The Sweetest Thing

Wait, you're listening to Radio Lab from WNYC. Yeah, we're going to go on a hunt that actually starts in my car. I was with my two kids. I think at that point my kids were six and three maybe, and the U2 song, The Sweetest Thing, comes on. Do you know that song? Of course. Damn it. Damn it. Damn it. Damn it. Yeah. Of course. It's a pop. Yeah. It's my favorite of their songs. Yeah. And my kids who have never heard the song for it. They're listening to the song, and they ask, what is the sweetest thing? Did you try love? Were you like love? Yeah. No, my kids didn't care about that. They were just like, no, no, but what really is the sweetest thing? So just, what's the sweetest thing I can get in my mouth? Yeah. They're kids. They love sugar. Yeah, of course. Right now they're obsessed with gummy bears, and they just wanted to know, is there some other thing out there we've never had before that's even sweeter? So I figured like, I'm a journalist. I can answer this. Well, lots of bless your amazing children who I adore. Do you care about this question? Yeah. Yes. Why? Because, okay, because it sounds like a dumb, simple question or not a dumb question, but it seems like it has an answer, and then you're like, yeah, I kind of expected it would be that way too, but then this question turned out to be so much more. More than just a hunt for like a substance, it became like this thing where I was trying to get to the edge of human experience. And sweetness as one of those experiences is this basic familiar thing that we all know, it's like almost mundane, but I kept finding that way to second, like no, no, no. The edge is even further to these levels of sweetness that I didn't even know existed in the first place. And there's some mind hacks and brain lasers and space for asparagus. There's a lot of fun stuff along the way. All right. All right. Let's go. Okay. All right. So the very first thing that I found right off the bat, I found all these scientists. Check, check, check. Okay. Hey, okay. Hello. Who are out there trying to answer rigorously, scientifically, this exact kid question. My name is Eric Walters. Can I call you Eric? Please do. You don't have to doctor me. Eric here, a biochemist who used to work at NutriSuite, where he developed artificial sweeteners. I spent a lot of my career working on sweeteners, studying sweeteners, and ultimately writing a book about sweeteners. And what scientists like Eric in the food industry do is they find or even make new sweet molecules, tweaking the structure in small ways, and seeing, does it get better or worse? And then they literally rank them in terms of sweetness. Yeah. Like a list of the sweetest things on earth. Oh. And I want to walk you up my top five of the list using table sugar as our baseline here. Because that's the most common sugar that we use every day. Okay. Great. So. Number five. Honey. You know, honey. I heard of it. Honey is about 1.5 times sweeter than sugar. Which one is that meat? It's just, what does that mean? So typically in the food industry people do this with trained taste panels. These specialized taste testers who are really good at noticing differences in sweetness. I haven't done it in years, but I used to be very good at it. And here's what they generally do. They take a little sugar. One gram of sugar, like a pinch, dissolve it in water, call it a cup of water. Taste it. Sip and spit. Then they mix the same amount of the thing they're testing. Let's say in this case, honey, with the same amount of water. And again. Yeah. To see which is sweeter. Yeah. Now, to be able to say how much sweeter this thing is than sugar, what you do is you just add water until it's the same until it's the same. So like with honey, you would theoretically need to add 1.5 times as much water for them to taste the same. Then you can say it's 1.5 times as sweet. Yep. There you go. Okay. That's a good way to like come up with a scale. Yeah. Okay. That was honey. Honey was number 5 on the list. Now, one level sweeter. Number 4. Aspartane. Aspartane, which is used to sweeten equal. Sure. Okay. It's about 200 times as sweet as sugar. So it takes 200 times more water. Wow. Wow. With aspartane. To taste the same as a cup of sugar water. That's wild. Yeah. Next. Number 3. This one actually comes from nature. Ooh. This is a catamphate fruit, which is a little red berry that grows in West African tropical rainforests. And it is 2,000 times sweeter than sugar. Oh. Orders of magnitude. Yeah. But then, number 2. Adventame. How sweet. Tages. Take a guess. 5,000. Adventame is 20,000 times sweeter than sugar. Oh my gosh. That means just a pinch of Adventame could sweeten 500 gallons of water. That's like a jacuzzi of sugar water. That's freaky. Yeah. Okay. Number 1. The number 1 sweetest thing, according to these expert sweetness sippers, sitting around in their food labs, is. Lugdenum. Yeah. I don't even know how to pronounce it, Lugdenum. I always say Lugdename, but I. Lugdename. Okay. Okay. This is 300,000 times sweeter than sugar. Oh. Yeah. That's what we said. Oh my God. Yeah. That's insane. Okay. So, what is this? This is a swimming pool. This is a full swimming pool. Wow. What was the mood and the reaction and nutrients sweet to this news? I was jealous. Yeah. Wish I thought of that. Because in his line of work, they're always trying to push this limit a little bit further. And I discovered a sweetener that was 28,000 times as sweet as sugar. Interesting. So, I didn't win. I didn't win the prize on that one. But the prize goes to this, like, Frankenstein of a molecule called Lugdenum. Okay. Sit down. The wise man. You want a very little amount of this one. Okay. You ready? So, I set up a little tasting for my kids. Yeah. That's a good amount. Five or two much. Two. Couldn't actually get my hands on any Lugdenum because it turns out it's not FDA approved for human consumption, because apparently if you try it, there's a chance. It turns your blood, the color of chocolate. What? But, why don't you guys drink some water? I did give them some adventame, number two on our list. Okay. Ready, guys? Yay. Okay. Yeah. Okay. What do you think? Ugly. Ugly? You sat it out all over the floor. Yay. Okay. Huck is now scraping his tongue with his fingers. What are you doing? No, no, no, no, don't spin on the couch. That's gross, man. That's gross. That's gross. So, the thing that scientists say is 20,000 times sweeter than sugar does not actually taste sweet. Yeah. Now, isn't that remarkably dumb? According to psychologists, Linda Bartoszek, this whole ranked list is ridiculous. Like this is the dumbest way to measure this. Huh. Have you ever heard anybody say that saccharine is 100 times the sweetest sugar? Yes. Have you ever tasted saccharine and sugar at the same time? No. Well, I assure you, you will not think the saccharine is 100 times the sweetest sugar for God's sake. Well, these sweeteners, they do have some off flavors. Eric says that the problem with coming up with a perfect sweetener is that there's only one sweetness receptor, but on the other hand, humans have 20 or 30 different bitter taste receptors. So it's like a minefield that you have to kind of tiptoe through to get to the promised land of the sweet receptor? Yes. Yes. So it's like a compound that triggers the sweet receptor, but doesn't trigger any of the bitter receptors as well, which is why you get those off tastes from so many sweeteners. But the food chemists, when they're ranking sweeteners, they are just looking at one very specific thing. And that's a value that we refer to as potency. They just want the thing you can use the smallest amount of to turn on that sweetness receptor. The weakest thing you can just taste as sweet. Got it. Okay. And that kind of measurement is very, very helpful if you are a soda company or making chewing gum or something and you have a giant vat of something and you want to put in the least amount of a thing to make the most money, putting the least amount of that thing, right? Right. Right. But that's not what my kids are asking. That's not what I'm looking for. We're looking for a whole other thing. And that's intensity of sweetness. How sweet does it actually taste to you? Yeah. I think that's, that's right. 'Cause we're talking about sweetness and sweetness as a perception. - This is Paul Brezzlin. - Professor in the Department of Nutritional Sciences at Rutgers University. - And he says, you know, with things like Adventame, right? - You might think that if you just kept adding more and more of it to the water, it would-- - Keep getting sweeter and sweeter and sweeter until it went to the moon, but it wouldn't. You'll eventually reach a point where this sweetness intensity sort of reaches a plateau. - The amount of sweetness that you perceive sort of levels off. - The thing is that our sweetness receptor, it's not just like a regular light switch you turn on or off. It's more like a dimmer switch. - Okay, sure. - So we can get brighter and brighter and these sweeteners, they can only get a certain amount of bright. - Huh. - So what we really want to know is, what thing will turn that dimmer switch up the highest? - To the brightest bulb. - To what it'll get you the brightest bulb. - Okay. - And according to Eric, by that measure? - Maybe sugar is the sweetest thing there is. - No. - Because it can get you to a higher perceived intensity of sweetness. - He's never heard of or tasted anything sweeter than sugar. - Wait, so is that the answer? The sweetest thing is sugar? - Which feels like an extremely anticlimactic answer, right? - That's just why I mean, we're just back where we started. - We are, we are back where we started, but like, we're a kind of profound reason, actually. - Sugar plays a critical role in survival. Glucose is the best fuel the brain can use. - From the very beginning, Linda says. - The first thing when a baby is born, you want the baby to do is nurse. And the baby has reflexes that help it begin to nurse, but the sweet taste of mother's milk. - The sugar in the mother's milk? - It is what keeps it, nursing. So sweet taste is an incredibly important cue. - Our brains basically evolved this particular sensation, the reward of sweetness, as a way to get us to want sugar. - Yeah, the receptors have evolved specifically to respond to sugar. - Like, it's nothing the light switch was made for. - In fact, there have been theorists in the past who've thought that sweet might be the beginning of our understanding of pleasure. - Oh, that's interesting. And so I started to see sugar and sweetness as almost the same thing. - Right. - Like, sweetness doesn't describe sugar. It is sugar. - Yeah. - Which is cool, and which is revelatory of our basic human nature, but also, like, I don't know, I still was craving more. Like, there's a limit here. I just want to go beyond it. And lucky for me, I ended up stumbling into a whole world of things that could take us beyond that limit. - Really? - And I'm gonna take you into uncharted sweetness territory. And that's after the break. - This is Radio Lab. I'm Lulu. I'm here with Latif Nasser. Latif is on a quest to discover the sweetest thing in the world on the planet, the sweetest thing on Earth. And where we left off, you were at a potential answer that the sweetest thing is sugar. - Yeah, except maybe not. Okay, so Lulu, what is sweeter, a strawberry or a blueberry? - I think a strawberry. - So a blueberry has technically more sugar. - Really? - That's right, the blueberry has twice as much sugar in it. - According to Linda Bartoszek. - There are fruit that can make their sugar sweeter. - What? - Now, why do fruits care? Because animals that eat the fruit spread their seeds. So the fruit would really like that sugar to be sweeter. And maybe the fruit doesn't know how to add more sugar to it. I'm not talking about the fruits got consciousness. Of course, it doesn't. Evolution is doing this. - Right. - But what has happened through evolution is that some fruit are now using volatiles, which make the smell of the fruit to increase the sweetness. - Volatiles are just little molecules that float around in the air, they make things smell. - Now, there are two ways you can perceive volatiles. You probably only know about one of them, and that's you sniff them. - Right. - But what happens when you put food in your mouth, that is giving off odors? You chew it, you're releasing the odors in your mouth, and when you swallow, those odors are pumped through a hole in the back, then they go into your nose, and can intensify the sweet signal in the brain. - So the strawberry tastes sweeter than the blueberry, because it puts out all of these non-sugar smell molecules that send smell signals to your brain, which overlap with the taste signals, and give them a little boost. - Huh. - According to Paul Brezzlin. - As an ape, our species, our natural proclivity, is to mostly want to eat fruit. - Thanks to our long evolutionary history with fruit. - A lot of animals can make their own vitamin C, humans can't make their own vitamin C, so we have to eat fruit. - Even if something just looks kind of fruity, or reminds you of a fruit, it's like there's an extra little bell ringing in our heads. - So if you play with vision, if you make something very fruity that you associate with sweetness, you can perceive it as being more sweet, or if you color it red, so it looks like a nice ripe fruit, that can actually make the sweetness perception go up. - No. So if you were to take the same packet of sugar and die some of it red, the red would taste sweeter to me? - That's right. - That's hard to believe. - Well, did you bring this stuff? I told you to bring? - Yep. - Okay, you have some honey. - I have some honey. - Okay, why don't we first get our sort of baseline? Take a tiny bite. - Just normal old honey, here we go. - Yeah. - Okay, very sweet. - Okay, so number two, I want you to take that honey. - Okay. - Grab some strawberry extract and red food coloring. - Okay. - Mix that all up. - Ew, it looks like almost like cherry cough syrup. - Okay, so to keep that normal honey, we just add in my now taste to strawberry honey. - Okay. - And tell me if it's sweeter. - And I should like look, I guess. - Oh. Significantly. Significantly, yeah. - Wow. - It's kind of dramatic, right? - Yeah, it's interesting. It's not sweeter in like what I was expecting. Like a syrupy sweeter way. - Yeah. - It's almost like I picture all these like flowers. Like it's like flowery sweeter. - Okay, now. - There's another thing? - Yeah. I mean, by this point, I was obsessed with ways to jack up the perception of sweetness. And I found all these studies that suggest that along with smell and vision sound actually works for sweet as well. - What? - So there are certain high pitched tones that you can play and you can enhance sweetness by as much as five to 10%. - Wait, why would that be? What's the evolutionary, what's the why? - Such a good question. I looked it up and no one knows for sure. - Okay, fair. - It is a mystery. But they have seen it happen over and over in experiments. Okay, so like I'm about to play you a song. This was used in a study at the Science Museum of London. Here, let's just see if it works for you. - Okay. - Okay, you ready? - Okay, here it is. (bright music) - This is like the music you see in like 1950s animations of candy dancing. - Okay, eat the red honey again. - Okay. - Wow, it gives it like more dimension. It's sparklier, crystalier. - When you talk about the crystals, is it because your honey is like kind of hard? - My honey's a little old. (laughs) - So maybe the crystal equality is because of the old honey, really, instead of the music? - Okay. - Uh-huh. - Okay, but I do agree. I think there was a step up. - The strawberry step up was pretty dramatic. And I feel like the sound step was maybe harder to tell. - Yeah, a little subtler. - So at this point, I was like, okay, cool. These hacks definitely work. But also, they're not so dissimilar like the flavor and the color. It's not so dissimilar to what candy companies are already doing. Like, it just felt like I was like, oh, I feel like I'm back to gummy bears here. - Right. And then I was like, how can we get even sweeter than this? - Uh-huh. - So then I thought, what if we just went to the source of all of this? - Remember, you know, taste ultimately is in your brain. - Which took me to the lab. - Okay, here we are. We're at Columbia University with all these like brain scans on the wall here. - Of this geneticist and neurobiologist. - Oh, nice to meet you. - Dr. Charles. - I'll shake the microphone. - He was one of the people, along with other scientists like Danielle Reed, who discovered the sweetness receptor. - Oh. - And I've dedicated my career to study how detection gets transformed into perception. - And since then, he's been following that sweet signal from the taste receptor into the brain. - So it goes from the tongue to ganglia, from ganglia to brain stem, brain stem to a different station in the brain stem where it gets further processed. From the brain stem to the brain stem, From there, he goes to the talamos. Ambrotealamos goes to the cortex. - Somewhere along the way here, we know that sight and smell can join up and boost the signal. But regardless, the cortex. - This where you now say, ah, this is sweet. - Huh. - So I was saying, no, the typical laboratory, no, do you have benches and you have this? - So we actually visited Charles as well. - And then we have lots of specialty rooms where he studies this pathway. To see, okay, what happens if we move this over here, what happens if we change what happens, if we block it over here, to block the change there. - So normally the cells have the sweet receptor and that's why it's sweet activates that pathway all the way to the brain. But if instead there, I put, let's say, a bitter receptor, now the bitter chemical will activate the same sweet pathway. - Right. - Whoa. - To be clear, he is not doing all this for the reasons that we are to try to find the sweetest thing or the sweetest sensation. He is working to understand really how sweetness and taste work in the brain. And who knows, maybe that knowledge could help us deal with issues like addiction, obesity, eating disorders, diabetes. - Yeah, sure. - So one of the things he's doing is he takes some mice and he zeroes in on their sweetest sensation neurons. We introduce into only those neurons, a little light switch. - Meaning they genetically engineer these neurons and add genetic sensitivity to light. - And then we put a fiber optic in their head. - Ah. - And then we turn the laser on. - Which triggers the neuron. - And the brain will say, ah, sweet. - Yeah. - Oh my gosh. Oh my gosh. - So and they be, by beaming in light, it just, whatever it's tasting will taste sweet. - Yeah, even if it's not tasting anything. - What? Why are we then even bothering with candy instead? Why don't we just do that to ourselves? - Very good, excellent. Come on, people go around with pacemakers. - Yeah, sure. - And I could see a future that could be done. - Which I mean, in terms of lifestyle, that could be just imagine. That could be revolutionary. Think about like you could get the perfect sugar hit, no calories, no insulin spike. You could even pair it with whatever you want. Which means like your kids could be eating spinach and it tastes like candy, right? - Yeah, okay, that's kind of me. - Yeah, but because we're on this mission here for the sweetest thing, I was like, wait a second, but could you use that same thing? Could you use that same laser light and crank it up to the highest it can go and just blast that sweet neuron and get something that is the sweetest thing that anyone has ever tasted? - Like you could maybe get a sweetness that we have never known. A sweetness that has just been totally blocked off from us, just from the physical reality of sugar. So I asked him and Charles was like, - In principle, I could imagine gifts. - You could potentially create the sweetest sweet. You could transcend the sweetest thing could be light. Like could be nothing. - I don't like it. - You don't like it. - I don't like it. - Why not? - I don't know, it's like let's divorce ourselves from the real world even more. So that pleasure itself doesn't even have to be found. Your boys ask this question about what is there to find in the world? This just says you can get it from the inside and aren't we siloed enough? - Yeah, I mean, kind of, but like really it's, I feel like the my take away from all this reporting is like it's kind of all happening in your mind anyway. It's all a mind game. Taste and for me, like talking to Charles, I was just like, whoa, we're opening up a whole new world. Like what even is possible here? Like what can we do? What are the places we could go? - Yeah, but it's like the whole new world is just on your couch. Like at least with a search, you have to get out the door and be surprised. Like if somebody uses this, what incentive do they have to leave to leave the house? - Yeah, I mean, sure, but like, but if you could definitively know that this experience will be sweeter than anything you could ever experience out in the world. Wouldn't you try that? - Maybe. - Okay, okay. - I'm sure that's like. - Okay, I get your, I get your hankering for wanting to go someplace new. Let me take you one last place that this mapping of sweetness took me that I did not expect. - Okay. - So last month's a team of researchers at the Center for Astrobiology in Spain were looking at a cloud of interstellar dust and gas near the center of the Milky Way. You know, spectroscopy, you know, about that. - I think it's like you detect based on the light waves being emitted, you get clues on what the substance is. - That's right, so cool. - So they did this on this kind of cloud of interstellar dust and what they found in that cloud was a huge amount of a molecule called a Rithrilose. - A Rithrilose. - Okay. - It's a four-carbon sugar. This is the first time ever they found a, not only sugar, a relatively complex sugar in deep space. - What, and would it taste like sugar to us? - So the crazy thing, - Yes. - Is that this exact sugar or Rithrilose? - Yes. - Happens to be found. - Yes. - In raspberries. - Oh, wait, wait, space tastes like raspberries. - No, no, no, just this one cloud. But it does, it does make you wonder, right? Like if this is just out there as a raw material, just floating, like maybe that is a big clue for us. - That there is a space raspberry somewhere. - Whoa. - And do they now think maybe their sugar like all up in Neptune and burning out of the sun? - There has to be enough of it that you can read it on a mass spec. - The scientists have spec to us, if they need taste to us could be. - Hubble telescope, it's just like a giant tongue that they send out. - You know, you just make a rocket with just the tongues. You just add. - The James Webb tongue, yeah. And then you know you had in microgravity is that going to work like Sonic Seasoning James and am the sweetness the more? - Yeah, like what color? - Oh, oh, oh, oh, oh, oh, oh. - I think I'm going to color it. (light music) - Blotchiff, Nasser, who himself scores pretty high, on my list of the sweetest things on this planet. - If only my kids liked me as much as they liked gummy bears. Thank you to you, Lulu, thanks to my kids. Thank you to Geolin Deng, who composed the song that was our Sonic Seasoning. Thank you to Laura Rickman and everyone else at Columbia University's Mortimer B. Zuckerman Mind Brain Behavior Institute for hosting us. And a major thank you to Grant Dubois, to Charles Spence at Oxford University and to Danielle Reed at the Monel Chemical Census Center. They were all extremely helpful in explaining their work and taste in general to us. We're very grateful for their help. - This episode was reported by Lachiff Nasser with help from Jessica Young. - It was produced by Jessica Young with help from Mona McGowker, Maria Paz Gutierrez, Gabby Santis, and Maya Apple B. Melamed. - It was edited by Pat Walters, fact checking by Sophie Sammy E. This is Radio Lab, I'm Lulu Miller. And I'm Lachiff Nasser, say sweet, everybody. - Bye. - This is Lulu here from a couple weeks after we recorded this episode with a note that I'm passing along from Lachiff. He's not reading himself, you'll see why. Here we go. Okay, so hey folks, Lachiff here. Before we leave you, I just wanted to let you know, possibly TMI, that I injured my vocal cords. It's nature's way of telling me I talk too much and I am under doctor's orders to talk as little as possible for the next couple of months. So I'm off on medical leave, putting a sock in it, so to speak. While I'll be leaving you and your ears and brains in the capable hands of the rest of the Radio Lab team, we have fascinating episodes coming up from Matt and Molly and Annie in a veer. And of course, Lulu, thanks about everything from grass to sulfur, too, well, death. I'll be back before you know it. Take care of your throats. Lachiff, take care of your throats. Tee, rest, no talking. We love you, Lachiff, and again, don't worry, friends. We have so many goodies coming up, some of which Lachiff was already in, so he could probably be hearing him anyway, and he will be back in a couple of months. Thanks for listening. - Hi, I'm Eva, and I'm from Brooklyn, New York, and here are the staff credits. Radio Lab is hosted by Lulu Miller and Lachiff Nossar. Soren Wheeler is our executive editor. Sarah Sandback is our executive director, managing at the end of the week. is Pat Walters. Dylan Keefe is our director of sound design. Our staff includes Jeremy Bloom, W. Harry Fortuna, David Gable, Maria Paz Gutierrez, Sindu, Nannis and Bundam, Matt Kilti, Mona McGawker, Annie McEwan, Alex Nieson, Sara Cari, Natalia Vermirez, Joanna Strogots, Anisa Vita, Aryan Wack, Molly Webster, and Jessica Young. With help from Gabby Santos and Maya Applebee-Malamed, our fact checkers are Nora Belblidia, Hillary Elkins, Rachel Gross, Diane Kelly, Emily Kreiger, Natalie Middleton, and Sophie Simey. Leadership Support for Radio Lab Science Programming is provided by the Simon's Foundation and the John Templeton Foundation. Fundational Support for Radio Lab was provided by the Alfred P. Sloan Foundation.