Uh Oh... Copper on Induction--Boils Faster

kaleokahu | Jan 5, 201910:10 PM     3

This is for you Caroline1.

Used to be, we were saddled with the notion that we could never quite know how copper would function on induction because it would not "work" at the industry-chosen 20-24kHz frequency. Sure, there were converter plates, but those had extremely poor thermal contact, they negated responsiveness, and worst of all, endangered the appliances. Copper and aluminum (on the one hand) and premium ferromagnetic clad and disk-based (on the other) were viewed as simply incommensurable.

In a way, induction appliance owners found safe harbor in this, because it freed them to show off how fast heat energy created *within* the pan could boil water, etc., without the necessity of delivering heat *to* the pan bottom via flame or a coil or a hot placque. We were left to speak and hear opinions about how the induction-capable pans on induction fared versus copper-on-gas (or the same pan fared on gas). The incommensurability extended to calculations of heat-holding and whether there was a need to heat a pan's sidewalls. Gas could do the latter; induction couldn't. People speculated what would be most efficient without any real way to quantify or compare. And all sorts of claims were made about "wasting" heat, including from a copper pan's sidewalls into the room.

Years ago, Hounds like Caroline1 prophesied all-metal induction hobs, and tanukisoup even found one--in Japan. Then... virtually nothing. So it's with great pleasure that I tag this thread with both Induction and Copper.

A week ago, I found one (a Panasonic KY-MK3500) in my kitchen. I justified it out of need to compare the performance of our hyperconductive prototypes (including aluminum) with future clad and disk-based ones, as well as other makers' pans. But after all these years of speculation and conjecture, I couldn't NOT take a first stab at a real, empirical performance comparison. I chose to simply see which material/construction would boil water fastest.

Now then, this single hob, to work with copper and aluminum, needed to have a mode with a much higher frequency (around 110kHz). Panasonic figured out how to equip the appliance with sensors and detectors which would automatically choose the lower frequency for "regular", i.e., ferromagnetic cookware, and the higher one for copper and aluminum. But the power settings for each were different. The max wattage for "regular" was 3500 watts at Setting #20 of 20, whereas the max wattage for copper and aluminum was 2400 watts at Setting #18 of 18 (This relates to what happens to thin copper and aluminum pans at higher power).

Using a watt meter, I determined which power setting in the regular mode came closest to 2400 watts (It was #14). Then I dug out two 10" diameter pots of 8 quart capacity, one a tinned 3mm copper oven and the other a disk-base (about 5mm) pressure cooker bottom. In went 4 liters of 50F tapwater and the copper oven ran first, uncovered, at the max 2400 watts. It reached 211F in 36:41. Not a fast time

After the Ceran had cooled, I ran the disk-base at the same wattage, expecting that it would boil faster. I mean, the "wasted heat" canard makes *some* sense--obviously finished stock in a copper pan sheds heat into the room or icebath faster than stock in a SS-walled pot. But I wanted to see how *much* faster the disk-base would be.

Well... to my shock, not only did the 3mm copper pan boil first, but the disk-based pan refused to heat the water past 208F. Even then, it took 48:32 for the water to reach 207, and a full hour to get to 208F. For comparison, at the time the copper pot's water reached 211F, the disk-based's water was only 190F. And near the start of the race, at the 5:00 mark, the copper pot's water was already 10F warmer than that in the disk-based.

Here's another odd fact: The water in the copper pot first started releasing vapor bubbles around the periphery *at the surface* just like these pans do on gas! All these years, I attributed this phenomenon to the gas's hot combustion products flowing around and up the pan, when I could see with my own eyes the same thing happening when only the very bottom of the pan was being induced. SS-lined pans tend to nucleate first on the bottom. Turns out copper-on-induction emulates gas' side heating (or, alternatively, useful heat was being delivered from *within* the sidewalls).

I now need to fully calibrate the two power setting ranges in order to do equivalent lower-wattage comparisons. However, I am concluding that, watt-for-watt, copper pans will put more heat into their contents on induction. Let that sink in for a minute.

Next up: a scorchprint comparison. Photos with that one... And then I'll try comparing energy used to maintain the same temperature setting.


PS I also learned tonight that my (original 800W) Anova cannot maintain 185F in an open speckleware canner. As it struggled to do so, I felt the outside--quite a bit of heat being "wasted" into the room. I concluded that factor, as well as plain evaporative heat loss, was why Anova failed. I think these factors were in play--with some others--on the induction boil test.

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