Restaurant professionals know that bacteria responsible for food-borne illness can multiply by the thousands in very short period of time.
They also know that you cannot tell always tell that this has happened by the smell or the appearance of the food. Fresh chicken that was purchased in the morning and improperly stored can cause illness in the evening.
So, there is a golden rule, when it comes to the temperature in restaurant kitchens: Hot food hot and cold food cold.
This means that food that is hot or already cooked, needs to remain hot, and food that is cold, whether it is raw chicken or food that is eaten chilled, needs to stay cold. The question is, then, what is considered “cold” and what is considered “hot?”
What are the Safe Temperatures of Cold and Hot Foods?
Most pathogens that cause food-poisoning reproduce the fastest and thrive within a certain range. This range is between 41° F to 135° F (5° to 57° C). When a health inspector visits a restaurant kitchen and aims a digital thermometer at stored cold foods, they are checking to see that the food is colder than 41° F. If they are checking hot foods being held, they are checking to see if they are hotter than 135° F. In reality, this means restaurants try to go for below 40° F or to 140° or above, depending on the particular food.
When the temperature is below 41° F, the bacteria may not die, but they will not reproduce. Above 135° and many pathogens are destroyed. Even if they are not killed, they will, again, not reproduce. Between these two temperatures, however, is the danger zone, where bacteria enjoy conditions perfect for their life cycle. They will begin reproducing at an astonishing rate. Once present in high numbers, it is too late, the food is considered adulterated and not fit to serve.
The image below, provided by the USDA, gives a graphic representation of the safe temperature zones for holding foods, as well as some minimal cooking temperatures for meats, poultry, and other foods.
How Long is Too Long in the Danger Zone?
Generally, cut-off time for foods in the danger zone, after which they are considered hopelessly adulterated and cannot be used, is four hours. This period is cumulative, however.
This means that each time period during which food enters the danger zone is added to any other time period where the food is in the danger zone. If cold chicken, for example, is allowed to reach 50° F for ten minutes, is chilled back down, and then is allowed to warm up again for 30 minutes, it has spent 40 minutes in the danger zone. Most well-run kitchens do not flirt with the temps like this, if at all possible.
Although certain foods like chicken, meat, fish, and dairy are especially hospitable environments for dangerous pathogens, all foods must be kept at proper temperatures. It is easy for a busy kitchen to make mistakes in this area.
For example, soups might be transferred from a large pot to a steam-table to keep warm. What if a cook allows the soup to cool down in the pot, dipping into the danger zone, and then pours lukewarm soup into a hotel pan on a steam table? Steam tables are meant to keep warm food warm, not to heat cold foods up. The result, then, could be soup that inadvertently stays below 140 even though it was judiciously placed in a steam table. So, foods should be properly heated up before being transferred.
It would stand to reason that the same kind of thing goes for cold foods. You don’t place warm chicken on ice, you place ice cold chicken on ice.