# Copper Heat Diffuser/Defroster Plate...Any Opinions?



## mr drinky

Has anyone used one of these copper heat diffusers? 

I've been caught a few times in the last month defrosting food quicker than I like to, and I have heard some good reports on using these copper sheets as defroster plates. Usually I will just upend a heavy duty pan and use that, but with the copper, it has better anti-microbial properties, it is a better conductor so I imagine it will defrost quicker, and I can also use it as a heat diffuser for more even heat when needed. 

Just wondering. 

k


----------



## Zwiefel

I have an aluminum version of this that came with my cooktop, about 8" across and about 1/4" thick...it does a pretty darn good job tempering the heat from the burners.

Hard to imagine the copper version would perform on on par with the price difference though.


----------



## EdipisReks

Zwiefel said:


> I have an aluminum version of this that came with my cooktop, about 8" across and about 1/4" thick...it does a pretty darn good job tempering the heat from the burners.
> 
> Hard to imagine the copper version would perform on on par with the price difference though.



copper is a much better thermal conductor than aluminum. the copper plates work as advertised. i don't personally have any, but i wouldn't mind having a big copper plate to turn my range into a French top. i use a copper sauté pan for defrosting, and it works great.


----------



## franzb69

yep.

copper absorbs heat and cold longer but holds onto it longer than it absorbs it, aluminum will absorb heat and cold faster but release it just about as fast.


----------



## Zwiefel

I don't pretend to understand the units involved in this chart:

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

It shows that copper (401) has about 2X the thermal conductivity of aluminum (205). Taking the average of a couple of different sites the cost is around 3X higher for copper. 

The size of each of those gaps surprised me, I thought the thermal performance was closer and the cost differential was bigger. 50% higher cost for 2X performance is a pretty good deal, actually...2:1 payoff on the investment.

Thanks for making me check my assumptions. That's twice in as many days here on KKF


----------



## ajhuff

Cool link. Thanks. 

But back to your original question Drinky, anyone with personal experience ?

-AJ


----------



## kalaeb

Looks cool, love copper, but I just use my cast griddle. May not work as well, but it works.


----------



## Jmadams13

I leave my cast griddle (2 burner) on my electric range all the time, and it seems to help when using my non cast pans and pots. Not to hijack, but would the copper diffusers work on electric as well?


----------



## mr drinky

Jmadams13 said:


> ...would the copper diffusers work on electric as well?



The website says it works on electric stoves as well as glass and ceramic too. 

And btw they claim that you can defrost two chicken breasts in 40 minutes on it. Though I can't say that a frozen chicken breast has ever been in my house, I do always have frozen duck breast in the freezer.

k.


----------



## rahimlee54

I've never used an aluminum or copper diffuser. I wasn't aware you could defrost food quickly with these methods. As for using it for cooking modernist cuisine did something on using them a while back, they were big fans of thick steel ones I think.


----------



## franzb69

imho, steel is a better alternative to aluminum as it holds on to heat longer. takes a while to heat up though. just about as much as copper.

i kinda know this stuff coz i've played around with overclocking computers a few years back. still am a computer enthusiast. so i played around with heatsinks, watercooling, radiators and the like.


----------



## TB_London

Which would make steel slower to defrost on, and less responsive to heat changes when cooking, so IMO not as useful. 
I use thick aluminium trays to defrost on, no experience with Copper


----------



## heirkb

This seems relevant/might be of interest: http://modernistcuisine.com/2012/11/our-guide-to-picking-the-perfect-pan/


----------



## zitangy

I bought a cheap copper diffuser which was so thin and thus flimsy. IT left a dark coating which peeled off. technically I suppose copper has the best conductivity as compared to other metals.

Next, I tried Bella Copper a small one. ( http://bellacopper.stores.yahoo.net/ ) thicker, didnt peel. Pleased with it. I suppose no point polishing it as it will darken with each usage.

Looking to buy a bigger one which will span across the width of a new range cooker as on each side there is a single burner with one in a center. Wld prefer 4 tops With this I hope to be able to put 2 small pots on either side of the range cooker. That is my purpose adn not granular heat control for sauces. I suppose even heat across the bottom of teh pot or pan should contribute to better results in cooking

have fun..

rgds
d


----------



## mr drinky

heirkb said:


> This seems relevant/might be of interest: http://modernistcuisine.com/2012/11/our-guide-to-picking-the-perfect-pan/



Thanks for the video. That was interesting. 



zitangy said:


> ...I tried Bella Copper a small one. ( http://bellacopper.stores.yahoo.net/ ) thicker, didnt peel. Pleased with it. I suppose no point polishing it as it will darken with each usage.



Cool d, you've actually tried it out. I was hoping someone had. I think I might try out a copper one and then look around for some place where I can buy some thick aluminum to size once I know what other size would be perfect for my stove. If anything, it will be interesting to see how they compare.

k.


----------



## Notaskinnychef

my wife and I bought a 5 ply set from lagostina years ago, still going strong. http://www.lagostina.ca/html/product.asp?idstore=&idcat=26&idsubcat=32

uses SS, aluminum, copper, aluminum, then SS again. Seems to be quite even in terms of its heat, esp since the 5 ply construction runs all the way to the top of the pot/pan, so the heat transfer is even brought up to the top fairly well. 

Not a cheap set mind you, but would allow for better overall heat transfer when you factor in the heat is brought up the layers as well, something a plate can't do. I do set the appeal tho of getting one of these for when I wanna use my crap thin frying pans, since they have lots of hot spots


----------



## zitangy

http://www.youtube.com/watch?v=a5jvCNdr0Dw

a video touting the virtues of bella copper.

HV fun..

D


----------



## Notaskinnychef

the more i think about it, the more i want a single one of these, I can see us using it a lot, esp for defrosting


----------



## EdipisReks

franzb69 said:


> imho, steel is a better alternative to aluminum as it holds on to heat longer. takes a while to heat up though. just about as much as copper.
> 
> i kinda know this stuff coz i've played around with overclocking computers a few years back. still am a computer enthusiast. so i played around with heatsinks, watercooling, radiators and the like.



the situation on a stove is totally different. copper over a flame comes to full heat extremely quickly. thick aluminum does as well. steel is going to take longer than either, and won't be as even. i kinda know this stuff coz i have copper, aluminum and steel cookware, in various thicknesses, all used over flames.


----------



## mr drinky

Well, I will know soon enough how these things perform. I ordered the 10x10 inch bella copper heat diffuser and then had a 3/4 inch thick larger aluminum plate cut to size for my cooktop. 

I also just got a pressure cooker for xmas, and I have been reading that heat diffusers are useful for them to better control heat.

k.


----------



## Zwiefel

cool! Looking forward to a practical comparison.


----------



## rahimlee54

mr drinky said:


> Well, I will know soon enough how these things perform. I ordered the 10x10 inch bella copper heat diffuser and then had a 3/4 inch thick larger aluminum plate cut to size for my cooktop.
> 
> I also just got a pressure cooker for xmas, and I have been reading that heat diffusers are useful for them to better control heat.
> 
> k.



Who did you get the aluminium plate from?


----------



## mr drinky

rahimlee54 said:


> Who did you get the aluminium plate from?



I got it from onlinemetals.com. Here is the link. After picking thickness, you can choose a standard size or plug in a custom size at the bottom.

k.


----------



## DeepCSweede

mr drinky said:


> I got it from onlinemetals.com. Here is the link. After picking thickness, you can choose a standard size or plug in a custom size at the bottom.
> 
> k.



I am finding the 12x24 sheet of copper there somewhat tempting. I would like to get something I could spread over two burners and this could fit that bill. Hmmm.


----------



## mr drinky

DeepCSweede said:


> I am finding the 12x24 sheet of copper there somewhat tempting. I would like to get something I could spread over two burners and this could fit that bill. Hmmm.



Yeah, I was initially going to get that same two-burner thing (actually 12x20 to fit my stovetop), but I thought I would try the smaller ones out first. That copper gets expensive. 

k.


----------



## DeepCSweede

That was the Hmmm part. It was hard enough getting the blessing for two knives for this year but I think it would be a good buy overall. Question too is how thick should a person go on these? I know the Benna is 1/8" but for something with some indirect heat, should it be a little thicker? Then the weight comes into play too.


----------



## mr drinky

That Chow/Modernist Cuisine video up thread said .5 inch to 1.5 inch for aluminum. Not sure how that translates to copper though. My feeling was that I would test the thinner copper out agains the aluminum and then get a two-burner diffuser in aluminum if it is better and (if not) save up for a two burner copper one. 

k.


----------



## EdipisReks

2.5mm is typically considered about perfect for copper cookware, but a diffusor and cookware have different missions... i'd probably try the 1/8 inch.


----------



## Zwiefel

My aluminum version varies in thickness. in some places about 1/2" in others about 3/8" (eyeballing). been pleased with it...but only use it as a diffuser for stuff likely to scorch at the minimum flame my stove can produce....not for defrosting/etc.


----------



## heirkb

So if you were to use a diffuser plate, would preheating take longer? I'm curious to see what others think of thick aluminum vs. thin copper, since the video I sent out would definitely recommend thick over thin.


----------



## Zwiefel

heirkb said:


> So if you were to use a diffuser plate, would preheating take longer?



That's been my experience. A significant difference in fact (never measured it but my subjective sense of the time is about 3X). I prefer to bring (close) to temp on one burner, then move to the burner with the diffuser.


----------



## mr drinky

Zwiefel said:


> That's been my experience. A significant difference in fact (never measured it but my subjective sense of the time is about 3X). I prefer to bring (close) to temp on one burner, then move to the burner with the diffuser.



That's sounds like like it would work.

Btw, I just ordered an aluminum plate in the same size and thickness as my copper one just to compare things. It was only $16 and they added it to my order without any shipping cost. 

k.


----------



## Zwiefel

mr drinky said:


> That's sounds like like it would work.
> 
> Btw, I just ordered an aluminum plate in the same size and thickness as my copper one just to compare things. It was only $16 and they added it to my order without any shipping cost.
> 
> k.



Definitely interested in your practical experience with the two materials vs the "thermal conductivity chart"


----------



## rahimlee54

Any update on this?


----------



## franzb69

[video=youtube;X81xYQL27Wk]http://www.youtube.com/watch?v=X81xYQL27Wk[/video]

just wanted to share

=D


----------



## mr drinky

Interesting hack.



rahimlee54 said:


> Any update on this?



No updates from me. I have used my copper plate several times for defrosting meats and a couple of times on the stove, but a new baby is taking serious time away from playing with my metal shiny things. 

k.


----------



## jayhay

franzb69 said:


> [video=youtube;X81xYQL27Wk]http://www.youtube.com/watch?v=X81xYQL27Wk[/video]
> 
> just wanted to share
> 
> =D



That pie plate is pretty paper thin. It would only work with low temps, very low temps. Anything more and it would buckle and the effect would be nominal. 

And that is a pretty nice (home) stove. She should see the junk I have in my apt, junkkkkkk. I'd kill for that thing. For a slow reduction you can always set the burner to low and offset the pot/pan on said burner. 

I hate any thin pan. But I like her resourcefulness and the fact the her brain is on the kitchen. BIG props for that


----------



## UCChemE05

While I didn't watch that "hack", don't use an aluminum pie plate. With the low melting point of Al, you could have a little disaster pretty quickly when using a decent amount of heat.


----------



## sharpmaker

Modernist Cuisine has grossly exaggerated their point of view.

Sorry for necro'ing this thread, but I wanted to say a few words to explain why.

1) Metal on metal will always have air pockets, unless they are perfectly polished with no dings or scrapes or food particles or anything stuck to them, which is unrealistic for a number of reasons. For example, a soft metal like aluminum will inevitably get dinged up by your cookware so as to introduce air pockets. And simply washing your pots will introduce stuff in-between the pot bottom and the heat diffuser, maybe as very thin layers of dried detergent or hard water or whatever. The point is that you will have plenty of air between the metal surfaces. Air is a HORRIFIC heat conductor so you lose efficiency there already. This is why computer heatsinks don't have bare heatsinks on heatspreaders; they use thermal paste to help fill in those crevices where air pockets would gather. (Paste isn't anywhere near as good as metal, but it does a better job of flowing into the crevices in the metal surfices.) But cooking temps can go well above 100C (above 450C!) which makes me think that there isn't a safe thermal paste to use for heat diffuser purposes, not to mention that you'd need to re-apply every time you switched cookware.

2) MC is flat out wrong in their book when they advocate for steel. Steel is a horrible heat conductor as far as metals go, something like 30 times worse than copper. Cast iron is better but still leagues behind aluminum, which is itself somewhat behind copper.

3) Even with copper/aluminum which transfer heat efficiently, it's a waste of energy to have to heat up a big plate of metal. It helps create a large heat reservoir for searing steaks or whatever, so that temperatures don't plunge too fast when you throw cold meat onto the pan, but in most other cases it's just a waste of energy and time (spent waiting for the plate to heat up).

Given that copper is harder and denser than aluminum and not THAT much more expensive if you get scraps at your local industrial metal dealer, if you must go down this path, get 1/8th inch copper which is harder than aluminum and won't get all dinged up as fast. You can try 3/16th inch too, but that is probably overkill and just adds to the energy inefficiency and longer cooking times because you are waiting for so much metal to heat up first. Note that even relatively inexpensive cookware typically has a 1/4 inch of aluminum disc bottom, so adding 1/8th thick copper to that is like adding another 1/4 inch of aluminum. If HALF AN INCH of aluminum isn't enough to give you even-enough heat, your burner must be tiny or your pan must be huge, or both. And many types of cooking don't even need even heating, such as boiling things in water, since water convection currents will even out heat.

I have actual experience with using 12x12 inch 1/8th and 1/4 inch plates, as well as a 12x24 inch 3/16th inch plate. In the end, I stopped using them and decided induction was the way to go: no air pockets between the heating element and the pan, because the heating element is the ferritic layer on the bottom which has already been bonded to the cooking vessel above it. Induction has other advantages too, like easy cleanup, safety, etc.


----------



## ms4awd

I Have a Pair i used to use at home. Now i use them over burners at the restaurant for the deep frying pots keeps oil temp more constant than an open flame.
They also work great for defrosting items evenly or turning a burner into a small flat top that can be used for multiple small pots. works great when braising also. The heat is more even and you can braise/simmer like you would in an oven but on the stovetop. They respond quickly to temp change also.


----------



## mr drinky

Thanks sharpmaker for sharing your experience. I definitely understand your points, and from an efficiency standpoint, a heat diffuser is probably not the best way to cook. I use mine with my cast iron dutch oven and heating it up takes a long time, and the instructions for the copper heat diffuser is to not heat it up on high, so it's slow and steady the whole way. And I would never dream of using it to boil water. 

With that said, I often use it as a defroster plate and always use it now with my dutch oven. I would never use it without now. With my gas range I used to have problems with evenness of heating, but no longer is that the case with my heat diffuser. So while it may not be a winner in terms of efficiency, IMO it is very helpful when cooking anything where you want more evenness of heating. 

k.


----------



## Zwiefel

I thought the whole point of a diffuser was to be an inefficient way to transfer heat...? If you want efficient thermal transfer, why put an extra piece of material between the heat source and the pan? Defrosting would seem to be the opposite though....


----------



## mr drinky

Zwiefel said:


> I thought the whole point of a diffuser was to be an inefficient way to transfer heat...? If you want efficient thermal transfer, why put an extra piece of material between the heat source and the pan? Defrosting would seem to be the opposite though....



Exactly.

k.


----------



## sharpmaker

Zwiefel said:


> I thought the whole point of a diffuser was to be an inefficient way to transfer heat...? If you want efficient thermal transfer, why put an extra piece of material between the heat source and the pan? Defrosting would seem to be the opposite though....



I'm just sharing my experiences, because MC did not even MENTION the downsides to using slabs of aluminum. Yes you gain more even heating, but it comes at a price: loss of energy efficiency and loss of time. And it's worse with aluminum than copper due to aluminum's softness and ding-ability (with resultant loss of thermal conductivity), plus aluminum is more prone to warp, which is probably part of why MC recommended no less than half an inch of it. So I'm just saying, if you really want to go down that path, get an 8" diameter 1/8" or 3/16" thick copper disc (or 8x8" square). It will be enough for anything up to 12" diameter cookware (even the crappiest cookware should be able to move heat a paltry 2 inches, on either side of the copper disc's edges; plus 12" skillets often have bottom diameters less than 10" so you really only need to worry about >12" saute pans), won't warp or ding as much as aluminum, and it won't cost THAT much more if you get it from a local scrap dealer or something.

I originally HAD to get a slab of copper to deal with my 13+ quart cast iron oval dutch oven which was too big for any one burner, so the 12x24" 3/16" slab was to help it even out. (I eventually got rid of the 13+ quart oval dutch oven because it was too much of a pain in the butt to work with and wouldn't easily fit into ovens, either... ovens by the way are a great way to get around uneven heating.) I got a few more copper plates but eventually gave up on the concept because it was energy- and time-inefficient and a pain to clean up. Induction for me, with appropriate cookware (like my Demeyere skillets which have 3.7mm aluminum wrapped in about 1.1mm of stainless steel), works much better and is easier to clean (saves time.. no more cleaning the black buildup on the copper plate or the burner or the hob) and more efficient (time and money). However, induction has a very high startup cost for those who already have natural gas or electric. If you are interested in induction, you can give it a try with portable countertop units of at least 1300W (for boiling water or lower-temperature stuff like sauteing). 1800W is the max for most such units due to the limitations of 110V 15amp wall sockets but you only need to go that high if you want to sear a steak or something. If you have 220V wall sockets you can get pro-grade portable units or simply replace your gas/electric range with an induction unit. The cheaper units will have very small coils, maybe 4 inches or less, while the more expensive induction cookers will have larger-diameter coils; coil diameter is analogous to burner diameter, so buy accordingly.

Time is money. And money is money, too, in terms of electric or gas bills.

That said, I don't want to turn this into an induction cooking thread, so I will just end by repeating my recommendation of copper diffuser plates over aluminum for reasons I've stated in this post and my previous post in this thread.


----------



## Zwiefel

I think I understand your point now. BTW Mr. Drinky: I didn't ever see a report on your experience with the aluminum vs copper diffusers....


----------



## sharpmaker

mr drinky said:


> Thanks sharpmaker for sharing your experience. I definitely understand your points, and from an efficiency standpoint, a heat diffuser is probably not the best way to cook. I use mine with my cast iron dutch oven and heating it up takes a long time, and the instructions for the copper heat diffuser is to not heat it up on high, so it's slow and steady the whole way. And I would never dream of using it to boil water.
> 
> With that said, I often use it as a defroster plate and always use it now with my dutch oven. I would never use it without now. With my gas range I used to have problems with evenness of heating, but no longer is that the case with my heat diffuser. So while it may not be a winner in terms of efficiency, IMO it is very helpful when cooking anything where you want more evenness of heating.
> 
> k.



Oh yeah, I agree it's a great way to diffuse heat. I just wish Modernist Cuisine at least mentioned the drawbacks and had compared aluminum to copper plates given that even copper plates are quite affordable so spending a little extra for a harder metal would seem like a good deal imho. It's not even spending that much extra because you will get paid back with faster heating and thus lower energy bills and also save time (compared to using a 1/2" thick or more aluminum plate). And yes you can also defrost with it or cool down a pressure cooker quickly or whatever with a copper plate. The heat reservoir effect is also good for searing steaks since thin pans alone could lose a lot of energy when you toss relatively cold metal onto them.

One way of looking at this: using a thick slab of aluminum or copper is like transforming all of your non-cast iron cookware into cast iron cookware EXCEPT that this time, it's even heating (http://www.seriouseats.com/2010/02/everything-you-need-to-know-about-cast-iron-cooking.html shows how uneven heating real cast iron is). If someone is ok with the relatively slow pre-heating process of cooking with cast iron, they are probably also ok with using a heat diffuser plate.


----------



## Zwiefel

Sharpmaker, I guess the disconnect on this issue is: If you can't lower the heat output of your heat source to the point at which the thermal conductivity dampens it to the required level, you'll want WORSE thermal conductivity. This is entirely dependent on the equipment and process involved though...of course, this scenario is the only* reason why you'd want a diffuser for cooking (vs defrosting) in the first place.Induction is a good alternative to this though.*I suppose pots/pans that heat very unevenly could also be a reason, but I doubt many folks here have that issue.


----------



## ajhuff

While the conclusions are correct in the serious eats article, I disagree with the reasoning. The hot spot I am more than convinced is metallurgical in nature. But, cast iron shines in an oven and I don't think there is any dispute of it's even heating properties in the oven. The diffuser is mimicking the oven I believe on a cast iron pot, albeit poorly as Sharpmaker has described.

-AJ


----------



## sharpmaker

Zwiefel said:


> Sharpmaker, I guess the disconnect on this issue is: If you can't lower the heat output of your heat source to the point at which the thermal conductivity dampens it to the required level, you'll want WORSE thermal conductivity. This is entirely dependent on the equipment and process involved though...of course, this scenario is the only* reason why you'd want a diffuser for cooking (vs defrosting) in the first place.Induction is a good alternative to this though.*I suppose pots/pans that heat very unevenly could also be a reason, but I doubt many folks here have that issue.



I would not phrase it that way. You almost NEVER want WORSE thermal conductivity. If you wanted to keep the sentence structure of what you wrote, I would rephrase it like so: "If you can't lower the heat output of your heat source to the point at which the thermal conductivity dampens it to the required level, and you can't change your cookware, then you will want to buffer it with an underlayer of material. How thick that underlayer of material has to be to achieve even heating depends on the thermal characteristics of the material--the more thermally conductive the material is, the thinner that layer has to be."

My points were to address MC which framed it this way: ideally you would want a burner diameter to be pretty close to the diameter of the bottom of your cookware and for your cookware. (The middle of the pan is less of a problem since heat doesn't have anywhere to go but into the food anyway; it's the edges of the pan that keep losing heat and thus need heat replenishment continuously). But what if your largest burner isn't very large?

You have these options:

1) get a new cooktop with larger burners
2) don't use larger-diameter cookware on undersized burners
3) get more thermally-conductive cookware
4) get thicker-bottomed cookware
5) expand the size of the burner via plates/sheets/slabs/whatever of metal

1) and 2) aren't always realistic, so the real debate is on 3) vs 4) vs 5), and many people don't want to replace cookware so it's really just a discussion of 5).

Regarding 5), MC and I diverge on the value of thermal conductivity here. MC does not seem to care much about thermal conductivity and diffusivity, as they even recommend thick steel. MC greatly stresses how thickness is FAR more important than thermal qualities of the material going so far as to put steel in the same sentence as aluminum, which is crazy. It would be only a slight exaggeration to say that in MC's fantasy world, you should just find the lowest-density material available and use that as your heat diffuser, regardless of how good or bad of a thermal conductor it is. That way you maximize thickness without increasing weight to the point where you can't lift the plate up anymore.

MC isn't entirely wrong, but the truth is more complex. Thermal conductivity and diffusivity DO MATTER when it comes to even heating. This has been proven repeatedly, such as at http://www.seriouseats.com/2010/02/everything-you-need-to-know-about-cast-iron-cooking.html (The cast iron was about 6mm thick and was very uneven-heating compared to the All-clad stainless pan which is roughly 3mm thick, of which roughly 2mm is aluminum and the rest stainless steel.) For a list of thermal conductivity numbers see http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

The fact of the matter is, the better thermally something is, the thinner you can get away with making the slab and still achieve the same degree of even heating. The thermally worse stuff needs thicker thicknesses to achieve the same degree of even heating.

MC says use plates of aluminum 0.5 to 1.5 inches (12.7mm to 38.1mm) thick. IMHO that is overkill for most people. Let's put this in context. All-Clad (and its clones like Cuisinart MCP, Calphalon, etc.) have only 1.6-2mm of aluminum. MC is basically saying with a straight face that in order to have even heating, you need an aluminum layer 6.35-24 times thicker than what you find in tri-ply clad, IN ADDITION TO what you already have in your pans themselves. (Either that, or aluminum is even worse than I thought about warping, and you need at least 0.5 inches thickness to guard against aluminum slabs warping over time. Which actually sounds about right, now that I think about it.)

What I'm telling you is that 1/8th thick copper (~3.2mm copper) is good enough for most realistic scenarios (i.e., putting your largest pan on your largest burner, not putting your largest pan on your smallest burner). A 1/8th-inch (3.2mm) thick copper slab is roughly equivalent in heat-spreading power to 4mm of aluminum due to copper's superior thermal conductivity and diffusivity. And you add that 3.2mm of copper to whatever you ALREADY HAVE in your cookware, such as the 1.6-2mm of aluminum in All-Clad. But beyond sheer heat-spreading power, copper is simply more efficient at transferring heat, so you have less pre-heating wait time and wasted energy (heat that goes into your kitchen rather than your pot); plus copper is harder than aluminum so it can take more abuse before getting dinged up or warping.



ajhuff said:


> While the conclusions are correct in the serious eats article, I disagree with the reasoning. The hot spot I am more than convinced is metallurgical in nature. But, cast iron shines in an oven and I don't think there is any dispute of it's even heating properties in the oven. The diffuser is mimicking the oven I believe on a cast iron pot, albeit poorly as Sharpmaker has described.
> 
> -AJ



ANY metal is going to heat evenly in an oven because heat is bombarding the material from all directions. There is nothing special about cast iron in that respect; a copper, aluminum, or stainless steel dutch oven will also heat evenly. (The biggest advantage of cast iron dutch ovens inside of ovens is the heavy lid sealing in moisture, whereas you may need to weigh down the lid with something if you use, say, a flimsy aluminum dutch oven.) A stove is different, where you have a hot heating element circle at one extreme end of the cookware (the bottom end). A square or circle heat diffuser is essentially stretching that little heating element circle and making it into a solid square or circle. This has the effect of evening out the heat on the bottom.


----------



## sharpmaker

I can't edit my post anymore but I would like to add that copper of 3.2mm actually has heat-spreading power more like 5.6mm-thick aluminum, not 4mm, going by thermal conductivity. I was a little too conservative. The point remains though that 3.2mm copper is already plenty thick enough for even heating.


----------



## Zwiefel

sharpmaker said:


> I would not phrase it that way. You almost NEVER want WORSE thermal conductivity. If you wanted to keep the sentence structure of what you wrote, I would edit it to say: "If you can't lower the heat output of your heat source to the point at which the thermal conductivity dampens it to the required level, and you can't change your cookware, then you will want to buffer it with an underlayer of material. How thick that underlayer of material has to be to achieve even heating depends on the thermal characteristics of the material--the more thermally conductive the material is, the thinner that layer has to be."


AFAICT: Not quite...if what you are doing requires N BTU's of heat to be transferred to the pan, and your lowest burner setting is N+M BTUs, then you want to have an inefficient transfer of heat..you are very specifically looking for a way to dissipate >=M BTUs of heat. Diffusers aren't just about even heating, but the "wasting" of heat as well.Or else we are talking past each other


----------



## ajhuff

Cast iron has a hot spot on the stove top due to graphite morphology not the burner. This is something unique to cast iron. I am convinced of this.

-AJ


----------



## sharpmaker

Zwiefel said:


> AFAICT: Not quite...if what you are doing requires N BTU's of heat to be transferred to the pan, and your lowest burner setting is N+M BTUs, then you want to have an inefficient transfer of heat..you are very specifically looking for a way to dissipate >=M BTUs of heat. Diffusers aren't just about even heating, but the "wasting" of heat as well.Or else we are talking past each other



Ah I see what you are saying and agree w/r/t simmering. This was the original purpose of flame tamers, after all. I was thinking more about even heating in a frying situation where you aren't concerned with the BTUs per se but with the evenness of heating.

To AJ, I am not a metallurgist and have no idea what you are talking about re: graphite morphology. I do know that cast iron simply does not conduct heat as well as aluminum or copper, and you can wind up with a hot spot that corresponds to the burner circle as a result. See, for instance:

http://www.cookingissues.com/2010/02/16/heavy-metal-the-science-of-cast-iron-cooking/ (already posted photos via SE but this is a fuller treatment)
http://www.nytimes.com/2008/10/08/dining/08curi.html?pagewanted=all (they have a photo gallery, author talks about the familiar ring of fire problem with cast iron)
http://chowhound.chow.com/topics/804287 (see his revised shootout numbers and how copper and aluminum were head and shoulders above cast iron in terms of even heat)
http://www.discusscooking.com/forums/f32/sauteeing-without-burning-oil-78265-2.html (not cookware but just the grating, still, gives a good visual on how heat drops off as you get away from the burner, on whatever the grating material is--which is definitely not copper or aluminum!)

If you have an IR gun and some black tape, you can set up your own experiment (I've done this myself with my cookware). Take the temperature of the black tape on the side of anything shiny to reduce errors due to emissivity. Cast iron isn't shiny and doesn't really need tape. I can already tell you the results: cast iron will be slow to even heat out and can't maintain the evenness of heat the way aluminum and copper of equal thickness can, and even when you compare 6mm cast iron to say, 2mm copper, the Cu will STILL win (see tanuki soup's shootout results on induction via chowhound, linked above; too bad he didn't have exact measurements of thickness but we know the PM is 1.8mm copper, 0.2mm stainless, and a thin layer of ferritic material, and the cast iron was undoubtedly much thicker than 2mm). That is not to say cast iron is unusable, just that you may need to move food around a little bit more often. Plus 1/4-inch thick cast iron has the high heat capacity to withstand the sudden insertion of cold meat without losing TOO much heat, something that would require extra-thick aluminum or copper to match (4mm Al, 2.5mm Cu ought to do it). Some people also like cast iron seasoning's quasi-nonstick surface. But in terms of stovetop even heating, Al and Cu are way better than cast iron.


----------



## ajhuff

First my apologies for the thread drift. Yes, cast iron would rank #3 behind copper and aluminum. But, cast iron in the grand scheme of things is a phenomenal heat conductor because it contains graphite flakes which conduct heat almost 5x better than copper _along[/] the crystal axis but 70x worse than copper across the crystal axis. Sparing you a lot of detail but these flakes are distributed in different sizes and thicknesses. They will be thickest and longest in the center of the pan, maybe slightly off center toward the handle. That's why there's still a hot spot with the cast iron pan on an induction cook top. Didn't that strike anyone as odd? There will always be that hot spot.

Sorry for being so technical. I'm not refuting or arguing anything. Just explaining.

-AJ_


----------



## sharpmaker

ajhuff said:


> First my apologies for the thread drift. Yes, cast iron would rank #3 behind copper and aluminum. But, cast iron in the grand scheme of things is a phenomenal heat conductor because it contains graphite flakes which conduct heat almost 5x better than copper _along[/] the crystal axis but 70x worse than copper across the crystal axis. Sparing you a lot of detail but these flakes are distributed in different sizes and thicknesses. They will be thickest and longest in the center of the pan, maybe slightly off center toward the handle. That's why there's still a hot spot with the cast iron pan on an induction cook top. Didn't that strike anyone as odd? There will always be that hot spot.
> 
> Sorry for being so technical. I'm not refuting or arguing anything. Just explaining.
> 
> -AJ_


_

Ok thanks for the explanation. But the all-clad also had a hot spot on the induction cooker: http://www.cookingissues.com/2010/02/16/heavy-metal-the-science-of-cast-iron-cooking/ So it's not just a graphite flake issue unless that also applies to Al. The simplest explanation, imho, is that they used a too-small induction coil and the 1.6-2mm of Al in all-clad wasn't thick enough to spread the heat much. . This coil/cookware diameter mismatch is what MC warned against._


----------

