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A very long time ago, I was at a friend's house where her father took out this piece of ribbed metal from the cupboard.

It was a dark piece of metal about the size of an adult hand. It had grooves on one side, and was smooth/flat on the other.

He asked me to touch it and it felt cold to my touch.

Next, he placed an ice cube on it and it began melting immediately. It did not require plugging in, it was just a slab of metal.

At that time, I was just amazed at how it worked and forgot to ask him what it is called. He tried to explain to me the physics behind it but I was just gobsmacked at the thing.

Now many years later I realized that its a thawing utensil and I am trying to search for it but as you can guess from the question, I don't know what to look for.

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The first time I reached into a 350F oven and pulled out food that was sitting on tin foil, my wife shrieked. But as long as the tin foil was dry and not folded over, it doesn't contain enough heat to burn. Heat and temperature are two different things. This is similar to your question, the metal pulling away the heat. In your case it's actually warming the meat sitting on it. –  JoeTaxpayer Aug 4 at 17:53
    

4 Answers 4

up vote 12 down vote accepted

How nice to have a question I can just answer. I remember the ads for that thing. You can still buy it, it is called The Miracle Thaw. Now there are knock offs.

I am so pleased that you didn't ask how. It's too close to my bedtime for that.

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It works because the metal is superconductive for heat. It takes the ambient heat from the room and uses it to warm whatever's on it. If you were to put something really hot on it (like a seared steak fresh from the pan), it would cool that down really fast as well. If you were to put a digital thermometer near it, I think you could see the ambient temperature of the nearby air drop. –  Nate Kerkhofs Aug 4 at 9:23
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It is not superconductive, just conductive. That word has a meaning which does not apply. –  JamesRyan Aug 4 at 10:45
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@NateKerkhofs, superconductive is a term used in electrical conductivity, not heat conductivity. –  GdD Aug 4 at 11:22
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@JamesRyan Just repeating what's on the product description on Amazon: It's made of a super-conductive metal alloy that absorbs heat from the air and transfers it directly to the frozen food. I also thought that term was kinda misused in this context, but it was the best description I could use. –  Nate Kerkhofs Aug 4 at 11:23
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the hyphen makes all the difference –  JamesRyan Aug 4 at 11:30

reference: http://www.engineeringtoolbox.com/conductive-heat-transfer-d_428.html

Let's take a moment to look at the heat transfer equation. Looking at it, we can see the ways to get more efficient heat transfer

q / A = k dT / s 

q / A = heat transfer per unit area (W/m2)
k = thermal conductivity  (W/mK)
dT = temperature difference (oC)
s = wall thickness (m)
  1. use a material with a high thermal conductivity constant (like copper)
  2. thinner (!) material
  3. maintain a higher difference in temperature

The way these thawers work should now be easy to understand. (1) They are made of a material that has a very high thermal conductivity constant, like copper. The higher a material's thermal conductivity, the faster it can equalize it's temperature with that of the surrounding material.

Things that touch each other want to be the same temperature. When you put an ice cube on a sheet of room temperature copper, they are very different temperatures. But as soon as they touch, they want to be the same temperature, so heat transfer begins. Heat "flows" from the copper to the ice, increasing the temperature of the ice, and melting it. Heat also flows all throughout the copper itself, meaning that even the parts of the copper that are far away from the ice are losing heat.

With the copper losing heat, it quickly falls out of temperature equilibrium with the surrounding air. But the air and copper also want to be the same temperature, and so heat from the air "flows" into the copper, bringing it back closer to room temperature, which in turn allows the copper to heat up the ice some more....

The top of the copper plate is probably flat, to increase the amount of surface area in contact with the ice. The bottom of the copper plate, however, is probably ribbed or finned, to increase the surface area with the surrounding air, but without (2) creating more thickness!

We could also address (3) and heat the copper electrically, above room temperature, but then we run the risk of heating part of the food to that temperature as well. The benefit of using a passive copper heatsink is that the temperature will never rise above room temperature!

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HOW was not a part of the question. Write a question asking how, answer that question (a very encouraged practice), then this answer will get the credit it deserves. –  Jolenealaska Aug 4 at 9:55
    
Thanks for the tip. Check it out here: cooking.stackexchange.com/questions/46088/…. I hope I did it correctly! –  pabo Aug 4 at 10:03
    
NICE! I need to take a closer look, but I think you did great. –  Jolenealaska Aug 4 at 10:06

As @Jolenealaska said it's a defrosting tray like a miracle thaw or the like. There's nothing magic about it, it's simply a piece of metal that has high thermal conductivity. Materials that have a high thermal conductivity transfer heat more efficiently than those with a low conductivity. Aluminum is cheap and has a high thermal conductivity relative to other materials, so it's almost certainly just a chunk of aluminum.

However, defrosting trays don't really work as well as the commercials would have you believe. The same reason that your food thaws slowly without a defrosting tray limits how quickly it will thaw with one, and that is because air is a poor conductor of heat. When you thaw something what is happening is that heat is being transferred from the environment (air, the counter surface, etc) to the object until the environment and the object are in equilibrium, that is the temperatures of both are the same. A thawing tray still has to get heat from the environment to transfer, and how quickly it can do this is limited by the fact it still has to get heat from the air. When you put a cold object on a thawing tray the tray will quickly transfer it's heat to the object, but once the tray gets as cold as the object the rapid thawing stops and it's all down to how quickly the environment can transfer heat, which isn't that fast.

So thawing trays are great at making ice cubes melt quickly, and they will speed up thawing a bit, just not that much.

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A cast iron pan will do the trick. You probably have one (thus don't need to purchase and store another piece of metal). I will frequently forget to take something out of the freezer. So, when I do, I just place it in the pan (or turn the pan over to place on the flat bottom). Items in contact with the pan thaw significantly faster than items simply placed on the counter. No need to make a purchase.

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