Questions on handling, preparing, and storing food in ways that prevent foodborne illness.


The food safety branch of food science is about mitigating or eliminating the risk of food-related illness, specifically illness caused by foodborne pathogens ("food poisoning") including bacteria and mold (fungi).

Rancidity and decomposition are other types of food spoilage which are not necessarily caused by pathogens but often discussed within this tag.

Dietary needs are not a component of food safety. If you have concerns about the overall "healthiness" of a food or technique, please consult with your doctor or dietitian; we are not qualified to provide nutritional advice.


The top 5 things you need to know about food safety are:

  1. When in doubt, throw it out. You cannot see or smell bacterial contamination. Mold that appears to be growing only on the surface may grow invisible roots into softer foods. Do not rely on a visual inspection or "smell test" to tell you whether or not a food is safe.

  2. Raw or perishable food that stays in the temperature "danger zone" for more than 2 hours should be discarded. The danger zone is 40-140° F or 4-60° C. Keep cooked food hot until ready to eat, then refrigerate immediately. Separating large items into smaller containers will help them to cool more quickly.

  3. Follow the cooking time and temperature guidelines set out by your local regulatory agency. For Americans this is the FDA and USDA. Before you ask a food safety question, please check the USDA Fact Sheet to see if your question is answered there. Failure to follow these guidelines (or your local regulatory equivalent) is irresponsible if you are serving guests and likely to be illegal if you are serving customers, as many local health codes are based on the FDA Model Food Code. You have the right to take risks on yourself, but please do not risk the safety of others and please do not ask us for an excuse to do so.

  4. Bacteria leave behind harmful protein toxins that cannot be "killed" (denatured) by cooking. The cooking times/temperatures are only effective against live organisms, not their toxic waste products. Spoiled food cannot be cooked back to safety and must be discarded.

  5. Cooking is pasteurization, not sterilization. Pasteurization means killing most microbes, so as to render the food safe for human consumption. This resets the clock but does not stop it; cooked food can and will still spoil after 2 hours in the danger zone. Sterilization methods (e.g. high-pressure canning and irradiation) are the only safe methods for longer-term room-temperature storage.


  • Always cook food to the recommended time and temperature.
  • Avoid cross-contamination by using separate utensils and cooking/storage vessels for raw vs. cooked food.
  • Wash your hands and sanitize your work areas after handling raw foods.
  • Defrost frozen foods in the fridge or under cold running water.
  • Use a thermometer, appearance/colour is not a reliable indicator of doneness.
  • If you suspect spoilage or contamination, please, throw it out.

The most asked question: I left this out... is it still safe?

See rule number 2 above: The general guideline for perishable foods is that you want them to be in the danger zone (40-140°F, 4-60°C) for no more than 2 hours (1 hour on a hot day).

If you can ensure uninterrupted heating above 60 Celsius, the life time is not limited food-safety-wise, but there are practical limits due to reduced palatability. For storage time at temperatures below the "danger zone", see databases of standard storage times, for example Still Tasty.

The time in the danger zone is cumulative. So it includes time bringing the food home from the grocery store, time before cooking, time after cooking, and so on. The reason is that while cooking may destroy bacteria or other pathogens, it doesn't always destroy the toxins that they have produced.

So in general, regarding perishable foods like meat, dairy, eggs, cooked casseroles, and so on: if the food (or its perishable components) have been at room temperature for more than two hours, you should discard that food.

Helpful Resources

Further Reading/Frequently Asked