Uncovering the Secrets of Wok Hei

Chef Wayne Liew tossing fried rice to capture wok hei at Kee Eng Kee
Chef Wayne Liew tossing fried rice to capture wok hei at Kee Eng Kee

Fire. It is all about the fire, the chefs tell us when we quiz them about wok hei. Wok hei, or (镬气) in Chinese characters, literally means wok (镬) — awkwardly described as a deep-frying pan (more accurately a skillet; note that a skillet has sloping sides while a sauté pan does not) with a round-bottom—and energy (气), which has also been described as breath.

There is nothing quite as satisfying as a stir-fry. Think: wok-kissed morsels of succulent meat or seafood, crisp yet moist vegetables or flavoursome fried rice and hor fun (flat rice noodles). Author Grace Young thinks of wok hei “as a breath of a wok—when a wok breathes energy into a stir- fry, giving foods a unique concentrated flavour and aroma.”  In her book The Breath of a Wok, she points out that the stir-fry is a culinary art form in Hong Kong and Guangzhou. The word wok (镬) itself is a Cantonese expression, the vessel is called guo (锅) in Mandarin.

Indeed, while researching through old Chinese cookbooks and encyclopedias, I found that the concept of wok hei is not considered a major element in the world of Chinese cuisine. In fact, it is hardly mentioned, and where there is reference (one such tome is the 中国食经 published by the Shanghai Culture Publishing House), it is often associated with stir-frying and the handling of the Chinese ladle or Chinese spatula.

Chinese cuisine dates back thousands of years, and over time, various regional styles of cuisine have emerged. Globally, Cantonese cuisine from Guangdong, a coastal province in Southern China, is the most widely recognised, largely due to the wave of Guangdong emigrants, who moved to the United States and parts of Europe in the 1800s. And within the Cantonese cuisine repertoire, which include soups, stews and roasts, stir-fries gained popularity for the alluring aroma that is wok hei .

Of Fire And Oil

fire power
Fire power

Wok hei is the soul of Cantonese cuisine,” says Cheung Siu Kong, the Chinese executive chef of one-Michelin-starred Summer Pavilion at The Ritz-Carlton, Millenia Singapore. “The key lies in the relationship between fire and oil. You have to control the power of fire, what we Cantonese call fo hao (火候), to get the oil to optimum temperature within a specific time frame to achieve wok hei.” Cheung, who hails from Hong Kong and whose culinary career spans 28 years, puts achieving wok hei down to experience and practice.

Chef and culinary researcher David Yip shares that wok hei is about “capturing the smoke”. “There are three main layers of smoke to take note of,” he says. “First, there is the smoke from the wok: when you heat up a well-used wok (which has developed a patina), you will see smoke emitting from it. Then there is the smoke from the oil: this smoke is denser and is the main contributing factor to wok hei. Lastly, you have the smoke from seasoning such as alcohol, but this gives the dish a mellow fragrance we call chun xiang (醇香): this is highly aromatic, but not exactly wok hei, though many have mistaken this as such.”

Wok hei is also not to be confused with flavours from caramelisation or charred food. “It should yield a fragrance that lingers in the mouth,” says executive chef Charlie Tham of York Hotel, who is renowned for his repertoire of scrumptious wok-fried local delights served at the hotel’s White Rose Café.

More specifically, chef Eric Low expresses wok hei as “smoky aromas from combustion of oil droplets in mid-air”. The chef-owner of Lush Epicurean Culinary Consultancy, and former R&D chef for food and beverage conglomerate Nestlé, adds that in addition to high heat and oil, “water (whether moisture from the ingredients or added sauces) causes oil to splatter into droplets and catch fire to create that smoky effect captured by the ingredients during the tossing process”.

In other words, as written in the masterpiece that is Modernist Cuisine: The Art and Science of Cooking, a cookbook by Nathan Myhrvold, Chris Young and Maxime Bilet, wok hei is “the almost indescribable flavour that is the defining quality of great wok cooking. Intense Maillard reactions on food surfaces combine with the partial breakdown of cooking oil at extremely high temperatures to produce this potent melange of flavour compounds”. It explains that the chemistry only works “if the burner has enough power to bring the surface of the wok to peak temperatures well above the boiling point of water”.

Wok-fried beef hor fun by chef Tse Kit of Lucky8
Wok-fried beef hor fun by chef Tse Kit of Lucky8

Time Is Of The Essence

Tse Kit, chef-owner of Lucky8 at Shaw Centre, who does a mean stir-fried beef hor fun, emphasises that the fire has to be big. “You have to brave the fire and not be afraid of the flames. It is not just about getting food cooked. You also have to note when you should turn up the fire, when you should cease the fire. For good wok hei, the wok has to be screaming hot and you have to move extremely fast, especially in the last 20 to 30 seconds of cooking when you raise the temperature.” And by temperature, we are talking about the heat going as high as 300°C.

Tse, who has been in the industry for over 26 years, explains that the bulk of cooking happens at the stir-fry (or chao, 炒) stage, when the heat is medium-high. This is when most of the seasoning takes place. It is only during the last 20 to 30 seconds, when he would increase the temperature and do intense stir-frying (or bao 爆) to capture the wok hei. For him, this is also when the “tossing of the wok” (pao guo, 抛锅) occurs. More accurately, imagine this: the chef uses the curved side of the wok to fling the ingredients into the air away from himself, and the food should, in a circular motion, fall back towards the chef into the wok, like a boomerang of sorts. Tse tosses his ingredients possibly a good 50 times in 30 seconds.

It is a race against the flames: during that short span of time it takes to develop the complex flavours, the ingredients also have to be cooked appropriately. In that intense heat, it is a matter of seconds between being perfectly cooked and being burnt to a crisp. Curious, we requested Tse to dish out a hor fun before he cranked up the heat, and true enough, it was seasoned and tasted fine, but it did not have that extra spark. Whereas the finished product, having gone through the blazing flames, had layers of smokiness and marvellous intensity of flavour.

For budding chefs, he offers this tip: “Do a visual check, if the smoke is white, you are good. If the smoke turns yellow, then something is burning.”

A Race Against The Flames 6
Chef Charlie Tham working the wok in the kitchens of White Rose Cafe

Tools Of The Trade

“The way you handle the wok is also important. The wok on average weighs 3kg. So you should not use brute strength as, over time, it takes toil on the hands and the body. There is technique and grace in the motion, one should ‘borrow strength’ from the momentum,” Tse adds.

Chef Wayne Liew of local zi char joint Keng Eng Kee Seafood shares the same sentiments. “Every chef has his own way of handling the wok, so you have to find your own groove. The chef also has to know his stove well and realise where the flames are the most intense and target those hotspots,” says the third-generation chef-owner, who picked up his wok skills from his father and uncle.

It is interesting to note that, unlike the Northern-style Chinese wok that has a long handle and is usually 12 to 14 inches in size, the Cantonese wok has no handles (instead, it has two “ears”) and is larger in size  (typically 18 to 20 inches across, or more), so having a Chinese metal ladle or Chinese metal spatula is essential with cooking.

For chefs who specialise in Chinese cuisine, the control of fire is a fundamental skill. It is the handling of the Chinese metal ladle or spatula that differentiates the novice from the master. With that one tool, the master executes the pushing, pulling, lifting, flipping, turning and tossing of the ingredients within the wok. The magic is all in the wrist, enabling the chef and his tool of choice to become one. The tool acts as an extension of the chef’s hand: the strength is concentrated at the tip of the ladle or spatula, allowing the chef to, seemingly, handle his ingredients with ease. A veteran with precise wok and spatula control can even coax the ingredients into performing front somersaults, backflips, pike jumps and cartwheels. Technically, when executed with skill, using these tools can yield the same wok hei effect even when the chef chooses not to move the wok.

Smoky Goodness On A Plate

A Race Against The Flames 7
Chef Tham's seafood hor fun

Can every dish be fragrant with wok hei? Most dishes can be, the chefs tell me, as long as the fire is hot enough, the oil is brought to the right temperature, and there is not too much water. As the preferred cast iron woks gain and dissipate heat relatively quickly, too much water will lower the temperature in the wok and if the heat is not high enough to evaporate the water, the ingredients will simply boil, instead of gaining that lovely brown colour and almost crispy texture. As such, making sure the ingredients are drained properly is essential.

In his kitchen, Cheung applies both wok-tossing and the use of tools depending on the ingredients he is working with. The Chinese metal spatula, which is shaped like a shallow shovel, works well to ensure small bits of food are evenly seasoned, as in the case of fried rice or vegetables. Once the chef has nurtured a strong relationship with his wok and stove, and understands his ingredients well, the technique of capturing wok hei can be applied to most ingredients. Even dishes such as stir- fried mushrooms with kailan stems, and bamboo clams stir-fried with bean sprouts and qing long vegetables can have the intoxicating perfume of wok hei as aptly demonstrated by Cheung.

For Liew, his delicious wok hei-infused fried rice is achieved through stir-frying the rice with its condiments at constant high heat to infuse every plump grain of rice with smoky flavour. When it comes to savouring a wok-fried hor fun with gravy, Tham shares that the secret to good wok hei for this dish lies in “locking” the flavours during the stir-frying of the hor fun. Then, when the luscious savoury gravy is ladled over the smooth, smoky flat rice noodles, the gravy is infused with the smoky goodness.

Why does the “capturing of the wok’s breath” only happen at the last seconds of cooking, you may ask. Tze puts it succinctly, “It is like perfume, you would apply it just before you leave the house. If you capture the wok hei too early in the cooking process, the fragrance would have dissipated long before it reaches the table. So you should always aim for it only at the very last moments of cooking.” This also explains why it is essential for the dish to reach the diner’s table as fast as possible, still piping hot and imbued with wok hei. Diners, in turn, should consume the dish almost immediately to relish the fragrant stir-fry at its finest.

A version of this story appeared on SALT magazine's June/July 2017 print issue.