Vol. XXI · Grains, Rice and Noodles Plate 4 of 10fried rice, 炒饭, 蛋炒饭, day-old rice, leftover rice, retrogradation, wok, wok hei, Bacillus cereus, cooling rice, egg fried rice, Yangzhou fried riceTM

Fried Rice.

Freshly cooked rice in a wok turns to a sticky paste; yesterday's rice from the fridge tosses into separate, toasty grains. Overnight, its starch changed.

Freshly cooked rice is soft, moist and sticky on the surface, and in a hot wok its grains glue together and steam. A night in the fridge changes it: the starch begins to recrystallise (VII.3), firming each grain, and the surface dries, especially if the rice was spread out uncovered at first. Firm, dry-surfaced grains separate when tossed, take a coat of oil, and can toast and pick up the smoky edge of a very hot wok (XV.5) before they soften. Higher-amylose rice firms faster and makes the most separate fried rice (XXI.2).

Day-old rice carries a known hazard. Bacillus cereus spores survive cooking, and if cooked rice is left warm they germinate and make a toxin that reheating does not destroy (XII.9). So rice for frying must be cooled quickly — spread thin on a tray, within an hour — and kept in the fridge, not left on the counter overnight. When fresh rice is all there is, spread it on a tray and chill it uncovered for 30–60 minutes, or use slightly less water when cooking it. The workshop chills rice.

Below: the firming of cooked jasmine rice over the hours you choose in the fridge or left on the counter (course retrogradation model), and the counter's other effect: growth of Bacillus cereus from cooked rice held warm (microbe bench).

What you will learn
Workshop
Firming: the course retrogradation model at 4 °C (fridge) or 21 °C (counter). Bacillus cereus: course growth parameters, from 100 spores per gram germinating in rice left at 25 °C (counter) or 4 °C (fridge); the emetic toxin is a risk from about 10⁵ per gram upward (teaching threshold).

Cold, dry grains in a very hot wok

After twelve hours in the fridge the course model has the rice about 0.85 firmed, on the counter at 21 °C about 0.38 — but the counter rice has also let Bacillus cereus grow from 2 to about 5.8 logs at 25 °C, against 2.0 in the fridge. So the fridge wins on safety, and on texture too. The rule from XII.9 holds: cooked rice is cooled within an hour and refrigerated, eaten within a day or two, and reheated only once.

Method for egg fried rice for two: break up 400 g of cold cooked rice with your hands; beat two eggs; heat a wok until smoking, add oil, scramble the eggs into soft curds and take them out; add more oil, then the rice, and toss and press over the highest heat for 3–4 minutes until the grains are hot, separate and lightly toasted; season with salt (or a little soy round the hot rim of the wok), return the egg, add scallions, toss and serve. Home burners are weak (II.6): fry no more than two portions at a time. 扬州炒饭 adds diced ham, prawns, peas and mushrooms; Thai fried rice adds fish sauce and lime.

At the stove

Fry a portion of freshly cooked rice and a portion of rice chilled overnight the same way. Compare how the grains separate.

"Fried rice syndrome" was the name given in the 1970s to outbreaks of vomiting traced to restaurants that cooked rice in bulk, left it at room temperature to cool slowly and fried it to order the next day — the textbook case of Bacillus cereus emetic toxin.

Terms

Day-old rice
Cooked rice chilled overnight; firm and dry-surfaced.
Retrogradation
Starch recrystallising as it cools (VII.3).
Bacillus cereus
A spore-forming bacterium whose toxin in rice survives reheating.
Wok hei
The smoky taste of a very hot wok (XV.5).
Fried rice wants firm, dry-surfaced grains: rice chilled overnight, its starch partly recrystallised. Cool rice within an hour and keep it cold — warm rice grows B. cereus. Fry hot, in small batches.

Sources

  1. 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).
  2. 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.
  3. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.