Food Poisoning Alert: High-Risk Leftovers You Should Never Keep Too Long

If you are planning a takeaway meal this evening, you might already be anticipating tomorrow's leftovers. However, as tempting as cold pizza can be, there is a significant risk of food poisoning if you are not cautious. This warning comes from Dr Primrose Freestone, a microbiologist at the University of Leicester, who has identified surprising leftovers that are 'high risk' when kept in your refrigerator. Alongside cold pizza, the scientist advises caution with risotto, burritos, and fried rice. Additionally, if you have half a tin of baked beans lingering, this could also expose you to food poisoning, the expert cautions.

Understanding Food Poisoning Risks

'Food poisoning is caused by consuming food that has become contaminated with pathogenic bacteria, fungi, or viruses,' Dr Freestone explained in an article for The Conversation. 'Although most people recognise that food poisoning can result from poorly cooked foods or risky food preparation habits, improperly stored leftovers are also a major cause. It is therefore extremely important to take care when storing leftovers to avoid harming your health.'

1. Leftover Pizza

While cooked pizza might appear harmless, it can lead to food poisoning in several ways, including through dried herbs and spices. 'Surprisingly, the dried herbs and spices that people often sprinkle on their pizzas, such as basil, pepper, and oregano, can be susceptible to microbial contamination,' Dr Freestone noted. 'This contamination can occur during harvesting and production phases, or due to improper storage by consumers. Some foodborne pathogens that can survive on dried herbs include bacteria like Salmonella, Bacillus cereus, and Clostridium perfringens, which cause food poisoning.'

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Even if these dried herbs are sterilised by the heat of a freshly baked pizza, leaving the pizza at room temperature for too long after cooking allows these toppings to become a perfect breeding ground for harmful germs. According to the expert, leftover pizza must be refrigerated within two hours of delivery. 'If the pizza is left at room temperature for more than a few hours, germs will multiply rapidly, making it unsafe to eat the next day, regardless of how appetising it looks or smells,' Dr Freestone warned.

To prevent contamination from airborne germs, ensure you cover your pizza before refrigerating it and consume it within two days.

2. Leftover Chicken

We are all aware of the dangers of eating raw chicken, but what about when it is cooked? Cooked chicken becomes 'highly perishable' once it cools down, due to its high water and nutrient content and low acidity, which promotes bacterial growth. 'To stay safe, once you have removed your cooked chicken from the oven or rotisserie packaging, any portion you do not plan to eat immediately should be covered and refrigerated as soon as possible after cooling,' Dr Freestone advised. 'Ideally, it should spend no more than two hours at room temperature.'

While leftover pizza should be eaten within two days, you have slightly more time with leftover chicken. 'Cooked chicken can be stored for up to three days in the refrigerator,' Dr Freestone stated. However, if you notice blood in any parts, do not eat it, whether cold or reheated. 'This indicates it has been undercooked and may be contaminated with germs,' the expert added.

3. Leftover Rice Dishes

Whether it is fried rice, risottos, or burritos, leftover rice dishes carry a significant risk of food poisoning. 'Uncooked rice can contain spores of Bacillus cereus, a common food poisoning bacteria that prefers starchy foods,' Dr Freestone explained. 'Although Bacillus cells are killed by cooking heat, their spores are heat-resistant and can survive. If a cooked rice dish is left at room temperature for more than two hours, the Bacillus spores have time to develop into bacteria and multiply. These spores can also release toxins into the cooked rice, potentially causing severe vomiting and diarrhoea lasting up to 24 hours.'

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If you wish to save any rice-based leftovers, the expert recommends covering them and refrigerating them promptly. Unfortunately, you do not have long to eat them safely. Dr Freestone added: 'Cooked rice can be eaten cold, but only if it has been cooled quickly after cooking and stored as soon as possible in the refrigerator. It is also best to consume cold cooked rice within 24 hours, as B cereus spores can germinate during longer storage periods.'

4. Leftover Canned Foods

Finally, be cautious with leftover canned foods. While it is acceptable to keep them in the original can, they must be covered and refrigerated to avoid contamination from airborne germs. How long they remain safe to eat depends on the food type. Highly acidic foods, such as canned tomatoes, can be stored for five to seven days, as the acid inhibits bacterial growth. However, low-acidity foods, including meats, fish, fruit, vegetables, and pasta, can only be stored for up to three days.

Dr Freestone concluded: 'Leftovers can be safe to eat cold. Just ensure you refrigerate them as quickly as possible after cooking and consume within a day or two.'

Essential Tips for Avoiding Food Poisoning

Keep a Clean Workspace: Germs can survive on various kitchen surfaces, so maintaining cleanliness in the cooking area and washing your hands is crucial.
Avoid Cross-Contamination: Raw meat, poultry, seafood, and eggs can spread germs to ready-to-eat foods if not kept separate. Use separate cutting boards and plates, and store them separately in the refrigerator.
Use a Thermometer: To cook food safely, the internal temperature must reach a level high enough to kill harmful germs. Use a food thermometer to ensure proper cooking, as temperatures vary by ingredient.
Store Food Properly: Perishable food should be refrigerated within two hours of purchase, and the refrigerator should be set below 40°F (5°C).
Do Not Rely Solely on Expiration Dates: Expiration dates are not the only indicator of food safety. If food has a strange smell or colour, it is better to discard it.
Do Not Thaw Frozen Food on the Counter: Thawing frozen foods on the counter allows bacteria to multiply quickly as outer parts reach room temperature. Thaw frozen foods in the refrigerator, in cold water, or in the microwave.