If you want to get a sense of the vigorous, animated nature of stir-frying, the best place to start might be with physician and writer Buwei Yang Chao’s definition of ch’ao, the Chinese word for the technique. “Roughly speaking,” she writes in How to Cook and Eat in Chinese, the seminal 1945 cookbook she produced with her husband and daughter, “ch’ao may be defined as big-fire-shallow-fat-continual-stirring-quick-frying of cut-up material with wet seasoning. We shall call it ‘stir-fry’ or ‘stir’ for short.”
The main thrust of Chao’s definition is that stir‑frying employs high heat and constant motion to cook food so rapidly that proteins brown uniformly and vegetables lose their raw edge but retain vibrant color and fresh crunch. As soon as the food hits the wok, it’s repeatedly pushed, flipped, and swirled all over the vessel’s surface, which allows its moisture to evaporate quickly. When that happens, existing flavor compounds in the food become concentrated, and new, more savory compounds develop as the cooking surface gets hot enough to produce Maillard browning.
I spent weeks stir-frying rice, green beans, and beef to suss out the mechanics of both woks and the act of stirring in them, and I came away with some informative discoveries.
Woks Are Precisely Designed for Stir-Frying
One obvious benefit of cooking in a wok is that its high, sloping walls allow you to easily move food around the surface without spilling it over the sides. I also discovered that a wok’s tall sides create two distinct heat zones that work in tandem to cook food efficiently and evenly.
SEAR ZONE: The bottom of a wok is the hottest part (it can exceed 750 degrees when set over a conventional gas burner) because it makes direct contact with the heat source. Food that passes through this part of the pan cooks rapidly and acquires flavorful browning.
STEAM ZONE: A couple of inches above the wok’s base, a layer of steam forms as moisture escaping from the food is corralled by the vessel’s tall sides. As this steam heat hits the food, it helps the food cook through quickly.
Stirring Helps Food Cook Faster and Develop More Flavor
Though it might sound counterintuitive, constantly stirring food helps it cook through faster than it would if you stirred it only periodically. The movement brings new surfaces of the food into contact with the hot pan and releases steam—both of which expedite cooking. In fact, when I compared stirring thin slices of beef constantly to stirring an equal amount of meat only occasionally, I found that the food stirred constantly cooked about twice as fast (for more information, see “How We Proved That Stirring Speeds Cooking”). (Note: This testing was done over gas burners. Woks behave differently over electric coils and induction and glass‑top electric burners.)
That evaporation also improves flavor. As water is driven away, flavor compounds concentrate and the cooking surface can heat up to the temperatures necessary for Maillard browning. The solids that remain break down and form new flavor compounds that add rich savoriness to stir-fries.
Wok-Cooked Food Tastes Better
Food cooked in a well-seasoned wok can acquire wok hei, a savory, fragrant essence that is the ultimate reward of a great stir‑fry. Cooks and food scientists have long struggled to precisely describe its unique flavor and aroma, but terms you often hear include “smoky,” “allium-like,” “grilled,” and “metallic.”
How We Proved That Stirring Speeds Cooking
To prove that constant stirring makes food cook faster, we used an infrared camera to measure the temperature of two different batches of stir‑fried beef after about 1 minute of cooking: one that we stirred constantly and another that we stirred every 30 seconds. The color of the meat that we stirred constantly (bottom left) is noticeably brighter and more yellow, indicating that it got hotter than the meat that we stirred only periodically (bottom right), which is darker purple.
Wok hei is most commonly encountered in dishes fresh from the flame-licked, blazingly hot, use-blackened steel woks of restaurant cooks. But I suspected it was easy to develop beautiful wok hei at home, too—and when wok virtuoso Grace Young whipped up a fragrant batch of fried rice for my colleagues and me on a regular stovetop, my suspicion was confirmed.
Young and other experts attribute wok hei flavor to a few complementary factors: aroma compounds formed when oil gets very hot (in restaurants, oil sometimes even catches fire briefly when food is tossed from the wok into the air), chemical interactions between the food and components of the wok’s seasoned steel, and the accelerated Maillard and caramelization reactions that happen when the heat is turned way up.
Since Young was able to create great wok hei without any acrobatic tossing or pyrotechnic flare‑ups, I didn’t try that. Instead, I stir-fried identical batches of lightly seasoned beef, pad thai, and fried rice in both a wok and a skillet and held side-by-side tastings. In each case, we noticed that the wok-cooked batch tasted more savory and complex—further evidence that a wok is worth owning if you do a lot of stir-frying.