Food Safety

Do be careful with rice when reheated. Most rice contains a viral spore, cannot remember which one, that can withstand cooking. As a spore it activates when soaked by reproducing and doublng in numbers. But cooking at boiling point doesn’t kill it.

The practical upshot is that rice can be reheated once. But you are getting on dodgy ground if reheated twice. And very dodgy ground if it is reheated a third time.

As was explained by my food safety course when I was running a guest house.

Bacillus cereus. B. cereus is a bacterium rather than a virus.


Do not reheat rice more than once.

I should be dead long ago. As a student we fried and refried leftovers also rice all the time.

That site contains good information. I started already long ago cooling down the rice after use after reading about the bacteria. I love to wok Chinese fried rice from leftover rice straight out of the fridge and that sometimes up to five days after cooling the rice. Never had any trouble but I have a good fridge. The trick is to prevent bacteria growth or seriously slow it down.


I’m not a professional. I only cook at home, on my ‘home-shift’. I never heard of this villain bacillus.

I always had many rice variants stocked at home, for different plates. Now, I only have a stock of round-corn risotto rice from Italy and a long-corn rice from SE-Asia.

Is this bacillus in all rice, or only in some geographical provenances?

In a study 178 samples of raw rice from retail food stores were analyzed for the presence of B. cereus spores. Spores of Bacillus species were found in 94 (52.8%) of the rice samples with an average concentration of 32.6 CFU/g (3.6-460 CFU/g for B. cereus and 3.6-23 CFU/g for Bacillus thuringiensis).

There seems not to be a geographical link to certain rice producing areas. The rice seems to be contaminated in a random fashion. Most common illness is diarrhea which is normally speaking not a life threatening disease. There will be exceptions depending on the health condition of some consumers.

More information can be found here.

Healthy individuals usually recover from B. cereus illness within a day or two but patients who have other health issues might suffer serious complications. To control this bacterium in food, proper cooking and rapid cooling are required to prevent spores from germinating.

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And I thought my days of living dangerously were over when I stopped kayaking class V whitewater. Apparently not.


Maybe it’s a poor man’s version of eating fugu.

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Fugu, that is for the very brave especially the home made version…

CFU – Colony Forming Unit. Bureaucratese for a single live/active bacterium. Can only be determined by culturing them and counting the colonies.

The minimum B. cereus load to develop symptoms is about ten thousand per gram, which would represent four-and-change bacterial divisions from an initial load of 32 CFU/gram. I don’t know how fast it divides after coming out of the spore form, but some bacteria can divide every twenty minutes at 37C

EPIDEMIOLOGY : Worldwide Footnote2. Diseases cased by B. cereus are commonly found in places where there is improper food handling. Between 1973–1985, B. cereus caused 17.8% of the total bacterial food poisonings in Finland, 11.5% in the Netherlands, 0.8% in Scotland, 0.7% in England and Wales, 2.2% in Canada, 0.7% in Japan, and 15.0% (between 1960–1968) in Hungary Footnote10. As of 2008, 103 confirmed outbreak cases have been reported in the US Footnote11. In Norway, B. cereus was the most common microbe isolated from foodborne illnesses in 1990 Footnote10. [emphasis mine :wink: ]

The emetic [vomiting – d] type of food poisoning has been largely associated with the consumption of rice and pasta, while the diarrheal type is transmitted mostly by milk products, vegetables and meat. It forms spores and spreads easily

While B. cereus is associated mainly with food poisoning, it is being increasingly reported to be a cause of serious and potentially fatal non-gastrointestinal-tract infections. The pathogenicity of B. cereus , whether intestinal or nonintestinal, is intimately associated with the production of tissue-destructive exoenzymes. Among these secreted toxins are four hemolysins, three distinct phospholipases, an emesis-inducing toxin, and proteases. The major hurdle in evaluating B. cereus when isolated from a clinical specimen is overcoming its stigma as an insignificant contaminant. Outside its notoriety in association with food poisoning and severe eye infections, this bacterium has been incriminated in a multitude of other clinical conditions such as anthrax-like progressive pneumonia, fulminant sepsis, and devastating central nervous system infections, particularly in immunosuppressed individuals, intravenous drug abusers, and neonates [emphases mine – dgb]

That PMC article sheds a more sinister light on these bacteria! It is also widely distributed in nature, including soil, air, dust, water and various dairy products such as raw milk, long life pasteurized milk, yoghurt and infant powdered milk formulas apart from raw and cooked rice. I was unaware of the complexity of the problem and it put me to thinking I must say.

I donot know what the consequences are in poor Asian countries with insufficient cooling equipment like fridges. I have been in a number of these places and very often did I eat street food. The high heat wokking proces would kill all bugs was the theory. I never got sick though.

B. cereus is one of a group of seven closely related species. One of the other members of the group is Bacillus anthracis, so it’s not shocking that this one might have some sort of sting in its tail.

Wikipedia says it takes more than five minutes of wet heat at minimum 250F/121C or an hour of dry heat at same temps to kill the spores.

Yes, that are tough cookies, we got to nuke them…

Rice also contains arsenic.

Ok, I am done now with rice…

A diet that consist only of foods that can be cooked and then safely eaten after being left out at room temperature AND contain no arsenic… what would be left?

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Yep you might get sick from eating reheated rice but it won’t kill you. But it’s got a lot to do with the digestive tracts immune system. I got a bit of food poisoning in Thailand and the only thing the doctors in Thailand could trace it back to was the rice bacteria. They said it’s a foreigners disease as most people on a rice diet have built up immunities to the bacterium. I am not sure about that but I do know that after a few bouts of illness while working and traveling over many years it now seems I can eat almost anything with no ill effects. Women cooking some soup on a sidewalk, I’ll try some if it looks good. Mystery meat on a stick? As long as it is hot and I am hungry I’ll give it a try.

Re the arsenic, Consumer Reports recommends limiting your (adult) weekly intake to one and a quarter cups of dry sushi or white basmati rice from Pakistan, California or India; or half a cup of any other dry rice. That’s very roughly 250 grams and 100 grams respectively. Again very roughly, brown rice doubles and white rice triples in both volume and weight when cooked.

^^That would be a big surprise to my Lao neighbors.

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