Mechanical engineers have studied Chinese chefs to mathematically model their wok-tossing techniques. Fast-moving wok cooking enables the Maillard reaction without allowing frying rice to burn.The findings could help scientists develop devices to support chefs, technology for frying bigger batches, and more.
Physicists have paired China’s long culinary history with kinematics in order to “identify an optimal regime for making fried rice.” To do this, they studied five restaurant chefs, using slow-motion video footage to track how the chefs’ movements moved the rice around the wok.
In the Journal of the Royal Society Interface, Hungtang Ko and David Lu, both of the Georgia Institute of Technology School of Mechanical Engineering, describe the history of wok tossing and the much more recent history of robots that can be programmed for cooking motions. Anyone who’s tossed sautéing food in a pan knows it’s a subtle, tricky move that can go wrong and messy very fast. Could a robot ever manage it?
Ko and Lu cite Spyce, a real restaurant in Boston where robots try to mimic human chefs using woks. Spyce “uses rotating drums to mix and heat Chinese food at frequencies of 0.5 Hz, which, as we will see, is six times less than the wok tossing of professional chefs,” they write. “The low speed reduces the jumping of the food, and likely precludes the high temperatures that permit the Maillard reaction.”
Basically, the defanged robot wok chef is missing the two most important aspects of wok tossing—or, not even tossing, in this case. By cooking in a rounded-bottom wok in constant motion over an extremely hot flame, chefs can fry rice at up to 1,200 degrees Celsius—nearly 2,200 degrees Fahrenheit, and almost hot enough to melt iron—without ever burning it. The Maillard reaction is the way proteins in food become flavorful and brown, like when you sear a steak or bake a loaf of bread. It’s related, but not the same as true caramelization of sugars.
But the inimitable human chefs end up with structural problems of their own: The authors say 64.5 percent of Chinese restaurant chefs have shoulder pain they attribute at least partly to the repetitive strain of wok tossing. Robots may never be able to wok toss, but robotic technology could help reduce strain and support these chefs. And to do that, researchers have to fully understand what’s happening when a chef tosses a wok of frying rice.
The researchers recorded footage of five chefs and then studied the footage. They derived a harmonic function to describe the action:
This and a consequent series of equations describe the kinematic shape of the wok, the trajectory of the rice mixture inside, and any “failed catch” grains that could escape. The overall motion the chefs use creates a pendulum effect. “First, the chef pushed the wok forward and rotated it clockwise to catch the falling rice. Then, the chef pulled the wok back while rotating the wok counterclockwise to toss the rice,” the researchers write.
The chefs naturally optimized the motion of the wok. “Despite the variability in cooking conditions, we found the tossing frequency to be consistent at 2.7 ± 0.3 Hz (N = 276). Noticeably, when chefs toss the wok for many cycles in a row, the frequency also increases slightly. The variation is because the wok moves more slowly in the first few tosses before reaching steady state,” the scientists explain.
Any automation that can truly model this cooking motion could revolutionize food preparation. “Although cooking in big batches is strenuous for chefs, it can potentially reduce heat losses by having a relatively smaller surface open to the air per unit weight. Thus, large-scale cooking has the potential to save energy, especially for large numbers of customers,” the researchers say.
They found that making three servings at once took just 25 percent more time, reducing the required energy. They suggest that the added strain of a heavier, larger serving is counteracted by how much less time chefs would spend cooking.