You know that leaving leftover pizza on the kitchen table overnight and then eating it the next morning probably isn’t the safest bet. So it should hold true that the reverse—immediately putting piping hot leftovers in the fridge—is the better way to go…right?
Sounds good in theory, but sticking steaming, just-cooked meals right into the fridge raises its own set of questions. Namely, does it mess with the food’s ability to cool down properly? And can it warm up the leftovers already in the fridge to the point that they’re no longer safe to eat? SELF connected with a few food safety experts to find out.
There are some solid reasons to keep your leftovers cold.
Before we get into the safest way to refrigerate your meal, let’s take a step back to talk about why it matters: Cooling leftovers properly “is a really important component of food safety,” Nicole Richard, MS, a food safety research associate at the University of Rhode Island and the chair of the RI Food Safety Task Force, tells SELF.
Doing so limits the amount of time your dish hangs out in the “danger zone,” or that temperature limbo between 40 and 140 degrees Fahrenheit in which pathogenic bacteria—bugs that can cause disease—flourish. When you’re dealing with cooling food, the main threat comes from two specific species, Clostridium perfringens and Bacillus cereus, Donald Schaffner, PhD, chair of the Rutgers University Department of Food Science, tells SELF.
Those bugs are different from notorious food-poisoning players like salmonella and E. coli, which are killed by thorough cooking. C. perfringens and B. cereus, on the other hand, can form heat-stable spores capable of surviving high temperatures, meaning they can lurk even in properly cooked meals, according to Dr. Schaffner. These bacteria can multiply if the food hangs out in the danger zone for too long and can make you sick, Dr. Schaffner says. The result? Gnarly food poisoning symptoms like vomiting and diarrhea.
Some foods are higher-risk than others, according to Dr. Schaffner. These include meat and poultry (associated with C. perfringens) and grain products like rice and pasta (linked to B. cereus). So if your leftovers include steak, spaghetti, or paella, for example, it’s even more crucial you cool them properly.
So does this mean sticking leftovers in the fridge ASAP is your best bet?
Not necessarily. Proper cooling is crucial to preventing food poisoning, but you can take some time to refrigerate your leftovers—just not too long. Food should be just fine to sit out for up to two hours, says Dr. Schaffner.
In fact, it’s probably best practice not to refrigerate leftovers right away, he says. For one, it actually doesn’t speed the process along in any meaningful way. Hot food will actually cool almost as fast on the counter as it will in the fridge, Dr. Schaffner says, because the difference between the temperature of the food and that of the room is “not that much bigger.”