The Recipe with Kenji and Deb - The Science of Stir-Fry with J. Kenji López-Alt [Milk Street Radio]

Episode Date: December 30, 2024

We are taking a break this week. Please enjoy this classic interview from our friends at Milk Street Radio.For more information, visit Milk Street Radio's homepage, and follow Milk Street Radio on Apple Podcasts. Learn about your ad choices: dovetail.prx.org/ad-choices

Hey there, I'm Yuri, the managing producer of The Recipe with Kenji and Deb. Like many of you, we're taking a wee break from the show for the holidays, so we're bringing you today a classic from our friends at Milk Street Radio. If you've been loving The Recipe, you will probably also love Milk Street Radio. Every week, they bring you the most fascinating stories about food from all over the world, like the detective who tracks down food thieves and scientists who study if vegetables have souls.

And they talk to some of the most exciting people in food like Jose Andres, Padma Lakshmi, and Kenji, who is a regular on the show. I highly recommend checking it out wherever you get your podcasts. So in this piece, Kenji breaks down the science of stir fry, so you can get ever closer to that restaurant quality you may have been chasing at home.

It is, not surprisingly, one of Milk Street Radio's most downloaded episodes. So check it not surprisingly, one of Milk Street Radio's most downloaded episodes. So check it out, The Science of Stir-Fry with J. Kenji Lopez-Alt. This is Milk Street Radio. I'm your host Christopher Kimball. Right now it's my interview with J. Kenji Lopez-Alt about his latest book, The Walk. Kenji, welcome back to Milk Street. Thank you. Thank you for having me. You know, I'm fascinated by the walk. I think we talked about this when I was in Taipei a few years ago. I watched someone fry, steam, stir-fry, do all these things

within a space of a few minutes in the same walk. And I do think it's the ultimate cooking vessel. But let's start at the very beginning. You said originally it was something used for holding or drying grains, right? It wasn't even used for cooking. Yeah, I mean the history of the wok goes back, I don't remember which dynasty it was, but right around zero AD, it was right around when the wok started showing up. And they were originally made out of stone or clay and used as giant vessels for a drying grain. And eventually as metals and other materials started being used they became much more versatile. So when cast iron came around and people started making walks out of cast iron

you could then sear and fry and sizzle and do all these other things in walks. And of course modern walks most of the time these days are made of carbon steel, which is even more versatile than cast iron because it's not as brittle. And it's lighter so you can do things like stir fry very effectively in them. But yeah, the original woks were sort of fixed in place, big things that were used to dry grains. concern slash problem, which is if you're not in a restaurant and you don't have, you know, one of these massive burners, you just don't have the same amount of heat output in a home kitchen, which means that you effectively, some people would argue, can't really stir-fry or use a wok because you don't have enough heat. Now you're gonna disagree with this, but I'd love to hear the answer because this has been bugging me for 20 years. I'm going to, yeah, I am going to disagree with it. So the first and easiest answer to that is that the vast majority of people

in the world who cook with walks, like we're talking hundreds of millions of people cooking in a walk every day, don't have a restaurant style burner at their house, right? So there are, you know, people who are cooking for their whole families on regular home burners throughout Asia. And of course, you know, scattered around the world as well. Um, so the idea that, that cooking in a wok requires this 150,000 BTU restaurant burner is, is sort of silly, right?

Um, you know, I think, I think a lot of that is colored by our experience as Americans, where most of our exposure to Chinese food is restaurant style Chinese food. You know, so like for me, I grew up in New York and we grew up eating Cantonese and Hong Kong inspired Chinese American food in Chinatown, right? And so dishes like beef chow fun, right? So that would be one of those quintessential dishes that really has that strong, uh, wok hay, that smoky flavor that really requires a very strong restaurant style burner.

But there's an entire wealth of home cooking that you don't necessarily find in, you know, of course there is some overlap between home cooking and restaurant cooking, but there's a lot of stuff that is cooked at home that you wouldn't necessarily find on a restaurant menu. So just so I understand wok hei is that very smoky aroma, really, and flavor you get from guac cooking. And usually, we're talking about a high heat burner in a restaurant. But I think what you're saying is you can still get some guac a at home without a high heat burner by using different kinds of recipes and different techniques, but not by trying

to replicate how someone cooks with a wok in a restaurant, right? Yeah, exactly. I think, you know, it's sort of like saying, I can't cook a steak the way they cook it at Peter Luger because I don't have a 1600 degree broiler at home, right? But when you cook a steak at home, there are other ways you can cook steak at home that are equally delicious. They're just different, right? So home cooking and restaurant cooking are just two different types of cooking. Let's pull a real Kenji.

Okay. And let's do the science of these oscillations in a stir fry. I thought this was really interesting. So take us briefly through the science of stir fry. Okay, so there's a few steps in stir frying. And honestly, stir frying is a misnomer for the actual term.

It's really much more of a toss frying. So you're not, you know, stir frying to me gives you the idea that you're sort of leaving the wok in place and you're stirring it around with a spatula, which is not really what you're doing. With stir frying, most of the action comes from shaking the wok as opposed to shaking the tool that's in there.

There was a study done where this team went out and took some slow motion video of people cooking in woks to really sort of break down the motion and understand what's going on. And what they found is that there's basically four steps, you know, so that you initially start with the walk flat on the burner, but a little bit angled up. So tilted towards the back. And then you start to kind of push the walk forward and then you flip the food up over

the other side and then you let it roll back and kind of a wave over the back of the wok and catch it near the handle before you start repeating that process again. So that motion is really essential to a stir fry because it does a couple things. So first of all, you're keeping the food constantly moving. And when you're working with small pieces of food, keeping it constantly moving is going to make sure that it all cooks evenly.

Secondly, you're throwing the food up. And if you're using a gas burner or you have properly preheated everything, there's this kind of hot column of air that moves up the back of the walk as you pull it forward and your food kind of flies up through that hot column of air. And that allows the steam that had been generated by the food in the walk, it's trapped in that column of air. And when you throw the food back through it, the steam condenses on the food.

And that action of condensing actually transfers energy to the food. And so what it does is that stirring and tossing process cooks your food much faster than just sort of letting it sit in a pot and stir around with a spatula. So let's get into the metaphysical issue here of the breath of a walk. Grace Young told me this. She wrote a book with that title. Her father, when they were younger, went to a Chinese restaurant. They'd sit right next to the door to the kitchen because he said that breath of a wok

lasts only a few seconds. When they came through with the food, he could smell it. And he thought that was just a wonderful experience. Could you just explain what the breath of a wok is? It's like the fajita platter at Chili's, right? You go to Chili's? Wait a minute. Hold on.

You know, I spoke to a number of different chefs and cookbook authors and asked them what they thought of the breath of the walk, this idea of walk hey. And virtually all of them gave different answers, ranging from the very physical, you know, it's the smoky flavor of food that's cooked at a very high temperature in a carbon steel wok, you know, something very, very matter of fact, um, to something much more metaphysical. Like it's, it's the, it's the sound of the sizzling that you get from the wok when you're sitting outdoors on like a hot night in Beijing and you have a nice cold beer in front of you.

And it's, it's, it's much more about the overall experience and the aromas that are filling the street and the restaurant as opposed to one specific thing. So really I think it's a matter of your experience with it. Um, so for me, you know, what I learned as the breath of the walk, I mean, until Grace Young's book came out, I don't think, you know, many people called it the breath of the walk, and now that's just sort of the term that encompasses it. But for me, it was always when I went out to restaurants with my dad, you know, my dad was

obsessed with Chinese food. And so we would spend weekends going around Chinatown, both in New York and Boston. And the thing that he always particularly liked was when the chow fun had that nice smoky flavor. Like I, that was all, that was always the refrain I hear in my head. Like we would go to a place and he's like,

oh yeah, this is like great chow fun. It has that nice smoky flavor. And that's what he called it, right? Just that nice smoky flavor. And it's what he called it, right? Just that nice smoky flavor. And it was something that I heavily associated just with restaurants. It wasn't something that even when we tried to make chow fun at home,

it wasn't something that we ever really got at home. So part of it, I think for a lot of people is that overall experiential thing of going to a restaurant and having someone cook for you and being surrounded by the sights and the smells. So let's do a how to cook in a wok 101. And one of the things you start off with is if the dish includes meat, you talk about washing the meat,

vigorously washing the meat in water, squeezing it out as hard as you can, and then marinating it through massaging, slapping, lifting, and throwing. Um, yes. And I know you tested this because you test everything, but just take us through the washing of the meat please. Yeah. So if you're eating a steak in a Western restaurant,

you expect the meat to have some kind of chewiness to it. You want some chew, you want some give in there. So it's this balance of tenderness and toughness that you're looking for. Whereas a lot of times with stir fried meats, um, in Chinese restaurants, you want them to be very, very tender and you want them to almost have like a, like a sort of slickness,

a slippery texture to them. And there's two important steps to getting there. Um, the one that I had known about for a long time was the marination process and particularly using alkaline ingredients in the marinade. So brining meat with baking soda and salt, or, or in some cases, sodium carbonate, your baking soda. Um, or for example, um, in meats that are

velvet, you would use egg whites and egg whites are also alkaline. The other process though, is one that I didn't really recognize as very important until I saw people doing it online, particularly this chef, um, Wang Gang, a Sichuan chef who has a YouTube channel, you know, I started seeing these Sichuan chef who has a YouTube channel. You know, I started seeing these videos of Chinese chefs actually washing the meat and

the way they do it is extremely vigorous. It's like you're washing clothes, like you're scrubbing clothes and really wringing it out. And so I tried it at home and it was like, I mean, the difference between meat that's vigorously washed in water versus meat that is not washed and just marinated, it's enormous. Like it, it really completely changes the texture of the meat. Um, And why do you think that is? Well, I mean, I think it's, it comes down to just sort of mechanical tenderization, you know,

and it's really interesting to me because in a lot of Western cuisines, you know, like you think of like French cuisine, right. And, and a lot of the goals in French cooking is concentrating the flavors. So you might take like a chicken, right? You take the breasts off, you roast the carcass and make a stock out of that. And then you reduce that stock very slowly. And so you're really concentrating all the flavor of the chicken, and then you'll serve that reduced jus with the roasted breast, right? Whereas with a lot of Asian cuisines, that's not really the goal.

It's much more about balancing flavors. So a dish of like cuisines, that's not really the goal. It's much more about balancing flavors. So a dish of like beef and broccoli, right? We don't necessarily associate that with like a very strong beefy flavor. We really associated with more of the balance of meat and vegetables, the balance of sweetness and savoriness and aroma in the sauce. Um, and so when someone says, well, when you wash the meat, aren't you really washing out like the beefy flavor? Well, in some way, yes, you are, but then you just have to ask yourself again, it's sort of like

resetting your expectations. Like that's a bad thing in French cuisine, but it's not necessarily a bad thing. Uh, in some Chinese cuisines. Well, that's my speech. You just stole my speech, but we've both been giving the same speech for years. We've prepped the ingredients, the meat or the shrimp. Just take us through a basic approach to how to stir fry in a wok. Okay. I'll start this with the caveat that this is a very broad... There are many, of course,

many recipes that call for different techniques than what I'm about to walk you through. So, but, but as a very broad overview, um, the technique I would do at home, you know, so the, the first thing that I would recognize at home is that my home burner only has about, you know, 10 to 15,000 BTU probably. So about 10 times less than a restaurant burger. So the main thing to remember is that you want to cook in batches.

So typically what I'll do is I'll start by cooking my meat and I'll cook it no more than a third to half pound at a time. So if that means, you know, I'm cooking for four people, I might cook in two batches, my meat and each time what I would do is I would rub a very thin film of oil into my carbon steel wok and then heat that. And that thin film of oil is really just there as a temperature indicator. So I'll know that when the wok starts sort of lightly smoking, that it's at

the right temperature to start stir frying. What they do in restaurants and what some home cooks call for, um, is they'll preheat the wok till it's really hot. They'll dump in a whole bunch of oil and then they'll pour it out. Then they'll heat up that whole wok until it starts smoking and then add some fresh oil and start cooking. Um, in Western cooking, you would call for putting the oil in as you're preheating because generally you don't get the oil hot enough that it really

starts to break down, right? Whereas in wok cooking, you're, you're generally cooking at much higher temperatures. So if you try just preheating all the oil that you're going to be stir frying in from the very beginning, by the time it's hot enough to stir fry in by like really smoking hot, the oil will have started to break down and it develops some kind of

off burnt oil flavors. Um, so that's why I recommend just doing that really thin film as a temperature indicator than just before you start cooking, you add some fresh oil in there so that it doesn't have a chance to break down. And so once you do that, you would start by adding aromatics, um, depending on the recipe, you could add aromatics straight to that oil. So something like slices of garlic and ginger, um, stir fry them very briefly just to get the flavor into the oil and then add your meat. Stir fry it just until it's almost cooked

through and then transfer it out onto a sheet tray. And then you repeat that with as many batches of meat as you need. And then after that, you would switch over to your vegetables. So you do the same process, preheat the wok, add some fresh oil, add your vegetables in there, stir fry them, and then set them aside on a sheet tray. And then at that point, if you want to add some of that smoky, walk-hay flavor, if it's appropriate for the recipe, what you can do is you just take a kitchen torch. So I use like a butane torch and then just pass it over the ingredients that you have laid out on the sheet tray so that the oil on their surface vaporizes and burns a little and singes

and adds that sort of smoky flavor. And then finally, right when you're ready to serve, you preheat the wok again, you add all your ingredients back in at the same time, you drizzle your sauce in around the edges of the wok so that it really has a chance to reduce and cook really rapidly as opposed to sort of slowly trickling down through the food where it'll just steam. And then you toss everything together maybe 30 seconds maximum in there and then plate it up and you're ready to go. You're listening to Milk Street Radio. My guest today is Jay Kenji Lopez Alt. After the break we'll continue our conversation about his latest book The

Walk. Please stay with us. This is Mill Street Radio. I'm Christopher Kimball. Right now we return to my interview with J. Kenji Lopez-Alt about stir-fry techniques and his latest book, The Walk. Let's talk about walks. There are lots of different shapes. They're sort of flat bottom. They're the more conical original design. They're very light, very thin carbon steel. They're heavier ones. What do you buy? So my basic suggestion for anybody cooking on a Western range, um, buy a 14 inch wide flat bottom walk made out of carbon steel. That's 14 gauge.

So about two millimeters thick. You know, that's what I've used for the last 20 something years. And I think it's the most useful size and shape for a Western kitchen for someone cooking for a small group or for a family. It'll work on pretty much any Western range. It's large enough that you can fit a bamboo steamer in there. It's large enough that you can deep fry or simmer or steam or anything in there. But yeah, that would be my recommendation.

Are there some unusual things you do with the wok? I was in Thailand a few years ago and I, they would cook eggs in oil at the bottom of the wok. It's almost, I wouldn't say deep frying them, but they were almost poached in oil, I guess I would say. Pete Slauson Yeah. Pete Slauson Which was really interesting. Are there other things you do in your book or otherwise that people wouldn't normally think of doing in a walk? I mean, so there is like a huge egg chapter in the book, and I would say the range of textures that you can get out of an egg cooking in a wok outnumber even the range of textures that you find in typical Western cooking. And you know, in eggs, you can get so many textures from silky to crispy

to puffy to tender. And so, yeah, you know, one of my favorite recipes in this book is called slippery beef. And this is really a home style dish. It's not something you'd really find at a restaurant, but essentially you start by stir frying some aromatics and some strips of beef. And then you add wine and stock and quite a bit of stock, you know, a couple cups of it and then you thicken it up really heavily so that it's almost like the texture of like a, like a light gravy with a cornstarch slurry. So, um, so, and, and then after that, you, you beat your eggs and you very slowly

drizzle them in the way you would do for say something like egg drop soup. But, you know, instead of having that texture of a soup with, with silky strands of eggs, the whole thing becomes this really sort of tender, silky, I mean, you know, silky, slippery thing, all these textures that, that sound unappetizing in Western cuisine, but are extremely, I think, comforting and delicious when done in this context. Toasting salt in a wok. Talk about that. Oh yeah. So, one of my favorite dishes, we used to go to this restaurant in New York called Phoenix garden and their signature dish were these, um,

salt and pepper shrimp. And so they had these giant shell on prawns that they would deep fry and then tossed with the salt and pepper mixture. And it always had this really strong smoky flavor. And, you know, I, for a long time assumed, okay, they're deep frying it. And then they're stir frying it afterwards to get that flavor. But then as I researched the dish more, I found the flavor is actually not coming from stir frying the shrimp.

It's coming from salt that they've essentially stir fried. And so I thought to myself like, how on earth could just cooking salt in a wok, give it a smoky flavor? So I went on Twitter and I asked people like, I asked people to help me design some experiments and I spent a night just basically testing things out and posting the results. But as, as I wrote in that New York times story about walk, Hey, the three basic flavors that I associate with walk.

Hey, are the smokiness that comes from vaporized oil, the seared sauces that you get from adding sauces directly to hot metal and the flavor of that black oxide interacting with food. So the smokiness that comes directly from the wok surface itself. And that's what the salt will capture. So if you put salt in a wok and heat it up until it's basically smoking, the salt noticeably changes color. It becomes sort of darker gray.

And then when you take it out and season food with it, it has a very distinct sort of Wokhe aroma. And so, yeah, what I do is I toast a bunch of salt. I take it out, then I toast some, uh, Sichuan peppercorns and white pepper in the wok. And then I grind it all together, pound it all together in a mortar and pestle. And that's what I use as my sort of smoky salt and pepper blend that is great on fried shrimp, but it's also great on, you know, it's great on eggs, it's great on vegetables, whatever you want to add a little bit of smokiness to,

it's a good seasoning salt. Every time I talk to you, you surprise me. Well, that's good. I always learned something I just would never have thought about, like toasting salt at a wok. Kenji, it's been a pleasure, of course. Thanks so much for joining us here on Milk Street. All right, thanks, Chris.

That was J. Kenji Lopez-Alt. His book is The Wok, Recipes and Techniques. I've known Kenji for at least a dozen years when we started working together, and he always brought a knack for engineering. For example, he turned a Weber grill into a liquid smoke machine, and he also had a lot of curiosity. He found out that using vodka and pie dough, for example, makes a more tender crust because the alcohol evaporates during baking, resulting in less gluten development. His success is an appreciation that science is really just a tool, not an end in itself.

You know, most of us don't care about, let's say, Renaissance fresco techniques. We just enjoy looking at the Sistine Chapel. So I would say the arts, including cooking, are a reflection of our humanity, not our science. You know, good food is good food, no matter how you get there. That's it for this week's show. If you tuned in too late or just want to binge listen every single episode, you can download Milk Street Radio on Apple Podcasts, Spotify, wherever you find your podcasts.

To learn more about Milk Street, please go to 177milkstreet.com. There you can download each week's recipe, watch the latest season of our television show, or you can learn about our magazine and latest cookbook, Vegetables. You can also find us on Facebook at Christopher Kimball's Milk Street, on Instagram and Twitter at 177milkstreet. We'll be back next week with more food stories and thanks as always for listening. Christopher Kimball's Milk Street Radio is produced by Milk Street in association with GBH, executive producer Melissa Baldino, senior audio editor Melissa Allison, producer Sarah Clapp and Jason Tereschi, production assistant Amelia McGuire, and production help from Debbie

Paddock, additional editing by Sydney Lewis. Audio mixing by Jay Allison at Atlantic Public Media in Woods Hole, Massachusetts. Theme music by 2bob Crew. Additional music by George Brandel Eggloth. Christopher Kimball's Milk Street Radio is distributed by PRX.