Leftovers stored in the refrigerator are often eaten at the next meal. But food that smells and looks normal is not necessarily safe, because some bacteria, viruses and parasites that cause food poisoning may not noticeably change a dish's smell, taste or appearance.
EatingWell, a U.S. health and food outlet, recently outlined the main warning signs that leftovers have spoiled, drawing on advice from food safety experts, according to medical sources on the 7th.
An Unusual Smell May Signal Microbial Growth
Food taken out of the refrigerator that gives off a sour or unpleasant smell different from usual is best left uneaten. Krizzela Pascua, a food safety expert, said that as bacteria or mold break down the proteins, fats and carbohydrates in food, they can produce compounds that create an off odor.
Even if a dish was cooked recently, it is safer not to eat it if a strong, unfamiliar smell is noticeable when the container is opened. That said, the absence of an odor does not guarantee that food is safe.
Avoid Food That Turns Slimy or Grows Mold
If the surface texture becomes unusually slick or sticky, microbes may have multiplied. Such changes can appear in meat and processed meat, including cooked chicken, fish and ham.
Visible mold also calls for caution. In soft, high-moisture foods in particular, mold may reach deeper than the part that is visible. With these foods, it is safer to discard the whole portion rather than cut away only the moldy section.
A Bulging Container Suggests Gas Inside
If a sealed container looks more swollen than usual or the lid has lifted, it is best not to eat the contents. Microbes growing in the food may have produced gas, raising the pressure inside the container.
Bubbles forming on the surface where there were none before can also be a warning sign. If a container is expanding and bubbles appear at the same time, the safer choice is to throw the food out.
Do Not Judge by Color Alone
A change in color does not always mean food has spoiled. Oxidation or enzyme activity can naturally alter color during storage.
Still, if stains or unexpected color changes appear that were not there before, and the smell or texture has changed as well, the food is best avoided.
Experts stress that how food was stored matters as much as these visible changes, since pathogens that cause food poisoning can be present even in food that looks intact and has no odor.
According to the U.S. Department of Agriculture (USDA) and the Centers for Disease Control and Prevention (CDC), cooked or perishable foods should not be left at room temperature for more than two hours. When the surrounding temperature exceeds about 32 degrees Celsius, refrigeration within one hour is recommended. Refrigerators should be kept at or below 4 degrees Celsius.
Dividing leftovers into wide, shallow containers helps bring the internal temperature down faster. The USDA recommends eating most cooked leftovers within three to four days when refrigerated, and reheating them until the center reaches at least about 74 degrees Celsius.
Writing the date on the container is another way to avoid confusion over when the food was cooked. Vanessa Coffman, a doctor who works with Stop Foodborne Illness, a U.S. nonprofit focused on food safety, advised that labeling the cooking date makes it easier to track how long leftovers have been stored.
