You should probably know the circumstances under which cooked food can and cannot sit out, as well as how long it can do this for. Whether you are cool as a cucumber or the biggest worry wort on the face of the earth, you will eventually run into a situation where food has been out for a while, but you still want or need to eat it.
Cooked food should not sit out for longer than two hours. Sitting out at room temperature, bacteria is able to colonize and multiply within the food. After two hours, that bacteria will have multiplied to a point that the bacteria will be too embedded in the food to be cooked out.
It might be alarming to imagine that food can be colonized by bacteria in as short a time as two hours. But one must be careful not to oversimplify their notion of the function of bacteria, whether in food, or in the human body. Human bodies, after all, are filled with trillions upon trillions of bacteria. Our lives depend on it.
Strange as it is, this bacteria is not produced by human bodies, but human bodies could not function without it.
This is why certain medical treatments include methods of repopulating the bacteria inside the human body, particularly within the stomach, where the bacteria humans can coexist with fights the many other bacteria with whom humans cannot coexist. These are the bacteria that appear after about two hours of food being left out.
What you really need to watch out for is food left out in heat greater than room temperature. When you think of the differences between what happens at room temperature and what happens above room temperature, you should think of it as the “Two Hour Rule” versus the “One Hour Rule”.
The Two Hour Rule
The two hour rule is a rule for leaving out food that should be applied to any food that is left somewhere room temperature for around two hours. It is exactly what it sounds like: Really, horribly, no-good bacteria begins to form after two hours. What kind of bacteria? The kind your body should never interact with.
To begin with, it is possible for things as bad as staphylococcus aureus and salmonella to colonize food at room temperature. It takes a while, but it can happen.
The worst part of these kinds of bacteria is that they not only cause infections to develop by themselves, but they practically make you susceptible to infection for the rest of your life. This is because when a bacteria enters your body it also “colonizes” you.
Bacteria are almost impossible to completely purge from your body’s systems. They are smaller than red blood cells, so they can “hide” in your blood stream and digestive tract, remaining dormant until they are fed by other circumstances. These circumstances can be trauma, such as from injury or surgery, or other bacteria.
As such, if something such as staphylococcus enters your body, it will probably not leave. Do not be too alarmed if you are colonized by staph, as it is a treatable condition. It probably won’t take years off your life, but you should still be careful of it, as untreated staph infections can absolutely be lethal.
That is a worst case scenario, however. The great thing is, this can all be avoided. Just heed the two hour rule in room temperature environments, and you can completely avoid even the slightest risk.
The One Hour Rule
This rule is, obviously, more strict, but you will also have an exceptionally clear indication of the fact that you need to pay attention for it. Whereas the two hour rule is a matter of spaces where food is left out at room temperature, the one hour rule is a matter of spaces where food is left out at above room temperature.
The important difference is that bacteria propagate much faster at such temperatures. The United States Department of Agriculture actually has a name for these temperatures: The “Danger Zone”. It refers to any space between 40 and 140 degrees Fahrenheit.
A peculiar trait of the physical sciences is that heat speeds up chemical reactions. There is a breaking point for this, naturally; bacteria reproduces faster between 40 and 140 degrees, but it will definitely not be able to survive at 150 or 5000 degrees. This is why cooking and reheating food in the first place works.
But before that breaking point, everything that happens in a system happens faster. Molecules bump into each other and share their thermal energy, signals are sent faster, enzymes age faster, and so on and so forth. This includes reactions inside food, such as the reproduction of bacteria.
Due to this, the two hour rule becomes the one hour rule as heat increases. 90 degrees Fahrenheit is where you should really start worrying. This is why it is so obvious when the one hour rule becomes material to you: If your hour reaches 90 degrees Fahrenheit, you will know.
This is most relevant outside the house. Eating on a patio, cooking at a barbecue, indulging in a garden party, these are all activities that might require you to pay attention to the one hour rule.
And not only is the time shorter for the reproduction of bacteria, but the probability of making contact with dangerous bacteria is greater as well. The human body can keep bacteria floating through the air from colonizing it. It is once that bacteria is inside the human body that it begins to have issues.
Food, however, has no such immune system. If bacteria contacts it, it will grow in it, end of story. So, be careful if you are eating outside. Keep your food covered when you can, and eat it quickly if you can’t.
What To Do Instead Of Leaving Food Out
Rather than leaving food out, take a moment to wrap it in plastic and put it in the freezer. For most foods, this is enough precaution to keep it clean, safe, and protected from bacteria. Just as heat increases the rate of chemical reactions, the cold slows it down. Freezing slows it down to a crawl.
This requires a degree of foresight, however, especially when eating food outside. It cannot be avoided that the situations in which one is eating outside are higher maintenance than the situations in which one is eating inside. If you are having a barbeque or garden party, you might become distracted from your food.
Just try to keep in mind when all the food was served. The one hour rule is, technically, only for spaces hotter than 90 degrees Fahrenheit. But the amount of time food can spend being left out gets shorter as the temperature gets higher. If you want to be safe, apply the one hour rule to any warm day.
If your circumstances make it so where you have to choose between taking a risk by eating food that was left out for too long or creating food waste, then create food waste every time. No amount of efficiency is worth a lifetime of being colonized by staphylococcus.
Will Reheating Food Kill Bacteria?
Yes, if it is stored and reheated properly. Just remember that if the food is stored for more than four days, as per information provided by the United States Department of Agriculture, then the bacteria is likely too plentiful to be cooked out. Before that however, and you should be fine to reheat it.
Additionally, the United States Food and Drug Administration recommends heating your food to an internal temperature of 165 degrees Fahrenheit.
Remember, an internal temperature is very different from a surface temperature. If the exterior of a food is warm, but the center is cold, then there is a risk that there might be surviving bacteria in the center of the food.
Are Reheated Foods Healthy?
Reheated food will be as healthy as the food was before, most of the time. The freezing process does not kill anything in most foods that was not already killed when the food was made into food. To state that in a different way, consider beef: Once a cow is butchered for its beef, the beef is dead. It gets no more nutrients.
Freezing that beef will not make it more dead. The nutrients that remain in the beef are still dying, but their deaths have been slowed down by the cold. So it is about as healthy as it was when you froze it.
Keeping food out for too long can be dangerous, but not exactly risky. Science knows exactly when and how food spoils. And because of that, now so do you. It is not a matter of luck or probability. Rather, it is a matter of how safe you are willing and able to be, and how responsive you are to the situation you find yourself in.