Adair P. Hoover,
Home & Garden Information Center
A common question at the Home & Garden Information Center relates to whether food that has been left out at room temperature for more than two hours can be recooked to kill any potentially harmful foodborne pathogens. The following situation is a good example:
A SC resident recently experienced a slow-cooker failure. She was cooking a 4 pound pork roast in a crockpot, overnight, for the guests she was having the following evening. She turned the crockpot on low and went to sleep. When she woke the next morning she discovered that the electrical outlet to which the crockpot was connected had shorted out during the night and she estimated that the pork had been without heat for at least 4 hours. She wondered if it would be OK to go ahead and cook the pork at a high temperature for 8 more hours. She figured that cooking it at a high temperature for that long period time would kill any bad stuff that might be present.
The HGIC recommendation was that she throw away the meat and start over.
She persisted however, not wanting to waste her expensive meat. She wanted to know exactly why this was the recommendation. Seemingly, most pathogens can be killed at high temperatures, so why waste the meat?
It is true that many common foodborne pathogens are destroyed by cooking at high temperatures. That is why there are USDA recommendations for the temperatures at which foods should be cooked. What many people don’t realize though, is that some pathogens are heat stable. That means that they won’t necessarily be destroyed at a high temperature. Two of these dangerous pathogens are the bacteria Bacillus cereus and Staphylococcus aureus.
Bacillus cereus is a spore-forming microorganism. It is heat resistant when in the spore form and therefore is very hard, if not impossible to destroy during regular cooking processes. Favorable conditions for this spore to develop are in foods that are heated slightly and then temperature abused. One type of temperature abuse is allowing foods to sit at temperatures between 41°F and 135°F for more than 2 hours, which exactly describes the crockpot situation.
Staphylococcus aureus food intoxication is one of the most common foodborne illnesses in the US. When the microorganism is present in potentially hazardous foods (like the pork roast), it will multiply rapidly and produce an enterotoxin. The microorganism is readily destroyed under adequate cooking conditions. However, once formed in food the enterotoxin is heat resistant and is not inactivated by cooking. A typical scenario for which staph contamination occurs is when food has been handled by a person, followed by temperature abuse which allows incubation and growth of the microorganism. Again this is a perfect opportunity for our South Carolina resident’s pork to become unsafe.
The bottom line is that when food is left in the temperature danger zone (41° – 135°F) for more than 2 hours there is a real risk of contamination which can lead to a nasty case of gastrointestinal illness involving vomiting and diarrhea. So, when in doubt, throw it out!
Page maintained by: Home & Garden Information Center
This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.