Meats don't last indefinitely once they've been cooked, and even if a dish that was left out overnight looks the same in the morning, you should throw it out. This is because once cooked meats start cooling, they become breeding grounds for bacteria. Unrefrigerated leftovers start growing bacteria within just a few hours and after a night on the counter, they're unsafe to eat.
Cooked meat is a hotbed for bacterial growth -- and if you leave it out all night, it's likely to make you sick.
How Bacteria Grows
Meats, like beef and poultry, have to reach a minimum internal temperature before they are safe to eat. This temperature varies by the type of meat, but the reason for it remains the same: Before it reaches that temperature, bacteria can multiply in and on your food. Between 40 and 140 degrees Fahrenheit, your food is in what the U.S. Department of Agriculture calls the "danger zone." That range is referred to this way because it's the ideal environment for pathogens, like salmonella and Escherichia coli, to grow.
Cooked meats left out overnight should be thrown away, but you may not have to wait that long. To keep cooked meat out of the danger zone, it should be refrigerated or frozen within two hours of being cooked -- any longer at room temperature, and it becomes unsafe. If the temperature in the room is higher than 90 F, the timeline is even shorter, and your food shouldn't sit out for more than one hour before you pack it up and store it.
Throwing your cooked meat into the freezer or refrigerator doesn't necessarily make it safe. Large quantities of food, like whole roasts that haven't been carved and pots of soup, take longer than small portions to cool off in the refrigerator. This means that even though the temperature in your fridge is below 40 F, the food you store in there takes too long to reach the same temperature, and stays in the danger zone. To safely store cooked meat, you have to cool it quickly. Carve it and split it up into several shallow, airtight containers to keep bacteria out and to ensure the fastest cooling possible.
Even cooked meat that is properly stored doesn't last forever. This is because storing your food doesn't necessarily kill pathogens -- it only slows the growth. After a few days in the refrigerator, your leftovers will still grow bacteria, and eventually mold. Only save cooked meat in your refrigerator for three or four days -- if you want to keep it longer, it has to go in the freezer. While the meat will be safe in the freezer indefinitely at 0 F, the texture and taste start to deteriorate. Depending on the type of meat, it may last around six months in the freezer.