As I sat down at my desk, I realized that I hadn’t put away the pizza box before I left for work. Will the slices left in the box be “bad” when I get home? Details about the food decay process would be appreciated.
Sua
No simple answers to this one to answer Sua.
The general rule to be followed with food is “If in doubt throw it out”.
Me personally I wouldn’t hesistate in eating it. Look at what’s gone into it - pastry, cheese, various preserved meats like pepperoni, salami etc, pickled olives, capsicum, tomato paste etc. None of this stuff needed refrigerating before it was cooked. Of course there are reports of food poisoning from preserved meats but these are often due to poor manufacturing techniques. The cooking process has however altered the water balance of the foods and this becomes a real issue if things like fresh pineapple or tomato have been used. Added to this what were nice discreet packages of preserved goods have been broken up and exposed to the air and whatever was in it.
The food decay process depends on too many factors to go into in a few lines, but basically it’s not the decay process you have to worry about, it’s what’s causing the decay. The thing could be completely rotten and not give you more than an embarassing case of flatulence if the right bacteria were involved, or it could look and smell perfect and kill you in a matter of hours if the wrong ones are there. There’s no way of telling what’s growing on your pizza, and the eight hours you’re at work is more than enough time for a colony capable of causing illness to develop. So it’s basically a gamble.
In your favour:
The ingredients aren’t inclined to promote microbial growth.
The nastier bugs like those responsible for botulism need airless environments and they’re not likely to find many of those in a pizza.
Against you:
There are lots of nasties floating around in the air that could make you plenty sick, and a few that could be life-threatening.
You have no idea what the hygeine standards of the pizzaria staff were. While cooking kills 99% of germs something could easily get transfered from a dirty hand to the pizza or the carton after baking, and these have been given all day in a warm building with unlimited pizza to eat.
The choice is yours but if you’re really worried weigh up the expense of a week in hospital against the cost of half a day-old pizza.
SuaSponte, IANAD, but as a bachelor with many years of experience… no. Eat the pizza when you get home, and enjoy! 
OK, seriously… did you cover it? Where is it? What is the temperature there?
When cooked (unless I am horribly mistaken) the pizza will be more or less sterilized… but as soon as it cools a bit, bacteria will land on it from the air (imagine the little bastards parachuting in like a batallion of WWII soldiers!). Some of them will be harmless, and some of them will NOT be harmless… they will begin to eat your pizza (bastards!) and multiply…
I believe (as this is just a guess, I have no proof for it, so don’t ask) that the grease that congeals on top of the pizza is not very good bacteria chow, and will not allow then to multiply quickly.
The question here is: will the (bad) bacteria have enough time before you go home to multiply to the numbers in which they will make you sick? The answer: I don’t know!
In my experience, pizza is safe for a long time… IE: I have never gotten sick from eating pizza that was left out for several hours, or even overnight, but that does not guarantee that you will not…
There will be a doctor along shortly to scold and correct me, I’m sure!
Peace? Dr.Paprika?
hmmm… Gaspode answered this better than I did… go with his advice!!
Kudos Gaspode!!
Astroboy, you wimp!
As an experienced bachelor, are you going to let some egghead talk you out of a perfectly good day-old pizza with obviously made-up words like “microbial” and “botulism” and “capsicum”? Shit, I’m coming to your house for the Super Bowl…
Sua, I’ve eaten many pizzas in my life. A significant percentage of them were ultimately dispatched the morning (ok, afternoon, but I get to sleep in on Sundays) after being left sitting on the counter overnight. Periodically, the top of the box was even left open-- a man in a drunken state careth not for bacteria.
None of these ever resulted in any gastric distress that could not otherwise be traced to a hangover. Sure, if you happen to live in a bus station or locker room, you might want to worry about bacteria sullying your leftover slices, but barring any unusual situation, I’d venture to say that you can safely consume your pizza even after 24 unrefrigerated hours without being overly concerned about any ill-effects.
If not, send the leftovers to me and I’ll eat 'em.
Looks like I’m dining in style tonight then!!
Sua
Just stick the thing in the Microwave when you eat it. There was a mooch in my Artillery Battery that would beg food/beer from everyone. We gave him a quarter of pizza Sunday evening that we ordered on Friday evening that was left under my bed. (In the box.) He even knew how old it was and ate it anyways, and yes he is still alive. One of the few times I didnt mind the mooching. I personally do not recomend this method of food preservation. ;’)