Wok hei: the science behind “the breath of a wok”

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(CNN) – Chef Kwok Keung Tung throws the wok with one hand, using the other to stir with a metal spatula. With both hands busy, he uses his knee to push the gas cooker lever up and down to control the fire fan, sporadically engulfing a third of the burning wok.

It only takes three minutes for the piece of white rice to turn into a bowl of golden fried rice that he places on the serving counter.

“This is what you’re looking for – wok hei (the breath of the wok),” Danny Yip, co-founder of Hong Kong restaurant The Chairman, told CNN Travel.

“The wok is the very essence of Chinese cuisine in southern China. And Cantonese chefs are masters of the fire and the wok. “

Wok hei: An invisible but essential ingredient in Cantonese cuisine.

Maggie Hiufu Wong / CNN

If anyone is an authority on wok hei, it’s Yip.

For those who grew up in a Cantonese family, it is almost impossible to go to a Chinese restaurant without hearing someone – usually older – comment on “gau wok hei” (quite wok hei) or “ng gau wok hei” ( not enough wok hei) when establishing a benchmark on the authenticity of a Chinese restaurant.

Hei (also romanized as “hay”) is the Cantonese word for “chi”, which means flow of energy. It was once a difficult concept to explain and largely ethereal, mainly popular in the southern region of China. In other parts of China or Asia, even though they used woks, they did not focus on wok hei.

It wasn’t until the legendary Chinese American food writer Grace Young poetically coined it as “the breath of a wok” in her book “The Wisdom of Chinese Cooking: Classic Family Recipes for Celebration and Healing” in the 1990s that the concept of wok hei was officially introduced to the international public.

“Wok hei isn’t just hot food; it’s that elusive, gripping taste that only lasts a minute or two, ”Young wrote.

In other words, it’s a combination of that smoldering aroma you breathe in and the almost burning sensation on your tongue that somehow enhances the flavors of the dish.

How a wok works

In recent years, a growing number of culinary writers and scientists have modernized Chinese cuisine while deepening its origins, including wok hei.

After realizing how little scientific research has been done on Chinese cuisine, Hung-tang Ko, a doctoral student at the Georgia Institute of Technology, co-published a research paper titled “The Physics of Fried Rice” with David Hu – a most famous scientist for his studies of fire ants and an Ig Nobel Prize-winning investigation into why wombats have cube-shaped poop.

“The wok hei and the Maillard reaction require high heat. Chinese commercial pans emit an astounding amount of heat, ”says Ko, who has spent months studying how and why chefs tossed fried rice with a wok, while simulating rice trajectories.

The Maillard reaction is a chemical interaction that occurs between amino acids and reducing sugars in foods placed at high temperature. It browns food and releases aromas and flavors.

But why does it have to be cooked over high heat and in such a hurry?

“This is how to extract the maximum amount of wok hei in the shortest time. Thus the aroma that you have released from the Maillard reaction will not escape ”, explains Yip from the President.

Therefore, an important part of wok hei – apart from fire and the actual wok – is the chef’s throwing skill.

The correct way to throw a wok

Throwing a wok is a skill that takes time to develop.

A young chef at The Chairman spends more than a year practicing woks preparing staff meals before he can stir-fry a dish for customers.

“Why don’t the other chefs use a wok? It’s heavy and the fire can be intimidating and difficult to control – now you know why none of the Chinese leaders have left arm hair, ”Yip says, half-jokingly.

Why is stirring not enough? In the case of fried rice, every time it leaves the hot surface of the wok, it cools down and avoids getting burned, as shown in the video above.

“Throwing the wok allows for better mixing, which is essential when you have very high heat. Stirring at high temperature will likely result in combustion, ”says Ko.

During Ko’s research, he found that chefs often rotate their woks using the edge of the stove – instead of lifting the entire wok off the stove – to save energy and increase speed.

Two movements occur simultaneously with each throw: “Back and forth push and pull”, and “tilt and rotate the wok back and forth” in a swinging motion.

So what makes the round bottom, highly conductive wok such a unique piece of kitchen equipment?

“Potentially, other utensils would work as well. But you just need to mix at incredible speeds to make sure the heat gets evenly into your ingredients, ”says Ko.

On average, the study leaders launched their wok at a speed of 2.7 times per second.

This is also why many Chinese chefs suffer from muscle injuries.

One of the goals of Ko’s study was to see if it was possible to create a robot that could help chefs throw their woks to reduce the physical strain on their limbs. Ko believes that his published research has the potential to be applied to other aspects of life.

“Can you imagine a clothes dryer that uses the wok-throwing mechanism to toss clothes? My feeling is that it will be more effective – and funnier, ”says Ko.

How to Make Perfect Fried Rice

Kwok Keung Tung has been a chef at The Chairman since it opened in 2009.

Maggie Hiufu Wong / CNN

Fried rice was in the spotlight in July, with a viral YouTube video titled “Uncle Roger TASTED by this egg fried rice video”.

In the clip, ‘Uncle Roger’, a character created by British comedian Nigel Ng, reacts to a BBC video on how to cook fried rice with eggs.

It highlights everything that went wrong in the original egg fried rice video, a response that has garnered over 17 million views to date. Among the major infractions of the original video? Watery rice.

This is a question close to the hearts of chefs in Hong Kong.

“Fried rice and fried beef noodles are the two dishes often used to judge a restaurant’s wok hei,” Yip explains. “It’s hard to lightly toast each piece of rice or noodles and mix them evenly with the rest of the ingredients without burning it. “

Ko agrees.

“Fried rice is a very symbolic cuisine,” he says. “It’s surprisingly difficult to make perfect fried rice, even if it sounds really simple. The general principle is to keep it warm – avoiding putting in a watery content which cools the materials – and mixing a lot to avoid sticking and burning. “

Ko suggests using rice cooked the night before.

“It comes down to the high heat argument. When you put (leftover dried rice) in the wok, the humidity will be minimal… this prevents the cooling of the wok or the rice from sticking, ”explains the scientist.

The president, however, does things a little differently.

“We know that most people use leftover rice because it is drier. We don’t want to keep the inside of the rice moist and retain as much flavor as possible. The trick is to use eggs, ”Yip explains.

Kwok, the leader, demonstrates.

He first quickly fry the finely chopped ingredients in the wok, drying them before setting them aside. Then he separately pours the oil, the egg mixture and the rice.

“Eggs dry faster than rice. The chef must act quickly and mix all the ingredients. See, you don’t even see the egg anymore, ”Yip says, urging this writer to take a bite before the aroma escapes.

It is true. The lightly toasted, steaming rice is dry on the surface and each grain is perfectly coated in golden yellow – you can’t see the egg. Every bite of fried rice is still steaming and full of flavor.

“Taste this? »Asks Yip. “It’s wok hei. ”

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