves.

According to the Wikipedia article, "Thermal runaway is more typical of electrically conductive liquids such as salty water", and I think the salty and somewhat sugary water in the veins of the leaves superheats in an absence of oxygen, then boils out of the cut ends at the stem, upon which sparks from the rapidly evaporating salt water ignite the sugar vapor, which then burns in the oxygen of the air, and you end up with sparks and flames.
posted by jamjam at 5:52 PM on December 24, 2013 [2 favorites]

Dave Berry had an old humor column about when he tried nuking a carrot: http://www.carrotmuseum.co.uk/dbarry.html
posted by zscore at 6:19 PM on December 24, 2013 [1 favorite]

Given the passions of little boys, this seems like a good wayto get them to eat vegetables.

I confess that I have microwaved broccoli many times and never seen this effect. I rinse it off and put it in a lidded glass bowl. Maybe the water boiling off keeps the veg below the flash point.
posted by bad grammar at 6:53 PM on December 24, 2013

The key to microwaving veg is put it in a bowl with a little bit of water and a plate on top.
posted by sweet mister at 7:55 PM on December 24, 2013 [2 favorites]

I forgot to say that when I make kale chips in the microwave I cut out the stems and just use the leafy bits. Maybe jamjam's right and it's the stems that spark?
"The key to microwaving veg is put it in a bowl with a little bit of water and a plate on top"
true, but no, no, no, NOT for kale chips! Chips must dry out to be deliciously crispy.
posted by anadem at 10:57 PM on December 24, 2013 [1 favorite]

Response by poster: A follow-up on this: the culprit appears to be the stems! I made another batch of microwave kale chips recently. I cut out the stems and cut each leaf into several pieces. There were no unexpected pyrotechnics and the kale was crispy and delicious.
posted by julthumbscrew at 10:22 AM on April 1, 2014

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