If you eat it, you are taking a chance–a significant one–of ingesting bacterium which could make you ill.
Anytime a food stuff with meat and cheese is left at room temperature for more than a couple hours, bacteria begins to grow and multiply. This ALWAYS happens, btw, there are no exceptions. What matters, however, is if your immune system will be able to effectively assimilate and destroy any of that bacteria that is harmful to your system.
This is why it is a Golden Rule of ALL restaurants and places of business who serve food to follow the “40-140” rule: Never leave food for more than 1 hour ABOVE 40 degrees or BELOW 140.
I would personally not eat it. It is not worth it. It would only be worth it if you were starving and the pizza was the only food available.
The rule in the restaurants I worked at and whatever the hell test we had to take was 2, hence my contribution. Of course, those places didn’t have room temp approaching anywhere near 90F.
Whatever you do, if you drank copious amounts of alcohol the night you bought the pizza, and decide you want to heat up a couple slices as a late night snack, remove the slices from the box first. Otherwise it can end badly, especially if you fall asleep on the couch while waiting for said pizza. Smoke detectors make amazing alarm clocks, by the way. A friend told me about this.
It’s always been 2 hours as I’ve known it (minus the one caveat, I guess.) The 4-hour rule I’ve heard was in cooking foods, that you should get them from 40-140F within 4-hours. You hear it quoted every so often in barbecue/smoking forums.
A related question: what’s the “rule” about refrigerating hot or warm foods? I see on the web that perhaps you shouldn’t saran wrap hot food and shove it into the fridge.
In fact, my brother, whom is a certified chef, has advised me that when I make chili to plunge a bag of ice into to the pot prior to sticking it into the fridge after I’ve taken it off the heat. He says that it preserves the texture much better by rapidly cooling it rather than allowing it to cool very slowly. I always do this, my chili is always really good, but I don’t know if what he says is true or not.
I’ve personally always been taught to get the food cold as fast as possible so, yes, it would go from being hot straight into the fridge (and all that stuff about never put hot food into the fridge is some leftover advice from an era where fridges weren’t as good). The ice bag would help chill it more efficiently and faster. (Note, this is not a rule I follow in my personal kitchen.) No idea about the texture stuff or anything like that.
Reheating the pizza might kill any bacteria in it, but it won’t necessarily destroy any toxins that the bacteria might have produced meanwhile.
On the other hand, the nastiest toxins are produced by anaerobic bacteria like botulism, which won’t grow in food sitting on a counter. And most pizza toppings are salty enough that bacteria are only going to grow very slowly in them.
Okay, here’s what you do with leftover pizza. Put it in a nonstick skillet. Don’t add anything. Cover it; I use a pizza pan, but anything that makes a tight seal will do. Heat it on medium heat until the crust is browned and the cheese is gooey and bubbling. Buon appetito!
And the real rule, which is too complicated to be a restaurant rule, is that it depends on both the food and the temperature. Food that isn’t salty or sweet of sour spoils very quickly at 90F. It keeps pretty well at 60F. Not as well as it keeps at 40F, but food spoils slowly in a cool room. And foods that are very salty (like most pizza) or dry (like most bread) or very sweet (like jelly) or sour (like pickles) keep pretty well even at warmer room temps.
Maybe not so well that a restaurant wants to risk it, but if there aren’t any immune compromised people eating it, and if your kitchen is cool at night, it’s not all that dangerous. I don’t like leftover pizza, but I wouldn’t have any concerns if my pizza-loving family members ate it.
I left some bean soup out overnight by mistake recently. I put it in the fridge the next morning and ate it over the next week. That’s much riskier than pizza, as it’s an excellent medium for bacteria. So I did bring each serving to a vigorous boil before I ate it. And even so, I wouldn’t have served it to someone with health issues. But it looked and smelled fine, it tasted great, and I didn’t get sick.
