Kousha Navidar: You’re listening to All Of It on WNYC, I'm Kousha Navidar. Think about the last time you ate something that just blew your mind. Was there a certain flavor that was surprising or intense or satisfying? It turns out there's a lot of science behind flavor and how we experience taste and scent. A new book from Arielle Johnson is all about how our senses create the experience of food from our taste buds to the complex neuroscience of smell that create the more subtle hints of flavor.

Johnson actually has a PhD in Flavor Science, and she joined me recently to talk about her book. It's called Flavorama: A Guide to Unlocking the Art and Science of Flavor. We also took your calls and questions, but a reminder everyone, this is an encore presentation, so we can't actually take your calls live. I started by asking Arielle how she ended up on the path to become a flavor scientist.

Arielle Johnson: Well, so as the short version, always very interested in both food and science. Eventually figured out that there was a lot of science behind, not only industrial food, but also cuisine and gastronomy, and you could use chemistry to learn a lot about those things. Ended up going to UC Davis in Davis, California in the wine department specializing in flavor chemistry, so doing a lot of chemistry, sensory analysis, modeling of things.

Since then, I do a lot of work with restaurants on research and development, and experimentation, so making a lot of flavors with fermentation and other stuff. At this point, there're so many bits of science that I work on that I just say flavor scientist.

Kousha Navidar: Do you remember the first food in your life where you thought, "That flavor will stick with me forever. Wow, I want to learn more about that flavor"?

Arielle Johnson: It was definitely the smell of coffee, specifically coffee beans. When I was about three years old, I would start taking the coffee beans out of the shopping bag on the way home from the grocery store and smelling it really deeply. I was disappointed that brewed coffee didn't taste exactly like that smell, but it definitely piqued my interest in coffee, which I still am interested in.

Kousha Navidar: Now you have written a book and there are recipes in the book. It looks and feels like a cookbook, but it's not really a cookbook. How do you advise people to use this book?

Arielle Johnson: I would say it can be used as a cookbook, it can be used as a reference book. If you are interested in understanding the generals of how flavor works and how knowing about the science of flavor can apply to cooking at all, just flip through it and there’s a lot of shorter pieces of information that'll hook you in even if you're not a cook. If you are a cook, I would recommend thinking about flavors, tastes, smells that you like, and there's a whole section that's almost a field guide to all of those flavors, so that's a good place to start to understand what is sourness, what is an acid, where can I find sourness?

Kousha Navidar: It's funny because those questions lie at the very science of how taste and flavor works. Help us understand the sense of taste and the sense of smell. How do they combine together to create our sense of flavor?

Arielle Johnson: When we say flavor is taste and smell, usually if you're taking a bite of an apple, what you feel as flavor feels like it's just taste. Smell is actually a very big part of that, and that's not actually sniffing the apple before you bite it, although that is a little bit. You can actually smell food in your mouth as you're chewing it. We call that retronasal olfaction. It is responsible for pretty much everything about flavor beyond sweet, sour, salty, bitter, and umami. Fruitiness, roastiness, floral flavors, that all comes from smell.

Taste comes from taste buds on your tongue. That gets routed into the brain. Smell gets routed a slightly different route into the brain, and eventually, they come together in the orbital frontal cortex where we can recognize them, not just as tastes and smells, but as unified flavors, and then come up with descriptions and names for them.

Kousha Navidar: You mentioned that they get routed differently. Is there a special reason behind that, why that routing is different?

Arielle Johnson: It's a physical question actually. Most of our senses pass through the brainstem and through the "lower parts" of the brain before they get to emotions and thoughts. Smell is actually sensed directly with brain cells, that’s one side is anchored in your brain, one side passes into your nasal cavity, your nose, the inside. That, rather than going through the brainstem, goes right into the emotional centers of our limbic system, especially our amygdala. The Proustian story of dipping a madeleine in tea [unintelligible 00:06:06] --

Kousha Navidar: You stole my next question.

Arielle Johnson: Oh, sorry. Sorry.

Kousha Navidar: It's okay. It's okay. Go ahead.

Arielle Johnson: Yes, it is biologically and neurologically true and valid. That is exactly what happens. In fact, you'll often have an emotional connection or a memory of a flavor before you can even recognize what it is.

Kousha Navidar: We have Stephanie in Greenpoint with a question. Hi Stephanie. Welcome to the show.

Stephanie: Hi. I like to make fermented loaf without using much wheat, and I would like to know, for one thing, why things get tangy when you culture them. Also, what does it really do to the grains or to the chickpea flour, or barley, or whatever when you ferment it? Then any other thoughts about fermented foods and how your body senses them would be interesting.

Kousha Navidar: Thank you, Stephanie.

Arielle Johnson: Great. Well, so when we're talking about culturing, for example, making sourdough, or even yogurt, or sauerkraut, we're talking about food that becomes sour. The way that it gets sour is through the fermentation action of lactic acid bacteria. These are bacteria that also live on our skin and all over different surfaces that will eat small amounts of sugars in whatever you're fermenting them in and convert that into lactic acid, which is both deliciously tangy and conveniently is fairly toxic to mold and spoilage organisms. We get this double bonus of delicious sourness, as well as improved food safety.

Kousha Navidar: If you're just joining us, this is All Of It. We are talking to Arielle Johnson, a food scientists and co-founder of Noma's Fermentation Lab, just put out a new book, Flavorama: A Guide to Unlocking The Art and Science of Flavor. We have a text that I'd love to read. "Any unexpected food combinations or tastes that pair well scientifically, but most people don't think of, and what about their chemistry makes them work?" Great text. Thank you for it.

Arielle Johnson: Yes, I would say the number one weird flavor pairing that makes chemical and scientific sense is salt on grapefruit or more generally, salty and bitter together. Generally, if your coffee is too bitter, you might add more sugar to it or try to dilute it to cover up the taste. You wouldn't necessarily think to add salt. Except salt will actually interfere with the bitter receptor on the surface of the tongue and make it less effective at sensing bitterness. The effectiveness if you put salt on a piece of bitter grapefruit, the grapefruit will actually taste sweeter in addition to being saltier.

Kousha Navidar: We're talking about taste buds as well right now. There's a common misconception about how taste buds are laid out on our tongues. Where did this wrong belief come from, that there is a sweet zone, and a salty zone, and a bitter zone on everyone's tongue, and what's the reality?

Arielle Johnson: The common graphic shows areas of the tongue like a map. That, I believe was published-- I know it was a textbook, I think it may have been a nursing textbook, just as an explanation of these are tastes, these are where they're on the tongue. I think the attractiveness of that very graphic image with colors and zones made it catch on, and so now, there is this belief that we only have sour taste buds on one part of our tongue. We actually have all kinds of taste buds all over our tongue. They're basically just mixed together to best sense as much as possible.

Kousha Navidar: Well, let's bring it back to the listeners. We've got Sarah from Queens. Hi Sarah, welcome to the show.

Sarah: Hi. Thank you. I love the show and I'm wishing Alison a speedy recovery. I have a question for the food scientist, and it's about Buddha's hand citron. I recently smelled it for the first time, and I was absolutely enchanted by the smell, and I learned that there's no fruit in it, you can't eat it, you can only taste it. I was wondering if she could explain the smell and explain why you can't eat it if it smells so good.

Kousha Navidar: Sarah, thank you so much for that and for the well wishes. Yes, go ahead, Arielle.

Arielle Johnson: Yes, so a Buddha's hand is a citrus. It's a very unusual looking citrus. Instead of segments on the inside, it has finger shaped things, so it looks sort of like a lemon crust with a squid. As a citrus fruit in the citrus family, same sort of family as lemons and such, it has a citrusy aroma, which is a basic way of saying it, but Buddha's hand has particularly floral, fresh lemongrass qualities, so it's like an extra citrus lemon kind of smell.

The reason why it's not easy to eat a Buddha’s hand is if you were to cut open an orange, you could- -peel out the orange segments and eat those, and they would be sour and sweet and tasty. A Buddha’s hand has almost no flesh and almost all pith and pith, if you have ever accidentally eaten citrus skin, is quite bitter. There's molecules called lemonides in there and unless you are candying it or adding a lot of sugar, it's best used just as a aromatic seasoning rather than a hand fruit.

Kousha Navidar: This is All Of It. I am Kousha Navidar in for Alison Stewart. We are lucky to be talking to Arielle Johnson, who is a food scientist and co-founder of Noma's Fermentation Lab. Arielle, you mentioned memory before and you mentioned Proust. For listeners who love French literature, you might be thinking about the French novelist, Marcel Proust, who wrote about how the crumb of a madeleine cookie unlocked memories of his aunt. You had mentioned that before, this connection between what we eat and our memories feels so strong. Can you explain why that connection exists?

Arielle Johnson: Yes. That smell and emotions connection feels very strong because, at a neurological level, it is very strong. The first place that we process smell signals in our brain once they get written on a structure called the olfactory bulb, is the limbic system. Especially the amygdala, all of them are what we use for storing emotions, emotional memories, responses to things. Before you even perceive what a smell is or could put a name to it, you'll already be having any emotional connotations and memories of the last times that you experienced that smell bubble up to the surface.

Kousha Navidar: That reminds me of one of the last laws of flavor that you have in your book, which is that it can be created and transformed. How so?

Arielle Johnson: Well, so flavor is molecules. There are molecules that make flavor. What makes a molecule have a flavor is just if it fits in a receptor that we have, either a olfactory receptor in our nose, a taste receptor on our tongue. A lot of molecules are just way too big to do that. We can taste a glucose molecule- -with our sweet receptor. Something like starch, which is 1,000 linked glucose molecules, way too big to fit in the receptor, so we just don't perceive it as having a flavor.

But if you do some chemistry, which in the case of cooking might be browning a loaf of bread in the oven, you can change molecules. You can break them down. You can make smaller pieces. Once you're cooking, doing fermentation, anything like that, you'll be taking molecules that don't have a flavor and then chemically transforming them into new molecules that do have a flavor.

Kousha Navidar: Wow. What's the experiment in the book that helps demonstrate that?

Arielle Johnson: One of the simplest, and I think most delicious demonstrations of this is brown butter. Brown butter just happens when you melt butter and continue heating it until the milk solids start toasting. That flavor creation is a process called the Maillard reaction. It's amino acids meeting with sugars and creating this whole kaleidoscope of byproducts. When you make brown butter from butter, it's delicious, but for me, I always want more.

Thinking about like, “Okay, what's the important part of brown butter?” these proteins, these amino acids, these sugars. There’s actually a lot more of them in cream than in butter, since butter is mostly fat. So if you start with heavy cream, which is what you would use if you were churning milk to make butter, and heat it down until it evaporates all the way, and then continue toasting what's left, you'll make a gigantic amount of super delicious brown butter.

Kousha Navidar: We've got one more caller. We've got Nancy in Manhattan. Hi Nancy. Welcome to the show.

Nancy: Thanks. I have a strange question. Every time I have kabocha squash and I feel like that's the only thing that I want to eat, and that's the only thing I want to eat for like three or four days, and then I inevitably end up feeling terrible and stop for a while, and it has this addictive quality. When I went online, I thought either I'm crazy, I found a number of other people that particularly with kabocha have that response. I just wondered if you'd come across that.

Kousha Navidar: Thank you, Nancy, what do you think, Arielle?

Arielle Johnson: That is so interesting. I have not come across that in the literature, although, I have read a paper about tomatoes, which eventually is connected. Both tomatoes and squashes are usually pretty good sources of vitamin A. There's actually a breakdown product of vitamin A that gets created in these plants that’s-- they're called norisoprenoids. They smell very deliciously fruity, floral, amazing.

There's some idea that we actually use those as a signal of where we might be able to find vitamin A because compounds similar to vitamin A that aren't vitamin A break down into things that we can barely smell at all, so we’re very sensitive to these signs of vitamins. I might consider thinking about whether you're getting enough vitamin A in your diet. That might be the trigger for this kind of thing.

Kousha Navidar: Interesting. Vitamin A deficiency you're saying?

Arielle Johnson: Could be.

Kousha Navidar: Could be. What's the art and science relationship here? What's your advice for how folks can make the most out of the relationship with food, where it's an art and a science?

Arielle Johnson: I think a lot of people associate science from their experience in school of like, there is a right answer and if you are too creative with it or you don't get it right, then you're wrong, which is a way that some people use science, but it's definitely not innate to science for me. I tried to keep the laws of flavor fairly broad and then give specific examples because I don't necessarily want to tell someone exactly how they should do things in their kitchen.

I can give them suggestions, but to me, I think it's much more rewarding and exciting, and fun to let my science instincts help out my cooking instincts. Both of them are ways of looking at the same thing, but giving you different kinds of insights. In the book, there's a lot of ways whether from my own cooking or from my time working in restaurants that the science of flavor is very helpful and just very tasty, straightforward, not complicated or difficult.

Kousha Navidar: That was my conversation with flavor scientist Arielle Johnson about her book Flavorama: A Guide to Unlocking The Art and Science of Flavor. It's part of our new Food for Thought series.

 

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