Containers made entirely of aluminum should not be used with induction cook tops. If it is too thick the aluminum will not heat up efficiently. If too thin, it could melt through or stick to the stove. For Jiffy Pop, it is probably more of a risk if the heat continues to be applied after all the corn has popped and there is less oil in the bottom of the pan.
Instructions for such stoves warn against putting aluminum foil on the surface, since it can overhead, stick to the surface, and damage the cook top.
Oh dear. You couldn’t be more wrong. Firstly, induction cooking only works with ferromagnetic materials. Aluminum is not ferromagnetic and won’t work at all on an induction cooktop.
Secondly, my glass cooktop uses radiant heat NOT induction, so not all glass top stoves are induction.
People who have induction stoves know that they don’t work with aluminum, so the OP obviously does not have an induction cooktop.
Instructions for such stoves warn against putting aluminum foil on the surface, since it can overhead, stick to the surface, and damage the cook top. Credit to Manlob, #41.
I placed an aluminum kettle on a glass top, went back to the shop “just for a minute”, the water boiled off, and when I returned to make tea, found the pot melted to a puddle, and the aluminum fused to the glass. Tried to gently lift the metal; no go. As things cooled, the glass cracked, possibly due to the differential contraction rates of the glass and aluminum.
Forget using a sheet of aluminum as a scratch pad/heat diffuser - might work for awhile, but…
I suspect some of the confusion around how induction cooktops work (and around which cooktops use induction) might be the real reason Jiffy Pop includes the warning about glass-top stoves.
Any mechanical engineer worth her salt knows that aluminum is much softer than glass/ceramic stove tops–especially the alloy/heat-treat state that Jiffy-Pop uses for their product–and therefore poses no threat to ceramic cooktops. Literally every material used for pots and pans (except copper) is harder than aluminum[sup]1[/sup].
Diamond omelette pans conduct heat fantastically well, but can definitely scratch ceramic cooktops. They’re also a little too pricey for home use. (Well, for any use whatsoever. Also, they don’t exist).
The problem with aluminum (and copper) on induction cooktops isn’t that it’s “inefficient,” but rather the opposite: it conducts electricity too well, so there’s not enough resistance to generate significant heat.
Induction cooktops induce eddy currents in the metal cookware above them. Cast iron and steel are relatively poor electrical conductors, so those eddy currents create a lot of resistance in steel and cast-iron pans. Resistive heating is the whole point of induction cooktops.
At least, this is true to a first approximation. A more precise explanation would cover things like the relationship between AC frequency[sup]2[/sup], material properties and skin depth. Wikipedia’s explanation is actually pretty good.
If you make aluminum so thin that it’s a small fraction of its skin depth (roughly as thin as a roasting pan) you can start to generate significant heat despite aluminum’s low resistivity. But then, as Manlob points out, it can be hard to dump heat fast enough, which means it’s possible to melt the aluminum.
I think Jiffy-Pop doesn’t want to be on the hook for ruining people’s induction cooktops. A serious home cook may have an induction cooktop and know not to use aluminum on it, but visiting in-laws making popcorn for the grandkids may assume the glass cooktop is a standard convection deal and melt the Jiffy-Pop pan.
My theory is that Jiffy-Pop/Con-Agra decided that it was much easier to warn against use on glass cooktops than it was to try to get consumers to figure out whether the cooktop before them was of the induction persuasion.
Nothing else makes sense, at least not to me. Scratching is absolutely not a risk, and non-induction glass cooktops heat pretty evenly. Aluminum poses a risk only to induction cooktops, and this thread itself demonstrates the confusion over which ceramic cooktops use induction and which don’t.
I’m persuaded that Jiffy Pop’s warning stems from an abundance of caution regarding induction cooktops.
For what it’s worth, I’m an enthusiastic amateur cook who lives in an apartment with a conventional electric stove. I’d much rather have gas, but my induction hob ($40 from IKEA) is about as good as a gas burner. It’s fantastic for delicate sauces, deep frying and boiling water very quickly. If/when I own a house again, I’m putting in a full induction cooktop as soon as I can afford it.
[sup]1[/sup]Anodized aluminum is a different story altogether. Calphalon pans, for example, are commonly “hard anodized,” which is known more precisely as type III anodization. This anodization creates a thick oxide layer on the outside of the aluminum. Aluminum oxide is itself a ceramic and hard enough to scratch a glass cooktop. Sapphire, which is nearly as hard as diamond, is also aluminum oxide, for what it’s worth: α-Al[sub]2[/sub]O[sub]3[/sub].
[sup]2[/sup] It’s entirely possible to build an inductive cooktop that works with aluminum and copper pans. Such “all metal” cooktops use AC that alternates a few million times per second, rather than the ~25,000 times per second of conventional induction cooktops. I don’t know of any all-metal induction cooktops currently available to consumers, but I imagine they’ll be commonplace in a decade or so.
I now think I spoke too soon when I said that aluminum posed no risk to non-inductive glass cooktops. It won’t scratch them, but enough molten aluminum will clearly crack them. You could just as easily melt a Jiffy-Pop pan on a conventional resistive-coil burner, but the burner would probably work just fine afterwards.
Radiant cermamic/glass cooktop owner manuals also warn against using aluminum (and copper). Aluminum and copper pans can leave marks that are hard to remove, but can still be used on radiant stoves. Aluminum foil can bond to the surface, even with radiant heat. I suppose if there is a small gap between the foil and a pot or food, it can’t radiate or conduct heat away fast enough to maintain a low temperature. This can be true whether heated by induction or by a radiant heating element, which would be at a very high temperature itself. Aluminum tends to stick well to oxides, such as the cooktop. Check out youtube for videos of people who have ruined their stove tops by having aluminum foil stick to them.
Thanks, Edel - now here’s another tidbit from personal experience, especially for the OP.
In the 90’s I bought an R.S.V.P. Perfect Popper, not for popcorn, but for roasting my own coffee. This is a sort of Rube Goldberg-ish hand-cranked stirrer in a pot, designed for corn. Sadly, the originals may no longer be manufactured but show up on Ebay as “vintage”, and if you check Amazon you’ll find similar new.
I decided to try a batch of popcorn before I dedicated it to coffee.
Never did roast coffee in it - OP, get one for your kid and start a new trend in her circle; the thing is wonderfully effective, and fun to operate, pops great corn. If you charge it with too much corn it will excitingly spill over.
This. Our glass range uses plain old hot elements below the glass. The element does cycle on and off (and glows red hot when on), but the glass stores heat, resulting in a relatively constant temperature for whatever is placed on top of it.