Vol. XII · Food Safety Plate 9 of 12heat-stable toxins, Bacillus cereus, fried rice syndrome, Staphylococcus aureus, enterotoxin, histamine, scombroid, kidney beans, lectin, reheatingS

What Heat Cannot Undo.

Rice left warm overnight and reheated until piping hot can still make people vomit within hours. The bacteria are dead; their toxin is not.

Cooking kills growing bacteria, but some hazards are not bacteria. Bacillus cereus, whose spores survive the cooking of rice and pasta, makes an emetic toxin, cereulide, as it grows in starchy food left warm; cereulide survives frying and boiling, and causes vomiting within hours — the "fried rice syndrome". Staphylococcus aureus, from hands, makes an enterotoxin in foods handled and then kept warm (ham, cream fillings, salads); boiling does not destroy it. Histamine forms in fish such as tuna and mackerel kept warm after catching, and cooking, canning or freezing do not remove it (scombroid poisoning).

And some plant foods carry natural toxins that need proper cooking: raw or undercooked red kidney beans contain phytohaemagglutinin, which a few beans can make you ill with; boiling for at least ten minutes destroys it, while slow cookers that never reach the boil can make it worse. The rule for all of them is the same: prevent, do not rescue. The workshop leaves rice out.

Below: the count of B. cereus in cooked rice left at the temperature you choose against hours, with the level above which emetic toxin is likely marked (microbe bench, teaching threshold), and the hours until that level.

What you will learn

Name hazards that survive cooking.
Explain why reheating does not rescue spoiled food.
Handle cooked rice safely.
Cook dried kidney beans safely.

Workshop

Microbe bench: B. cereus growth from spores at 2 log per gram (common in raw rice) with the cardinal-temperature model; toxin is taken as likely above about 5 log per gram, a teaching threshold consistent with the counts reported in outbreaks (FDA Bad Bug Book).

Prevent, do not rescue

In this model cooked rice with a typical load of spores reaches the toxin level in about 6.8 hours at 30 °C, 10.0 at 25 °C and 19.8 at 20 °C. A pot of rice left on the counter overnight, or kept on a "warm" setting that has drifted below 60 °C, can pass it. Reheating then kills the bacteria but leaves the cereulide, so the fried rice tastes and smells fine and still causes vomiting a few hours later.

So: cool cooked rice quickly — spread it on a tray — and refrigerate within an hour; keep it at most a day or so in the fridge; reheat once, until steaming hot throughout; never leave it in a rice cooker on warm for many hours. Keep handled foods (sandwich fillings, cream cakes, cooked meats) cold. Buy fish from sellers who keep it on ice and chill it at once. Soak dried kidney beans, discard the water, and boil them hard for at least ten minutes before any slow cooking. Canned beans are already safe.

At the stove

Next time you cook extra rice, spread it thinly on a tray to cool, cover and refrigerate it within the hour. Use it for fried rice the next day — chilled rice also fries better (XXI.4).

The term "fried rice syndrome" comes from outbreaks in Britain in the 1970s traced to rice boiled in bulk, left to cool slowly at room temperature, then fried to order; B. cereus had grown and made its toxin overnight.

Terms

Heat-stable toxin: A poison that survives cooking.
Cereulide: The emetic toxin of Bacillus cereus.
Scombroid poisoning: Histamine poisoning from temperature-abused fish.
Phytohaemagglutinin: A lectin in raw kidney beans destroyed by boiling.

Some hazards survive cooking: B. cereus and staph toxins, histamine, bean lectins. Prevent them — cool rice fast, keep handled food cold, boil kidney beans.

Sources

U.S. FDA, Bad Bug Book, 2nd ed. (2012): Bacillus cereus emetic toxin is heat-stable and is formed in starchy foods held warm; Staphylococcus aureus enterotoxin survives cooking; scombrotoxin (histamine) forms in temperature-abused fish and is not destroyed by cooking; phytohaemagglutinin in raw red kidney beans — a few raw beans can cause illness; boiling 10 minutes destroys it, while heating to only about 80 °C can increase toxicity.
Bacillus cereus forms heat-resistant spores and the emetic toxin cereulide, which survives reheating; cooked rice held warm is the classic vehicle (FDA Bad Bug Book, 2nd ed., 2012).