IRA FLATOW: This is Science Friday. I’m Ira Flatow. Last July, a Cincinnati woman created national headlines when she made a shocking, shocking discovery. Here’s how a Cincinnati TV station, WCPO and consumer reporter John Matarese covered it.

JOHN MATARESE: Christie Watson’s kids love ice cream. But one recent morning, she saw an uneaten ice cream sandwich sitting on her patio table.

CHRISTIE WATSON: I noticed that my son had left his ice cream sandwich outside. And I was wondering, why was there still ice cream there?

IRA FLATOW: Yes, why, after sitting out for hours in the summer heat, did the ice cream sandwich appear to be largely intact, just slightly melted, if at all? Was there some unnatural ingredient packed into this frozen treat that helped it withstand 80 degree temperature? What gives? That’s what we wanted to know.

So here to defrost the mystery of the seemingly unmeltable ice cream sandwich, just in time for National Ice Cream Day on Sunday– wink, wink– is Maya Warren. She is an ice cream expert and PhD candidate in food science at the University of Wisconsin, Madison, where they know their ice cream. She’s also the Season 25 winner of The Amazing Race on CBS. We’ll talk about that with her. She joins us now from Wisconsin Public Radio. Welcome to the program.

CHRISTIE WATSON: Hi, thank you for having me. And happy National Ice Cream Month to everyone.

IRA FLATOW: Happy Ice Cream Month to you too. Did this ice cream sandwich really melt, or not melt?

MAYA WARREN: You know, the cream sandwich actually melted. I haven’t heard of any one at high temperatures that they can have ice not melt. So the ice definitely melted. So therefore, the ice cream melted. But the structure itself did not collapse, which is really, really, really, cool, to say the least.

IRA FLATOW: Tell us, why is that so cool?

MAYA WARREN: So basically, in ice cream, you have a couple different parts. You have your ice crystals, of course, which melt. You have your air cells. So picture kind of like a soda with little bubbles around it. That would be kind of like your air cells in ice cream, dispersed throughout your ice cream.

And you also have your fat globules. And sometimes those– usually those fat globules are partially coalesced. They kind of agglomerate together. But they’re not fully coalesced like butter. But they’re held together through a partial crystalline network, which causes them to sometimes be really, really large in size. And that, along with the air structure sometimes causes ice cream not to collapse from natural gravitational force.

And so what that mom probably mostly encountered was the water basically, the ice that turned to water. But if it was outside, it probably evaporated off at some point. And what was left there was basically kind of like a foam that consisted of your fat globules, your air cells, and probably a couple sugars and some of the other ingredients in ice cream. So it actually did melt.

IRA FLATOW: Huh. So there’s no stuff inside of it that tries to make it keep it shape, like gelatin or any kind of stuff, binders, things like that?

MAYA WARREN: Sometimes in ice cream, depending upon the brand or how the person’s making it or the company, sometimes there are things in there that can help ice cream retain its shape. But actually, we can use something that’s free and that we’re in every day, air. Air really does help ice cream retain its shape.

So sometimes the more overrun, which is the amount of air that’s in ice cream, the more overrun in a product, the more it’s going to help retain its shape, generally speaking. And so I’m assuming that that Walmart type of ice cream probably had quite a bit of air in it.

IRA FLATOW: So you can adjust the amount of air you pump into it.

MAYA WARREN: Definitely. You can inject. You can decide to inject a certain amount of air. So for instance, if we’re looking at a ice cream like Haagen Dazs, that kind of ice cream has about 27% overrun, versus an ice cream like an Edy’s has almost upwards to a 100% overrun.

And so when you go to the grocery store, and you’re like, why is this pint of ice cream $5, versus this kind of ice cream is $2, usually the $2 pint has a bit more air in it, versus the $5 pint. So you are kind of paying what you get for.

IRA FLATOW: Well, we did our own, actually not so scientific experiment that you can see on our website at sciencefriday.com/totalmeltdown, where it seemed like ice cream. We put three ice cream cones up there. And we showed you. We have a time lapse of them melting. And they’re melting dramatically at different rates.

MAYA WARREN: Indeed, indeed. So different parts of the microstructure really, really do control how your ice cream is going to melt. So I looked at the video. And I saw that there was a Briar’s, a Ben and Jerry’s, and a Haagen Dazs. And with that, because of the differences in the microstructures, you’ll usually see different rates of melt.

But one thing that I did notice in the video was that they all started off at different sizes. And so we kind of threw in another variable into the experiment. And so unfortunately I can’t honestly say one melts faster than the other. Because we kind of threw in a different variable, especially if they didn’t all start at the same time.

But from the research that I do on the microstructure of ice cream and other frozen aerated desserts, we do know that there are certain parts of the microstructure that you can control which will then assist in controlling the rate of melt and/or the melt behavior. Because at the end of the day, all ice cream will melt. But does all ice cream collapse? That’s the real question.

And from the microstructure, the air cells– so the amount of overrun and the size of the air cells as well as the amount of fat, the type of fat, the agglomeration, the partial coalescence of that fat all come into play to create that one kind of particular ice cream. And those really have to do with our sensorial likings as well. So microstructure is really, really key in ice cream.

IRA FLATOW: Now, I know that– let’s talk about your Amazing Race. You and another fellow scientist, two scientists, won The Amazing Race?

MAYA WARREN: I know. Can you believe it? It’s awesome. Yeah, so my lab mate and I, Amy DeJong, she researches candy at UW, Madison, and I do ice cream. And we were deemed the Sweet Scientists, because we study really sweet things. But actually we were really, really sweet on the race as well.

And we traveled around the world, beat out 10 other teams of 2, travelled to 8 countries, 4 continents, over 26,000 miles, to win The Amazing Race, and become the third female-female team in 25 seasons to win. So I’m very, very honored, and really honored to represent women in science and continuing to inspire young people to get into such a cool and fascinating field as well.

IRA FLATOW: Must have shocked the heck out of everybody.

MAYA WARREN: Oh, we pretty much did. We were the underestimated team, to say the least. But when it came down to it and brain power came into play, we hit the nail on the head, and we ran to the finish line first. So it was pretty awesome.

IRA FLATOW: So is there a future? Can you be an ice cream scientist? It sounds like the dream job.

MAYA WARREN: Indeed. You can totally be an ice cream scientist. You know, Ira, I think you can be anything you want to be. And I’ve wanted since a young age to study and kind of play with ice cream.

And I’m ending my PhD In the next month or so and hopefully going out and doing some more things in ice cream. I’m working on possibly doing a television show on frozen desserts around the world and across the country, to explore more of the science behind food, and not just some of the culinary aspects, but really what goes into our food, and using ice cream as the medium to touch people all across the world.

But you can definitely, definitely look into becoming an ice cream scientist, a candy scientist, a cheese scientist, a hot dog scientist. You name it. You can pretty much do it all. Anything that we eat, anything that we wear, anything that we sit in, has a science behind it.

IRA FLATOW: Spoken like a true Badger.

MAYA WARREN: Indeed, indeed.

IRA FLATOW: All right, we’ve run out of time. I want to thank you, Maya. Maya Warren is an ice cream expert, a PhD candidate in food science at the University of Wisconsin in Madison.