Graphite core cookware: Does graphite heat under induction?

[severoon1]

Helping a friend research a cookware purchase, I ran across All-Clad's G5 graphite core cookware.

 

All-Clad says this new tech is induction-compatible, and of course it is because it's clad with stainless. But the question is, if used on an induction hob, what is actually heating? Is the entire pan heating from direct effects of induction, or is it like the Copper Core line, where the induction heats the stainless cladding only and the heat diffuses into the aluminum and copper layers?

 

The reason I ask is that I own a Breville Control Freak, and it's recommended to not use high power on layered pans that don't heat all the way through. Over time, this can cause the layers to separate because of the expansion of the different layers while heating (particularly relevant to enameled cast iron). I've googled a bit and gotten conflicting answers. It seems that some non-ferrous materials do heat under induction, and some sources say graphite is one of those materials. Other sources imply that only some graphite heats under induction, which doesn't make sense to me, but I can't tell if that's because the site is wrong or there are different forms of graphite with different properties, or what. (I've thought about contacting All-Clad, but I'll be shocked if they are willing to give any more detail than, "G5 is induction compatible, like the literature says.")

 

Thanks!

[Laurentius]

No, only the bottom ferritic layer of G5 is induced.

 

I have a G5 piece.  The line is a worthy try at advancing the state of the clad art.  However, IMO there isn't really any improvement in evenness over existing constructions.  What improvement there is relates more to weight (G5 is spooky light) and to some extent responsiveness.

 

If you're considering buying G5, you should understand that the graphite core is very thin and not continuous--it's a perforated grid or lattice of round holes.  I've not calculated the % of floor area that's actually graphite, but it's probably only 40-60%.  The "open" holes are necessary for the pan to hold together.

[severoon1]

I see. Upon further investigation I see what you're saying. I guess this is so light and conductive that it wouldn't matter much if it were induction compatible. I was thinking it was more like a big heavy block in the middle of the pan. I can't see how a thin sheet like this would make much difference … seems to me to be a way of capitalizing the work they've put in so far so they can justify further R&D funding?

 

I'm still interested to understand if pyrolytic graphite (the kind used in the pan) can be heated by induction directly, just for academic purposes. Everything I can find on the subject says that it's diamagnetic, which I'm guessing means no.

[AlaMoi]

. . . . which I'm guessing means no.

yes - that the best guess available because . . . . one has to muse....what exactly/else is used by AlClad in the 'layer' -

which mebets they're not gonna' tell you . . .

it's a good heat conductor - just a substitute for copper?

[Laurentius]

11 minutes ago, severoon1 said:

. I guess this is so light and conductive that it wouldn't matter much if it were induction compatible

 

It's a little like the thin copper A-C uses in Copper Core.

 

Also the conductivity of this graphite, while impressive in the lateral direction (about 1300W/mK), isn't spectacular orthogonally.  I would expect G5 not to mitigate the induction donut hole.  My piece is the small skillet, which isn't a good test bed.

 

People debate whether having upper layers heat is a good thing.  I say no, because it merely puts the donut closer to the food, avoiding what blunting and spreading would otherwise happen.  There are also skin depth issues.

[severoon1]

Quote

It's a little like the thin copper A-C uses in Copper Core.

 

Based on the cutaway diagram All-Clad provides, it looks like all the layers are the same thickness?

 

27 minutes ago, Laurentius said:

People debate whether having upper layers heat is a good thing.  I say no, because it merely puts the donut closer to the food, avoiding what blunting and spreading would otherwise happen.  There are also skin depth issues.

 

I wasn't aware of this (upper layers heat). I would assume the farther from the induction coil the metal is, the more diffuse the effect. Having said that, I have wondered how far above the glass the induction effect is present, it doesn't seem like it extends very far up at all.

 

It's also worth noting that the Control Freak ain't most induction burners, it has really good coverage compared to lesser units.

 

I didn't know anything about skin depth, but from a quick googling it seems like my entire question is perhaps moot…whatever's going on in the pan interior doesn't matter past ~1 mm if I'm reading correctly? (In terms of direct heating from induction, I mean. Obviously moving heat around matters a lot.)

 

So if I've got you right, you're saying that if induction was able to reach all the way through the pan, that would be a bad thing because the heat from induction would be created in the top and bottom surfaces, which is obviously bad for cooking. Better is to create heat only in the bottom surface and let it diffuse?

[Laurentius]

56 minutes ago, severoon1 said:

Based on the cutaway diagram All-Clad provides, it looks like all the layers are the same thickness?

 

This is definitely not scaled.  A-C is famous for not doing so, but rarely does any maker proportionally show relative thicknesses.

 

58 minutes ago, severoon1 said:

you're saying that if induction was able to reach all the way through the pan, that would be a bad thing because the heat from induction would be created in the top and bottom surfaces, which is obviously bad for cooking. Better is to create heat only in the bottom surface and let it diffuse?

 

Yes.  Actually to try to help it diffuse.  Imagine a 2.5mm bimetal copper pan that somehow had its lining made of induction-compatible 400-Series stainless.  It would approximate the performance of having no copper at all. 

 

[paulraphael]

On 5/27/2024 at 6:24 PM, severoon1 said:

The reason I ask is that I own a Breville Control Freak, and it's recommended to not use high power on layered pans that don't heat all the way through. Over time, this can cause the layers to separate because of the expansion of the different layers while heating (particularly relevant to enameled cast iron).

That's a little strange. It would pretty much limit you to cast iron or spun steel. People use clad pans all day long on restaurant induction ranges that are many times more powerful than a control freak. I suspect they just don't want you to get mad if you wreck a badly made consumer pan. 

 

" I've googled a bit and gotten conflicting answers. It seems that some non-ferrous materials do heat under induction, and some sources say graphite is one of those materials."

 

Possibly because induction can theoretically (depending on the oscillation frequency) heat anything that's conductive, including graphite. But no existing induction hob works at high enough frequencies to do this. They all only work on ferrous metals. I believe the problem with higher frequencies is that you'd have wildly different levels of efficiency (and heating ability) for different materials. Which would be confusing. And you might end up jamming all the radio waves for miles around. 

Edited June 3 by paulraphael (log)

[severoon1]

5 hours ago, paulraphael said:

That's a little strange. It would pretty much limit you to cast iron or spun steel. People use clad pans all day long on restaurant induction ranges that are many times more powerful than a control freak. I suspect they just don't want you to get mad if you wreck a badly made consumer pan.

 

After doing a bit more looking into it, it seems that this is limited to layered pans with layers that expand at very different rates. Enameled cast iron is one because the enamel can crack.

 

Most multilayer pans, especially high quality ones, don't have this issue.