< Scientists finally know the secret to creating — and storing — perfectly gummy candy

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EMILY KWONG, HOST:

You're listening to SHORT WAVE...

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KWONG: ...From NPR.

Hey, SHORT WAVErs. Emily Kwong here.

REGINA BARBER, HOST:

With Regina Barber.

ARI SHAPIRO, BYLINE: And Ari Shapiro.

KWONG: The one and only Ari Shapiro. Hello.

SHAPIRO: Hi.

KWONG: Dropping in a - on a break from hosting All Things Considered to hang out with us and help us close out the week with another science news roundup. Thank you so much for joining us.

SHAPIRO: What an honor to be here.

BARBER: Thanks, Ari. And as always, we've been combing through the headlines, looking at the latest journals and social media. And we've picked out three science stories to talk about.

SHAPIRO: OK. So I'm looking at the list here - building houses, yeast cells and gummy candy. Should listeners try to guess a theme?

KWONG: There is a hidden logic, I promise. All of these have to do with structure, about how things get built and become greater than the sum of their parts. You know, it's like a metaphor for life.

SHAPIRO: Love a theme.

BARBER: Ari, we hope you're ready to unwrap and snack on some science news with us.

SHAPIRO: As long as it doesn't involve dirty diapers, which I'm afraid it might.

BARBER: Uh-oh.

KWONG: Well, buckle up. All right. You're listening to SHORT WAVE from NPR.

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BARBER: As usual, Ari, we're going to tell you about three science stories in the news lately, one about building construction, one about the construction of complex microorganisms and one about how to build the perfect gummy candy.

SHAPIRO: OK. Regina, why don't you start us off? What's first?

BARBER: Yeah, Ari. I'm here to bring you news that will take some guilt away from parents around the world. Used, disposable diapers can be repurposed to produce concrete and build houses.

SHAPIRO: A diaper house? Why would you build a house out of diapers?

BARBER: Well, 'cause it's cheaper and greener. And aside from building regular houses, researchers think it could be useful in disaster relief when you need to build a new house quickly and at low cost and you need to do it with what's lying around. And at a time when there's actually a shortage of sand used in regular concrete, researchers are interested in finding more sustainable alternatives, like dirty diapers.

SHAPIRO: I'm sorry. Do the houses smell like dirty diapers?

BARBER: No, they're sanitized.

SHAPIRO: Tell us about one of these houses.

BARBER: OK. Yeah, they're testing this out in Indonesia, a country with a significant housing shortage. And a team of researchers led by Siswanti Zuraida actually built a small prototype house - about 400 square feet - using diaper concrete. They shredded the diapers, added chemicals to sanitize them and mixed them into concrete to replace some of the sand. And they published a paper about it this week in the journal Scientific Reports. And they said you can use about 10% of diapers for external, load-bearing walls. But for nonstructural walls or floors, it could be up to 40% diapers. And it could also be used for roads.

SHAPIRO: Driving on diapers. So, OK, this sounds like right now proof of concept. Could it actually be scaled up and be easy and inexpensive?

BARBER: I mean, that's the hope, right? And these scientists told me that they still need to work with local city governments to work on collecting the diapers like they do for recycling. And any community that wants to take this on will probably need to buy some machinery. And there needs to be some further research to make sure this process can be replicated easily and affordably. But yeah, that's the goal - a process where materials are provided locally, and the benefit is also local, like, everything within the community.

SHAPIRO: OK. So diaper houses is story number one about structure. Emily, I understand story number two is a little bit smaller.

KWONG: Much, much smaller, yes, in scale. Ari, we are going all the way back to biology class to that one chapter about single-celled organisms, as you might remember from school.

SHAPIRO: I can picture them under a microscope.

KWONG: Yes. Yeah, so at various moments in the history of evolution, single-celled organisms evolved into multicellular organisms, giving rise to complex life forms like my cat, your dogs and, of course, you know, us three. And there's a new paper out in the journal Nature describing how that process may have happened, how single cells started building themselves into a multicellular body capable of moving and metabolizing as one.

SHAPIRO: How did researchers in the present day unlock the secrets of this evolution that happened hundreds of millions of years ago?

KWONG: It's a fascinating story. OK. So it started when this guy, Will Ratcliff, an evolutionary biologist at Georgia Tech, was in grad school. He wanted to figure out how to encourage single cells to stick together and set up an experiment with brewer's yeast. And his question was, you know, how do you force multicellular evolution in a lab? Here's Will.

WILL RATCLIFF: We knew that we needed a way to give an advantage to things that form groups of cells 'cause we're starting out with just single cells.

KWONG: So every day, Will would swirl the yeast cells in their test tube and extract the ones that sank to the bottom the quickest. He then used that population to grow the next day's population of yeast and repeat it and repeat it and throw out all the other cells.

SHAPIRO: What was so special about the yeast cells that sank to the bottom?

KWONG: Well, it's because they stayed together. Basically, he's hacking biology, creating a selective pressure where yeast that stick together survive. And within two months, the yeast cells created this branching structure of dozens of cells that looked like a snowflake. Notably, Will had this breakthrough while snow was falling down from the sky.

RATCLIFF: This was sort of an homage to the fact that this started in Minnesota in the middle of winter. Big snowflakes were falling down.

KWONG: And he continued this work with yeast snowflakes, as he calls them, for years. A colleague at Georgia Tech, Ozan Bozdag, determined that if you deprive generations of yeast oxygen, they grow even bigger and stronger, each cell becoming more entangled, the bonds as tough as wood. And that is the kind of development that gives rise to true multicellularity.

SHAPIRO: So what does this tell us about how single-celled organisms became your cat or my dogs?

KWONG: It's a very good question. So that kind of evolution happened dozens of times. Our ancestors are different than yeast, but what these experiments do show is that multicellularity is possible not just because cells stick together. It's because the bonds between them are strong and lasting.

SHAPIRO: There's a metaphor there about strength as a collective. OK, we've saved dessert for last. You've got research about gummy candy? What's that?

BARBER: Yeah, I mean, we saved the most compelling structure for last.

KWONG: Yeah. Researchers at Ozyegin University and Middle East Technical University in Turkey basically wanted to know, how do you keep gummy candies optimally gummy?

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SHAPIRO: How do you define optimally gummy?

KWONG: So I'm really glad we could bring this to you today. OK. I just mean, like, shelf stable and chewy 'cause no one likes stale gummies...

SHAPIRO: Right.

KWONG: ...Right? So...

BARBER: I don't.

KWONG: Yeah. So these Turkish researchers published their paper in the journal Physics of Fluids this week, detailing a bunch of gummy candy experiments. They wanted to know how changing up, say, the glucose syrup to sucrose ratio or storage or temperature conditions would change the end result. And this matters for candy quality. You want to get the best product possible.

BARBER: Yeah, I mean, Ari, as a physicist and as a candy lover, I love this research. They had so many combinations of gummy creation that they had to use statistical modeling to describe it all. They even measured the average length of the bonds between molecules in the candy to make a judgment call about which candy-making method produced the best structure. This is material science at its finest.

SHAPIRO: All right. You're burying the lede. What's the conclusion here? What did they learn?

KWONG: So the best gummy combination - according to this research - for a stable candy with a long shelf life involves reducing the cornstarch and increasing the gelatin in the mix. And to keep them soft, storing them at, like, a warm room temperature 'cause if it gets too cold or too hot, they get stiff.

SHAPIRO: I'm going to take my gummy bears out of the refrigerator as soon as I get home.

BARBER: There is a fun fact, though, Ari. From a material science perspective, this actually totally makes sense because gummy candies are long chains of molecules. And they undergo something called the glass transition, meaning that when they get cold, they get harder and more brittle, like glass, and they start to lose some of that flexibility and chewiness that we love in our candy.

SHAPIRO: I think we all get a little less flexible in the cold. Wouldn't you say?

BARBER: Yeah.

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BARBER: Thanks again to Ari Shapiro for stopping by. And I want to say good luck to Siswanti Zuraida, who's a few weeks away from defending her dissertation on using diaper material in construction. And as always, if you see a science headline you'd like us to explain in the roundup, tell us about it. Email us at shortwave@npr.org.

KWONG: This episode was produced by Berly McCoy and Gus Contreras. It was edited by our managing producer, Rebecca Ramirez, Brent Baughman and Christopher Intagliata. Brit Hanson checked the facts. Ko Takasugi-Czernowin was the audio engineer. Special thanks, also, to Gilly Moon.

BARBER: Our senior director of programming is Beth Donovan. And our senior vice president of programming is Anya Grundmann.

KWONG: I'm Emily Kwong.

BARBER: And I'm Regina Barber. Thanks for listening to SHORT WAVE from NPR.

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