Reheating leftover rice until it steams will kill most active bacteria, but it does not undo the main risk. If cooked rice sat warm for too long, a common soil bacterium called Bacillus cereus may already have made a toxin that survives boiling, frying and microwaving. The fix happens before the rice ever goes in the fridge: cool it quickly, refrigerate it promptly, and keep the fridge cold.
Why rice is the usual suspect
Bacillus cereus lives in soil and dust and forms tough spores that ride along on raw grains and survive normal cooking. Once rice is cooked and left warm, the spores can wake up and multiply. A 2021 review on Bacillus cereus and rice notes that around 95% of cases of the vomiting form of this illness have been linked to rice, often from large batches boiled ahead and held unrefrigerated for hours before being fried or reheated. The bacteria can grow anywhere from about 4 to 48 degrees Celsius (roughly 39 to 118 degrees Fahrenheit), which covers a kitchen counter and a fridge that runs warm. Pasta and other starchy dishes can do the same. An analysis of 3,654 food samples from suspected outbreaks, cited in a review of Bacillus cereus toxins, also found the vomiting-type strains in vegetables, sauces, soups, salads, and milk and meat products.
A ring-shaped peptide toxin that shrugs off heat
The vomiting toxin is called cereulide. It is a small ring-shaped peptide, a cyclic depsipeptide in which amino acids alternate with related building blocks called hydroxy acids, linked partly by peptide bonds and partly by ester bonds. That compact ring is what makes it so hard to destroy. The toxins review describes cereulide as extremely stable against heat, acid and digestive enzymes: it does not lose activity even after two hours at 121 degrees Celsius, well above boiling, and stomach enzymes such as pepsin and trypsin do not break it down.
That is why the usual advice to “heat it until it is piping hot” works for many leftovers but not for this one. Heat can kill the bacteria, but once cereulide is in the food it stays. The same review says symptoms, mainly nausea and vomiting, can start as soon as half an hour after eating and usually pass within 6 to 24 hours.
When it is more than an upset stomach
Most cases are short and miserable rather than dangerous, but severe ones happen. Doctors in Graz, Austria, described five healthy young adults who became ill after eating fried rice balls. The cook had made them from rice boiled three days earlier and kept in a refrigerator running at 8 to 9 degrees Celsius, about 46 to 48 degrees Fahrenheit. He developed acute liver failure and kidney injury and needed intensive care, and the leftover rice ball held one of the highest cereulide levels ever reported in an outbreak. The report, funded by the Austrian Science Fund, is a small case series, but its details are a useful warning about warm fridges and multi-day rice.
Cereulide also made news in 2026 when it was detected in infant formula from several manufacturers, leading to precautionary recalls in a number of countries and a rapid risk assessment by the European Food Safety Authority.
Habits that actually prevent it
- Refrigerate cooked rice within 2 hours, or within 1 hour on a day above 90 degrees Fahrenheit, which matches the FDA’s general rule for perishable food.
- Spread it out to cool. The FDA advises dividing large amounts of leftovers into shallow containers so they chill faster. A deep pot of rice can stay warm in the middle for a long time.
- Check your fridge temperature. An appliance thermometer should read 40 degrees Fahrenheit or below. The Austrian case shows what a fridge a few degrees too warm can allow.
- Do not count on reheating to rescue rice that sat out overnight or for an unknown time. When in doubt, throw it out.
- Get care for vomiting that will not stop, signs of dehydration, confusion, or yellowing of the skin or eyes, and mention what was eaten.
By The Everyday Brief · AI-assisted editorial. Drafted with AI research assistance; claims checked against the linked sources (fetched 2026-10-08 PT). Not medical advice.
Sources
- Dietrich R, Jessberger N, Ehling-Schulz M, Martlbauer E, Granum PE. The Food Poisoning Toxins of Bacillus cereus. Toxins, 2021 (PMC full text).
- Rodrigo D, Rosell CM, Martinez A. Risk of Bacillus cereus in Relation to Rice and Derivatives. Foods, 2021 (PMC full text).
- Schreiber N, Hackl G, Reisinger AC, et al. Acute Liver Failure after Ingestion of Fried Rice Balls: A Case Series of Bacillus cereus Food Poisonings. Toxins, 2021 (PMC full text).
- European Food Safety Authority. Rapid risk assessment on acute reference dose (ARfD) of cereulide in infants and information on acute consumption of infant formulae. EFSA Journal, 2026 (PMC full text).
- U.S. FDA: Safe Food Handling