kas - use of silpat on induction cooktop?

jadeiteJune 9, 2012


In the past you have mentioned that you use a silpat to protect the surface of your cooktop. Is the silicone affected by high heat cooking?

We just got our cooktop installed a couple of days ago. I put two large Roul'Pats on the surface. Roul'Pats are similar to Silpats, only they have silicone on both surfaces. Where we have used high heat, the mat is discolored by the bottom of the pans. Has this happen to you? I assume the pans are getting over the limit that silicone can withstand - around 500 degrees, I believe.



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There is a limit to operational silicone rubber temperature, and it is in the 500F range, as I recall. Above that it starts to disassociate. At threshold, it will darken.

Pans left on to boil down to nothing will damage the silicone before the (my) induction cooktop shuts off. Normal frying doesn't seem to bother them.

Generally, depending on the oil, smoking the oil is not desirable. Of course, oils have widely ranging temperature limits, so what smokes olive oil may not bother peanut oil. Some oils will smoke well below the silicone limit, while peanut oil and a few others, perhaps, will smoke at the limit of the silicone.

Where I can get oil smoking normally is wok cooking, but my wok hob has a metal ring at the top to keep the wok off of the glass, so a silicone pad isn't needed.

I have found that the heat load on the silicone is least if three small (1.5 - 2.5 inches diameter) circular pads are used instead of one large piece. Three pads form a tripod, and provide an air gap that keeps the temperature of the ceramic glass lower, and hence the heat into the silicone rubber somewhat lower. I can also see the hob limit marker rings with small pads.

The silicone pads that I use are just that, thin silicone rubber. There is no cloth or other material in them. Normally high temperature silicone is loaded with iron oxide and has a dull rust color. I recently purchased some blue silicone sheet that I haven't cut up yet that claims higher than normal temperature limits (probably not by a lot).

These materials are typically sold as cookie tray pads. Industrial sources should still exist if manufacturing hasn't been driven offshore.


    Bookmark   June 9, 2012 at 11:48PM
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I didn't realize you weren't using silpat sheets across the entire element. Going with small pieces makes the problem simpler. Is the small clearance sufficient that you don't have scratches on the cooktop?

I've found a source of 1/8" silicone rubber sheet, supposedly high temperature (525 degrees). I could cut that into smallish squares and use them around the element. It's not too expensive as a experiment.

Another (related) question: I've looked at the induction disks which are basically aluminium surrounded by ferromagnetic steel. This seems unnecessarily inefficient to me. Cooks Illustrated compared the time to boil water with this disk and the time with straight induction, and the time with the disk was twice as long.

It seems to me that you could use a thin plate of galvanized steel over the induction element. It should heat up, turning it into a radiant element. If you use an aluminium (or copper, or other nonmagnetic but thermally conductive material) pot on top, I think you would get heating at higher efficiency. It's basically the same as stainless cookware with steel/aluminium/steel base. What do you think?

I understand the steel plate would be very hot, but no more than the existing cookware. DH tells me the edges could be smoothed out so it wouldn't be dangerous.


    Bookmark   June 10, 2012 at 8:08AM
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"What do you think?"

I think the thermal conductivity between the two non-bonded metals would not be that good. I would not waste my time with it. If I wanted a radiant cooktop, I'd go buy one.

The only danger with using a silicon matte is getting it so hot that it melts. Then it is next to impossible to chisel off the glass.

    Bookmark   June 10, 2012 at 10:43AM
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The cost of a carbon steel plate to fit over the element is under $15. On top of it I would have my Calphalon pot which is constructed of an excellent conductor. No, it wouldn't be bonded, but the miniscule air gap will make little difference to thermal conduction. I think it's worth a cheap experiment to see if it works or not. I can't see a downside.

I bought an induction cooktop but I have a LOT of anodized aluminium cookware, including some pieces which would be expensive or hard to replace. Yes, I have induction-ready cookware, but if I can use my 12 qt Calphalon braisier with a cheap plate, why not?

    Bookmark   June 10, 2012 at 11:04AM
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The silicone sheet I use is closer to 1/16 inch. An eighth should still work; I don't think many field lines will sneak under the pan.

Conduction between a pan and an induction disk will be improved if both are very flat and smooth.

It seems to me that the better approach would be to put a disk of susceptible stainless steel inside the pot to be induction heated. The pot bottom would have to be relatively thin, such as exemplified by Revereware. (Note: some ancient Revereware is susceptible and works on induction.)

I fear that in order to get reasonable response, users will heat the induction disks to a temperature hotter than the pan would be heated for whatever cooking was in use. The temperature might exceed the ceram top limit, although one hopes in that case that the hob shuts down.

The thermal mass of the disk may also degrade the induction advantage (over coils) of rapid thermal response.


    Bookmark   June 10, 2012 at 11:24AM
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Kas - I can find 1/16" silicon, or 1/32", but at some point isn't there danger of the material tearing?

Why would you prefer stainless over carbon which is a better thermal conductor?

I think a metal sheet, with very small thermal mass would be more efficient than the disks. You can get carbon steel in very thin sheets. I don't know how well galvanized steel would hold up to high heat, I'd be afraid the coating might come off.

The cooktop shuts down if the temperature exceeds 1000F (or thereabouts). While I'm intrigued by the notion of this experiment, I'm too cowardly to play around with temperatures this high.

    Bookmark   June 10, 2012 at 11:39AM
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I have been reading this post with interest as I have never heard of using silicone pads on induction. Have I got this right? - you place three small 1/16" silicone pads around each burner you use. I presume this is to protect the ceramic cook top from scratching. Are there other reasons? Could you explain further, for the non technical?
Thank you.

    Bookmark   June 10, 2012 at 1:03PM
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The idea of a stainless steel disk was that it wouldn't react with the contents of the pot or pan it was put into. I wasn't recommending it for under the pan. 'Twas a mere speculation.

OK, on silicone sheet. I used to buy sheets from whatever sources I could find on the web or mall. Sooner or later someone would ruin the middle part from walking away from a pan on high. (This wouldn't be me of course.) It occurred to me that smaller pieces would allow me to utilize the still good outer corners and allow me to see the lines for hob alignment. So I used some templates (old cans) to cut out circular pieces (because they look better than random shapes). I use three per pan. I have 1.5 inch circles for the smallest hob, and larger circles for larger pans used on larger hobs. They are easily cleaned.

The silicone pads perform two services. One, the pans are off the ceram, reducing scratching, including the potential of micro-scratching that boiling water could induce by vibrating the pan.

A second benefit is easier cleaning of spills. The temperature of the ceram at a hob is determined by how much heat conducts or radiates from the pan to the ceram. With spacing by silicone pad, or better by an air gap using a tripod of pads, the temperature is minimized and the already greatly improved cleanability of the surface due to induction is further improved because the ceram may not be hot enough to burn the spill.

After boiling eggs for 9 minutes on my smallest hob, the ceram is too hot to keep one's hand on it, but it won't crisp one's skin as a radiant surface would.


    Bookmark   June 10, 2012 at 8:35PM
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Thanks kas. I'll have my induction top in a couple of months and look forward to experimenting.

    Bookmark   June 10, 2012 at 11:18PM
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Maybe you can experiment some time with boiling water. No pad, full pad 1/16", full pad 1/8", etc. It would be interesting to know how much speed is lost by increasing the air gap (well, non-ferrous gap). There also is some heat loss in your "tripod" pad vs. continuous, but that has to be pretty small.

    Bookmark   June 11, 2012 at 1:11PM
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attofarad - I plan to do something like this once I get my silicon rubber sheet. But I have boiled water using my Roul'Pat and I can tell you it's PDQ.

BTW I got the Thermador with sensordome, mainly because I found it at a great price. No sensor strips were in the box, but Thermador says they will send. Once I've gotten some experience with the cooktop, I'll post a full review. I bought Thermador in part based on your positive comments.


    Bookmark   June 11, 2012 at 1:53PM
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My time for new experiments is probably measured in zepto seconds, but I'll try to fit it in. Defining a boil got a few hot under the collar, as I recall in some other thread, so I need to decide what that is. Also, equalized starting conditions need to be carefully planned.

There could also be a difference in field line compression between the thin 404 (probably) Revere Ware I use for egg boiling and thicker bases such as All Clad/Emeril Ware/etc.

My belief, however, is that the boiling time difference between no pad and a 1/16 pad will be very slight, if measurable, and the difference between a tripod of small pads vs. one large pad will be unmeasurable. I expect the tripod air gap to only affect the temperature of the ceram surface under the pot.


    Bookmark   June 12, 2012 at 8:39AM
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I am very curious about this.. Can you please post a photo of our set up? Why do ou do this.. Is this to make cleanup easy?

    Bookmark   June 13, 2012 at 1:31AM
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I'll try to take a photo soon. Getting it on-line may be delayed depending on how annoying the process is.

Advantages include scratch avoidance, ease of clean-up, and reduced heating of the ceram surface.


    Bookmark   June 13, 2012 at 6:05PM
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Time consuming, if not annoying. Here are some photos of the silicon pads as I presently use them.


    Bookmark   June 23, 2012 at 3:16PM
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I installed a Kenmore Elite induction cooktop.in December 2005. I have yet to scratch the glass although the stainless steel frame has developed quite a bit of "patina". Glass is very hard to scratch. I don't do anything special to protect or clean it.

    Bookmark   June 23, 2012 at 8:00PM
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Mine came with a blurb marked "Euro Kera Vitroceramique" describing the eponymously named surface material as a "glass ceramic." The blurb included instructions for when special cleaning and protection were called for.

Whether vitroceramic or glass, it would still be susceptible to scratching from minerals with a higher Moh's number hardness, and various harder metals and ceramics. Keeping it perfectly clean and never dragging a pan can avoid scratching.

I applaud your success so far in cooking directly on it for 6.5 years without inducing any scratches.


    Bookmark   June 24, 2012 at 7:47AM
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You have a lovely set up there. However, in my experience the induction cooktops are super easy to care for. I wipe mine down with the washcloth after doing the dishes, spritz it with "multi-surface cleaner" to remove the streaks and only use the cooktop cleaner when I start to see a sort of film over the cooking surfaces. Routine daily cleaning takes about 30 seconds. It's as good as new, if you ignore the stainless at the front and back. I followed the instructions when I first installed mine for a while, but decided I'd rather tolerate a little wear. However, there is still no evidence of wear after this amount of time.

I don't want to discourage anyone from selecting induction because the think it is fragile or requires difficult care. It isn't and it doesn't. The thing is the absolute bomb in my experience. It's wonderful for cooking and easy-peasy for clean up. We're house hunting again and I don't want a kitchen with one of those big, fancy gas ranges ... now the racing red Viking induction range would be another matter!

    Bookmark   June 25, 2012 at 11:33AM
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