JOHANNA MAYER: Kikunae Ikeda was born in Kyoto, Japan in 1864. And he was something of a foodie, or whatever the 19th century equivalent of a foodie was. As a kid, he loved to slurp these big bowls of boiled tofu that simmered in a seaweed broth called dashi. And this broth was something else-- hot, steamy, and once a little bit salty, a tiny bit sweet. And the thing was, it was really a very simple broth, just made out of seaweed. But it had this deep, mouthwatering, meaty taste.

Little Kikunae Ikeda grew up to be a chemist and a philosophical kind of guy. He taught classes on Shakespeare for some extra cash. He wore delicate, round spectacles, sported a bristly mustache, that he sometimes twisted up at the ends. And throughout his life, from those bowls of tofu in dashi as a kid, until he wound up as a chemistry student, he just couldn't shake this question of that seaweed broth.

So everyone knew that there were just four basic tastes-- salty, sweet, sour, and bitter. But this broth somehow had another taste. And think about it, this would be revolutionary-- discovering another taste would be like discovering another color, one that's always been there, but until we named it, never truly seen. And yet, that's precisely what Kikunae was about to do. He was about to discover umami. From Science Friday, this is "Science Diction." I'm Johanna Mayer. Today, we're talking about umami.

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So you probably know what salty or sour tastes like, but umami, a lot of us couldn't say.

SPEAKER 1: Because we haven't had a word for it in English, I think people think of it as unfamiliar, but it really isn't. The taste is not unfamiliar.

JOHANNA MAYER: This is [? Neera ?] [INAUDIBLE]. She's a neuroscientist.

SPEAKER 1: If you think of a tomato, the juice that trickles out of a really ripe tomato at peak season, and you just put a few drops of that in your mouth, and it just fills your mouth. Well, it might have a little bit of sweetness, it might have a little bit of saltiness. But that rich mouth-filling taste is umami.

JOHANNA MAYER: Whether or not you could describe it, we've all been tasting umami for ages. Close your eyes, spin a globe, and any spot that you pick there will be food rich with you umami-- ground crayfish from Nigeria, salted Herring from Russia. Things like tomatoes, mushrooms, bacon and gravy, aged Parmesan cheese, all of that is just brimming with umami.

And yet, for the longest time people were in full blown umami denial. They didn't think it was real. Because a century ago, scientists had already mapped out the tastes on our tongues. And they were pretty confident that they had it right. You've probably seen this tongue map in your high school science textbook, the one that says you taste sweet in the front, salt and sour on the sides, bitter in the back. Map finished, case closed.

But our foodie chemist, Kikunae Ikeda, just knew there was something else going on with that broth. So in 1907, Kikunae, by then in his 40s, and a chemistry professor in Tokyo, set out to figure out exactly what this nameless thing was.

He started with more than 80 pounds of seaweed, and let it simmer, and simmer, and simmer. I like to imagine Kikunae playing with the ends of his curly mustache as he watched. After separating out some old familiar culprits, natural sugars, some salts, nothing to write home about, he ran it through a series of reactions until he'd isolated this compound. It formed tiny crystals, like bits of sand. And when he bit into one of these crystals, there was that taste.

SPEAKER 1: The compound that he had extracted he discovered, to much to his amazement, I suspect, was a well-known amino acid, glutamate.

JOHANNA MAYER: Glutamate occurs naturally in the human body. It's a building block for proteins. Our cells actually make it. And Kikunae had just figured out that it was glutamate that was responsible for that deep, mysterious taste. He decided to call this new taste umami, a Japanese portmanteau, combination of the word umi, which means delicious, and mi, which means taste.

The meaning of both of these words gets boiled down a little here-- ha-ha. But it essentially means delicious taste. So Kikunae was sitting on this major game-changing discovery of a fifth taste. And he also had a product. Because the sodium salts of glutamate is shelf stable, easily packagable, basically umami in a shaker jar.

Almost immediately, Kikunae turned around and decided to patent the method for extracting those crystals. He co-founded a company called Ajinomoto, which means a sense of taste. But maybe you know the product simply as monosodium glutamate-- yep, MSG.

This was big. MSG meant having umami on command, no longer confined to foods where it occurred naturally, like tomatoes and asparagus. Suddenly, it could be sprinkled on anything. Just like you can add sugar to make something sweet, shake some salt to make things salty, now you could add MSG to make food umami. Turn your super salad from drab to fab.

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This is one of Ajinomoto's Mr Umami ads from a few years ago, featuring a very cool chef in a track suit and a fedora.

KUMIKO NINOMIYA: Everyone knows Ajinomoto.

JOHANNA MAYER: Kumiko Ninomiya used to work for Ajinomoto. And she's now the director of the Umami Information Center, whose mission it is to spread the good word about umami, and well, MSG. She grew up with MSG.

KUMIKO NINOMIYA: When I was a little girl, every house has a MSG shaker on the table-- soy sauce and MSG shaker.

JOHANNA MAYER: This was thanks in no small part to Ajinomoto's years of intense marketing. For decades, they targeted well-to-do housewives. They used to package their MSG in elegant glass bottles. And for 15 years, the company sent a cookbook and a sample bottle to every graduate of elite women's high schools. Soon, cooking columns began to list Ajinomoto in their recipes. And by 1931, MSG was officially designated for use at none other than the table of Japan's emperor.

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So Kumiko grew up with MSG, eventually went on to work for Ajinomoto. And then, she learned that in the United States, people think MSG is dangerous.

KUMIKO NINOMIYA: So, I was very surprised, because as you know, it's very popular in Japan. Most of the people know how to use MSG.

JOHANNA MAYER: You've probably heard about MSG's reputation in the US, that it's bad for you, that it can make you sick. Maybe that's all you've heard. But it wasn't always that way. In the '30s, outside of Japan and Taiwan, the US was the world's leading consumer of MSG. It used to be in all kinds of foods, and not just the Chinese food that people associate it with.

It was in Campbell's Soup. It was in baby food until the '70s. Some food manufacturers would actually rub raw chickens with it. Even though Americans at the time probably weren't thinking about umami, most probably hadn't even heard of it, they sure liked what they tasted. Umami, by way of MSG, was everywhere.

And then in 1968, a letter changed everything. It was in the New England Journal of Medicine from a Chinese-American doctor named Robert Ho Man Kwok. He wrote, quote, "Several years since I've been in this country, I've experienced a strange syndrome whenever I've eaten out at a Chinese restaurant. The syndrome, which usually begins 15 to 20 minutes after I've eaten the first dish, lasts for about two hours without any hangover effect. The most prominent symptoms are numbness in the back of the neck."

He rattled off the rest of the symptoms numbness in the arms and back, general weakness, heart palpitations. So, what's the deal? Could it be the soy sauce? Nah, he used the same kind of soy sauce all the time. So, maybe it was the cooking wine? The high sodium content? Or maybe the MSG.

Soon after Kwok's letter, more started pouring in, many written by doctors, piling on, and agreeing that yes, people are experiencing these symptoms. The Journal called it Chinese Restaurant Syndrome-- yeah, not a great name. Also, not great news for MSG. Because pretty quickly that was the culprit people zoomed in on.

The letter landed at a time when Americans were particularly freaked out about synthetic chemicals. In the '60s, environmentalism was in full swing. Rachel Carson, Silent Spring in 1962 had people taking a good, hard look at their food.

SPEAKER 1: I think people suddenly sort of took a pause, and said, wait, what happened to more normal tasting food, food that tastes like it was property made in your kitchen or came out of the ground?

JOHANNA MAYER: Pesticides and food additives under fire. Food dyes, artificial sweeteners, uh-uh, people wanted nothing to do with them. And monosodium glutamate, sounds like another bad chemical. And then, the second wallop. A year after Dr. Kwok's letter, a troubling study appeared in the journal Science. Laboratory mice injected with MSG developed brain lesions and other neurological disorders, also stunted skeletal development, obesity, female sterility. It was bad, bad news. And suddenly, it seemed like everyone was talking about MSG and not in a good way.

SPEAKER 2: It's a killer that's worse than alcohol, worse than nicotine, worse than drugs.

SPEAKER 3: Heart palpitations, headache, dizziness.

SPEAKER 2: It's called monosodium glutamate.

SPEAKER 4: When I complained about stomach aches, they did exploratory surgery.

SPEAKER 3: The range of reactions is amazing to those physicians.

SPEAKER 5: By the time doctors found out--

SPEAKER 2: People don't know that MSG is in thousands of processed foods.

JOHANNA MAYER: Those "No MSG" signs began to appear on packaging, in restaurant doorways. Chinese Restaurants Syndrome became an actual entry in Merriam Webster Dictionary in 1993, defined as a group of symptoms affecting, quote, "susceptible persons eating food, and especially Chinese food, heavily seasoned with monosodium glutamate."

So, in the '90s, when MSG had become a full on pariah chemical, Nirupa Chaudhari, the neuroscientist, was thinking a lot about food.

NIRUPA CHAUDHARI: How did I become interested in food? We all eat. I love to eat.

JOHANNA MAYER: Neuroscientists, they're just like us.

NIRUPA CHAUDHARI: My grandmother was a fantastic cook. I learned to cook, and so, things like that. So, this has been a personal interest of mine, really not a scientific thing to start with.

JOHANNA MAYER: So here's Nirupa, doing all this neuroscience work, while also constantly mulling over food and taste. She had some colleagues who did work on taste, but talking to them, she kept running into the same problem.

NIRUPA CHAUDHARI: Every time I asked them a question about how the molecules worked for taste and how the cells worked for taste, they'd say, oh, we don't know anything about that, because this hasn't been studied.

JOHANNA MAYER: By the late '90s, scientists had identified light receptors in our eyes and smell receptors, but taste receptors, total black box. So Nirupa's like, all right, somebody's got to figure this out. How does our tongue actually sense that something is sweet, or salty, or umami? What is going on the molecular level. So she and her team got on it. And they decided to go hunting not just for any taste receptor, but umami receptors.

NIRUPA CHAUDHARI: At the time, it seemed like the obvious choice.

JOHANNA MAYER: Actually, in some ways, it was the least obvious choice. See, even though it had been a century since Kikunae's famous broth experiment, there were still a lot of people who did not believe that umami was real. Maybe it was because they thought that tongue map was done and dusted, or because we all know what sweet tastes like, but umami really can be hard to pinpoint. Whatever their reasons, Western scientists, especially, not buying it.

On the other hand, if umami was real, and umami is the taste of glutamate, Nirupa had a pretty great lead for how to find the receptor. Because researchers had just found a glutamate receptor in our brain.

So glutamate does a bunch of things in our bodies. And it turns out that one of those things is communicating between different neurons in our brains. It's a neurotransmitter. So if brains have a receptor for glutamate, maybe tongues have the same kind of receptor. And that's how we taste umami.

NIRUPA CHAUDHARI: We were like, oh, glutamate is doing these two different things. And we know about the receptors for the one of these two things, so let's see if there's a match.

JOHANNA MAYER: So, how do you go about seeing if there's a match? Well, the researchers started with the special drug that they knew would bind to the glutamate receptor in the brain. They just had to check if it binds to the tongue too. They couldn't do this experiment with humans, so they consulted with rats.

They put some of the special drug in the rats' water, and they found that, yep, rats have very strong opinions about it. And that meant it was binding to glutamate receptors on their tongue, umami receptors. And by the way, those receptors are found throughout the tongue. That tongue map that appeared in every textbook, the one with just the four basic tastes, it's since been flatly disproven. We don't just taste salty on the sides of our tongue and sweet in the front. We experience all tastes, including umami, all over it.

Back at the turn of the century, Kikunae Ikeda knew he tasted umami, but the Western world didn't believe him. Now, almost 100 years later, there was proof. Umami was not just some abstract, salty yumminess. Umami was real.

SPEAKER 6: I view it more as a way to tantalize the palate.

SPEAKER 7: I guess everybody knows the four basic flavors-- salty, sweet, bitter, and sour. But umami's kind of-- the best way to describe it is that indescribable flavor.

JOHANNA MAYER: If you're like me, maybe you grew up never hearing about umami until you were hearing about it all the time. By around 2007, 2008, it suddenly seemed like umami was everywhere.

SPEAKER 8: It's a little bit umami, a little bit of seasoning.

SPEAKER 9: Umami, tsunami sort of thing.

SPEAKER 10: Has that umami that truffles have.

SPEAKER 11: And I want to share the biggest umami--

JOHANNA MAYER: Articles about it in The New Yorker, a restaurant chain called Umami Burger. So umami got the thumbs up from chefs, from scientists. Umami was the cool kid at the party. And MSG got an invite too.

ANTHONY BOURDAIN: What's your feeling on MSG?

SPEAKER 12: I don't mind MSG.

ANTHONY BOURDAIN: Yeah, I think it's good stuff.

That last guy was Anthony Bourdain in an episode of Parts Unknown. Having influential celebrities in your corner didn't hurt.

ANTHONY BOURDAIN: You know what causes Chinese Restaurants Syndrome? Racism. Ooh, I had a headache. It must of been the Chinese guy.

JOHANNA MAYER: Just this year, Merriam Webster updated its entry for Chinese restaurant syndrome. There's a note under the definition. It says, dated, sometimes offensive.

MSG's spectacular makeover, it is no accident. In the '70s, marketers at Ajinomoto made a very clear choice to pivot their marketing from MSG as a scientific wonder chemical to umami seasoning. The company established a umami seasoning and promotion center, an umami research center. They funded studies and conferences on umami.

And yep, even Nirupa's research had some support from the Umami Manufacturers Association. It's a consortium of MSG makers, led by Ajinomoto, though the vast majority of their funding came from the NIH. But to truly exonerate MSG, we still had to set the record straight on a few things.

First, that letter about Chinese Restaurant Syndrome, it was just that, a letter, not a study. And Dr. Kwok never even pointed to MSG as the culprit, just one suspect. And as for that study in the journal Science with the scary brain lesions, well, the doses of MSG given to those mice were off the charts, like orders of magnitude higher than what you would normally eat. And the mice didn't eat them the MSG, they were injected with it.

There have been lots of more realistic studies of MSG since. And it seems like MSG is generally totally fine. just like anything, probably best in moderation, and maybe don't go injecting it.

At Tokyo university where Kikunae Ikeda taught, there's still a little bottle of the monosodium glutamate that he extracted from those 80 pounds of seaweed. Over the years, the bottle's been passed down from one professor to another, a small glass bottle with a cork topper and a yellowing label, little clump of white crystals at the bottom-- MSG.

Today, the scientific consensus on it is crystal clear. MSG is safe. And umami, delicious, by definition.

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"Science Diction" is hosted and produced by me, Johanna Mayer. Elah Feder is our editor and producer. Nathan Tobey contributed story editing. And Kaitlyn Schwalje contributed writing and research. Thanks also to Lauren J Young and Attabey Rodríguez Benítez for research help.

Our composer is Daniel Peterschmidt, and they also did sound design. Chris Wood mastered the episode. We had fact checking from Michelle Harris. Special thanks to Sarah Tracy for some background on MSG in the United States. Nadja Oertelt is our chief content officer. And when we asked her what she thought of our food season extravaganza, she said--

NADJA OERTELT: I view it more as a way to tantalize the palate.

JOHANNA MAYER: One last thing, help us figure out how to make more "Science Diction" and take a quick survey. It's actually quick, I promise. You can take the survey at sciencefriday.com/sciencedictionsurvey. Thanks. See you next week.

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