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Is it safe to reheat food more than once?

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#1 shelendra


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Posted 18 July 2010 - 01:41 PM

Dear All,

Why its restricted to reheat the food only once ?

As my understanding is if you cool the food completely/safely than while reheating ill be killing all the bacteria and spore germinated to bacteria than if I cool it again safely than if again i ll reheat it ll kill more bacteria it means more safer food . Other quality what is the food safety issue here ?

Thanks in advance

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#2 GMO


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Posted 19 July 2010 - 10:52 AM

I'm no microbiologist but I'll explain it as I see it.

Three reasons; you're unlikely to kill all vegetative bacteria, just reduce their levels, however, the main issues are spore formers would not be killed by most reheating activities as they require high temperature / time combinations, e.g. from memory clostridium botulinum needs >90 degrees for more than 10 minutes (or equivalent)! Not temperature / time combos which are often reached in a microwave. Also there are heat stable toxins and even combinations of spore formers and toxin formers.

Imagine reheating rice for example. You cook it for the first time. b. cereus will be present to some degree and once cooked very happy to grow as the Aw will have increased. So during the cooling time, b. cereus is growing and producing toxin but if it's quick there will be few bacteria there and very little toxin. Then you reheat. During the reheat it gets a second shot at it and then when it gets too hot the vegetative bacteria form into spores to protect from the heat and the toxin also survives, then it gets another shot at growing when the rice is cooled again as the spores germinate. The added benefit for the bacterium is that the other vegetative bacteria if any are present are killed off by the reheating so it then has no competition! You can see how reheating it repeatedly will just make the situation worse.

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#3 Charles.C


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Posted 20 July 2010 - 05:14 AM

Dear Shelendra,

I think GMO gave an appropriate reply ( :thumbup: ) however if you would like to see an expanded version with some official links included, can try this rather nice discussion -


Rgds / Charles.C

BTW, Welcome to the forum ! :welcome:

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