IRA FLATOW: This is Science Friday. I’m Ira Flatow. I want you to think about the best meal you’ve ever eaten. Maybe it was something delicious you had while you were traveling to a far off city. Or perhaps it was home-cooked by somebody you love made from simple ingredients.

And now think about what made that meal so good. I’m guessing the odds are that the answer lies in the flavor. Sure. Flavor is arguably the most important part of a meal. If the flavor of something is off or undetectable, it can jeopardize your enjoyment, right? There’s so much science that goes on and behind what we taste. Did you know that?

Our next guest wrote a whole book about it. Arielle Johnson, author of Flavorama– Unlocking the Art and Science of Flavor. She’s in New York City. Welcome to Science Friday.

ARIELLE JOHNSON: Thank you so much for having me.

IRA FLATOW: You’re welcome. You have such a– you have quite a resume. I mean, you have a PhD in Flavor Chemistry. You’ve worked at some of the best restaurants in the world, including Noma in Copenhagen. That is something. How did you get interested in the chemistry behind flavor?

ARIELLE JOHNSON: Well, I was always pretty interested in science generally and pretty interested in food. And I guess eventually, while I was in high school, Ferran Adria, the chef at El Bulli, which is like a super influential experimental Spanish restaurant– so he was on the cover of the New York Times magazine. And he was holding this little container of carrot foam. And I was like, What is that?

And it was a whole article about how they were they were using a sort of scientific understanding of food to make insane, novel, completely out there cuisine. And I was like, oh, clearly, that’s what I need to be doing.

IRA FLATOW: Yeah. Well, that’s what I want to get into, you being a chemist and a flavor specialist. I want to ask you the chemistry behind flavor. When we taste something in our mouths, what’s the chemistry that’s going on in there?

ARIELLE JOHNSON: Well, so flavor is a mix of mostly taste and smell. The other senses feed into it. But if you’re thinking about the main players here, it’s taste and smell. And the flavored part of anything you eat is really like a tiny, tiny component of it– less than maybe 5%. In the case of smell, it can be one part per million.

IRA FLATOW: Wow.

ARIELLE JOHNSON: So there’s– yeah, there’s molecules in food that we have either taste or smell receptors for. And those molecules eventually find those receptors that are shaped sort of like a special catcher’s mitt. A lot of them grab onto the molecules and then send a signal to the brain, which sort of knits it all together to create our perception of flavor.

IRA FLATOW: Speaking of flavor, then, are there some flavor molecules that are easier for us to taste than others, or hit our tongues faster than others?

ARIELLE JOHNSON: I think we’re probably, in terms of taste, most sensitive to bitter compounds just because we have our sense of bitter taste to protect us from potentially toxic materials. And since toxic things can be toxic in very small quantities, I think generally our most acute taste is for bitter.

When you get into smell, there’s some aroma compounds in bell peppers and sulfur compounds and wine and in garlic that we’re almost ridiculously sensitive to. They’re actually– while I was in grad school, some of my colleagues were working on methods to actually measure these things quantitatively because our nose is more sensitive than our chemical instruments were.

So there were materials that were in such tiny concentrations that you could absolutely smell and taste them but would not show up at all on your gas chromatograph mass spectrometer. So yeah– very, very, very sensitive.

IRA FLATOW: [LAUGHS] Especially wine tasters. They’ll say things about wine that you have no idea what you’re talking about. But they do. So that’s what’s important, I guess, right?

ARIELLE JOHNSON: Yeah. Yeah. Well, I mean, I think the sort of second component to a lot of my research was doing sensory analysis, which is basically very careful tasting. So I actually trained a lot of people to get good at describing the flavors that they were tasting.

IRA FLATOW: Now, speaking of flavors, I remember when we were all kids learning about the body parts. We were seeing a map of our taste buds. And it had certain sections dedicated to certain tastes. But is it true it turns out that’s not exactly right about our taste buds?

ARIELLE JOHNSON: Yeah. We’ve pretty much got all five kinds of taste buds all over our tongue.

IRA FLATOW: We do?

ARIELLE JOHNSON: More on like the front and the sides and the back, but there isn’t really a special region just for bitter or umami or sour. That’s a fairly persistent myth, unfortunately.

IRA FLATOW: Wow. Now, if you go to the grocery store, you see there are many different types of salt. And I use salt a lot in cooking and making bread and stuff. There’s sea salt. There’s a pink Himalayan salt. There are more expensive salts than others. Are there really various types of salt that are chemically different?

ARIELLE JOHNSON: Well, so all salt is sodium chloride. So in that sense, all salts are the same. Yeah. But there’s also small amounts of impurities. So those are the things that make you know Himalayan salts pink and things like that.

And there is research that has found that when you dissolve sort of specialty salts in water, so to remove any effects of texture because they’re all dissolved, you can actually taste differences between them. So these sort of trace minerals and other, quote unquote, “impurities” are contributing something to the flavor of the salt. It’s minor, but it’s definitely there.

IRA FLATOW: Wow. You were talking about how important it is that you use your nose when you’re tasting something because your nose and your taste buds are working together. How does that actually happen? Is there a pathway or–

ARIELLE JOHNSON: Yes.

IRA FLATOW: How do they coordinate?

ARIELLE JOHNSON: There is a pathway. When one says, when one hears that smell is an important part of flavor, most people hear smell and think like sniffing. So like, oh, when the food is in front of my face, I’m sniffing it. And that smell is part of flavor. And that’s a small part of flavor.

But once you have food in your mouth, the smell molecules in it will travel up the back of your throat and through the back of your nasal cavity and then attach to your olfactory receptors there. So it’s a special kind of smell. We call it retronasal olfaction, or sniffing would be orthonasal olfaction. Yeah. So–

IRA FLATOW: So that’s why when you have a cold, it never makes that journey from the back up to your nose because your nose is stuffed.

ARIELLE JOHNSON: Exactly. Yeah. And that’s, I think, one of one of the best ways to get people to understand that smell is a part of flavor is when– if you have a cold and everything tastes flat, or like, oh, the flavor is very muted. That’s flavor minus smell. So that’s taste on its own.

IRA FLATOW: I didn’t know that. Wow. That is good to know. I also didn’t know until reading your book that we have 400 types of smell receptors.

ARIELLE JOHNSON: Yeah, approximately 400 different types of smell receptors. Each one has their own gene, and that family of genes– it’s actually a superfamily of genes– is the largest group in our genome.

IRA FLATOW: So you have one for smokiness, another for sweetness in our noses?

ARIELLE JOHNSON: Yeah. I mean, smell is a little weird compared to taste. So taste you have– it’s almost like pressing a piano key, and you get one note from that. So you press the C key, you get C. Activate– put salt on the salt receptor, it tastes salty.

With smell, we’ve kind of developed a more flexible system. So it’s a little less like pressing a piano key and a little bit more like reading a bar code. So each of our 400 receptors will bind to different degrees with many different smell molecules. And any smell molecule will bind with several different receptors.

So you generate essentially like a two-dimensional QR code. That’s the pattern that gets created on your olfactory bulb. And then that gets sent to your sort of emotional and memory and eventually cognitive parts of your brain.

IRA FLATOW: I like that vision. Yeah. A big focus in your book and in your work you do is fermentation. Now, I do fermentation in my kitchen from my sourdough bread to some vegetables. What is it about fermentation that makes it such a driver of flavor?

ARIELLE JOHNSON: Well, so when you do fermentation, you’re essentially transforming ingredients with microbes. So the microbes might be yeast. They might be lactic acid bacteria. They could be certain molds or acidic bacteria. But basically, you’re giving these microbes a nice environment to live in and the food that they like to eat. And, in exchange, they’ll consume that thing and then produce byproducts essentially that happen to have a lot of flavor.

So with lactic acid bacteria, the biggest one is lactic acid, which is nice and tangy. So that’s why you know sauerkraut tastes so different from raw cabbage. But there are also a lot of minor metabolites, we call them, because it’s a product of the metabolism that add to the aroma of ingredients. So we love fermentation because it makes more flavors.

IRA FLATOW: Well, when I opened my jar of starter as it’s getting ready and it’s blooming, it smells so wonderful.

ARIELLE JOHNSON: Yeah. Yeah.

IRA FLATOW: It’s amazing what that smells like. Now, flavor is largely a personal preference, right? I mean, some people love sweet things. Others don’t. Same goes for a sour or a spicy.

So how do you, as a chef, grapple with this, making something unique and flavorful? I mean, do you take those differences of people in mind? Or you just say, I want it this way, and I don’t really care what the public thinks about it– what most people care?

ARIELLE JOHNSON: Well, I mean, I think you want people to have a good time. Otherwise, you wouldn’t be in hospitality. But–

IRA FLATOW: That makes sense.

ARIELLE JOHNSON: [LAUGHS] But I think when we’re doing a new dish– so not just like a version of an existing dish, but some kind of totally new dish– generally, what makes it successful is if some part of it is novel and not seen before, but that there is some familiarity there, whether that’s in format or flavors or something. So as long as people are willing to be like a little bit adventurous, generally if you give them something that’s a little bit familiar and a little bit novel, they will have a good time.

IRA FLATOW: That’s interesting. Does sight– when you look at food, does it influence how you think it might taste and what the flavor might be?

ARIELLE JOHNSON: Oh, a huge amount.

IRA FLATOW: Yeah? Tell me about that.

ARIELLE JOHNSON: Absolutely. So if we think of flavor as a sort of tool that humans as an organism use to figure out what to feed ourselves, to get good things and not get bad things, so, of course, you’d use as much information as possible to get that fully fleshed out picture of whether something’s good and what it’s going to taste like. So yeah, vision is a big one for setting expectations.

There’s a classic sensory science experiment where when you add green dye to orange juice and give it to a taste panel, they will generally think that it tastes like limeade instead of orange juice just from the color. So they get this signal of like, oh, citrusy and sour and sweet. It’s something, but it’s green. Got to be limeade.

IRA FLATOW: Right. I once did a TV show, a science TV show, where we took a scoop of mashed potatoes and put it on an ice cream cone.

ARIELLE JOHNSON: Oh, man.

IRA FLATOW: And boy, the faces people thought when they thought it was going to be vanilla ice cream. They had no idea what they were eating. It took quite a while for them to figure this out.

ARIELLE JOHNSON: Yeah. No. Expectations and context are huge for being able to understand what you’re eating. So yeah, I’m sure they were big fans of you after that.

IRA FLATOW: Let me remind everybody that this is Science Friday from WNYC Studios. In case you’re just joining us, we’re talking about flavor with Arielle Johnson, author of Flavorama. All right. Tell me some tips a beginner can take advantage of harnessing the power of flavor in our cooking.

ARIELLE JOHNSON: Yeah. Well, so lots of different ways. Since flavor is a perceptual and psychological phenomenon, sometimes that’s the most important thing happening in a flavor situation. A lot of cooking techniques are about selectively moving flavor molecules around. I know that sounds very abstract. But essentially, brewing a cup of coffee or making chicken stock or both– that moving flavor molecules into water.

And then there’s lots of cooking techniques we’re actually doing chemical reactions. So smoking, caramelizing, and browning are big ones. And fermentation is huge for reacting molecules.

So taking a step back– some simple things. So if you have food that’s too bitter, there are actually some tricks that you can do to make it taste less bitter without actually removing bitterness. The big one is to add salt.

So if you have any kind– like a salty dog cocktail, which has grapefruit juice. Or, in fact, some people like to put salt on their grapefruit. The salt will actually interfere with your perception of bitterness and reduce how bitter the thing tastes to a statistically significant degree.

IRA FLATOW: No.

ARIELLE JOHNSON: Yeah. Yeah.

IRA FLATOW: No kidding.

ARIELLE JOHNSON: Acid and sweet are also good at that, but salt is particularly good. A lot of people love browned food. We love coffee. We love chocolate. We love toast, roasted chicken, roast beef.

IRA FLATOW: Barbecue.

ARIELLE JOHNSON: pretzels, Barbecue. Yeah. So all of that comes from one reaction, or family of reactions, called the Maillard reaction. It is the reaction that creates brown color and sort of toasty brown flavors. That’s a reaction between amino acids and sugars.

So if you want more browning, you can think about adding more sugar, obviously. People do that to add caramel color. Right but if you can increase the amount of protein and amino acids you have, you’ll get much more browning.

It’s also very sensitive to pH– to acidity and alkalinity. You get more browning under alkaline conditions and less browning under acidic conditions. So if it’s going to brown, you can add some acid.

If you want as much brown as possible, you can add, for example, a little baking soda. And that has to do with actually whether the amino end of the amino acid is protonated– not that you have to think about that as a cook. But it’s weird where these things will eventually take when you look into their mechanisms.

IRA FLATOW: Last question and observation about your book. When I opened it immediately, it is a fun book. I mean, I thought it was a kid’s book when I first opened with all the pastel colors and the wonderful drawings.

ARIELLE JOHNSON: Thank you.

IRA FLATOW: What made you decide to do it that way?

ARIELLE JOHNSON: Well, so I actually illustrated it as well. And I’ve done a lot of illustrating of talks and things that I write just because I feel– the point of writing something or talking to someone is communication and getting a point or a message or helpful stuff across.

So, to me, I think there’s– certainly, as an academic myself, there’s a strong pressure to take a very serious tone. But you don’t have to. And it’s actually more fun to read if you don’t. And I want people to understand, and pictures help with that.

IRA FLATOW: It is beautifully illustrated, beautifully written, and a joy to read, Arielle. Thank you for the book and for taking time to be with us today.

ARIELLE JOHNSON: It was a great conversation. Thank you for having me.

IRA FLATOW: You’re welcome. Arielle Johnson, author of Flavorama– Unlocking the Art and Science of Flavor. She’s based in New York. And if you want to read an excerpt from the book– yeah, this is a great book– you can go to our website, sciencefriday.com/flavorama.

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