The Library

Your Leftover Rice Is Probably Fine

The CDC's own estimate for deaths from this bacterium is zero a year. Zero. Hold that thought while we explain why leftover rice still deserves a fridge.

Raw rice carries spores of Bacillus cereus, and they survive boiling. Left sitting warm, they germinate, and some strains make cereulide — a small ring-shaped molecule stable from pH 2 to 11, untroubled by proteases, measured surviving more than two hours at 121°C.

That is the uncomfortable part. Reheating kills the bacteria and leaves the poison exactly where it was. You are not eating an infection that has to establish itself. You are eating a finished product, which is why symptoms can arrive in under half an hour.

Now the proportion. CDC foodborne illness estimates put B. cereus at roughly 63,000 US illnesses a year, about 20 hospitalizations, and zero predicted deaths. The viral version of this story is not supported by the numbers everyone is implicitly citing.

Severe cases exist and are genuinely severe. A 2022 Austrian case series describes a rice ball with 37 micrograms of cereulide per gram, several times prior reports; of five patients, one went into acute liver failure and four recovered without intensive care. That is not nothing. It is also not what happens when you eat Tuesday's rice on Wednesday.

The real advice is boring and complete: cool it fast, ideally within an hour, refrigerate, eat within 24 hours, reheat once.

One thing the panic always leaves out — cereulide is not a rice problem. Pasta and dairy do it too. Rice gets blamed because rice is what people leave in a warm pot, in bulk, for six hours.

Sources

  1. Food Standards Scotland, "Rice" — cool within 1 hour, eat within 24 hours, never reheat more than once.
  2. 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 2022;14(1):12.
  3. Scallan E, et al. Foodborne illness acquired in the United States — CDC pathogen estimates, Emerging Infectious Diseases 2011.
  4. Food Research Institute, University of Wisconsin — brief on cereulide stability (summarising Rajkovic et al., 2008).