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TERRY GROSS, host:

This is FRESH AIR. I'm Terry Gross.

In the world of food, my guest, Harold McGee, is famous as an authority on the science of cooking. He writes about why people perceive taste differently, how heat moves in cooking, whether it's an oven or a microwave and how to take advantage of that; why eggs solidify and how to best cook them or use them in custards and creams; why some meats are juicier when cooked at a low temperature; why beans give you gas and why it's so hard to roast a whole turkey. Wait until you hear his suggestion of how to solve that problem. McGee also writes about food safety and how to sanitize your kitchen.

Harold McGee's books can make you a wiser cook or, as in my case, help explain why you're not a very good one. His new book is called "Keys To Good Cooking: A Guide to Making the Best of Foods and Recipes." He's also the author of the bestseller, "On Food and Cooking: The Science and Lore of the Kitchen." He writes the Curious Cook column for the New York Times.

Harold McGee, welcome back to FRESH AIR.

Mr. HAROLD McGEE (Author, "Keys To Good Cooking: A Guide to Making the Best of Food and Recipes"): Thanks, Terry.

GROSS: One of the things I found really interesting about your book that kind of sounds obvious, but I never thought about it this way before, you say people perceive flavors differently.

And it's just not it's not just that we like different things, we're actually physically equipped differently.

Mr. McGEE: That's right. That's something that we've learned just in the last, I don't know, 10 or so years. When we taste something, experience the flavor of something, that involves two of our senses, the sense of taste, which happens on our tongue, and the sense of smell, which happens in our nose. And we have receptors on our tongues and in our nose to detect the chemicals that create flavor, and it turns out that we all have different sets of receptors and different numbers of receptors.

And so some of us are more or less sensitive to some flavors. Some of us can't perceive flavors, certainly flavors. It's kind of like the flavor equivalent of colorblindness. And so we all live in different worlds when it comes to tasting foods.

GROSS: Yeah, you say some people have more taste buds than other people do.

Mr. McGEE: That's right. That's right. Again, this is something that we've only really known for the last 10 years or so. And it goes a long way, I think, to explaining why it is that people have such strong opinions about what they like and don't like and how they can vary so much.

GROSS: And cravings.

Mr. McGEE: Yes, although cravings then gets into psychology, which is a whole other area of variability and interest.

GROSS: I suppose. So while we're talking about taste, you write that the best time to season food is shortly before serving it and often, like, when it's at the serving temperature.

I always thought see, whenever I read your books, I always learn that I'm even worse cook than I thought.

(Soundbite of laughter)

GROSS: Which is saying a lot. But I always figured that if you put in the spice early, it gives the spice more time to flavor whatever it is that you're cooking.

Mr. McGEE: Well, that's absolutely true. But it turns out that during the course of long cooking, with flavors that you've added at the very beginning, those herbs and spices are modified. Those flavors are modified, and they do kind of integrate into the dish as a whole, but they lose some of the freshness that they have when they haven't been cooked yet.

And so sometimes that's fine. Sometimes, all you want is that kind of slow-cooked, relaxed, melded flavor. But sometimes you want a little bit of that herb or spice to be a bit more prominent, a bit more noticeable on its own. And that's when it's useful to taste at the end and then add a little bit of whatever it is that you really want to taste to make sure that it's there.

GROSS: So right before serving?

Mr. McGEE: Yeah, and you're right that doing it at serving temperature is important because flavor balances change with temperature. Foods taste different when they're piping hot compared to when they're room temperature or warm.

And so it's important to wait until the food is around the temperature that you're going to serve it at and then do the seasoning.

GROSS: While we're talking about spice and flavoring, why is that lemon juice or vinegar can make flavor brighter? I mean, you say acidity is especially undervalued as a general flavor booster.

Mr. McGEE: That's right. And it turns out that again, one of the things we've learned about the experience of flavor is that taste and smell really work together as a kind of combined sensation for appreciating foods.

And so the aroma of a food can actually be changed by taste elements like saltiness and acidity. And so it turns out that when we adjust things like salt and acid, we're actually helping to make the aroma, the whole experience of the food, that much more vivid.

And salt and acid are the two tastes in particular that help to bring out all the other components of a food's flavor.

GROSS: Why does salt help enhance a food's flavor? I mean, you don't smell salt. I don't think you do, anyway.

Mr. McGEE: That's right. So a couple of things happen. One is that salt changes the chemistry of the food in such a way that it makes aroma molecules want to leave the food. And strange as it may sound, the more an aroma molecule, a flavor, wants to leave the food, the more easily we can perceive it because it has to get up into our nose for us to notice that it's there.

So salt does that. Salt helps flavors kind of jump out of the food and into our nose, and so we sense them more vividly.

And the other thing is that it seems to have an effect in the processing that the brain does to the experience of flavor. If we eat a food that's got a certain aroma, and it has no salt, our brain registers that and kind of gives us not much of a sensation.

But if we add a little bit of salt, then the brain seems to be making a judgment. Well, you know, there's something useful here nutritionally, and so pay more attention to that flavor. And so the flavor becomes more prominent.

GROSS: So is there a difference in terms of how much aroma the salt releases if you put the salt in while you're cooking or if you just sprinkle the salt on the salt shaker after the dish is done?

Mr. McGEE: Well, it's true that when you add salt to a food as it's cooking, it's going to encourage some aroma molecules to leave more readily than they would otherwise, which means that they end up in the kitchen air so that the kitchen smells nice while you're cooking, but the aromas have left the food. And that's maybe not so desirable.

If you add it at the very end, then you don't have that kind of cooking period loss, and the aroma molecules leave the food when you want them to leave, which is in the process of eating.

GROSS: And since you value acidity as a flavor booster, and you talk specifically here about vinegar and lemon, how do you use them in the cooking process?

Mr. McGEE: Well, at the very end of cooking, when I'm making the last-minute adjustments to flavor, I simply taste whatever it is, say a pasta sauce or something like that. And then I actually do go through kind of a checklist, a mental checklist, because we have only four or five basic tastes, and so I just ask.

You know, does this have the right balance of salt? Does it, could it maybe use a little sugar, a little sweetness not to make it sweet, obviously sweet, but to just kind of round out the flavor? And the same with acidity.

Acidity is one of the flavors that is mouthwatering. Acidity makes our saliva flow, and in the process of eating, that's a very pleasant experience. That's why we talk about food as being mouthwatering, and acidity can really contribute to that.

So I just try to run through that checklist and make sure that the sauce has everything that it needs to taste as good as it can taste.

GROSS: Is acidity more mouthwatering than sugar and sweet?

Mr. McGEE: It is, yeah. It causes more saliva flow, you know, to take mouthwatering absolutely literally. There are two tastes that are especially mouthwatering. One is acidity and the other is umami, which is the flavor, the taste of MSG, which we it's a Japanese term, umami. The best translation for it, I think, is savory.

It's again this kind of hard-to-define but mouth-filling, mouthwatering flavor that you get from things likes aged cheeses, tomatoes, meat stocks, things like that. And that's especially mouthwatering, as well.

GROSS: You mention MSG. I always think of that as just, like, a chemical that's thrown in to make cheap food taste tastier.

(Soundbite of laughter)

Mr. McGEE: It is that. It is that, but the reason people add it, manufacturers add it to food to make it taste better is that they discovered that it's there in foods naturally, and this is their way of giving you the flavor of or an aspect of the flavor of tomato or parmesan cheese without actually giving you a tomato or parmesan cheese.

GROSS: If you're just joining us, my guest is Harold McGee. He writes about the science of food and cooking, and his new book is called "Keys To Good Cooking."

So you write about how heat moves in cooking, to help us better understand the principles of what makes our food taste especially good or what kills the flavor and makes everything tough and bad. So what are some of the basic principles we should know about how heat moves in cooking?

Mr. McGEE: Well, the most important thing in the case of something like meat -meat and fish, and actually eggs and any protein food which is especially sensitive to heat - is that we're trying to reach temperatures inside the food, around 150 degrees Fahrenheit, something like that.

And of course, when we're cooking in an oven, the temperatures on the thermostat go up to 500 degrees, and we're often cooking at 350 or 400, which is much higher than that 150 that we're aiming for in the center of the food.

So what that means is that it's very easy to overcook. We're always using higher temperatures to cook foods than we're actually aiming for in the centers of the foods themselves. So it's good to realize that, and realizing that helps you appreciate the value of low-temperature cooking.

So you can get some great flavor on a roast, for example, by starting it at a high temperature in the oven to get some nice browning on the outside surface on the roast.

But then what you want to do is turn the heat way, way down so you cook the meat through much more gently and have a bigger window of opportunity when the meat is the correct temperature inside, which is much lower than the cooking temperature.

GROSS: Now why should you start with a high heat as opposed to ending with a high heat?

Mr. McGEE: That's a very good question, and in fact, back in the old days, and by the old days I mean the Middle Ages, that's exactly what people did.

And actually from the Middle Ages through about 1850 - I can be fairly precise about that, because if you look at old cookbooks, as I love to do, many of the old cookbooks say when you're roasting a piece of meat, start it far away from the fire to begin with to cook it through very gently and then bring it close to the fire at the very end to develop a nice color and flavor on the outside.

That was standard operating procedure until about 1850, when a German chemist got into the act. He was not a cook, but he thought he knew how foods cook, how natural materials heat and so on. And so he came up with the theory that actually it's much better to start the meat at a very high temperature to seal in the juices.

This man, Justus Liebig, was the originator of the theory that searing a meat at a high temperature to begin with seals in the juices, and it turns out that even though he was a chemist, he was completely wrong, and it was actually a much better idea to cook things the old-fashioned way than his version.

That said, if you sear the meat at the very beginning, you get the high-temperature cooking out of the way, and then you can cook as a gentle temperature just as long as you need in order to get the center just right.

If you do it the other way around, if you cook gently until the center is just right and then brown at the very end, then you risk, if you overdo the browning, overcooking the inside. So it is actually practically easier, I think, to do the high-temperature cooking at the beginning.

GROSS: Yeah, well, because I'm always in such a hurry, I've murdered a lot of meals by, you know, just turning up the heat real high, figuring it's going to cook faster this way.

Mr. McGEE: Yeah, yeah, and it does. But it's a bit like, you know, driving a car you're late for an appointment. You're driving fast down the road in order to get there, but you don't know exactly where you're going, and so you have to kind of check every driveway to see what the number is. And if you're going too fast, you'll go right by the place you're trying to get.

And it's the same with cooking. If you're cooking at a high temperature, then it's true that the food is cooking through faster, but it's much harder to put on the brakes and stop it at just the right point, and that's why you end up usually overcooking.

GROSS: So the principle here is that you want to pour in the amount of heat into the food that can be conducted into the center of the food because otherwise, the outside's going to get tough and burned before the inside gets hot?

Mr. McGEE: That's right. That's another part of the story. And so ideally, what you would do is cook the meat at a very high temperature to begin with, get a nice flavor on the outside, and unfortunately, that's the only way to get that wonderful browned, roasted flavor is with very high temperatures.

But then turn the temperature down almost to the temperature at which you want the meat to end up on the inside because that way, there's no way to overcook it. If you're shooting for 150 on the inside, and you cook it at 155, for example, then you're going to have a much better result than if you cook it at 350 all the way through and end up with part of the meat, much of the meat in fact, that's overcooked, and only the very center will end up at just the temperature you're looking for.

GROSS: Okay, so you're talking about the low-temperature, slow form of cooking meat. But if you look at the Chinese form of cooking, cooking that's done in the wok is done on a very rapid process. So are they using a different principle?

Mr. McGEE: Yeah, they are. They're cutting the meat up into very small pieces that cook through in seconds. And they start with a very hot wok. The wok is much hotter than the hottest oven is going to be.

And so what happens there is that you preheat the wok very hot, through in these small pieces of meat that only take 15 or 20 seconds to cook through, and that's about the same time that it takes for the outside to brown because of the very high temperature.

And so they hit the perfect balance by means of the strategy, very high temperature, very small pieces, very quick cooking.

GROSS: If you're just joining us, my guest is Harold McGee. He writes about the science of food and cooking, and he has a new book, which is called "Keys To Good Cooking." Let's take a short break here, and then we'll talk some more.

(Soundbite of music)

GROSS: If you're just joining us, my guest is Harold McGee. He writes about the science of food and cooking, and he has a new book, which is called "Keys To Good Cooking."

Do you ever use a microwave, and if so, what do you use it for?

I do use a microwave a fair amount, and I use it for all kinds of things. Microwaves are another very efficient way to heat foods because they are generally absorbed most efficiently by water.

And so you can put a ceramic container into a microwave oven, and it will absorb very little of the energy. Most of the energy goes into the food itself.

And it turns out when studies have been done on retaining vitamins in vegetables, for example, that microwave ovens do a much better job than boiling or even steaming. It's a very good, very quick way to heat foods, and I do cook vegetables in the microwave.

I cook thin fish fillets in the microwave in just a matter of a minute or so. It's also a reasonable way to cook something like polenta, which traditional recipes would have you stand at the stovetop and drizzle - and bring the pot to a boil and then drizzle the polenta grains slowly into the pot, stirring all the time to make sure they don't stick to each other and so on.

In a microwave, you just mix cold water, polenta, put them in the microwave, turn on the microwave, and basically the polenta grains swell and absorb the water as they heat up, and you end up with without having to worry about all the usual things that you worry on the stovetop, and you get a very nice polenta.

GROSS: I'm so surprised to hear that you maintain more of the nutrition of vegetables in a microwave than if you're cooking it on top of a stove because most people think of microwaves of, like, zapping the food and just basically killing it, convenient but not nutritious. And you're saying the opposite.

Mr. McGEE: Right, and that's I have to say that of course you can cook vegetables badly in the microwave by overdoing them, but if you cook them with as much care as you would boiling for example, so checking them every once in a while to see what the color looks like and whether they're, you know, just done, just past crunchy, it does turn out that because the process is so rapid, microwaves will kill enzymes in the vegetables that actually degrade the nutritional value.

So if you heat green beans, for example, as the temperature goes up, there are enzymes in the beans that will essentially use up the Vitamin C that's in those green beans, and if you let the enzyme do that, it'll do it until there's almost none left.

But enzymes are sensitive to heat, but if you put them in boiling water and keep the water at the boil, you kill those enzymes and maintain much of the Vitamin C. The same thing is true in a microwave, where the energy is going straight into the food immediately, and so it kills those enzymes very quickly, as well, but without the problem you have in boiling of nutrients being leeched out into the water.

In a microwave, you just often you don't need to add any water at all, otherwise maybe a tablespoon, and there's no cooking medium in which to lose the nutritional value. So it stays in the food.

GROSS: My guest, Harold McGee, will be back in the second half of the show. His new book is called "Keys To Good Cooking." I'm Terry Gross, and this is FRESH AIR.

(Soundbite of music)

GROSS: This is FRESH AIR. Im Terry Gross. We're talking about the science of cooking with Harold McGee, who is an expert on why foods behave the way they do when they're cooked and how to apply that information to recipes. McGee is the author of the bestseller "On Food and Cooking: The Science and Lore of the Kitchen." His new book is called "Keys to Good Cooking."

So you debunk some myths in your book and one of them is that cooking in liquid will make food moist and you say that's especially not true if the food is meat, fish, shellfish, dairy products, eggs. Why isn't that true? I mean something swimming in water, shouldn't it be more moist?

Mr. MCGEE: Well, that's what you'd think and I think that's why the myth persists is that it seems commonsensical. The problem is that protein-rich foods are very sensitive to temperature. And so take an egg, the egg white is 90 percent water and just 10 percent protein. So you cook it and the protein denatures and you end up turning the liquid white into a solid, where there is this kind of structure created by the proteins and the proteins are holding the water - the 90 percent water in the crevices between the proteins.

What happens when you cook something in water, often you'll let the water get up to the boil. And if you let the water get up to the boil then the temperature is 212 degrees, usually you want to cook protein-rich foods only to about 150, that's when they coagulate and form that solid superstructure that retains the moisture. If you cook them above 150 then that structure begins to contract - begins to squeeze. It's almost like squeezing on a sponge which has a lot of water in it. And what happens when you squeeze is that the structure shrinks and the water gets squeezed out.

And so if youre cooking in hot water, it's very easy to let that hot water go way above 150 degrees - we're often cooking as I say, at the boil or at a simmer. And if you let that happen long enough then you're going to overcook the proteins and squeeze the moisture out.

GROSS: So is that why eggs become hard-boiled in boiling water?

Mr. MCGEE: That's right. And that's why you can get much tenderer eggs - hard-boiled eggs, hard-cooked eggs, I prefer to call them, because you actually don't want to boil them. You can get very tender and delicious hard-cooked eggs by cooking them at a much lower temperature than the boil. Again, because it's gentler on the proteins and so they don't get overcooked and their water squeezed out.

GROSS: Is that also why milk curdles when you cook it - when you cook it past the boiling point?

Mr. MCGEE: Actually, milk is a special case because it's proteins are actually fairly resistant to heat. In fact, you can boil fresh milk until it reduces almost to the point of solidifying. That's the basis of a lot of wonderful Indian desserts, cooking sugar and milk down until it's this wonderful thick paste - delicious. But what makes milk curdle more often than not is acidity. Its proteins are resistant to heat but very sensitive to acidity. That's why we can make yogurt, for example. And so if milk has been sitting around for a while, it's not perfectly fresh, it's developed some acidity and then you heat it, that's when it curdles.

GROSS: In writing about vegetables, you say - and I never knew this - that the flavor of most vegetables are there to serve as chemical weapons to deter insects and other creatures from eating them.

Mr. MCGEE: Mm-hmm.

GROSS: That sounded really surprising to me, especially because some of the like broccoli or zucchini when it's growing isn't particularly fragrant or anything.

Mr. MCGEE: Well, exactly. It's not fragrant. But then you bite into it and it's a different story. Zucchini is pretty mild, but broccoli is a good example. Broccoli and all the members of the cabbage family have a very distinctive flavor, which is due to chemicals that are there to deter insects for the most part, from eating them. And so broccoli - raw broccoli - for example, is pungent. Mustard greens, which are exactly in same family, has much, much more pungency, so it is kind of a spectrum of strengths. But most of the flavors that we enjoy in strongly flavored vegetables let's say, so cabbage family, onions, garlic, things like that, are due to defensive compounds that the plants make in order to prevent creatures from consuming them.

GROSS: Why does the flavor of those vegetables change so much when they are cooked?

Mr. MCGEE: Well, because heat is a form of energy and whenever we heat anything, if we heat it enough, we begin to transform the molecules that make that material up. And the aroma compounds in foods are especially vulnerable to, or maybe susceptible to change by heat and air because we are always cooking in an atmosphere that contains plenty of oxygen. And so the more we cook a food the more we're going to transform the molecules that make it up and so more different the flavor is going to be.

GROSS: My guest Harold McGee. His new book is called "Keys to Good Cooking." We'll talk more about kitchen science after a break. This is FRESH AIR.

(Soundbite of music)

GROSS: If youre just joining us, my guest is Harold McGee. He writes about the science of food and cooking and he has a new book called "Keys to Good Cooking."

In writing about food safety while you cook, you say equip your kitchen with small and gauze bandages, antibiotic wound cream, and the fire extinguisher -which leads me to ask, what was your worst mishap in the kitchen?

(Soundbite of laughter)

Mr. MCGEE: Let's see, I was once not in my kitchen, but in another kitchen, flamb�ing something, you know, adding it was - I think it was duck - and I was adding some brandy and then put a match to it in order to flamb� it, and that's a wonderful way to get a nice kind of caramelized flavor in the food as well as the flavor of the alcohol, and I had the vent on - the vent fan. So air was being sucked from the stovetop surface up into the vent. And I lit the pan and the flames leapt up and leapt onto the screen over the vent which was covered with grease and the grease caught on fire.

(Soundbite of laughter)

Mr. MCGEE: And so I had this kind of column of flame from the frying pan up to the vent and then I imagined through the vent and into the vent shaft up to the roof. So that was pretty bad. I turned the fan off, covered the pot, and just yanked the screen off onto the stovetop surface and it smoked a lot but it didn't burn any further.

GROSS: So we asked some of the members of the FRESH AIR staff for some questions that they want answers to pertaining to science of food and cooking.

Mr. MCGEE: Mm-hmm.

GROSS: So I've got a couple of those for you.

Mr. MCGEE: Okay.

GROSS: What's the difference between baking powder and baking soda?

Mr. MCGEE: Baking soda is sodium carbonate - bicarbonate. It's a pure chemical and it's an alkali that reacts with acids to produce carbon dioxide gas. So it's a very pure material and a single material. Baking powder is a mixture of baking soda and an acid that will react with it in order to make carbon dioxide gas together with some cornstarch to kind of give you more material to work with so that it's easier to measure out. So baking powder is a complete leavener, baking soda is half of a leavening combination.

GROSS: Which do you usually use? Does it depend on the recipe?

Mr. MCGEE: Yeah, it depends on the recipe. If the batter, for example, contains an acid of some kind, like buttermilk is frequently used in griddle cakes, pancakes, that kind of thing, then the baking soda will react with the acid in the buttermilk to make bubbles. But if you are making a pancake recipe with just milk, then you need baking powder because it doesn't have an acid in the rest of the batter.

GROSS: Okay. Another question. Would you recommend wooden or plastic cutting boards?

Mr. MCGEE: That has been a long-running controversy between manufacturers of each, and it turns out that wooden cutting boards are good in a couple of ways. One is that they're porous and so they tend to soak up juices - cutting juices from cutting meats and fish, for example, and that carries the bacteria down into the cutting board where they're not at the surface anymore. And the other thing is that woods often antibacterial compounds in them and so they help -they're kind of natural antibiotic in the surface of the wood.

Plastic cutting boards are easier to clean and are safer to put in the dishwasher, for example. But they also will tend to develop scars and bacteria can lodge in the scars and cause problems later. So I actually have a couple of each and use both. And when the plastic cutting board develops scars, it gets kind of rough to the surface, then I replace it.

GROSS: Okay. When you are thickening a sauce when should you use cornstarch, when should you use flour and do they work on different principles?

Mr. MCGEE: Flour contains starch and so that's why it will thicken the sauce in the same way that cornstarch does. Cornstarch is a pure starch. Flour has some protein in it as well. And so when you make a sauce with flour the sauce is quite to the opaque because it contains the proteins as well as the starch. When you make a sauce with cornstarch it's going to be not exactly clear but more translucent because it doesn't have the proteins to get in the way of light passing through the sauce. So you can use both. They have different appearances and they have different strengths because one is pure starch, the other is only 70 percent or so starch, and so you need more flour in order to get the same amount of thickening.

GROSS: Are they five, like, must-have kitchen items that you would name?

Mr. MCGEE: Well, let's see, I think two items that many cooks don't have but that can make a huge difference are a scale and a good thermometer. And by a good thermometer I don't mean the standard, what's called instant read thermometer, which in fact, is nothing of the sort, but a digital thermometer which are no longer that expensive. They're, you know, very reasonable - $50 or so, it'll last for a good long time. And you want to look for one with a very thin probe because the thicker the probe the longer the thermometer needs in order to register the correct temperature, and because you've got that big thick probe in there - in the middle of the steak or piece of fish - it'll actually cool the thing that you are trying to cook down so you'll end up with a lower temperature reading than the actual temperature of the food and so you'll end up overcooking it. So a good digital thermometer that registers quickly is a godsend.

And then scale because measuring ingredients by volume - cups, spoons, things like that - just isn't accurate. You're weighing - youre measuring with a spoon or a cup not just the ingredient itself, but also the air that it happens to trap because of its particular structure. So kosher salt, for example, is much less dense than regular granulated table salt. And if the recipe calls for a tablespoon and doesn't specify which, you can be off by a factor of two, even though youre measuring exactly a tablespoon. So a scale measures the actual amount of salt, not salt plus air and just gives you much more control over cooking.

GROSS: If youre just joining us, my guest is Harold McGee and he writes about the science of food and cooking. His new book is called "Keys to Good Cooking."

Now, you say that the thing that got you started along this path of studying the science of food and cooking was when after watching the great Mel Brooks Western comedy "Blazing Saddles," there's a great scene where everybody is sitting around eating beans and then, shall we say, releasing gas, and so you said that that got him to ask you the questions like why does that happen after you eat beans, and you went and investigated and that got you down this path of science and cooking. So answer the question for us.

Mr. MCGEE: Yeah. So it turns out that all seeds have storage foods in them to nourish the seedling until the seedling is big enough that it can nourish itself by photosynthesis, and so different seeds use different foods to feed the seedlings. And it turns out that the bean family tends to feed its seedlings with carbohydrates, that unlike starch or sugar our bodies are not capable of digesting. We can handle starch and sugar molecules just fine but we cannot deal with these oligosaccharides, as they're called. And so what happens when you can't digest something, well, it just stays in your digestive system instead of being absorbed. And it turns out that the bacteria that live in our large intestine are perfectly capable of digesting these oligosaccharides and when they do so, they generate a variety of gasses actually, hydrogen, methane, and that's why we end up with gas when we eat beans.

GROSS: Does cooking the beans help at all?

Mr. MCGEE: It does, because it can break those oligosaccharides down into smaller subunits that our bodies can actually deal with and also just transform some of them into other molecules that dont cause the same problem. So cooking does indeed help.

GROSS: Youve been writing about food and the science of cooking for at least a couple of decades now, right?

Mr. MCGEE: Yeah, since the late '70s.

GROSS: Okay. So what's one or two of the ways that you think the food landscape has most dramatically changed since you started?

Mr. MCGEE: Oh boy, it has changed so much. When I first started writing, there was not that much interest in specialty coffee, or coffee quality in general, and nobody knew anything about olive oil, and balsamic vinegar had not arrived on our shores. So much of the world food culture was unknown to us, and we weren't as a people that interested in food. And then, I think for a variety of reasons, we've become much more interested, much more aware, things are now available - readily available in our local markets that were never available before, and so it just seems to me that people are eating a much more varied diet, much more interested in what they eat. And in the case of people who still cook, they're interested in understanding that process and in how understanding can help them do it better.

GROSS: So Thanksgiving is coming up, Christmas too, which for a lot of people will be making turkeys, and one piece of advice I want to ask you about from your book regarding turkeys is you say it is very difficult to roast a whole bird and do it well. Why is that?

Mr. MCGEE: It's because the whole bird has two very different kinds of meat on it, the breast meat and the leg meat. Breast meat is very delicate and really dries out very easily above 150 degrees. The leg meat has a lot more connective tissue, it's fattier, and it's actually much better at something more like 165 or even 170 degrees. But they're both on the same bird. They're both in the same oven when you are cooking the bird whole, and so the question is, how can you possibly get two different donenesses is in two different parts of the same bird? It takes some thought and planning and some tricks to come as close as you can.

GROSS: Share one trick with us?

Mr. MCGEE: Take the bird out ahead of time and let the legs warm up a little bit while you keep the breasts covered with ice packs. That way you keep the breasts cold, the legs warm up by maybe 10, 20 degrees, and that way when you put the bird in the oven, youve already built in a temperature differential. The breasts are going to end up at a given time less cooked than the legs, and that's exactly what you want.

GROSS: Wow, that was going to look a little weird.

(Soundbite of laughter)

Mr. MCGEE: It looks weird, yeah, to begin with, especially if you use an ace bandage to hold the ice packs in place...

(Soundbite of laughter)

Mr. MCGEE: ...because they're kind of slippery and - so that's what I do. So, yeah, it does look a little peculiar, but what you care about is what the bird looks like when it comes out.

GROSS: Well, Harold McGee, thank you for the explanations and the advice. Thank you so much for talking with us.

Mr. MCGEE: Pleasure. Thank you, Terry.

GROSS: Harold McGee's new book is called "Keys to Good Cooking." You can read an excerpt of the book and find a list of all the tips he gave during our interview our website, freshair.npr.org.

This is FRESH AIR.

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