“I like the food here,” my dad would unfailingly say to me as he pulled open the aluminum-framed, oil-smudged glass door at Sun Lok Kee, a Mott Street stalwart that served beef chow fun and other Cantonese classics at any hour of the day until it burned down in 2002. “It has that nice smoky flavor.” My family moved to New York in the early ’80s, when I was 4-years-old, and those stir-fries from Sun Lok Kee, with their savory char and smoky aroma, are among my first and fondest taste memories.
Wok hei is the Cantonese name for that aroma (literally “wok energy” or “wok breath”). My dad has always been a wok hei fiend, first scouring the streets of Chinatown and later the suburbs of Boston for smoky clams in black bean sauce, fire-kissed stir-fried greens, beef chow fun that almost tastes grilled, or noodles that are singed just right.
As a professional cook and recipe developer, I’ve spent a good 15 years attempting to identify the elements that go into creating wok hei, so that I might capture that flavor in a basic home kitchen. Last year, as I researched and tested for a book on wok cooking, I finally got there. True wok hei flavor right in my own kitchen.
Of course, some folks would say wok hei is incongruous with home cooking. “That smoky flavor” is the kind of matter-of-fact flourish-free description my dad excels at, but it’s by no means the agreed-upon definition. In her 2004 book, “The Breath of a Wok,” Grace Young identifies wok hei as “when a wok breathes energy into a stir-fry, giving foods a unique concentrated flavor and aroma.” In “The Chinese Kitchen,” Eileen Yin-Fey Lo says it’s when “the proper amount of fire is made to curl up around the bowl of the wok to cook foods precisely to that point of optimum flavor.”
When I asked my friends Steph Li and Chris Thomas, the couple in Shenzhen, China, behind the popular YouTube channel Chinese Cooking Demystified, their response jumped between descriptive and evocative. “Wok hei is this ethereal thing,” Steph said. It’s “that taste of the first bite of a hot restaurant stir-fry. It’s got that taste of the restaurant oil, the slightly deeper restaurant browning, the heavier restaurant seasoning.
“Seeing home cooks outside of China being obsessed about wok hei has always been kind of bewildering to me,” she added.
She has a point. Most folks in China don’t have restaurant-style equipment at home, and even the concept of wok hei is not widely known outside of the Cantonese regions of Southeastern China. But it is perhaps because most Chinese food in America has its earliest roots in Cantonese cuisine that American diners so strongly associate good Chinese food with that flavor. (According to Andrew Smith’s “Eating History,” there were five Chinese restaurants in San Francisco by 1850, started by Cantonese immigrants who arrived during the Gold Rush.)
But what is the flavor? Where does it come from? What’s so different about cooking in a restaurant? In my own testing, I’ve managed to narrow it down to a few key elements.
Most of these traits are intrinsic to woks, particularly those made of carbon steel, a material that, like cast iron, can be seasoned to a jet-black, nonstick coating and unlike cast iron, can be cast or hammered thin and light enough to make tossing food a possibility.
When I was a test cook at Cook’s Illustrated, I conducted a number of blind taste tests, stir-frying noodles, beef and vegetables in Western-style skillets (the magazine’s recommended method at the time) side by side with a nonstick wok, and my own well-seasoned carbon steel wok. The carbon steel wok unanimously won those taste tests, producing flavors that tasters described as “grilled” or “caramelized.”
As Lan Lam has written in a more recent article from Cook’s Illustrated, this has to do with the chemical interactions between the food and the layers of polymerized oils on the surface of a seasoned wok. It’s also tied to the unique action of stir-frying in a wok. “Modernist Cuisine” describes how when a morsel is tossed up through the heavy cloud of steam that forms above a hot wok, that steam condenses on the surface of the food, a process that “deposits formidable amounts of latent energy that rapidly heats the food.” It then drops back down onto the hot surface of the wok where that surface moisture is re-vaporized, and the cycle repeats. A wok allows you to constantly toss food through its own vapors, speeding up its cooking, which concentrates flavor and promotes the development of new flavor compounds through the Maillard reaction better than a flat skillet can.
The wide rim of a wok factors into another key element of wok hei. In her 2010 book, “Stir-Frying to Sky’s Edge,” Ms. Young emphasizes the importance of adding soy sauce and other liquids around the perimeter of the wok, so as not to decrease the temperature of the searing zone in the center, which can cause meat and vegetables to steam rather than sizzle. This advice is common among Chinese chefs and cookbook authors.
But as I watched Sichuan chef Wang Gang splash soy sauce around the perimeter of a wok full of home-style egg fried rice on his YouTube channel, I noticed something: how rapidly it sizzles and sputters. I was reminded of a Mexican cooking technique I learned from the late chef David Sterling at his home in the Yucatán: As he tipped fresh salsa into a ripping-hot saucepan, it superheated in an instantaneous steamy sputter, giving it a richer color and smoky undertones. Could this concept of a seared sauce also be a factor in wok hei flavor?
To test this, I made two identical batches of lo mein, changing only the manner in which I finished them. For the first, I finished by splashing two tablespoons of soy sauce around the perimeter of the wok, while simultaneously splashing two tablespoons of water into the center of the wok. For the second, I swapped the water and soy sauce. (Adding water to the test ensured that both batches would experience the same cool-down effect of liquid added directly to the center, while only one would develop seared soy sauce flavors.)
The difference was stark. Adding soy sauce to the center of the wok left the noodles with a raw soy sauce flavor, while drizzling it around the hot edges of the wok created smoky flavors reminiscent of grilled meat. I’ve since found that adding a small splash of oil to the perimeter of the wok before adding the soy sauce will prevent the soy sauce from ending up caked onto the side of the wok.
Given that it’s the shape of a wok that allows for tossing through steam and searing sauces, is there any hope for capturing wok hei in a Western skillet? Fortunately, yes there is, and it has to do with the final, most important contributor to wok hei: burnt oil.
Watch a Cantonese restaurant chef in action and you’ll see that, just as the author Ms. Lo described, flames will lick up the back of the wok, sometimes even spreading down into the wok itself. This happens because as food gets tossed through the hot zone behind the wok, tiny droplets of aerosolized oil will ignite and flare up. That singed oil then leaves small, sooty deposits on the food as it gets tossed through the smoke. It’s this flavor — the same flavor that develops as a hamburger drips fat onto red hot coals below it — that I most strongly associate with wok hei.
The problem is that Cantonese restaurant wok ranges, which can output 200,000 B.T.U.s per hour or more, are an order of magnitude more powerful than even the most powerful home burner. It’s that massive jet of flame that makes igniting vaporized fat possible, but I’ve found a reasonable workaround.
If I can’t bring my food to the flame, why not bring the flame to my food? A camping-style fuel tank, along with a brazing head (such as the Iwatani Pro butane torch head or Bernzomatic TS8000 propane torch head) that I point directly at the food inside a wok for a few brief moments as I toss, can lend that vaporized oil flavor.
In practice, this technique, which my colleagues at Serious Eats independently arrived at and cleverly coined “torch hei,” is tricky. Even with two hands, stir-frying takes practice. To simplify things, I’ve found that transferring the stir-fried food to a rimmed baking sheet, spreading it in a single layer, and giving it a few leisurely passes with the torch before returning it to the wok for final saucing and garnishing is a simple and effective workaround.