A spore-forming bacterium that causes food poisoning, most famously from cooked rice left warm or cooled too slowly.
A spore-forming bacterium that causes food poisoning, most famously from cooked rice left warm or cooled too slowly. Bacillus cereus is a bacterium found naturally in soil and on many raw foods, particularly starchy staples like rice and pasta. It forms heat-resistant spores that survive cooking, then germinate and grow if the food is held in the temperature danger zone. It can cause two different types of illness. One is a vomiting type, with nausea and vomiting starting within one to five hours, caused by a heat-stable toxin that forms in the food itself, classically in cooked rice left standing warm. The other is a diarrhoeal type, with cramps and diarrhoea appearing 8 to 16 hours after eating. Both forms are usually mild and short-lived, resolving within a day, but they can be unpleasant and are largely preventable. The vomiting toxin is heat-stable, which means reheating rice does not make it safe once the toxin has formed. This is why Bacillus cereus is so strongly associated with cooked rice that has been left at room temperature, then reheated or fried the next day without having been chilled properly in the first place. The main control in Australian kitchens is to avoid holding cooked rice, pasta and similar starchy foods in the temperature danger zone. Rice should be served hot straight after cooking, kept hot at 60 degrees or above, or cooled quickly and refrigerated at 5 degrees or below. Spreading rice in shallow trays and getting it into the fridge promptly stops the spores from multiplying and producing toxin. Because the vomiting toxin survives reheating, cold-chain discipline matters more than a final blast of heat. Cooked rice should not be left out overnight or held warm for hours, and leftover rice should be chilled fast and used within a day or two. Fried rice made from properly cooled, refrigerated rice is much safer than fried rice made from rice that sat out at room temperature. A takeaway cooks a large pot of rice in the morning and leaves it covered on the bench all day to use for fried rice. The rice stays warm, and surviving spores grow and produce a heat-stable toxin. That evening the rice is flash-fried and served, but the quick fry does not destroy the toxin. Several customers vomit within a couple of hours. Cooling the rice quickly and refrigerating it would have prevented the toxin from forming.
Frequently asked questions
Why is Bacillus cereus linked to rice?
Rice commonly carries the spores, and cooked rice left warm or at room temperature lets them grow and produce a heat-stable toxin. Reheating does not destroy that toxin, so cooled rice held out is a classic source of illness.
How fast do symptoms start?
The vomiting type usually starts within one to five hours, while the diarrhoeal type appears 8 to 16 hours after eating. Both are generally mild and clear up within about a day.
Does reheating leftover rice make it safe?
Not always. Reheating kills the growing bacteria but the vomiting toxin is heat-stable and survives, so rice must be cooled and chilled quickly in the first place rather than relied on being made safe by reheating.
How should cooked rice be stored?
Serve it hot straight away, hold it at 60 degrees or above, or cool it quickly in shallow containers and refrigerate at 5 degrees or below. Use leftover rice within a day or two and do not leave it out overnight.
Which foods besides rice can be affected?
Pasta and other starchy foods, sauces, cooked vegetables and dairy can also be involved. Any cooked food held in the temperature danger zone can support Bacillus cereus growth.
