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!  

From GastroLab with Love: Bonito Fish Stock Essence Fried Rice (quasi-vegetarian)

One of the most famous Chinese dishes (besides chop suey, whose mythical origin is unclear) is fried rice.  I imagine most Chinese culinary enthusiasts have had fried rice at least once during their tenure.  Some may have even attempted to make it at home.  I would dare say that virtually every Cantonese family has made fried rice at home at least once a year if the family dines at home.  For most, fried rice is a great way to get rid of day-old rice:  it’s tasty, it’s quick, and it takes care of the leftover problem.  At least, that’s how my mom runs my family’s culinary ship (the other is to make leftover rice porridge, a Chiu Chow specialty, but that’s another show).  Since fried rice is made with leftover rice at home, my parents usually tell us not to order fried rice when we’re out, especially in the US, “because all those are day-old rice”, as they would say.  I’m not exactly sure how a typical restaurant would have unintentionally leftover so much rice that there would be enough to sell as fried rice the next day, so this leads to two possible conclusions:  

1.  They deliberately save enough leftover, day-old rice, accounting for their fried rice business the next day
2.  They do not use day-old rice for fried rice

Of course, one doesn’t preclude another.  It’s possible that they use a hybrid of method, but option 2 sounds more reassuring.  

I happened to have leftover rice at home today.  Since I haven’t made fried rice for a while, I decided to make some.  A family friend (super awesome cook, by the way; made a 15 course meal for my family a couple years back when we visited her in Vancouver.  I have never been so full in my life...) passed the secret ingredient list to me.  Check out the family shot below:

Super simple ingredient list:  
2 cups cooked rice (I have a mixture of red and white rice here, but white rice is fine)
2 eggs
1 packet (4 grams) bonito fish soup stock essence
Salt (not shown)
White pepper (not shown)

The secret ingredient is the bonito fish soup stock essence.  Here’s a shot of the packet I used.  It’s already in 4 gram packs, but if you ended up finding a big box of bonito fish soup stock essence, I would use about ¾ - 1 teaspoon.  This already contains salt so unless you like your food very salty, no extra seasoning is required.  

As with all simple recipes, it’s all about the ingredients and technique, technique, technique.  You can deduce from my prelude that there is another option for rice dishes besides leftover rice.  Obviously, the rice will have to be cooked beforehand, but what other witch-sorcery do we need to apply to make this fried-rice-eligible?  

As it turns out, the first question we need to ask is:  what makes a good fried rice?  A good fried rice has rice kernels that are dry on the outside but still tender on the inside (a sign of good moisture control).  It is not clumpy, not oily, allows one to taste every ingredient in one bite, and ideally tastes of a wok’s air (or wok hei, which is what it sounds like in Cantonese).  If a dry, non-clumpy fried rice is optimal, then we need to start with dry, non-clumpy cooked rice.  When freshly cooked and steamy hot, either in a rice cooker or over a stove, the rice still carries a lot of moisture:  some of this escapes via steam and some stays with the rice to keep it hydrated.  Moisture is the worst enemy of fried rice:  there will be no dry-on-the-outside rice kernels if the rice is still moist.  Also, moist rice kernels stick together-- another enemy of fried rice.  Once the rice cools down, and provided your water to rice ratio is correct, the steaming will eventually cease, the outsides of the rice kernels will also dry up a little bit and thus promotes de-clump slightly.  This will make a good stock for fried rice.  In a restaurant setting, they would turn on a big fan and have crosswind blowing over the freshly cooked rice to cool and dry the outside.  Once in a while, a kitchen helper (usually an apprentice) would come over and stir the rice for de-clumping, even drying and cooling.  De-clumped rice at room temperature would be ideal for fried rice.  Leftover rice, having sat around for some time, would have already been cooled and meet the dry criterion.  However, sometimes the kernels clump up so you will have to break the clumps apart before starting the process.  Another possible problem with leftover rice is that some of the rice flavor may have been lost as it ages.  Usually, this is not too much of a problem since most fried rice are doctored up to the 9th degree, but I figured I would mention it here.  I would also make sure the leftover rice is back to room temperature before the cooking process.  While the sauteing process provides additional heat to heat up the rice, a shorter thermal journey ensures the rice will be dry on the outside, but still tender on the inside.  

After declumping my leftover rice, I turned my attention to the eggs.  I beat the eggs and added a small amount of salt and white pepper for seasoning.  The white pepper helps take away some of the “eggy but gamey/fishy” smell.  

Once the eggs and the rice are ready, it’s time to saute!  NOTE:  check your ventilation before you start turning up the heat.  This can be a high smoke (or at least, smell of grease) process because the cooking will be done at very high heat.  Obviously, there’s smoke in the kitchen. So you better hide your books, hide your clothes, and hide your linens ‘coz it’s getting very smoky out here (Thanks Antoine!).  All kidding aside, items that absorb smell and within 50 miles (er, I mean, 7 ft or so...  Chernobyl reference) of the kitchen area should be removed if you don’t want it to succumb to grease/smoke.  If possible, you should crack the outside window or door that is closest to the kitchen open to get the smell out.  Most home range hood units are useless to counter this smell unless they are exhausted to the outside and contain a powerful blower that will suck all the food smell out;  these type of units don’t typically exist in an American kitchen.  Another important point:  make sure you have everything in place before you get this started!  Once you start the sauteing process, it will be a fast-going freight train and you do not want to mess around.  If you do, the food will stick and burn, just like the runaway train on Unstoppable.  

Warning aside, I would like everyone to meet my smoking hot, cast iron wok:  

What’s the smoke?  That’s the leftover seasoning on the wok.  The seasoning is one of the keys to mostly non-stick performance that you can achieve via a non-teflon pan (more on seasoning later).  The wok needs to be smoking hot because a.  who doesn’t like to be smoking hot, and b. more importantly, this is how you generate “wok hei.”  A great saute is nothing without wok hei.  Scientifically, “wok hei” should be the volatile and non-volatile by-products of amino acids, carbohydrates, and maybe very little bit of fat pyrolysis (for amino acids reacting with carbohydrates, it’s called Maillard reaction).  For pyrolysis to occur, there must be extreme heat, low oxygen and minimal moisture.  A smoking hot wok provides the heat, and the dry surfaces of the rice would allow for pyrolysis to occur.  Since the amount of air trapped in between the surface of the cooking item and the surface of the wok is minimal, combustion will only occur in a very small amounts. It’s hard to describe the taste of wok hei, but you can certainly taste it (which is likely mostly smell considering it’s usually the upper part of my mouth that “tastes” it), and sometimes smell it from afar when a dish has wok hei.  The tricks are to turn the hottest burner (usually the largest one on the electric stove, and you would have to muck around to find out which one is the most powerful on a gas stove) to the hottest setting, then you (patiently) wait for the element and the wok to heat up.  A thicker cast iron wok will hold the heat in better, giving you better results.  

The next item on the agenda is to make scrambled eggs.  Some of you may have experienced eggs sticking to the cooking vessel when you cook with a non-teflon surface.  Here’s a good restaurant trick:  hot wok, cold oil.  Start with an extremely hot wok.  Then pour a little bit of oil to coat the surface.  After that, dump all the oil into a different vessel, put the wok back on the stove, and add in enough cold oil (I believe I added about 2-3 tablespoon).  The beaten eggs (or whatever you would like to cook) go in right after.  

I added my first coat of oil here.  

Following the mostly-non-stick protocol listed earlier, I dumped the oil and added more cold oil.  The beaten eggs then went into the wok.  

Then I started stirring and mixing.  This is the scrambled egg part of the program.  Here’s an action shot.  

I then removed the eggs and loaded them in a bowl once they were mostly cooked.  Check out the wok in the picture here.  Minimal sticking!  

Why are the eggs cooked first?  Remember, a great fried rice’s worst enemy is bad moisture control.  Just as we did everything to prevent moisture saturation with the rice, we should not ruin our progress and over-saturate the rice with the eggs since they contain high level of moisture.  Adding the uncooked eggs with the fried rice would delay pyrolysis because most moisture must be driven out first before pyrolysis can occur.  Also, the eggs would have taken more than 2 minutes to cook.  If the rice is cooked for too long, eventually the kernels will be dehydrated and it will make the rice too hard to eat (although in this case, it won’t be too much of a concern because there’s plenty of moisture with the eggs).  This principle applies to anything else that you would like to add to the fried rice.  If you do add the eggs in with the rice, it can be done, just keep in mind that your cooking time will be significantly longer.  

After removing the eggs, I waited for the wok to reheat, and repeated my mostly-non-stick protocol.  I then added the rice and kept it moving.  If you have the strength and the finesse to do the wok toss (拋鑊 in Cantonese, here’s how you do it), this is the time to do so.  Do you need to do the wok toss to get the wok hei?  No, but you’ll be charming all your potential partners because it’s really cool looking.  Sorry for the blurry shot. It's supposed to be me in action!

The goal is to char the outside of the rice without drying the rice or having sticking issues.  Keeping the rice moving will help with all of the above.  After stirring for about 20 - 30 seconds or so, I added the bonito fish soup stock essence and mixed it up.

I then added the eggs back in and stirred.  I also used my stirring metal spoon to break the eggs apart a little more so the chunks are smaller.  

Another 20 - 30 seconds later, time to evacuate.  And look ma, no sticking!  

Here’s the finished product.  

Total elapsed time:  15 - 20 min, with actual wok time around 5 min.  

This is only the beginning of the fried rice journey.  As long as you follow the key points in this post, you can make any kind of fried rice you like.  

Key points recap:

a.  Rice must not be still steaming!  The rice surface must be a little dry.  
b.  The rice must not be too sticky or moist.  Watch your water level carefully when you cook the rice.  
c.  Rice must be de-clumped before cooking.  Room temperature is ideal, but a little warmer than that is probably OK as long as it doesn’t violate rules a and b.  
d.  Use ultra-high heat to achieve best wok hei.
e.  Use the hot wok, cold oil protocol on a seasoned cast iron wok to achieve minimal sticking.  
f.  Pre-cook anything that has a longer cooking time than 2 minutes, or has high moisture content.  If the rice is cooked too long it will dry up both on the outside and the inside.  

Bon appetit!  

Notes:  

1.  Fried rice doesn’t taste as good without eggs, but you can skip the eggs and add in veggies if you like.   

2.  If you like the eggs, but also like veggies, adding veggies would not impart bad flavors to this dish.  My family usually throws in a handful of the frozen mixed vegetables (you know, the kind with carrots, corn, peas, and somehow green beans...).  Since they’re small, you can throw them in with the rice and they will defrost and cook by the time the dish is done.  Refer to rule f when in doubt.  

3.  I would not add meat to this dish because the bonito fish soup stock essence already carries the flavor you need.  

4.  If you like your fried rice to look a little brown, you can add about 1 tablespoon dark soy sauce.  The key is to be able to spread the soy sauce evenly throughout the dish, which means you may have to also add a small (likely equal) amount of water/soy sauce (in that order) to provide enough volume for spreading it around.  Dark soy sauce’s color bodies are very potent (unlike its salt content, which is very weak in comparison to regular soy sauce), and the axiom “less is more” is definitely true here.  I didn’t add it in mine because I already have color from the red rice.  

5.  If you would like to make other kinds of fried rice, any ingredients are probably good as long as you follow rule f.  Remember smaller pieces cook faster, and uncooked meat/protein would likely take longer than 2 minutes to cook.