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I own a cheap Rival brand rice cooker. Here is a link to the product page. Note that there is an inner removable bowl where the rice is cooked. This bowl is coated in Teflon.

After cooking rice last night, I forgot to turn the cooker off, although it automatically switches to a 'warm' setting after the rice is done. (The two settings can be seen in the product page linked above.) I forgot to unplug the cooker, and it remained on overnight (8-9 hours) in a small, poorly ventilated apartment. Should I be worried at all about possible Teflon fumes? The bowl was only mildly warm when I found it in the morning, and there was no evidence of burning. I was under the impression that Teflon is only dangerous at very high temperatures, but I wanted to be sure.

More generally, suppose I want to start making rice at lunchtime so that I have warm rice ready for me when I come home. Is it safe to leave the cooker on for this period of time?

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There is no risk to the Teflon itself, or from it; PTFE breaks down at about 500 F, which rice cookers will not achieve, especially on warming setting. Other than that, PTFE is one of the most inert substances known to man, as the atoms are already bound in energetically very favorable bonds: little is as able to displace them without significant input energy (thus the high breakdown temperature).

On the other hand, you should not hold rice for a long time without either refrigerating it, or having it above 140 F (60 C) as there is some risk of Bacillus cereus growing and causing food borne illness.

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    I would upvote you, but I lack the reputation.
    – sls
    Sep 12, 2013 at 14:31
  • I would say that unless your rice cooker is faulty (or perhaps poorly made) that it should be holding the temperature at a safe level, but I would put a instant read thermometer in there to make sure.
    – djmadscribbler
    Sep 12, 2013 at 17:19
  • FYI, I used to use a rice cooker on warm overnight to soak steel cut oatmeal (then wake up, hit the switch, and after showering I'd have hot cereal). There was never any issue. One thing you may notice is that there seemed to be a slightly bitter off flavor that only occurred when using the PTFE dish. If I'd make it on the stovetop, there was no such off-flavor. I'd be interested if it could have contributed to the off-flavor or not.
    – Matthew
    Sep 13, 2013 at 15:58
  • @Matthew PTFE is as close to non-reactive as things come. If you perceived a bitter flavor using it, it might be because of a lack of masking affects from interactions with more traditional surface.
    – SAJ14SAJ
    Sep 13, 2013 at 16:21
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If your rice cooker has a warm setting then it is designed to be left on after cooking the rice. You can leave your rice in the bowl for days on warm and your teflon will be fine.

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