IRA FLATOW: Thanksgiving is right around the corner, and for many people, that means we need to start thinking about what’s going to be on the menu for dinner that night. I know lots of us have already started thinking about that. Are you doing a classic turkey? Maybe you’re sticking to vegetarian? How you prepare your food for the holiday takes a lot of thought, and if you want to get competitive edge on the food front, there’s a ton of science, a ton of chemistry in food preparation and cooking and no one better to answer your Thanksgiving food questions than my guest, Kenji López-Alt, cookbook author and food scientist based in Seattle, Washington. Welcome back to the show, Kenji.

KENJI LÓPEZ-ALT: Hey, thanks for having me.

IRA FLATOW: So much chemistry in food, isn’t there?

KENJI LÓPEZ-ALT: Yes, quite a bit.

IRA FLATOW: Let’s start, then, with the centerpiece of most people’s or many people’s Thanksgiving meals, the turkey. Now, I know there’s a big argument that seems to happen every year, and that is to brine or not to brine.

KENJI LÓPEZ-ALT: Right.

IRA FLATOW: So what is brining, and what does it do to the meat?

KENJI LÓPEZ-ALT: Right, so brining, what it does– so the act of brining is when you take your turkey or your chicken or whatever it is and you dunk it in a saltwater solution and let it sit there, generally overnight or so. What it does is that that saltwater dissolves some of the muscle proteins that are kind of wrapped around the individual muscle fibrils, and so when your turkey cooks, what happens is those proteins contract.

And that’s what causes juices to kind of squeeze out. And so the hotter you cook it, the tighter those proteins contract and the more juices get squeezed out. What brining does is it kind of loosens up some of those proteins. It dissolves them so that they don’t squeeze as tightly, which means that, cooked to the same temperature, a turkey that has been brined will retain more moisture, about 7% more moisture, than a turkey that hasn’t been brined.

IRA FLATOW: Now–

KENJI LÓPEZ-ALT: Now, of course, the debate is whether it’s worth it or not. What I recommend is a process called dry brining, which is it gives you all of the advantages of a wet brine– plus, I think it tastes better, and it also means that you don’t need to pull out that five-gallon bucket or the cooler to soak your turkey. So essentially, all you do is you seasoned the turkey pretty heavily with salt. If you can, you want to get a little bit of salt up in between the skin and the meat on the breast in particular.

IRA FLATOW: Your fingers going under the skin then is what you’re–

KENJI LÓPEZ-ALT: Exactly, yeah, yeah, yeah, exactly. And then you leave it uncovered on a rack in your fridge, at least overnight and up to two nights. And so you get a lot of the same effects as brining, so it will retain more moisture. But you’ll also get kind of crispier skin because you’re not soaking it in water for a couple of nights. So I– [COUGH] excuse me. I think it’s a better method than just traditional wet brining.

IRA FLATOW: Well, I know lots of brining recipes have sugar in it. What’s the deal with sugar versus salt here?

KENJI LÓPEZ-ALT: Yeah, well, sugar is mainly going to be for flavoring and also to help it kind of brown a little bit. So if you do want to put a little bit of sugar in your turkey, whether it’s a wet brine or a dry brine, that will help it brown a little bit. But you do have to kind of be careful that it doesn’t go too far because turkey skin that’s been rubbed with sugar, it can– if you’re doing it low and slow in a smoker that’s one thing, but if you’re roasting it in the oven, it could start to brown a little bit too fast in which case you just want to check your oven temperature and ease back.

IRA FLATOW: I want to bring our listeners in on this 844-724-8255 if you have a question or a suggestion, 844-724-8255. Before we go to the break, I’ve got to ask you about this latest turkey recipe published in the New York Times this month, which uses a key ingredient that I have to say as a New Yorker and reading the New York Times, I was a little more than a little surprised to see, and that was mayonnaise. You put mayonnaise on your turkey. What is it about mayonnaise that you think results in a good turkey?

KENJI LÓPEZ-ALT: Well, you don’t need it to get a good turkey, of course. But what I found is that, if I’m going to be adding some kind of herb flavoring to it– so in the past, I might have done like a butter, an herb butter, or maybe an herb oil. The difficulty with herb butters is that it’s hard to get the butter just that right temperature, I think, where you can kind of spread it all over the turkey and get a nice even coating whereas mayonnaise, whether it’s straight out of the fridge or at room temperature, it spreads and it holds its place fairly easily.

So it makes it really easy to get those herb flavors into a sort of wet mix that you can then get all an even coating on the surface of the turkey. The other thing that mayonnaise offers over butter is that the protein in the mayonnaise– and this is true whether it’s a vegan mayonnaise, which is stabilized with plant proteins, or traditional mayonnaise stabilized with egg proteins. The protein in there is going to help solidify it, so instead of butter, which kind of melts away and just drips off, the mayonnaise kind of helps keep all of the herbs and garlic or whatever it is you put in your mix, right up there against the turkey as it roasts.

And by the time it’s done roasting, of course, there’s no kind of– it doesn’t look like mayonnaise. It all breaks, and it just looks–

IRA FLATOW: I feel better now.

KENJI LÓPEZ-ALT: Yeah.

IRA FLATOW: You don’t put mayonnaise on your pastrami, do you? No.

KENJI LÓPEZ-ALT: No.

IRA FLATOW: Different topic.

KENJI LÓPEZ-ALT: God, no.

IRA FLATOW: This is Science Friday from WNYC Studios. We’re talking about the science of cooking, and we’re taking your calls at 844-724-8255. I have a tweet that came in, and it’s kind of interesting. Why do we preheat the oven, John on Twitter wants to know. Is it a logical thing about standardizing cooking times, or does the immediate heat do something different or better than letting the food come up to temperature with the oven?

KENJI LÓPEZ-ALT: So it depends on the situation– on the exact recipe and the situation, but by and large, it would be the first answer, which is that all ovens heat differently. And so an oven that could take 45 minutes to preheat– someone’s oven might take 45 minutes to preheat. Some ovens might take 15 minutes to preheat.

So if you’re putting your food in as the oven’s preheating, you’re building a lot of unpredictability into the timing and into that recipe. So allowing ovens to properly preheat does standardize time. In certain recipes, there might be certain types of styles of roasting, where you would start at a really high temperature and then kind of drop the temperatures as you go along.

With those types of recipes, definitely preheating is what gives you that sort of blast at the beginning that allows you to kind of sear surfaces. So in those cases, there is sort of a functional benefit to preheating, same with if you’re baking a pizza or a loaf of bread. You really want to properly preheat not just the oven but also the stone or the steel that you’re baking on because all of that absorbed energy in the walls is what’s going to help your pizza or your bread get the oven spring, the nice big bubbles in them and the nice char on the surface. So in many cases, the preheating the oven is sort of a functional thing as well as a practical thing as a recipe writer.

IRA FLATOW: Is there a better pan than– what kind of pan to put the turkey in, physics wise, that will absorb irradiate the heat best?

KENJI LÓPEZ-ALT: Yeah, so I would say do not use the standard deep-walled roasting pan. I have a roasting pan that has walls that are maybe three-inches tall, and it’s made of heavy stainless steel. And it comes with a v rack meant for poultry. I think this is one of the worst ways you can actually cook poultry because what it does is the pan kind of shields the bottom of the bird, so the area where the thighs are meeting the backbone. It’s kind of shielding that area, and it’s preventing both radiant heat from the oven and, more importantly, convection, so hot air flowing around the oven, from getting to that area.

And so what ends up happening is that area cooks really slowly, and that’s the part where you’re always supposed to take the temperature because that’s the part you want actually cooked to the highest temperature. And so by the time that comes up to the right temperature, everything else, in particularly the breast, is heavily overcooked.

You should be using just a regular rimmed baking sheet, like a sheet pan, so a half-sized sheet pan, I think it’s like 23 inches by 18 inches. That’ll fit a 14– up to 14 pound or so spatchcock turkey or whole turkey, so that with a wire rack set in it. So the idea is that you’re going to get a lot better circulation under and around the turkey than you would with a deep-sided pan. And so your cooking is going to be a lot more even.

IRA FLATOW: All right, let’s go, lots– of course, you can imagine lots of folks want to talk about cooking. Paul in Conway, Arkansas. Hi, Paul.

PAUL: Hey, Ira. Long, long time listener, sir. Great program, previous–

IRA FLATOW: Thank you.

PAUL: Great programs before. I’d like to comment. I’ve cooked many a turkey over the years. I like to cook, and I really appreciate your guest’s smarts. What about fried turkey, guys? You Northerners are missing out.

[LAUGHTER]

IRA FLATOW: We have it up here. We’ve tried it. We’ve almost scalded ourselves with hot oil.

[LAUGHTER]

KENJI LÓPEZ-ALT: I love a fried turkey. I love a good fried turkey. Yeah, I think, space wise, it’s a little hard. It’s more intimidating.

IRA FLATOW: Well, what does frying do physically to the turkey? And thank you, Paul, for that call. What goes on in the turkey that’s different from roasting it to frying it?

KENJI LÓPEZ-ALT: Well, so the main thing is that you’re transferring heat at a much faster rate, so you’re really going to get extremely crispy skin. And all the meat around the outside is also going to crisp up. And then you’re going to be getting– you’re cooking really fast. So one of the important things that frying does is that you’re circulating– so in an oven, when you have a whole turkey, you can imagine the space inside the turkey, the cavity, where you might traditionally stuff it, for example, even if it’s unstuffed, even if there’s air in there, it kind of ends up sitting in place.

And so you don’t get very much good circulation inside the turkey as far as heat goes. So that’s one of the reasons why it takes so long to roast a turkey and why spatchcocking is so much faster. But deep frying a turkey, because oil is much more viscous, it kind of flows in and out. And so you’re really getting hot oil inside the turkey as well as outside, so you’re cooking it from both sides really, really fast.

So what that means is that it drastically cuts down on the total cooking time while also giving you really sort of crispy skin. And as long as you don’t overshoot the final temperature, as long as you’re very careful about using your thermometer, it can also be an extremely juicy way to–

IRA FLATOW: OK, we’ve talked turkey long enough. Let’s move on to– because there are a lot of people who are making vegetarian dishes. And we’ve got questions about what’s the best way to make a really good vegetarian gravy. Is it the heat, the cornstarch, or something else that really makes it work?

KENJI LÓPEZ-ALT: Yeah, well, so I think one of the things that makes it difficult to make a good vegetarian gravy compared to a meat-based gravy is that meats give you those amino acids, so glutamic acid, endogenic acid, and these things that we associate with savoriness.

So you want to look for sources to replace or enhance those savory notes and so– [COUGHS] excuse me, when it comes to vegan or vegetarian gravy, I think making a really good mushroom stock, maybe adding some kombu, like Japanese-style kombu seaweed, sea kelp, to it, to really sort of boost the umami factor.

Using dried mushrooms, like porcinis, can really improve the umami factor in a stock. And then also doing– using fermented things, so things like soy sauce and miso paste– I think I have a recipe for a vegan gravy on Serious Eats that uses all of those things, and then you just thicken it up at the end. And it can be really, really delicious.

IRA FLATOW: I really enjoyed your talking about the physics of roasting in the oven, and we have a question from Karen in Kansas City, Missouri. Hi, Karen.

CARRIE: Oh, it’s Carrie.

IRA FLATOW: Carrie, I’m sorry.

CARRIE: Oh, no problem. One of my biggest issues is always oven space on the day and trying to make sure I’m not overcrowding. And I’ve learned that crock pots can be a great alternative for some sides, so what’s some good suggestions on, when you’ve overcrowded your oven, how much space do you need if you’re kind of time lining out to have everything ready at the same time and let the turkey rest and all that stuff?

KENJI LÓPEZ-ALT: Yeah.

IRA FLATOW: Good question.

KENJI LÓPEZ-ALT: So I think, yeah, a good crock pot can definitely work well for some things. Having some of your dishes be OK at room temperature is also, I think– you can make a grilled vegetable salad or a roasted vegetable salad that is good warm but is also fine at room temperature, so thinking about dishes that you don’t really have to worry about as far as sitting goes is a good idea.

When it comes to oven space, at Thanksgiving, I grew up in a New York apartment, so little galley kitchen with a tiny stove. And I think the way we treated the oven on Thanksgiving was that, towards dinnertime, it would just become the warmer. So [COUGHS] excuse me, everything else is baked ahead of time, so the turkey was roasted. The sides were– the stuffing was baked in its dish. The Brussels sprouts were roasted and all kind of in heatproof containers.

And then once the last thing that you actually need to bake or cook in the oven is done, then you can just pile everything back in to rewarm. And I think, with dishes– Thanksgiving-type dishes are almost built for that. There are a lot of casseroles and baked things and things that are just fine reheated and are almost even sometimes better reheated.

IRA FLATOW: Yeah, they taste better.

KENJI LÓPEZ-ALT: So I don’t think you have to worry too much about– for most Thanksgiving dishes, I don’t think you have to worry about them going straight piping hot directly out of the oven onto the table.

IRA FLATOW: All right.

KENJI LÓPEZ-ALT: I think reheating them and holding them is totally fine.

IRA FLATOW: Let’s go to Slushy in California. Hi, Slushy. I’m sorry. I got your name correct?

SLUSHY: Yeah.

IRA FLATOW: Hi, go ahead.

SLUSHY: Hi. My question was are biscuits something that you can have for Thanksgiving? And also Kenji, do you have a solution for every time someone makes biscuits, the dough comes out not sticking together well and, when you bake it, it comes out hard?

IRA FLATOW: Yeah, what is Slushy doing wrong there?

KENJI LÓPEZ-ALT: [LAUGHS]

SLUSHY: I know.

KENJI LÓPEZ-ALT: So I definitely think you can have biscuits for Thanksgiving. Yeah, I can’t think of any occasion where you can’t have biscuits. I think they’d be great for Thanksgiving.

As far as the second question, I think I’d need to a little bit more about exactly what’s going on. So it sounds like the dough is coming out too dry, but the biscuits are also coming out too hard.

SLUSHY: Yeah.

KENJI LÓPEZ-ALT: And all I can think is that maybe–

SLUSHY: They’re coming out.

KENJI LÓPEZ-ALT: –maybe you need to be using a lighter flour, so instead of like an all-purpose flour, using something like White Lily or a biscuit flour or a cake flour that will–

SLUSHY: That’s.

KENJI LÓPEZ-ALT: –be a little bit lower in gluten, so more tender.

SLUSHY: That’s a good idea, but my mom, she’ll use– she’ll make– she’ll use all the ingredients because we have a whole book of ingredients that we kind of use for the biscuits. And whenever she makes them using the recipe, they turn out incredible. But I’ll use the same recipe, and they’ll turn out like literal cookies.

SLUSHY: So.

KENJI LÓPEZ-ALT: It sounds like maybe you need to– maybe you need to work with your mom more closely.

IRA FLATOW: Yeah.

SLUSHY: Yeah, that is a good solution.

IRA FLATOW: All right.

SLUSHY: So is that– when I kind of have family over, and I feel like if I do a baking assignment for my class, and I give them that, they’re going to– my reputation is kind of going to be ruined.

IRA FLATOW: It’s embarrassing. It’s embarrassing. All right, Slushy, we got to go on. But thank you. That’s an interesting phone call. Maybe your mom can help you out. Thanks for calling.

Let’s talk about– you mentioned before a little bit about leaving stuff out on the counter, and this is a question we get asked all the time. How long can I leave things out on the countertop and feel safe that the bacteria is not going to do its thing when it’s out?

KENJI LÓPEZ-ALT: It depends on– so there’s no hard and fast rule for this. There are what the government requires restaurants to do, too, which the easy version is that it can’t spend more than four hours between the temperatures of 40 degrees Fahrenheit and 140 degrees Fahrenheit total. So that includes the time that it takes to heat it up, the time it takes it to cool it down if you’re putting it in the fridge, and the time it takes to prepare and serve. So that’s–

IRA FLATOW: That’s not very long.

KENJI LÓPEZ-ALT: –limit.

IRA FLATOW: That is four hours.

KENJI LÓPEZ-ALT: Four hours, yeah. And realistically though, that’s sort of like the extremely safe version. Realistically, if you’re cooking in your own home kitchen and you roast a– you pull the green bean casserole out at 2:00 PM and dinner’s not until 7:00, I would feel totally comfortable serving that as long as you don’t have the cat jumping over it or the kids stepping in it or anything. But as long as you keep a relatively clean house and your ingredients are not moldy to begin with, I think that it’s totally safe.

IRA FLATOW: OK, before we run–

KENJI LÓPEZ-ALT: But follow those rules exactly.

IRA FLATOW: Sounds good. Before we run out of time, I got some other questions, some of them from our own staff members, and one of them is sometimes bad mashed potatoes are described as gluey. What’s going on there from a chemical perspective, that gluey, and how do you ungluey them?

KENJI LÓPEZ-ALT: You can’t ungluey the gluey mashed potatoes, so essentially, what’s happening is that you’re overactivating the starch. And so there’s a couple of ways that can happen. One of them is that you could be– the potatoes could be kind of boiled too violently for too long before mashing them, and so they’re kind of getting waterlogged. And then the starch molecules kind of expand and burst and [AUDIO OUT].

IRA FLATOW: Oh, we sort of lost him there.

[LAUGHS]

Let’s see if– well, see what happens when you’re talking about gluey mashed potatoes. You lose the line. Let’s see if we can get some phone calls in while we’re waiting. Let’s go to Bob in Spokane, Washington. Hi, Bob.

BOB: Hi, there.

IRA FLATOW: Hi, there. Go ahead.

BOB: OK, well, my favorite way to prepare Thanksgiving turkey is using a sous vide method, and that’s where the food is placed in a food-safe plastic bag and then cooked at a lower temperature in a water bath. Typically, I’ll take and suction the turkey, remove the leg quarters, the wings, and the breast meat. And one leg quarter and wing goes in a one-gallon plastic bag, and then the breast meat goes in another gallon plastic bag.

And then that’s– it’s dry brined with salt, and you can use herbs and spices on it. And then it goes– the dark meat goes in, starting at only 153 degrees, I believe it is, and it stays in for about four or five hours. And then you add the breast meat to that and drop the temperature down to about 145 degrees, as I recall, and then the whole thing takes about five hours to cook.

IRA FLATOW: Wow.

BOB: And when it’s done, it’s juicy. It’s flavorful. And then you take it out of the plastic bags, put it in a hot oven for a few minutes to brown it, and it’s delicious.

IRA FLATOW: Wow, wow, that’s a lot of preparation, isn’t it?

BOB: It is, but it turns out so well. And people say, well, yeah, but it’s not good enough to the 165 degrees. Well, because it stays so long at those lower temperatures, it actually pasteurizes it, so it’s safe at those temperatures.

IRA FLATOW: Who knew. Thank you for that suggestion, Bob, and your experiences.

BOB: Yeah, you’re Welcome.

IRA FLATOW: Let’s see if we can get another phone call in before we have to say goodbye because we are running out of time. Let’s go to Danielle in Santa Cruz, California. Hi.

DANIELLE: Hi, is this–

IRA FLATOW: This is–

DANIELLE: –Science Friday?

IRA FLATOW: It is–

DANIELLE: I cut out for a second.

IRA FLATOW: It is Science Friday. We’re having a little technical difficulty, so we’re hoping you’re going to save us, Danielle.

DANIELLE: Oh, we’ll see about that. I just wanted to ask– my mom always cooked Thanksgiving turkey in a really deep Mexican clay pot or called olla de barro, and I’m wondering how that makes it juicier and whether that’s an actual scientific phenomenon that would make the turkey cook juicier.

IRA FLATOW: I think Kenji is back. Kenji, did you hear that question? No. We didn’t him. Why does it make it juicier? I wish I had an answer for you, but I’ll see if we can– I’ll if we can get an answer for you offline, OK? Thanks for calling.

DANIELLE: All right, thank you.

IRA FLATOW: Thank you. Let’s see if we can get one more call in here. Let’s go to Frank in Dillsburg, Pennsylvania. Dillsburg, where is that, Frank?

FRANK: That’s right outside of Harrisburg, PA. It’s about maybe 20 miles West of Harrisburg, little rural town.

IRA FLATOW: And you have a–

FRANK: [INAUDIBLE]

IRA FLATOW: You have something you’re going to share with us.

FRANK: Yeah, just a quickie here. I know you’re almost done with the mayo issues, but I stumbled on a couple of years ago to using mayonnaise on the salmon that I grill. And I used to use butter and then put spices on it and grill it on both sides. And it sounds really disgusting when you explain to people or they looked at you’re putting mayo on it, but it is remarkable.

And I just understood why today because it doesn’t drain off, and The tenderness and the taste and, I guess, the conveyance of some of the spices makes it really good. My wife is a really great cook, and she thinks it’s the best salmon she’s ever had. We go all over and eat it.

So it’s really tender, tasty, really easy to do. Just put the mayo on both sides. Put your spices on. Grill it, and it’s wonderful.

IRA FLATOW: My mouth is watering, Frank.

FRANK: It’s really good, although it sounds really disgusting.

IRA FLATOW: And you discovered it on salmon, and you did it for your turkey.

FRANK: Yeah, yeah, I’m going to try it for the turkey now. I never heard of that, but it makes sense. It really does seem to work.

IRA FLATOW: Well, I will thank you for– thank you for taking time to be with us today, Frank. It’s a great suggestion.

FRANK: Well, thank you. Your program is wonderful. The diversity is great. I love you, so thanks.

IRA FLATOW: Thank you. Thank you. And we have run out of time. That is about all the time we have for now, and of course, if you want to hear from– if you want questions about what to do behind all your favorite Thanksgiving foods, we’ve got some hits up there on our website.

I want to Thank Kenji López-Alt cookbook author and food scientist based in Seattle for, well, so we had him on for most of the hour. We had a little bit of technical difficulties at the end. But boy, I learned a lot. I hope you did, too.

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