Aluminum (Metal) Instant Defrost Disks

[Anna N]

Hubby works in a machine shop and last night he brought home a disc of waste aluminum (10 inches in diameter, about 3/8" thick). He thought it might be useful in the kitchen. A fellow employee told him that stuff defrosts really fast on aluminum. Ever skeptical, I tested this hypothesis - put an ice cube on the aluminum disc and another on a ceramic tile - both at room temp and very close to one another. The answer was almost instant - the ice cube on the aluminum melted almost immediately. Why?

Given safety concerns about defrosting food, does this have any really practical applications?

Thanks

[Rachel Perlow]

There used to be an "as seen on TV" product called Magic Defrost (or something like that), which was basically a sheet of aluminum. You were supposed to run it under hot water to "charge it" and then lay your frozen meat (like chicken breasts) on it to defrost, turn after 15 minutes or so. It did work, but I guess I really didn't find it that useful as I haven't used it in years. I suppose it's somewhere in my garage.

Obviously, they don't make it anymore, this is all I could find in a google search.

[KHT20]

Nathan's makes a griddle/defroster. One side fits over your stove top burners, with grill marks for your hot dogs; the other is flat for defrosting on the counter. I always wondered if the defroster would work... now I know.

Begs the question - would a regular aluminum cookie sheet do the same thing?

[JAZ]

According to Robert Wolke in What Einstein Told His Cook, a heavy flat piece of metal (aluminum seems to work best, he says) is extrememly efficient at conducting the heat from the room into any food placed on top of it. If you have steaks or chops, or any other flat foods, they'll thaw considerably faster if placed on one of those "miracle" defrosters, or a heavy aluminum skillet, because the surface area in contact with the pan is so great compared with the total volume of the food.

On the other hand, they don't make much difference for roasts or whole birds or other big bulky foods.

So, yes, any aluminum pan will work, but the heavier the better, so a sheet pan is probably too thin to make much difference.

[ellencho]

Anna N you are so lucky. The retail defroster trays go for close to 20 bucks.

I've been wanting my own hunk of aluminum for defrosting for years.

[slkinsey]

Anna N is correct. The chunk of aluminum works because aluminum is a very good conductor of heat.

[Anna N]

Thanks to all - still not sure I will use it as a defrosting device but I won't be able to resist a few "experiments".

My eyes lit up when I saw it not because it was aluminum but because it was flat, round, and a convenient size for serving certain appetizers (covered with a food-safe plastic or something first). All of my serving plates seem to have sloped edges so that food, no matter how carefully arranged, eventually ends up in a pile in the centre.

[lueid813]

The answer was almost instant - the ice cube on the aluminum melted almost immediately.  Why?

As has been mentioned, aluminum is a good conductor of heat (or cold) so it draws the cold away from the ice and dispurses it through the entire pan and into the air.

Think of it this way: Suppose you had a room with both a tile floor and a carpeted area. At any given time, both will be the same temperature, i.e., room temperature. Yet if you sat on the tile floor your bottom would feel cool and if you sat on the carpet your bottom would feel warm. Why is that, if both surfaces are actually the same temperature?

The floor feels cooler because tile is a good conductor, it has a very large capacity to draw heat away from your body and dispurse it, so your body can do little to warm the floor where you are sitting. In the case of the carpet, you feel warm because the carpet is an insulator (note, that's the opposite of conductor). The warmth from your body stays in one place and raises the temperature of the carpet enough for you to feel the difference.

Edited April 29, 2004 by lueid813 (log)

[mrbigjas]

As has been mentioned, aluminum is a good conductor of heat (or cold) so it draws the cold away from the ice and dispurses it through the entire pan and into the air.

So if you had a nice chunk of copper, it would work even better?

[jsolomon]

So if you had a nice chunk of copper, it would work even better?

Yes, copper is a better conductor of heat than aluminum, but not by a whole lot. Law of diminishing returns and all.

[rooftop1000]

just checked to see if anyone had discussed this topic.....cause I dropped a couple of 2 pound rib eyes frozen solid into my big aluminum pan an hour ago and they are ready for grillin'. I used to have a magic defroster a couple of houses ago. Running the pan under warm water first speeds it up too

tracey

[budrichard]

HEAT FLOW (BTU/HR) = Specific Conductivity (Cp) * Temp Differential (DELTA T)

i.e the higher the Cp or the Delta T, the greater the heat flow and the faster things will defrost. Ceramics are in a class called Insulators and as your experiment showed are not as effective as Al which is a Conductor. The movement of the outer electrons causes heat transfer and in some materials with weaker bonds between the outer electrons and the nucleus, electrons move easier. -Dick

[jsolomon]

The other thing is that aluminum has a very healthy specific heat (a description of how many calories it takes to make a certain amount go up a certain temperature). Pound for pound, aluminum's is actually higher than that of iron--not true volume for volume, though.

So, you've got a large chunk of a good heat conductor that contains a lot of heat because of its nature.

[SuzySushi]

I suppose I could experiment myself but...

Does anyone know, if the aluminum is coated with Teflon -- e.g., if I use my Teflon-coated skillet -- will that work too?

[rooftop1000]

my pan is teflon coated worked fine.....

t

[budrichard]

Specific Conductivity in the formula above should in fact be Specific Heat.

The teflon coating should not have much effect because it is so thin but I don't know what the Specific Heat of Teflon is?

[kelautz]

I use my cast aluminum double sided griddle/grill to defrost flat things all the time. Works great, esp. for pounded chicken breasts (paillards, some folks call them) and hamburgers. The food has to be flatter than it is round. Helps to flop the food over on its other side now and then.

Hence, I am careful when I freeze things, to freeze them flat. Dinner can then be ready fast.

[Smithy]

I use my cast aluminum double sided griddle/grill to defrost flat things all the time. Works great, esp. for pounded chicken breasts (paillards, some folks call them) and hamburgers. The food has to be flatter than it is round. Helps to flop the food over on its other side now and then.

Hence, I am careful when I freeze things, to freeze them flat. Dinner can then be ready fast.

←

That (freezing things flat for quicker defrosting) is a great idea!

I don't have a griddle/grill of any sort. Hmm, now maybe I have an excuse?

[mharpo]

The answer was almost instant - the ice cube on the aluminum melted almost immediately.  Why?

As has been mentioned, aluminum is a good conductor of heat (or cold) so it draws the cold away from the ice and dispurses it through the entire pan and into the air.

Think of it this way: Suppose you had a room with both a tile floor and a carpeted area. At any given time, both will be the same temperature, i.e., room temperature. Yet if you sat on the tile floor your bottom would feel cool and if you sat on the carpet your bottom would feel warm. Why is that, if both surfaces are actually the same temperature?

The floor feels cooler because tile is a good conductor, it has a very large capacity to draw heat away from your body and dispurse it, so your body can do little to warm the floor where you are sitting. In the case of the carpet, you feel warm because the carpet is an insulator (note, that's the opposite of conductor). The warmth from your body stays in one place and raises the temperature of the carpet enough for you to feel the difference.

←

You've got the right idea, but cold isn't conducted, only heat. What happens is that the aluminum gives up its heat to the colder object and is able to replenish its heat relatively quickly, thus allowing more of it to be transferred to the colder item.

Also, copper would work much better having 40% or so more conductivity than aluminum.

[MGLloyd]

I think the term we are looking for here is 'heat sink'.