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I see a question here about stock out overnight, but in my case it's a bit different in that I used a pressure cooker.

My question is, is there anything that could possibly have survived an hour of high pressure cooking? I've essentially gone far beyond what's done in pressure canning, and never opened the cooker.

Is it really possible that anything survived that inferno? Pressure cookers by definition have an air tight seal, so I can't see how anything would crawl in after the deed.

Safe to eat?

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  • Did the cooker still have pressure? If not, it's possible that something might have gotten in through the pressure vent at some point in the cooling process.
    – logophobe
    May 6, 2016 at 16:43
  • I'm not sure anyone would dare to declare your stock "safe" - me included, hence no answer. But personally, I would probably eat it.
    – Stephie ♦
    May 6, 2016 at 16:59
  • I would say it exceeds canning at that point.
    – paparazzo
    May 8, 2016 at 18:45
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    @Paparazzi If by that you mean it's safer than canning... no. Canning relies on having an airtight seal, which was not present here.
    – Cascabel ♦
    May 9, 2016 at 5:07
  • @Jefromi Right?
    – paparazzo
    May 9, 2016 at 7:33

5 Answers 5

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No, it is not safe. As soon as a pressure cooker loses pressure it is not hermetically sealed. Stock, in particular, is often used as a culture medium in petri dishes to GROW bacteria. They love the stuff.

Pressure cooking or pressure cookers do not confer magical powers to food - once the pressure is gone all the regular food handling rules apply:

  1. Always refrigerate perishable food within 2 hours (1 hour when the temperature is above 90 °F).
  2. When in doubt, throw it out.

Here's a little story about Bending the Rules on Bacteria and Food Safety, wherein a cookbook author feeds lethal week-old stock to his family - and the expert opinion on why this is NOT ok.

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    According to the article you reference, the food scientist actually "gave a pass" to allowing stock to cool overnight. And that wasn't even using a pressure cooker, which would have destroyed the lamented botulism spores as well. He says that stock left at room temperature for a week is unsafe. I'm talking about a very different situation.
    – DougW
    May 27, 2016 at 20:02
  • @DougW In that case, the stock was boiled again before refrigerating in the morning to deal with potential contamination in the meantime. You don't mention doing that in your question.
    – Cascabel ♦
    May 27, 2016 at 20:47
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I've read a number of opinions since posting this and I have to say that I think the top answer is conservative to the point of absurdity.

According to a strict reading of the FDA food safety rules, yes this stock should be considered a lethal poison. However there are a number of mitigating factors here, which I believe render this food completely safe. The FDA rules will keep you safe, but they are written to keep you safe under any circumstances.

To be clear, after cooking there were zero bacteria in this stock or on the stockpot. There were zero botulism spores in the stock or stockpot. Pressure cooking on high for an hour has completely eradicated everything. So the only potential source of contamination would have been from airborne bacteria or bacterial spores happening to float through the extremely small aperture of the vent after de-pressurization.

There is probably a tiny bit of ongoing air exchange due to convection between the heated air inside and cool air outside the pot. All told though, this is clearly going to be a tiny amount of air overall. Heck, let's say it's a few liters, which I think is generous.

So, what we're terrified of here is that there was enough airborne E. coli or botulism or something evil in a few liters of kitchen air to colonize a stock to the point of being unsafe (even with reheating) in maybe 5-8 hours. I have to believe that if that was even remotely possible, we'd all be dying left and right simply from breathing our kitchen air for more than a few minutes at a time.

Do what you feel is right, but in my opinion saying to throw this out is 100% about fear of legal liability and 0% about science or sense. Yes, I ate the stock. It was delicious. YMMV.

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  • Perhaps the issue here is in how you're reading the FDA food safety rules? They make no claims about "lethal poison". They make claims about what is a safe level of risk. None of their rules are "do this or you'll die" they're "do this, or too many of you will get sick sometimes".
    – Cascabel ♦
    May 27, 2016 at 20:48
  • As for the risk assessment... airborne contamination is quite real, not super likely, but it is a real risk. And since you don't mention reboiling, if you're unlucky and do get contamination, the 5-8 hours is absolutely long enough to multiply to dangerous levels. Sure, as you say, the air that contaminated it would never be dangerous, but once that bacteria gets into an ideal growth medium like stock, it can multiply to become dangerous in hours. I totally agree with you that this is much lower risk than a lot of things, but it doesn't appear to be a safe practice unless you reboil.
    – Cascabel ♦
    May 27, 2016 at 20:57
  • Sorry, that was a linguistic flourish. Obviously the FDA doesn't use the term "lethal poison". I disagree with the assessment that the risk is "quite real". I think in this case, the probability of getting sick is in the neighborhood of being struck and killed by a meteorite. Is that a "real" risk? Depends on your definition. Yes it could happen. My personal level of risk tolerance is many orders of magnitude greater. The FDA guidelines' level is not. Would I serve this to immune compromised individuals at a restaurant? Probably not.
    – DougW
    May 27, 2016 at 21:40
  • We defer to government agencies on levels of safe risk because we're not at all sufficiently qualified or well-informed to make judgments about risk levels otherwise. Your answer is a good demonstration of this: we can agree the situation is lower risk than a lot of common dangerous ones, but we have no real quantitative idea, and yet you're comparing it to a meteorite strike nonetheless. So if your claim were "this is unsafe but probably not that awful", okay. But your answer is more like "the FDA is way too paranoid and this is totally safe", no, you can't really conclude that.
    – Cascabel ♦
    May 27, 2016 at 21:51
  • Sure, I get your point. Government has a team of scientists that have crafted guidelines that will keep even the stupidest of persons safe in even the most dangerous of situations. That is true. Maybe it's egotism but, in this case, I personally feel confident enough in my abilities of deductive reasoning to come to a different, yet safe, conclusion. I'll still accept the answer that will keep everyone alive, Darwin be damned.
    – DougW
    Jun 4, 2016 at 6:25
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No, it's not safe, even withe a closed pressure cooker air must enter in order to equalize pressure.

This goes for everything you cook: The temperature danger zone goes from 41f to 149f and you need to reach the bottom bound within these margins: 149f to 70f in 2 hours max 70f to 41f in 4 hours max After that you have to put the food in the fridge or the freezer.

What this does is to minimize the reproduction of microorganism such as fungus and bacteria, since you don't give them enough time on their "comfort zone".

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  • Pressure is created by boiling water. The extra pressure is caused by the steam which takes up more space than its liquid water form. Outside air is not pumped in.
    – Matthew
    Dec 27, 2020 at 7:08
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Have you guys heard of the famous experiment done by Pasteur to disprove the spontaneous generation theory? In this experiment, he boiled broth to sterilise it, then kept it in an open glass jar, a glass jar with cotton covering the top and a glass jar with a long swan neck. Both the cotton (as a filter) and the swan-shaped neck stopped contamination. The same principle that applies to a swan-shaped glass neck applies to a Petri dish: the seal is not airtight, yet no contamination can enter due to the shape of the minuscule gap.

I would argue that it depends on your pressure cooker seal, but if it can seal off pressure then the gap that allows air exchange is probably also preventing contamination. In fact in autoclaves (fancy pressure cookers) we sterilize media with the lid slightly loose to prevent the bottles from exploding, and then let the whole system cool down for hours, pick up the next day, and nothing grows on it.

In conclusion: I don't think anything will grow overnight if the pressure cooker is left unopened. Happy to be disproven otherwise by anyone who wants to experiment!

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I often make a pressure cooked stock, turn off the gas, leave the pot alone (allowing the pressure to dissipate naturally), leave the lid undisturbed, and return to it the next day to strain, package and use or freeze. Depending on your altitude, the temperature inside your pressure cooker can reach 250 degrees F. This is well beyond the temperature to kill off any potentially harmful bacteria. As you state, if you don't open the lid, nothing can enter. Bacteria don't crawl or fly around, so it is hard to imagine something getting in through the pressure release...unless you dumped some tainted liquid on the pressure cooker...then....maybe... Draw your own conclusions, for me it is a routine practice.

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  • Bacteria don't literally fly, but they can definitely drift around in the air all the same. And the pressure cooker isn't airtight anymore after cooling. In fact, it may even pull some air in - the pressure will equalize while it's still warm, then as the steam inside condenses and the air inside cools, it'll end up lower pressure inside than out. When you're canning, you regard things as unsafe if they don't get a good seal; seems like the same should apply here. Not saying it's as risky as uncovered food left out, but doesn't seem entirely safe.
    – Cascabel ♦
    May 9, 2016 at 5:03

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