I have made some food in my pressure cooker and left it in room temperature for over a week. When I opened it, there was no mold. I threw it out because it might have still been bad, but this got me thinking.
Since canning is basically cooking food in a sealed environment, isn't pressure cooking similar when I do not open the pressure cooker? Could the food be left in the pressure cooker at a room temperature for a longer time, given that I pressure cook it every time I close the lid?
When you take the pressure cooker off the heat, it's filled with high-temperature, high-pressure steam. As it cools, that steam condenses, leaving a vacuum. Pressure cooker valves are designed to allow air to enter to fill the vacuum (to avoid damaging the pressure cooker, and to make it possible to take the lid off). So it isn't really sealed once it's not at high pressure.
The (old-fashioned Central European) pressure cookers I've worked with have outlet valves which in pressure cooking position let gas out (at defined pressure), but not in. These cookers do have an underpressure after cooling which you manually relieve before opening (it's plain impossible to move the lid unless you do that). Either with a lever pushing the rubber sealing or by twisting/screwing the valve into an "all directions open" position. I don't know whether/how long they keep the full bar of underpressure, but after some days you still get the "ffflump" sound when air goes in and the rubber detaches from pot wall and lid.
I'd certainly not expect this to last years like with a jar, but I do use it for several days or a week. Whether you do, is up to your own judgment.
There's also the question of what is in there: keeping fruit from molding until I have time to finish and jar the jelly a week later => fine. The risk here is to have to throw away the food and work, but it's not a risk of not being able to detect if that stuff went bad.
Personally, I also don't have a problem with, say, a goulash kept that way since (and iff) it's properly heated again before eating (the 2nd heat treatment will destroy any botulinum toxin that may have formed - such a twice-cooked-scheme is btw an officially recommended option over here).
For everything else in terms of microbiological contamination, I think the probability of anything I cannot detect by sight and smell getting in without any detectable microbial contamination is negligible. Note that this is the same heuristic as for canning: underpressure OK and no mold, no smell, no bad taste => everything as it should be.
I wouldn't keep fish that way - but then I don't pressure cook fish anyways.
Note also that
Sterilisation usually is done for longer than pressure cooking. The process will still be pretty bad for bacteria, partly depending on how many solid pieces there are in the cooker. After cooling off, the cooker is no longer sealed: the cooker I know has one valve that closes only after a short time of boiling in order to replace air with steam. This valve will be open again after cooling off.
However, the amount of air exchange through that hole will be small, so both processes driven by oxygen and contamination with mold spores will happen at a significantly lower rate than usual.
I would expect botulism bacteria not to survive pressure cooking, and new infections will only arrive with new air so I consider the anaerobic environment required for them to be not there.
Mold can either take hold or not. If it does, it will be from the surface and relevant contamination should be visible.
Other processes only driven by oxygen will turn into discoloration and/or bad smell and/or acidification (which may not be dangerous but usually spells the end of something tasting well).
In short: if it looks ok and smells ok and the cooker was as closed as it will be after depressurisation, my personal "don't waste good food" reflexes would likely prevail, but I'd not hide history and my personal judgment about it from others who possibly might eat from it.
