Arielle Johnson (3:01)

It was definitely the smell of coffee, specifically. 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 like, 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 I'm interested in.

Arielle Johnson (3:25)

And 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 (3:37)

I would say it can be used as a cookbook. It can be used as a reference book. If you're interested in understanding sort of 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 sort of shorter pieces of information that'll like, 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, like, what is sourness? What is an acid? Where can I find sourness?

Arielle Johnson (4:17)

Well, you know, it's funny because those questions kind of lie at the very science of how taste and flavor work. So 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 (4:32)

So when we say flavor is taste and smell, usually to the, you know, 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, you know, a little bit. You can actually smell food in your mouth as you're chewing it. We call that retronasal olfaction. And it is responsible for pretty much everything about flavor beyond sweet, sour, salty, bitter, and umami. So fruitiness, roastiness, floral flavors, that all comes from smell. So 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 orbitofrontal cortex, where we can recognize them not just as tastes and smells, but as, like, unified flavors and then come up with descriptions and names for them.

Arielle Johnson (5:28)

You mentioned that they get routed Differently. Is there a special reason behind that, why that routing is different?

Arielle Johnson (5:35)

It's just a. It's a physical question, actually. Most of our senses pass through the brain stem and through sort of like the quote unquote, lower parts of the brain before they get to emotions and thoughts. Smell is actually sensed directly with brain cells. That one side is anchored in your brain. One side passes into your nasal cavity. Your. No, the inside. And that, rather than going through the brainstem, goes right into the emotional centers of our limbic system, especially our amygdala. So you know the Proustian story of dipping a madeleine in tea?

Arielle Johnson (6:11)

You stole my next question. It's okay.

Arielle Johnson (6:13)

It's okay. Go ahead. Yeah. It is biologically and neurologically true and valid. That is exactly what happens. In fact, you'll often have an emotional connection or, like, a memory of a flavor before you can even recognize what it is.

Arielle Johnson (6:27)

We have Stephanie in Greenpoint with a question. Hi, Stephanie. Welcome to the show.

Stephanie (6:32)

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. And also what does it really do to the grains or to the chickpea flour or barley or whatever when you fermented? And then any other thoughts about, you know, fermented foods and how your body senses them would be interesting.

Arielle Johnson (7:08)

Thank you, Stephanie.

Arielle Johnson (7:09)

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. And the way that it gets sour is through the fermentation action of lactic acid bacteria. So these are bacteria that also live in 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. So we get this, like, double bonus of delicious sourness as well as, like, improved food safety.

Arielle Johnson (7:54)

If you're just joining us, this is all of it. We are talking to Arielle Johnson, a food scientist and co founder of noma's Fermentation Lab. Just put out a new book, 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 (8:22)

Yeah, 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. You know, generally if your coffee is too bitter, you might add more sugar to it or try to dilute it to kind of like 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 and sort the kind of effect of this. If you put salt on a piece of bitter grapefruit, the grapefruit will actually taste sweeter in addition to being saltier.

Arielle Johnson (9:01)

So 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. So 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 (9:15)

So, yeah, there's this common. The common graphic shows sort of 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. And I think the kind of, you know, attractiveness of that very graphic image with colors and zones made it catch on. And so now there's this belief that, you know, 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, you know, best. Best sense as much as possible.

Arielle Johnson (9:49)

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 Madeleine cookie unlocked memories of his aunt. You had mentioned that before. This connection between what we eat and our memories feel so strong. Can you explain why that connection exists?

Arielle Johnson (10:12)

Yeah, that. That smell and emotions connection feels very strong because at a neurological level, it is very strong. The. 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. So 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 sort of emotional connotations and memories of the last times that you experienced that smell bubble up to the surface.

Arielle Johnson (10:53)

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 (11:01)

Well, so flavor. 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, have either a olfactory receptor in our nose, taste receptor on our tongue. A lot of molecules are just way too big to do that. So, you know, we can taste a glucose molecule with our sweet receptor, something like starch, which is, you know, a thousand 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. So 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.

Arielle Johnson (11:55)

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 (12:00)

Well, I think like a lot of people associate science from their, you know, 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, you know, I tried to keep the laws of flavor fairly, fairly broad and then give specific examples because, like, I don't necessarily want to or, you know, 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. So, you know, both of them are ways of looking at the same thing but giving you different kinds of insight. So I in the book, there's a lot of ways, whether from my own cooking or from my time working in restaurants, that, you know, the science of flavor is very helpful and just very tasty, straightforward, not complicated or difficult.

Alison Stewart (13:04)

That was Kusha Navadar's conversation with Dr. Arielle Johnson about her book A Guide to Unlocking the Art and Science of Flavor. Coming up, a book called Sing Like a How Sound Rules Life Underwater. It explores the sonic ecosystem of the marine world. Stick around.

Arielle Johnson (13:27)

This.

Alison Stewart (13:28)

This is all of it.

Ira Flatow (13:32)

I'm Ira Flato, host of Science Friday. For over 30 years, our team has been reporting high quality news about science, technology and medicine. News you won't get anywhere else. And now that political news is 24 7, our audience is turning to us to know about the really important stuff in their lives. Cancer, climate change, genetic engineering, childhood diseases. Our sponsors know the value of science and health news. For more sponsorship information, visit sponsorship.wnyc.org.