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As someone who lives in an apartment with a small kitchen, I often find myself repurposing the stovetop as a food prep space. I've always tried to avoid putting plates down on a (gas) burner that was recently on, in case there's any residual heat in the guard (the iron part that actually holds up the pot...not sure of the correct word). I have cracked warm glasses by pouring cold liquid into them, and I don't want that to happen with a plate.

However, I'm putting hot food straight from the pan onto that plate, and the pan was just recently on that burner. If the heat from the food doesn't crack the plate, does that mean that it would be safe to put the plate on the burner?

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3 Answers 3

I disagree with the other answers. The plate will be warmed, but not enough to shatter.

First, I assume that you are talking porcelain plates. Glass (or Luminarc, etc.) is another matter. Porcelain is much more heat shock resistant.

Second, while the metal has both a higher heat capacity and a higher mass than food (as Jefromi mentioned in his comment), it also has a much higher heat conductivity than food (80 W/(m.K) for iron, 0.58 for water, and food is mostly water) which means that it loses heat quicker than food, not slower.

Third, look at the shape of the gas burner. Unlike a resistive electrical stove, you don't put the plate on a heated plane surface. There is a metal grid which supports the plate. Yes, its bars are hot. But they are small and thin, and sit in the air. Which means that, due to their shape, they lose their heat quickly.

Fourth, look at the plate from below. All plates I have seen have a small rim on the underside. This means that you don't even have the whole metal bars come into contact with the plate (which still wouldn't have been too bad); the only part you get heat exchange are the small points where the plate rim touches the bars.

Take all this together, and you see that the heat transfer is very small. A broken plate can't be completely ruled out, but based solely on the strength of the thermal shock, the chance for it happening is way below the chance of a room-temperature porcelain teapot shattering when somebody pours boiling water into it. And people do that all the time, so I would see it as an acceptable risk level. (My urge to tell them to preheat their pot for better tea notwithstanding).

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The small contact points do mean that if significant heat is transferred, it will put more thermal stress on the plate. But I agree: this should be safe, particularly if the plates are oven-safe. –  Jefromi Dec 18 '11 at 18:08

I don't recommend it. I have had a plate crack before after being placed on a recently turned-off burner, and on another occasion ended up with burned fingertips when I totally forget that I had done so. I have in the past used a cooling rack over recently used burners that gives you a bit of elevation, and an automatic work space/storage space. Hope this helps.

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rumtscho makes a good point below. I should point out that my plates were not porcelain but a poorer grade earthenware. –  Nobby Dec 18 '11 at 18:41
    
Total rate of heat transfer is not what causes microfractures in ceramics to expand. A large temperature gradient, such as that around a point contact with a hot surface, is the culprit. –  Wayfaring Stranger Dec 18 '11 at 21:20
    
A recently turned-off electric burner, or gas burner? I don't think the grates on my gas burner have the thermal mass to heat a plate to burning temperature, even if I'd just pulled a 500°F pan off them. Given, I have a cheap stove… –  derobert Dec 20 '11 at 17:01

This is probably a bad idea - I forget the physical term for it, but the metal burner cover holds its heat much better than the food does - you would be willing to touch the food a few seconds off the flame, but you probably don't want to touch the metal for a good five or ten minutes.

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The term you are probably thinking of is thermal capacity. –  Aaronut Dec 18 '11 at 3:18
    
It's probably not heat capacity (in the usual per-mass/volume sense). Water actually has a higher heat capacity, whether per mass or per volume, than aluminum or iron, and really just about anything (see the table at Aaronut's link). There's probably more metal than you'd think; the burner is large, and coupled some to the rest of the stove. Second, the burner gets hotter than food can, since the water content of food tends to keep it below 100C, and the burner is hotter than the pan, which is hotter than the food. So it may store more heat, without having a higher specific heat capacity. –  Jefromi Dec 18 '11 at 14:23

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