Let's talk about: "Wok hei"

I have always intended this blog to have observations, analyses, and discussion on a variety of cooking-related topics with a science and engineering slant, and a big heaping tablespoon of acerbic humor.  

Since the inception of this blog, I have always wanted to write an article about “wok hei.”  I alluded to “wok hei” in my last GastroLab with Love article (I tend to get extremely verbose when it comes to items that I’m excited about, and I apologize... not!).  I purposely saved some of the discussion for here because I believe “wok hei” deserves its own entry.  It’s so abstract that it requires more than one paragraph to do it justice.  There’s a lot of bad information about “wok hei” out there, and I actually believed in more of those myths and lore than I care to admit (and I’m stabbing myself repeatedly in the heart for being a fool over the years).  Scientifically, “wok hei” is the pyrolysis of amino acids and carbohydrates under extreme heat, as I have discussed in my fried rice article.  Instead of talking about the actual chemical reactions that occur in creating “wok hei”, I would like to talk about the circumstances, the “ingredients” so to speak, to create this elusive creature.  

We Cantonese always talk about “wok hei” when it comes to saute dishes, so much so that even a little kid would fake food critics’ “this doesn’t have enough wok hei” talk.  Truth is, the poor kid has absolutely no idea what that means if he lives in Hong Kong or the vicinity.  One of the first cooking related items my mom gloated about when my family first settled in the west coast was “these American stove tops are terrible.  There’s no “wok hei” when you cook with these.  The stove is slow... (omitting 10,000 words thereafter)”  We started with a 30” electric stove and brought our own multi-layer metal wok, with stainless steel finish on the outside, with us.  This begins lore #1:  

Forget about creating “wok hei” with an electric stove-- it just NEVER works!

All of us perpetuated the lore.  We believed in the statement even more when a family friend (an accomplished home cook herself), said she went to get a gas stove because the “wok hei” is absolutely terrible in an electric stove.  Over the years, I heard even more of these statements from other Chinese moms.  

If you noticed in my fried rice article, I was able to create a dish with “wok hei” via an electric stove.  So what gives?  

Here’s a list of power consumption for some typical cook top configurations:  

Location	Power Source, Model Type	# of elements	Power (Watt)	Energy (BTU)	Energy  (W-hr)
US	Electric*	8	2,100	--	2,100
US	Electric*	6	1,250	--	1,250
US	Gas, 30” **	--	--	9,000	2,637
US	Gas, Viking, 30” ***	--	--	15,000	4,395
US	Gas, Viking, 48”  ****	--	--	18,500	5,420
US	Gas, Wolf, 30” *****	--	--	16,000	4,688
HK	Gas, built-in^	--	4,200	--	4,200
HK	Gas, table-top^^	--	5,500	--	5,500
HK	Gas, built-in, higher end^^^	--	5,800	--	5,800

Power and energy consumption are pulled from a base model stove top (either electric or gas) on Sears’s (US) or Towngas’s (Hong Kong, HK) website.  All values shown are maximum power/energy output according to product literature.  

To confuse consumers, electric and gas stove tops are in different units.  Wattage and BTU are not the same thing, not only by spirit (one speaks French-- SI, the other speaks British--  Imperial), but by what they measure.  Power is energy delivered over time.  To put them on the same footing, I converted them into W-hr, which is not really an SI unit (but it may make more sense than say “Joules” for most Americans) since it’s used by electric companies to bill your monthly usage.  The definition is that for a 100 W light bulb to light up for 1 hour, the energy used is 100 W-hr, or 360 kJ (stolen from wiki).  

If you look at the energy delivered by an American gas stove, it does edge out the 8 element electric stove slightly, so lore #1 isn’t entirely untrue.  However, if you wait long enough and your cookware has good contact with the element, the amount of energy (not power, because power is time dependent) delivered would match the gas stove, all else being equal.  Also, all else being equal, the energy delivered to the cookware is directly correlated to the cookware’s surface temperature.  The problem with crappy electric stove is lack of immediacy.  Because the element needs to heat up, and its inherent power is a little bit less, the time requirement to reach the acceptable temperature range for “wok hei” to occur increases.  Meaning, if your wok takes 2 minutes to heat up on a gas stove, you may need to wait another 2-3 minutes on an electric stove to reach target temperature.  This lack of immediacy also works against you when it comes to quick heat reduction.  On a gas stove, killing the heat would have been sufficient, but on an electric stove, there will be residual heat on the burner, and hence, the fastest way to reduce heat is to remove the cookware from the burner.  Based on this new information, Lore #1 is smashed... well, at least, it’s not as definitive.  

You can create “wok hei” in an electric stove, but it will take longer than a gas stove.  

In other words, you can “fake it ‘til you make it” with regards to generating “wok hei” for your dishes.  

I’ll leave you with several interesting tidbits.  I have listed in the table 2 base model stove tops and one higher end model from Hong Kong, along with the stats of the every man’s dream stove top brands (Viking and Wolf) .  Note that the energy output for a Hong Kong base model stove top is almost 60% to over 100% more than a base model American gas stove and over 100% more than the base electric model.  This explains my mom’s sentiments on how “useless” electric stoves are in general.  The Viking and Wolf ranges are the only ones that hold their own against the lower end foreign competitors. When it comes to high end competitor, the foreigner still delivers a powerful K.O.  Now the comparison is not entirely fair (All the US pageants have an oven, and the HK pageants, much like their city-women, are lacking of a... uh... ovens), but it’s a stove top to stove top performance comparison so it’s an even enough playing field.  Clearly, it’s not always about the power delivered but how you use it and how well the controls are, but the sad truth is, most of us cannot afford a Viking or a Wolf, so we have to make due with what we have.  Certainly, Hong Kongers place more value in “wok hei” whereas this concept does not exist in an average American’s lexicon.  This explains the big power divide between the stove tops.

What about induction cook tops?  Interestingly enough, I came across an article the other day relating to induction cook tops and wok hei.  As it turns out, a major Chinese restaurant chain in Hong Kong spent 4 million HKD on retrofitting their kitchen with induction cook tops in mid-2010 (news article here, translation here).  After adjusting their stir-frying method, the chefs were able to re-create “wok hei” without a super hot gas stove or wok toss-- only by good wok-to-induction-element contact and almost-motorized-hand stirring the food around.  In addition, kitchen temperature decreases a whopping 16 deg C (from a moist Grand Canyon temperature of 40C to the very pleasant 24C), power consumptions reduce by 30%, the chefs are less likely to be injured from all the chronic wok tosses they do, and unicorns and rainbows leap out from the kitchen to greet the customers.  Of course, their induction cook tops are custom made, and those cook tops probably will never see the light of day here.  However, it’s a good thought exercise (and proven by the expert) that no matter the fuel sources, you can create “wok hei” with the correct treatment.   

Obviously, there has to be more than just the stove that affect our chances of capturing this “wok hei” dragon.  I’ll talk about those in a future article.  Stay tuned!