It's 100 degrees Fahrenheit (37 degrees Celsius) in the shade and, after a long afternoon spent mowing the lawn, James is ready to eat. He doesn't want to turn on the oven and heat up the kitchen, so he rummages through the refrigerator, spying some Chinese leftovers that will suffice. As he eats forkfuls of cold rice, James isn't worried about his health. In fact, the way he sees it, eating cold rice is probably a good way to cool down. But is there danger lurking in that takeout container?
A casual Google search will unlock a treasure trove of cautionary tales about cold rice. According to a number of forums and message boards, ingesting cold rice could cause a variety of problems. Some people relate tales of vague digestive issues, while others warn of death. It's just rice. Right?
Turns out, there's a grain of truth to the rumors. The trouble starts with the rice itself, long before it's cooked. Raw rice can contain a bacterium known as Bacillus cereus, which originates in soil and has spores that can survive even when rice is fully cooked. When cooked rice is left at room temperature, Bacillus cereus spores can develop into full-blown bacteria that produce toxic byproducts. One of these toxic byproducts can cause nausea and vomiting for up to six hours, while the other toxic byproduct results in abdominal pain and diarrhea that persist for up to 15 hours. Both types of symptoms are classified as food poisoning; they usually subside within 24 hours [source: Foodsafety.gov]. In many cases, the ailments caused by Bacillus cereus are mild. However, these symptoms can become deadly for the young, old and immunocompromised (anyone with a weak immune system).
When you eat rice that's been left unrefrigerated for too long or that hasn't been thoroughly reheated, it's possible you'll ingest Bacillus cereus. The longer the rice is left at room temperature, the more time bacteria spores have to grow — and the greater the risk that the rice will make you sick.
Cooked rice should be eaten almost immediately, and leftovers should be cooled within an hour after they're served. Cooked rice should be stored in the refrigerator and then eaten within one day, but only after it's been reheated thoroughly. If you do ingest the bacteria, it may not make you sick right away because it can lurk in your body for up to 16 hours before symptoms develop [source: NHS]. But when that happens, you'll certainly know it.
- Foodsafety.gov. "Bacillus cereus." (Aug. 6, 2018) https://www.foodsafety.gov/poisoning/causes/bacteriaviruses/bcereus/index.html
- National Health Service (NHS). "Can Reheating Rice Cause Food Poisoning?" Sept. 6, 2015. (June 15, 2015) http://www.nhs.uk/chq/Pages/can-reheating-rice-cause-food-poisoning.aspx?CategoryID=51