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I'm a truck driver, and I have a minifridge, a microwave, an Instant pot, and an electric water kettle on the truck with me. I've been experimenting with various ideas on how to best feed myself. So here's my version of the question. If I cook the soup with some veggies and meat, scoop some out to eat, and seal the lid and keep the instant pot set to "Keep Warm" (145-175 degrees F) will it be safe? It stays sealed except when I'm dishing out a new dish, it stays above 140 degrees, and each time I add new stuff to it, I'll re-cook it, but will whatever I've left in there still be good?

I was just reading through this question: Never ending soup; is it actually safe? and I had a modified version of it to ask, but since that question hasn't been active in over a year, I thought I would make a new question.

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    Welcome to the site! I can imagine eating healthy on the road is a challenge. One option would be to swap the instant pot for a microwave, cook meals head of time and reheat on demand.
    – GdD
    Sep 9 '20 at 9:26
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    Would the pot ever lose power, or would it constantly feed off the battery when you have the truck off to sleep? Because while food > 140 degrees might be safe, food around 100 degrees for a 6 hour nap, multiple days in a row, would be the absolute worst case scenario. It's called "the danger zone".
    – user87599
    Sep 11 '20 at 18:38
  • I haven't given it a test with the Instant Pot, but you will likely need to actively change the cooking program once or twice a day, rather than leave it on 'warm' for extended periods. I think it happened to me once with my Instant Pot. I don't know if this is a UL thing or what, but it's a common complaint from the Jewish community about digital slow cookers, as they'll shut off if you leave them on for too long. (supposedly it's a common thing to prep everything the night before, then leave it in the slow cooker so you're not doing work on the sabbath)
    – Joe
    Sep 11 '20 at 20:08
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I've actually tried it. It didn't work very well for me, but it might work better for you.

The problem is, cookers like the Instant Pot are designed for quick pressure cooking first and foremost. While they have a "slow cook" or "keep warm" setting, the heating element is still driven at high power, just at a lower duty cycle. Over time, that encourages solids to settle to the bottom and dehydrate and burn. (In contrast, a slow cooker operates at a lower power and heats to a lower temperature.)

However, the motion of the truck might actually help you out here by agitating the soup. If the soup doesn't have anything starchy (like beans or potatoes) that might be sufficient to prevent burning.

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I agree with Sneftel's answer that the quality is likely to degrade over time due to contents settling and breaking down into stuff that doesn't taste good.

But just to add a thought regarding safety: food that's kept above 140F should in theory be safe indefinitely (see my answer to related question here). However, I'd be concerned about the proposed idea for several reasons:

  • Does the "keep warm" setting actually maintain temperature consistently? (Hopefully it does, but many devices fluctuate quite a bit on such settings.)
  • Can you guarantee that the cooker will basically have uninterrupted power?
  • Adding ingredients can bring down the temperature of stuff already in the pot temporarily. This thermal cycling may become a problem if the overall ingredients go down below 140F enough times and spend time there when stuff is added (which could happen if you add a lot of new cold stuff at once). Some toxins are not destroyed at temperatures in the 145-175F range (or even by boiling), and some bacteria found in foods can form spore forms that can survive high temperatures and reactivate when food is cooled temporarily. Every time the overall ingredients dip below ~130F, you could start to see growth of bad stuff.

In general, I don't see a problem keeping this going for a few days/few batches, as long as you can verify it's staying at temperatures above 140F, and that the remaining ingredients aren't thermal cycling into the "danger zone" for very long. But for quality reasons as well as cumulative safety issues, I'd personally just try to finish the pot and clean it out periodically.

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  • With the instapot being sealed, if the OP brought it back to a high temp after opening each time wouldn't that keep the contents sterilized? I've used a pressure cooker as a sterilizer in a non-cooking context before so just wondering how entering the "danger zone" works if everything inside the container is dead.
    – Myles
    Sep 9 '20 at 18:33
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    @Myles Bacteria that cause foodborne illness produce waste products that are toxic to humans. Even if you heat up the food to a high enough temperature to sterilize it, it won't neutralize any of those toxins that may be present.
    – Tristan
    Sep 9 '20 at 18:54
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    @Tristan When the temperature goes back down to "Warm" the pot itself acts like a can, if it was sterile when hot (greater than 100C for enough time) and doesn't get opened it will still be sterile at room temp. You are right though as you'd have to get it to sterilizing conditions over and over again so your ingredients would turn to mush, although depending on the type of soup mush might be ok.
    – Myles
    Sep 10 '20 at 21:19
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    @Myles The presence of a bacterial toxin has nothing to do with sterility. Once something like the Botulinus bacterium has been present to any significant extent in food you can cycle it up to sterilization temperature as many times as you want but the toxin will persist. Sep 11 '20 at 10:27
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    @Athanasius FWIW, I note that Wikipaedia agrees with you. Let's just agree that storing food warm probably isn't a very good idea... usual stories about doner kebab etc. being reheated. Sep 11 '20 at 15:57
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Considering this in the context of the earlier "everlasting stew" discussion, it's worth noting that there are certain ingredients which must be cooked using sustained high temperature. One notable example is red kidney beans which contain a protein which must be denatured (by boiling for ten minutes or so) before they are safe to eat.

The combination of some ingredients which must be cooked aggressively (e.g. beans) and some which are better cooked lightly (many fresh vegetables) or even eaten raw (for the sake of their vitamins) suggest that you'd be better doing your cooking in advance, chilling the portions, and thawing/heating when needed.

If you found somebody with a good stock of liquid nitrogen you probably wouldn't even need a refrigerator- just an insulated container.

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  • The "must boil beans" thing is a good point, though you also might want to note that that doesn't apply to canned beans, which have already been cooked to a safe temperature.
    – Sneftel
    Sep 11 '20 at 11:14
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    [In a shocking twist, the OP reveals he drives a liquid nitrogen delivery truck]
    – Sneftel
    Sep 11 '20 at 11:14
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    @sneftel Like it :-) Apropos food preparation on the road, I've seen the owners of heavy steam engines (in the UK we call them "traction engines" and "steam rollers", and they exist only in carefully-conserved preservation) removing foil-wrapped bundles from their smokebox. Sep 11 '20 at 11:35

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