As part of my ongoing induction testing of 32cm frypans (deBuyer Prima Matera, Demeyere Proline, and Fissler OP Serving Pan), I decided to frolic off into the realm of assessing the effect of placing increasing thicknesses of material between the pans and the glass.
Judging by posts here over the past 10 years, covering the glass is a popular method of preventing spatter from reaching the glass and cookware from scratching or scuffing it. I have read of people using newsprint (or easy disposal) and dish towels, even silicone potholders and trivets.
I decided to use silicone baking sheet material because: (a) It’s exactly 1mm thick; and (b) I have a lot of it. I used my Vollrarth Mirage Pro PIC, plugged into my Kill-A-Watt power meter. I intended to start with one sheet thickness and progress upward until I could detect a falloff in the drawn wattage or the pan center temperature. To assess temperature, I used both my commercial griddle probe in my Thermoworks ThermaQ 2-channel receiver and my Thermapen Contact handheld thermometer.
As some of you know, induction fields fall off as a function of the inverse of the square root of distance. So I expected that I would see something significant after adding just a few sheets. As it turned out, I *would*, but it wouldn’t be what I’d expected!
I had already determined that the power setting on the VMP which would stabilize the center of the 32cm Proline closest to 350F was 24/100, so I started there. After it reached thermal equilibrium, I added one 1mm sheet across all the glass. The wattage went UP by one Watt, but most surprisingly, the pan temperature ALSO rose by 24F! Two sheets (2mm) resulted in another additional Watt and another TWENTY degrees F! That’s 2 sheets causing a 64F rise in the pan. Three sheets caused the wattage to go up ANOTHER 2, and the pan interior reached 418F. Four sheets took yet another 2 watts and drove the pan to 424F. At this point I decided to measure the glass itself, and determined that it was now 12 F hotter than the bare pan had been with no silicone sheets!
At this point I started getting nervous about the VMP’s ability to cool its electronics. Vollrath’s engineers had clearly designed the appliance to vent heat being transferred through the glass, but here I was not only progressively sowing that transfer, but the heat had gone up dramatically.
I’ll replicate this with the deBuyer and Fissler pans to make sure this is a generalizabe result, but I am concluding that covering the glass of an active induction cooktop with anything of insulating value may not be a good idea and may change your cooking temperatures. I would feel bad If anyone damaged their appliance.
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