Rice: The Silent Killer in Your Fridge
Think that leftover rice from last night’s dinner is harmless? Think again. Uncooked rice can contain spores of Bacillus cereus, a bacterium that can cause two different types of food poisoning. It results from consuming a toxin produced by the bacteria while they’re growing in your food and has a short incubation time of 1-5 hours. It results from a toxin that is produced in your small intestine as the bacteria grow there and has a longer incubation time of 6-15 hours.
If a raw food is contaminated with B. cereus (as much rice is) and then cooked, some spores will remain in the cooked product (unless you’re in the habit of heating your rice to above 120 ˚C for extended periods of time). These spores, If left standing in temperatures between 10 ˚C and 50 ˚C, such as on your stove or countertop, find themselves in their ideal environment (wet and warm) to germinate, grow and produce the toxin that will make you sick.
Cooked Mushrooms: The 24-Hour Rule
As a rule of thumb, cooked mushrooms should not be left out for more than two hours after cooking to prevent contact with foodborne illnesses, per Chew the World. Cooked mushrooms need to be consumed within a day and should be reheated to a temperature of at least 165 F to kill off any potential lingering pathogens (via Valuable Kitchen). If you run past the 24-hour deadline, prioritize your safety and toss the mushrooms.
This is because drying removes the moisture bacteria need to thrive, while freezing makes an inhospitable environment for the bacteria to grow. If you’re looking for the maximum storage life on your sautéed mushrooms, we recommend preparing, freezing, and thawing air-tight portions as needed.
Salad Greens: The Bacterial Breeding Ground
When you think about foodborne illness, salad greens are likely one of the first foods to come to mind. Per the Canadian Broadcast Coalition, listeria and E. coli are common pathogens for salad greens because of the growing environment — near the ground with exposure to potentially contaminated manure. Salads can be safely left out at room temperature for about two hours — or one hour if the temperature is above 90 degrees Fahrenheit.
Harmful bacteria can multiply rapidly in cut produce, including salad greens, that have been left out at room temperature for extended periods. However, eating old, slimy, or foul-smelling lettuce can lead to adverse health effects (via Livestrong). If your lettuce has gone bad and you decide to eat it, you may be putting yourself at risk for gastrointestinal upset.
Seafood: The Pathogen Paradise
Fresh or raw seafood can be dangerous if left at room temperature for too long, so reheating leftover grilled salmon or tilapia may not always be the best call. Reheating might not kill off any remaining pathogens that can cause foodborne illness (via the FDA). The FDA also notes that fish and seafood should never be left unrefrigerated for longer than two hours, and the fridge needs to be 40 F or colder.
It is best used within 2 to 3 days to ensure optimal taste and freshness. Leftovers that have surpassed the recommended 3 to 4-day storage in the fridge should be discarded to prevent foodborne illnesses. Shellfish and fish are delicate, as these can harbor many pathogens or toxins like histamine that could make you sick.
Cooked Spinach: The Nitrate Nightmare
Cooked spinach is an example of a food that can become toxic when reheated. Spinach is a vegetable rich in naturally-occurring nitrates; these are different than the nitrates found in processed meats and other preserved foods. Foods with these natural nitrates can be beneficial to the body in reducing the risk of developing chronic illnesses and cancers, per WebMD.
Cooking and reheating spinach into a watery mess can concentrate the nitrates (converted to nitrite by stomach acid) in a small portion (via JHSSS). Consuming more than 100 milligrams of nitrites a day can increase the risk of cancer, pregnancy complications, and blue baby syndromes in infants. Populations especially at risk for nitrite consumption include those who are pregnant or thinking about becoming pregnant, older adults, and infants.
Foil-Wrapped Potatoes: The Botulism Bomb
Baked potatoes wrapped in foil are a popular and easy side. But potatoes can contain spores of Clostridium botulinum bacteria. These spores can survive oven temperatures. In the right conditions, like when foil locks out oxygen, these bacteria can grow and make the deadly toxin that causes botulism.
Paralysis and breathing problems usually begin 18-36 hours after eating food contaminated with these toxins. If you roast potatoes in foil, make sure to eat them or put them in the refrigerator within 2 hours.
Egg Salad: The Mayonnaise Minefield
According to FoodSafety.gov, if it has been properly stored, it is safe to eat the salad within three to four days. This rule also applies to similar mayonnaise-based salads like chicken, tuna, ham, and macaroni salads. Once you’ve made the egg salad, remember the two-hour rule: Throw out any leftovers that have sat out at room temperature for more than two hours.
Freezing egg salad is not recommended. The texture will change and the mayonnaise can separate and become watery. Eggs are another higher risk food, as they could transmit the bacterium Salmonella.
Milk-Based Dishes: The Bacterial Battleground
While refrigeration slows the growth of most bacteria, it’s important to keep in mind that certain microbes like Listeria monocytogenes can still grow in refrigerated temperatures. Bacteria thrive between 40°F (4°C) and 140°F (60°C). This temperature range is known as the “danger zone” (1). To keep foods out of the danger zone, refrigerate or freeze leftovers within 2 hours.
The diarrhoeal form has been linked with foodstuff like soups, meat, vegetables and milk products including formula. More than a third of Americans have too-warm refrigerators. This can lead to bacteria growth.
Reheated Rice and Pasta: The Double-Danger Zone
Bacillus cereus: Uncooked pasta or rice may contain spores of a bacteria called Bacillus cereus. Spores are tiny protective capsules that allow the bacteria to hibernate until they are ready to grow. These spores can survive at high temperatures, so cooking won’t kill them. After the rice is cooked and cools to room temperature, the bacteria “wake up” and start to grow.
The longer you leave cooked rice or pasta out, the more likely it is to have these bacteria and their toxins. If you eat the contaminated food, you’ll start to throw up or have diarrhea within a few hours. Eat the leftovers within 1 day. When you reheat it, check that all the rice is steaming. Don’t reheat it again: If you have any left when you’re finished, throw it out.
Leftover Meats: The Clostridium Trap
Clostridium perfringens: These bacteria are closely related to the germs that can contaminate baked potatoes, but Clostridium perfringens prefers leftover meat. Bacteria grow fastest at 40 to 140 F, or anywhere between the temperature of your refrigerator and a hot cup of tea. Always cook meat, especially large batches of it, to a safe temperature.
Leftovers can be kept in the refrigerator for 3 to 4 days or frozen for 3 to 4 months. Although safe indefinitely, frozen leftovers can lose moisture and flavor when stored for longer times in the freezer. You can’t see, smell, or taste the bacteria that can make you sick. To protect against food poisoning, toss out food after 3 to 4 days in the fridge or move it to the freezer.
Cookie Dough: The Frozen Fraud
Salmonella: You might have heard that you shouldn’t taste raw cookie dough. That’s because egg and flour can carry Salmonella bacteria. But what about the frozen cookie dough left over from last Christmas? Unfortunately, freezing does not kill bacteria. So frozen cookie dough still might carry Salmonella.
This type of bacteria can cause nausea, diarrhea, and fever within hours or days. Luckily, it’s easy to remove this type of bacteria from leftover cookie dough: refrigerate right away and before enjoying, simply cook or reheat. While freezing can slow the growth of bacteria, it doesn’t kill them. When you thaw leftovers, the bacteria may start growing again and make you sick.
Conclusion: Your Kitchen Safety Net
Hospitalizations, deaths from contaminated food doubled in 2024 as recalls from Salmonella, Listeria and E. coli increased by 41%; 98% of all illnesses linked to just 13 outbreaks, ranging from cucumbers to deli meat These numbers aren’t just statistics—they’re real families facing real consequences from something as simple as leftover rice or spinach. If you’re ever unsure, it’s safest to toss leftovers within 3 days.
The truth is, most of us have probably eaten these dangerous leftovers multiple times without getting sick. Then again, food poisoning with B. cereus is often confused with the 24-hour flu, so I may have already paid for my mistakes without even knowing it. Did you expect that your midnight rice snack was potentially more dangerous than that sketchy gas station sushi?
