FAO’s New Clostridia Review Puts Leftover Cooling Back in Focus

Food safety does not end when a roast, stew or tray of poultry comes out of the oven. A new FAO review of toxigenic Clostridia puts that everyday point back in focus: some foodborne bacteria form spores that can survive harsh conditions, including cooking, pasteurisation and certain sanitising processes.

The review covers Clostridium botulinum, other botulinum-neurotoxin-producing species, Clostridium perfringens and Clostridioides difficile. FAO describes these organisms as important human pathogens found across food and environmental settings. Their dormant spores can persist in farms and processing environments before reaching food, which is why food safety depends on several controls working together rather than on one cooking step.

Why the announcement matters in a home kitchen

For most cooks, the useful takeaway is not that normal cooking is ineffective. Proper cooking remains essential. The more specific lesson is that cooked food can become risky when it spends too long warm, cools too slowly or is handled as one very large batch.

This is particularly relevant to foods prepared in quantity. The USDA Food Safety and Inspection Service identifies meats, meat products and gravy among foods associated with C. perfringens, a bacterium often linked to food held for long periods at unsafe temperatures. A large pot of chilli, a deep casserole or a full roasting pan can retain heat in the centre while the surface appears ready to refrigerate. That delay creates a control problem even though the food was cooked thoroughly.

The practical routine for large meals

Cook with a thermometer. Use a clean food thermometer to verify the relevant safe internal temperature for the food you are preparing. Colour, texture and elapsed cooking time are not reliable substitutes for measuring the centre of the thickest portion.
Keep hot food properly hot. If a dish will be served over time, keep it at or above 140°F (60°C), the hot-holding temperature listed by FSIS. Stir thick foods when appropriate so that heat is distributed, and do not rely on a switched-off oven or a cooling burner to hold a safe temperature.
Start cooling promptly. Perishable food should not sit at room temperature for more than two hours, or more than one hour when the surrounding temperature is above 90°F (32°C). This includes food waiting on a buffet, picnic table or kitchen counter.
Split large portions. Transfer soups, stews, sauces and casseroles into several clean, shallow containers instead of placing one deep, steaming pot in the refrigerator. Smaller portions cool faster and more evenly. A large roast or ham can also be divided into smaller pieces before chilling.
Reheat only what you need. Refrigerated leftovers should be reheated to 165°F (74°C). Check dense foods in more than one place, especially after microwave heating, because cold spots can remain. Keep the remainder chilled rather than repeatedly warming and cooling the whole container.

These steps are consistent with the USDA’s consumer guidance on cleaning, separating, cooking and chilling food. They are not a special treatment for one organism; they are a repeatable routine that reduces opportunities for several foodborne hazards to multiply.

What the FAO review does—and does not—say

The FAO announcement is a scientific review, not a household recipe or a new cooking-temperature chart. It does not say that every food containing spores is unsafe, nor does it replace national food-safety instructions. Its contribution is to explain why spores deserve attention in food-control systems and why prevention may require monitoring, sanitation, process controls and rapid intervention across the food chain.

That distinction matters at home. A cook should not respond by adding arbitrary cooking time, using stronger household chemicals or tasting food to decide whether it is safe. Harmful bacteria and toxins cannot be reliably detected by smell, taste or appearance. When a perishable dish has been left out too long, the safe decision is to discard it rather than attempt to rescue it by reheating.

The bottom line

FAO’s review makes a familiar kitchen habit more consequential: treat cooling and holding as part of cooking. For batch meals, plan the storage step before turning on the hob, keep a thermometer available, use shallow containers and label leftovers so they are used within the recommended storage window. Good cooking kills many hazards, but safe food also depends on what happens during the next two hours.