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Ever made a succulent pork roast, had a wonderful meal with family or friends, then sat down for a favorite television show and realized three hours later that the leftover cooked roast is still sitting on the kitchen counter? Food left in temperatures between 40° and 140°F, the danger zone, for more than two hours should be disposed of. Unfortunately, that wonderful pork roast had the opportunity to grow harmful bacteria that could leave a person sick for days, weeks, or even months if consumed. Looking at the roast, there is no visible signs of "danger." Pathogens are microorganisms that cause infection and unlike mold, or other forms of spoilage, are not physically visible, can't be tasted, or have an off smell. In most cases of food poisoning, the bacterium that causes sickness isn't visible without a microscope. Just because you can't see it, smell it, or taste it, doesn't mean the harmful bacteria isn't present.

Why can't I just reheat the pork roast?

"The pork roast was only out three hours, I'll just reheat it, refrigerate it, and I won't get sick." Unfortunately after the roast sat in the danger zone for those three hours it had the opportunity to produce toxins and spore forming bacteria that could be heat resistant. In other words, no matter how hot you cook that roast heat isn't going to kill the pathogens.

When perishable foods such as meat, poultry, fish, prepared fruits and vegetables, dairy products, and cooked leftovers are when left in the danger zone for over two hours, they deteriorate rapidly and are more likely to grow harmful bacteria. Bacteria doubles in as little as 20 minutes when left in the danger zone. In optimal conditions, it only takes 5 hours for bacteria to go from one to one million. Keeping perishable food out of the danger zone is essential for preventing foodborne illness. Additionally, cooling, freezing, and drying are additional ways to stop or slow down bacterial growth.

What happens to bacteria when heated, placed in the refrigerator, and frozen?

  • Putting food in the refrigerator slows down the growth of bacteria.
  • Freezing stops bacteria from growing or inactivates it, but if harmful bacteria was already present prior to freezing this won't kill the pathogens. In other words, shoving the pork roast in the freezer after it was in the danger zone for three hours won't prevent illness. Once thawed, bacterial growth resumes.
  • Heating food to its corresponding safe minimum temperature destroys bacteria.

Not just temperature and time plays a key role in bacterial growth, but the type of food, acidity, oxygen present, and moisture can all effect how fast harmful bacteria can grow.

Quick tips for keeping food out of the danger zone:

  • Keep hot foods hot (at or above 140°F) and cold foods cold (at or below 40°F). Use a food thermometer to test temperatures frequently. Keep hot food in warming trays, in the oven at low heat, or slow cookers and keep cold foods cold by putting them on ice. Use a food thermometer to ensure food is at minimum internal temperatures. Additionally, when roasting meat and poultry, keep the oven at 325°F or higher.
  • Regularly check temperatures of refrigerator and freezer. Do not count on the built-in refrigerator thermostat to ensure food is staying below 40°F. Keep freestanding refrigerator/freezer thermometers in the center of the cooler for easy temperature monitoring.
  • Refrigerate leftovers in shallow containers and reheat to an internal temperature of 165°F. Avoid giving bacteria the opportunity to reproduce by cooling food quickly in the refrigerator. Separating food into shallow containers help food cool down faster in a shorter period of time.

September is Food Safety Education Month. Celebrate all year round by keeping food out of the danger zone, and practicing food safe techniques such as using a food thermometer, checking refrigerator and freezer temperatures, and cooling leftovers properly. More information on minimum internal temperatures, foodborne illnesses, and prevention can be found at foodsafety.gov.