Beef liver fireworks
March 11, 2012 9:15 PM   Subscribe

Why does beef liver spark in the microwave?

I make liver treats for my dog by boiling beef liver, dicing it, then keeping it in the freezer and defrosting in the microwave for 15 seconds when I'm going to use it. When it's in the microwave, it sparks in little random bursts, as if there are tiny grains of something bursting into flame. Today I absentmindedly put the liver bits in a sandwich baggie and tossed the whole thing in the microwave, and the sparking melted a bunch of holes in the baggie!

Google has absolutely nothing to say about this phenomenon, at least that I was able to find. Could it be the high iron content in liver causing this? Or what?
posted by HotToddy to Science & Nature (11 answers total) 2 users marked this as a favorite
Beef liver has a high iron content, but I am surprised it is high enough to cause arcing. I suspect that your microwave may be out of calibration.
posted by Ardiril at 9:23 PM on March 11, 2012

Is it possible you wrapped the liver in aluminum foil before putting it in the freezer, and small bits of foil are still attached to it when you put it in the microwave?
posted by Nomyte at 9:41 PM on March 11, 2012

Does it spark only when it's frozen? High mineral content in the food can cause arcing, apparently. Freezing can make it more likely. It happens in carrots too.
posted by WasabiFlux at 10:14 PM on March 11, 2012 [3 favorites]

The use of microwave energy to ablate tumors in the liver and other tissues has been widely studied (pdf).

Of particular interest to scientists is the dielectric property of the tissue. The microwave oven is a resonant cavity. Placing an item with a high dielectric constant in such a cavit will change the resonant properties of the cavity - and concentrate RF energy in the material while lengthening its wavelength.

Air has a dielectric constant of 1,0. Most plastics around 2,1, and as a result they are relatively transparent to RF energy. At 2,45Ghz (the frequency of most home microwave ovens) a normal healthy liver has a relative dielectric content of 57 (see table 4 of the linked paper) which is a huge freaking number. Certainly due to the high mineral content.

Heating smaller pieces, at a lower temperature, placing them off center will mitigate the problem.
posted by three blind mice at 3:04 AM on March 12, 2012 [4 favorites]

Science! I think it's been happening with carrots, too, but since I often toss a handful of frozen diced mixed vegetables in with the liver, I wasn't sure if it was really the carrots or liver. But it definitely happens with liver alone. Thanks so much!
posted by HotToddy at 7:19 AM on March 12, 2012

a normal healthy liver has a relative dielectric content of 57

And water has a relative dielectric constant of about 80 at room temperature. And obviously, you can heat water in a microwave without sparking.

Certainly due to the high mineral content.

Due to the high water content.

I can't say whether the sparking is related to the mineral content of liver, but I can say it's not directly related to the dielectric constant.
posted by DevilsAdvocate at 11:42 AM on March 12, 2012

I suspect that your microwave may be out of calibration.

Ardiril, this is a meaningless phrase. Microwave ovens aren't
posted by IAmBroom at 2:10 PM on March 12, 2012

I agree that it's more likely to be the water content than the mineral content. Specifically, if your liver bit sizes are comparable to the wavelength of 2.4 GHz microwaves in water (which is about 1 cm), then adjacent bits can act like an antenna and collect quite a bit of power. Grapes do the same thing; the explanation there doesn't rely on any hooey about "metal bits", and does suggest you can avoid the arcing by heating some water at the same time as your bits.
posted by fantabulous timewaster at 5:05 PM on March 12, 2012

"Microwave ovens aren't 'calibrated'."

Wanna bet?
posted by Ardiril at 6:08 PM on March 12, 2012

Well, the microwave seems to function in exactly the same manner as the microwave at work and the microwave at the food co-op in that it takes the same amount of time to heat the same frozen entree in each place. So I don't think it's out of calibration.
posted by HotToddy at 8:53 PM on March 12, 2012

Ardiril, well I'll be damned.

Bet it's a factory-only usage, but at this point - who wouldn't take my bets?!
posted by IAmBroom at 10:11 AM on March 13, 2012

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