Let’s say you cook a standard casserole in a standard household oven. 350* for an hour or whatever. Internal temp of the casserole easily reached 200* for an hour. The casserole is covered in the oven. The oven door remains closed. You turn the heat off, but get called away and forget that you left it in the oven.
How long would said casserole remain edible? It was cooked. It is covered. The internal oven surface temps were at 350* or above. The door was shut. The oven, while not being vacuum sealed, isn’t exactly exchanging volumes of air and airborne contaminants with the outside.
Would it make a big difference if it wasn’t a casserole, but was instead a beef roast or a ham that was in a roasting pan, covered by foil?
Yes, the question to Cecil about microwaves and bacteria got me thinking about this.
It should be sterilized since the oven (or more or less) is a sterile environment and that any bacteria in the casserole would be killed. I would reheat the casserole if you leave it in there for too long just to be sure.
The casserole would not be sterile- baking only reduces the number of pathogens, it doesn’t sterilize. General guidelines say that four hours is the maximum time you want to have most food within the temperature danger zone before tossing.
But first of all, the casserole will remain above the upper limit of the danger zone for a while, and second, that four hours is assuming that it’s sitting out on a counter in the open air, not in a quasi-sealed environment (at least, with no bulk air movement) where everything’s been exposed to potentially-sterilizing temperatures.
Hmm… Plenty of bacteria form spores that can survive 200° F. Clostridium botulinum, a textbook example of bacteria that causes deadly food poisoning, forms spores that easily survive boiling (212° F) for fairly long periods. The bacteria don’t infect humans, but they produce one of the most powerful toxins known to science. In the worst case, given the OP’s scenario, the casserole could have been contaminated with a large number of botulinum spores. They’ll survive the cooking, and eventually will start to grow and produce enough toxins to be deadly. This is the same reason why you should NEVER eat canned food that’s bulging.
There’s also Clostridum difficile, which also forms heat-resistant spores can cause very very nasty GI tract infections. If your casserole was contaminated with some of those, you could end up with another kind of potentially deadly food poisoning, even if you eat it immediately after cooking. You can get an infection by consuming a relatively small number of spores. Luckily C. difficile is relatively rare (though it can be common in hospitals and nursing homes) and the really nasty strains are rarer still.
ETA: Both of those are extreme worst case scenarios. I’d guess that most of the more common and benign food-borne pathogens and toxins would be completely killed off, such that your casserole could be safe for weeks.
It is important to note that food handling guidelines are just that, guides to cover a number of variables.
People have different immune systems and what might not make one person sick could poison another. You can’t know if the dish was cleaned properly before the food was added, if a contaminated utensil might have come in contact with the food after it was cooling down, if the ingredients were prepared properly, if the oven works as it should, if proper temperatures were reached, and so on. So the guidelines attempt to find the best, safe ground.
Many informal studies, some of them done in dorms at the finest universities, have shown that pizza is still just fine if left out all night in an open cardboard box until the next afternoon.
Right, and it’s a probability game as well. Eating day-old pizza, left at room temperature, might be safe 99% of the time. That remaining one percent it gives a healthy college kid a mild case of diarrhea. Personally, it’s not something I worry about.
But if you run a restaurant, you’d better damn well worry about it because 99% isn’t anywhere near good enough. You’re probably feeding a few dozen people every night. Call it 10,000 people per year. 99% food-poisoning free meals means you’ve made 100 people sick this year. And even a mild case of diarrhea can hospitalize the elderly or infirm. So restaurants have to stick to guidelines that are 99.99% effective (or better!) at preventing food poisoning.
Food safety guidelines are for worst case scenarios where food is inoculated with significant contamination post-cooking (ie: smearing your hands in raw chicken juice and then swirling it through some soup).
Note that what you’re doing is essentially canning except using the oven as a can. Canned goods, if canned properly can easily last several years.
In the ideal environment, salmonella can double every 20 minutes. Salmonella becomes a serious problem at around 1 million bacteria/gram so after about 30 doublings or ~10 hours after the first salmonella gets in, you could be facing a tainted casserole.
Except that canning really needs a temperature above 200° to be reliably safe. Ideally canned food is boiled at high pressure – something like 250° at 15 psi. In the oven, you can’t get the internal temperature of your casserole above 212° without desiccating it and making it inedible.
I’d guess that even in the OP’s case, at the very least there’d be a few non-pathogenic bacterial spores that would grow and make the casserole pretty unpalatable in a matter of weeks.
Even when doing high-pressure, high-temperature canning, you can’t say you’ve killed every hypothetical spore that was there. That’s one fun thing about microbiology - there’s no such thing as zero. Typically, in food processing, you define a process that will kill 90% of the botulism spores that may be in your food. You then repeat that process 6 times (or increase the temperature or time in an equivalent way). That is, current regulations are that processors must process canned foods so as to kill 99.99999% of any botulism spores that may be there. Even then, of course, they can’t say it’s really sterile, although it almost certainly is. There’s still that 1 in 100000000 that will make it through.
