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We were trying to prepare a chocolate cake using a Panasonic Microwave. We set the oven to auto mode for cake preparation. There was a time for preheating (180°C) and then asked us to place the cake tin inside which would cook for 35 minutes, but when it was just six minutes after process started, the vessel started to melt.

We first used the vessel provided by Croma which melted and then we tried using the vessel provided by Panasonic for microwave, that also melted.

What was the cause for this and can we eat the cake that was in the melted vessel?

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    In the future, people may be more receptive to answering your question if you take the care to type it in a more readable manner, using upper and lower case, and proper punctuation. Most folks here realize not everyone is a native speaker of English, and will make allowances accordingly, but the effort "shows willing" as the British say.
    – SAJ14SAJ
    Commented Jan 8, 2013 at 8:11
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    What does microwave oven have to do with it? If you heat the oven to 180C and put plastic in it, it will melt! Do not use plastic vessels in a conventional oven, even if it is a microwave oven also. And if you do, and they melt it is probably a quite bad idea to eat the food.
    – Stefan
    Commented Jan 8, 2013 at 15:54

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The cause is that the dish was not intended for use in convection mode.

Plastic melts under heat, period. "Convection" as used by oven manufacturers means that the air in the oven gets heated to the temperature specified (actually, ovens are so badly calibrated that it can be considerably more - I have seen an oven overheating by 40°C - so a considerable safety margin is needed). Any solid objects heat to high temperatures in this hot air, with the surface coming close to the air temperature. You cannot put plastic in a 180°C oven.

A microwave oven operates on a different principle. It heats certain types of objects from inside. Water (and some other nutrients, e.g. fats) get hot when irradiated by microwaves. Plastic or air don't get hot. Therefore, a plastic dish does not get hot when used for cooking in a microwave oven, and the air in the oven also stays cool and does not melt the dish.

What you have is actually two ovens in one. They use the same heating container, but with two different heaters. The plastic dishes supplied with the oven, as well as any other specialized microwave cooking dishes, can only be used in microwave mode. The convection has to be turned off when you use them, else they will melt.

If you want to cook with convection, you have to use a pan from a material which doesn't melt. For a traditional oven, this would be borosilicate glass, ceramic, silicone or metal. I would not use a metal pan. I have heard of combo ovens which don't turn off the microwave part when switched to convection mode (even if the user manual claims otherwise!), and even if yours does, it is still a safety risk because you might forget it and turn on the wrong mode. Metal gets much hotter than water in a microwave, up to the point where it can explode.

Summary: use oven-safe glass, or ceramic. If your glass dish has a plastic lid, remove it before baking in convection mode.

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  • I am impressed--how did you figure out from the question that this was a dual-mode oven?
    – SAJ14SAJ
    Commented Jan 8, 2013 at 21:09
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    @SAJ14SAJ I suspect the mention of a temperature. Microwaves don't usually preheat or specify temperature.
    – Yamikuronue
    Commented Jan 9, 2013 at 21:39
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    @SAJ14SAJ your comment made me re-read the question and I realized for the first time that it doesn't actually mention dual-mode. Why was I so sure that it is one? Possibly because all the other facts known about the case fit perfectly with this interpretation and are highly unlikely in any alternative interpretation I can think of. A temperature setting, a "Auto cake" mode, melting a "tupperware-like" microwave dish all speak of convection - but if the product is sold as a microwave, it must be one of those dual-mode microwaves which seem to be popular in Asia.
    – rumtscho ♦
    Commented Jan 9, 2013 at 21:49
  • @rumtscho I didn't know those were popular anywhere :-) Well done, in any case!
    – SAJ14SAJ
    Commented Jan 9, 2013 at 22:26
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Aren't metals (e.g. tins) a NO-NO in microwaves?

In any case, I wouldn't touch food whose container melted. Chemicals are bound to mix, and that doesn't seem safe.

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  • I used the bowl which came with the microwave like tupperware.. but it got melted at 180 degree Celsius. It was in auto matic option given for cake.. I need to know whether the microwave is problematic as it is the first time to prepare a dish with it.
    – user15125
    Commented Jan 8, 2013 at 9:31
  • @user15125 Is it plastic or metal?
    – geff_chang
    Commented Jan 8, 2013 at 9:32
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    @geff_chang If it melted in 180C it was very likely not metal :-)
    – Stefan
    Commented Jan 8, 2013 at 15:55

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