The Perfect Cheese Pairing? Science

24:11 minutes

It’s something of a biological enigma: not quite living, but not quite dead, either. It’s often infested with microbes—or sometimes, crawling with tiny mites. It might be covered in cheesecloth, or coated in ash. And you can smell it from across the room.

We’re talking about cheese, of course—one of the most captivating, delicious, and unusual foods. It’s the subject of a special SciFri spotlight, where we meet the “maestro of mozzarella” and learn about the cheddar-aging tricks of a Wisconsin cheddarmaker. Plus, we get a luscious lesson on the fluid dynamics of queso—yes, the melty cheese dip. David Hu joins to talk about its non-Newtonian nature.

And as David Hu said on-air, ants flow like melted cheese! See below:

Pulling apart ants is like pulling apart string cheese. Both demonstrate formation of long threads before fracture.
Pulling apart ants is like pulling apart string cheese. Both demonstrate formation of long threads before fracture.


Segment Guests

Chau Tu

Chau Tu is an associate editor at Slate Plus. She was formerly Science Friday’s story producer/reporter.

Luke Groskin

Luke Groskin is Science Friday’s video producer. He’s on a mission to make you love spiders and other odd creatures.

David Hu

David Hu is a mathematician and a professor in the departments of Mechanical Engineering and Biology at Georgia Tech in Atlanta, Georgia.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Our next subject is something of a biological enigma. It’s not living, but it’s not quite dead either. It’s often infested with bacteria or sometimes crawling with tiny mites. It can be covered in bandages or coated in ash, and you can smell it from across the room.

No, I’m not talking about a zombie. I’m talking about cheese– yeah, one of the most captivating and delicious and sometimes unusual foods out there. It’s one of my favorite foods. And it’s the subject of a special sci-fi investigation this week and next on the radio and on the web at sciencefriday.com/cheese. And here to tell us all about it are Chau Tu– she’s Science Friday’s story producer and reporter– and Luke Groskin, our video producer. Welcome to both of you.


IRA FLATOW: Chau, I know this project was your idea.

CHAU TU: Yes, it was.

IRA FLATOW: Why cheese, and why not? I mean, I love cheese.

CHAU TU: I love cheese too, so that’s pretty much where it started. But I also thought about the different varieties of cheese. There is brie, there’s cheddar. There’s vegan cheese. So I was thinking about the techniques that cheesemakers were using, the ingredients, the bacterial cultures, the aging processes. So it’s kind of rich for a scientific investigation.

IRA FLATOW: Kind of rich– I like that play on words. You profiled a cheesemaker from Wisconsin who makes a special kind of cheddar.

CHAU TU: Yes, so Willi Lehner of Bleu Mont Dairy in Wisconsin, he makes this bandage cheddar, which is a cheddar that’s bound in cheesecloth. And it’s a very, very popular chatter amongst cheese fans.

IRA FLATOW: Went very fast in our office.

CHAU TU: It’s a really, really good. So the thing about this cheddar is that it has a really important aging process. Because it’s just bound in cheesecloth, it needs to be protected as it’s being aged. So what Willi does is he dunks it in hot lard right after he brings it into his cheese cave. And that lard helps keep the cheese moist.

And it also protects it from different cracks or cheese mites. But there’s also a mold that grows on top of the lard. And so the cheese mites actually eat that mold as the cheese is aging. And these cheese mites are really, really tiny. They’re smaller than the size of a period at the end of a sentence. And they also can reproduce every nine days. So this can be a problem.

IRA FLATOW: I’m not eating the mites when I eat the cheese?

CHAU TU: You’re not.

IRA FLATOW: How does he get rid of the mites?

CHAU TU: He uses a vacuum. All these cheeses are vacuumed over the course of a couple weeks and over the course of a couple months as the cheese is aged. And eventually, it becomes a really, really tasty and earthy cheddar.

IRA FLATOW: I love it. And Luke, you stayed local for a look at making of mozzarella Describe it here in New York.

LUKE GROSKIN: I went up to a street called Arthur Avenue. It’s about three blocks from the Bronx Zoo.

IRA FLATOW: Very famous place.

LUKE GROSKIN: Very famous. It’s a street that’s lined with Italian delis, bakeries, and butchers– just really, really classic Italian ingredients, really delicious food. And I went to one such deli to meet a master of mozzarella, a true master of mozzarella.

[? RAZZO GACCIOTTO: ?] My name is [? Razzo ?] [? Gacciotto. ?] I’ve been making mozzarella about 30 years. And my business is called Casa della Mozzarella. “Mozarella,” “muzzarella”– no. M-O-Z-Z-A-R-E-L-L-A. Mozzarella. Best way to eat mozzarella– same day. So if you put something fresh in the refrigerator, you lose a lot, because mozzarella get dry. No refrigerated mozzarella.

LUKE GROSKIN: No refrigerated mozzarella– you hear it?

IRA FLATOW: Wow. Yeah– I had never– something new to me, because you get it and see it in the refrigerator all the time in the food store.

LUKE GROSKIN: Exactly. If you’re getting it fresh, don’t put in the refrigerator. Leave it out. If you’re going to eat it the next day, you do have to put it in the refrigerator. But you shouldn’t do that. You should eat it the same day. He’s got all sorts of tips like that to help you get the most of your mozzarella.

IRA FLATOW: Does he have a master recipe that he uses to do this?

LUKE GROSKIN: Actually, incidentally he doesn’t. It’s a very simple thing to make. It’s just cheese curd, salt, and boiling hot water. And you would think there would be a very simple master recipe for that. But with him, there isn’t. He’s been doing this for 30 years. His hand is his thermometer when he’s checking the temperature.

He knows exactly how much salt to add. And so even though he has this mastered, there are very specific variables that over the 30 years he’s experimented with. And he’s figured out. And if you watch the video, you’ll see what the trick of it is.

IRA FLATOW: It is a gorgeous video. And Chau, our celebration of cheese science is going to continue all next week.

CHAU TU: Yes. So you can make your own mozzarella at home. There’s an educational activity that we have on our site. We also have an article about vegan cheeses, where we talk about using tree nuts like cashews to make plant-based cheeses.

IRA FLATOW: If you don’t want to use milk in it.

CHAU TU: Exactly. Yeah, exactly. Next week on the show, what you’ll be talking to a microbiologist about the bacterial battle happening inside of cheese and how that affects taste and flavor. And then there will be a dairy scientist in South Dakota talking about the history of processed cheese. So all of this is on our website. It’s at sciencefriday.com/cheese.

IRA FLATOW: It’s all up there now. And your video–

LUKE GROSKIN: At sciencefriday.com/cheese.

IRA FLATOW: And we want to make his– he doesn’t say muzzarella. I thought that was interesting, because so many New Yorkers say “muzzarella.”

LUKE GROSKIN: Mozzarella.

IRA FLATOW: And he shows us how he makes that.

LUKE GROSKIN: Oh, yeah. I mean, one really amazing way that he does it– he’s been doing this 30 years. He actually touches the boiling hot cheese in order to stretch it quicker so that the butterfat milk doesn’t leave the cheese. The quicker you do it, the less butterfat milk comes out, the more rich your cheese comes out. So he’s just touching the cheese with his bare hands.

IRA FLATOW: He’s sticking his hand in the boiling water.

LUKE GROSKIN: Yes And it’s how his cheese tastes so good.

IRA FLATOW: And his hands show the effects, right?

LUKE GROSKIN: Yes. That’s right.

IRA FLATOW: And this is great. This is great. It’s up there on our website at sciencefriday.com. And now I want to thank you both for alerting us to Cheese Week coming up next week.

LUKE GROSKIN: Our pleasure.

IRA FLATOW: Thank you, Chau Tu and Luke Groskin, our video producer. Chau Tu is our story producer and reporter. Thanks, guys. Next up, speaking of melted mozzarella, ever wondered why it gets so stringy when you heat it up? Well, it turns out that melty liquid cheese like fondue and queso, they are the ideal subjects for a luscious lesson in fluid dynamics.

So grab your cheese dip and get a little of this on your chip. David Hu is a mechanical engineer and associate professor in the Department of Mechanical Engineering and Biology at Georgia Tech in Atlanta. He joins us from the studios of Georgia Public Broadcasting today. Welcome back, Dr. Hu.

DR. DAVID HU: It’s great to be here, Ira.

IRA FLATOW: The fluid mechanics of cheese– who would ever thought that that’s possible?

DR. DAVID HU: Cheese– cheese is a special kind of fluid. We call it a non-Newtonian fluid. And actually, most of the fluids around us are all non-Newtonian, especially ones made by nature.

IRA FLATOW: What does that mean, especially queso, non-Newtonian fluid? What does that mean to us?

DR. DAVID HU: A non-Newtonian fluid is a fluid that has kind of the properties of both a liquid and a solid. So it kind of mixes these both together. So an example of a solid is things that are springy, for example like you sit in a chair and it yields slightly. Fluids, you can fill up a container and they’ll sort of fill up all the spaces.

And now cheese is kind of this mix between these two worlds, because it’s composed of mostly liquid but then a lot of really small springs. And these springs allow the fluid to have a lot of– well, let’s call it personality. The cheese can remember what was done to it in the processing. And that affects its properties later.

IRA FLATOW: So let me see if I got that right. It remembers what was done to it in the process.

DR. DAVID HU: That’s right. For example, when you make the string cheese, you stretch these fluid molecules. You’ll stretch the little springs. And then this will make the springs aligned. And so when you pull it apart, you’ll get these long strings. But if you melt it, it sort of erases the brain of the non-Newtonian fluid.

It just starts it all over again. And it puts all these molecules– they’re just running around doing whatever they want. That’s why when you melt it, you can just pour cheese just like a liquid. But then when you solidify it, it remembers the manner at which it was solidified.

IRA FLATOW: That’s fascinating. Why do you think that non-Newtonian fluids are so pleasing to us when we eat them?

DR. DAVID HU: Once you start mixing fluids with solids, you bring in this concept of elasticity. It’s a degree of softness. And the amazing thing about our mouth– our tongue is very, very sensitive. We can really tell the difference between different levels of softness.

And the softness is an interesting variable, because it has a range of over a million-fold. If you think of the softest pillow all the way up to a piece of steel, it’s a range of a million different levels of softness. And we can basically taste these things. You imagine eating crackers and eating cheese. It’s mixing these two together. So we can really get a lot of texture and it gives it a new dimension.

IRA FLATOW: That is interesting. You know, I never thought about why cheese and crackers go together so well. But you’re saying it’s because they’re so totally opposite.

DR. DAVID HU: Yeah. It brings them– the solid, elastic nature of the cheese puts in the same realm as the crackers. We can start to compare them. I don’t think, for example, crackers and liquid– they’re sort of two different worlds.

IRA FLATOW: Yeah. Yeah. And I know the cheese industry and food industry must spend a lot of money trying to find that right cheese that your mouth loves.

DR. DAVID HU: Oh, yeah. There’s a whole industry of synthetic, fluid-like materials, things like chocolate, things like cheese. And not even just things that we eat, but the entire supermarket is filled with materials that have been specially tuned to exhibit both solid-like and fluid-like properties. For example, I used to go to Taiwan when I was young. And when I went, they actually didn’t have shampoo like we had it.

People used to use powder as shampoo. And so you imagine you want to put soap in your hair, you put a pile of powder on your hand. And it basically just spills everywhere. Now they invent shampoo, basically a kind of liquid that can basically act like a solid when it’s in your hand. But as soon as you start smushing it in your hair, it becomes liquid again.

IRA FLATOW: You know, I never thought about that. You always wonder why–

DR. DAVID HU: Someone had to invent that. Otherwise, you imagine you put a liquid, something just totally liquid-like, and it just goes through your fingers. How do you give someone a handful of shampoo? You just can’t, because it won’t fit in your hand.

So someone had to add these little polymers just like they have done with the cheese, to make it basically act like a dollop, but not like a hard dollop, not like peanut butter, but like a dollop that you can actually spread around.

IRA FLATOW: Well, I know that you actually had a run-in at the airport once where you used fluid dynamics to get you out of a tight situation. Tell us about that.

DR. DAVID HU: Oh, right. So these airlines, they don’t have food on the airline. So I would just bring whatever I had in my fridge. And there was one day I brought this split pea soup. It’s interesting, because when it’s warmed up, it’s a liquid. But when it’s cold, it acts like a solid.

And so they looked at the split pea soup. They’re like, that’s a liquid. You can’t bring that. I said, no, but it’s non-Newtonian. So I flipped it upside down and it didn’t fall out of the container. And they said, non-New– what? But anyway, they let me go through, because I could convince them that under certain conditions, this kind of non-Newtonian fluid can trick people into believing it’s a solid.

IRA FLATOW: This is quite educational. I’ve been talking with David Hu, mechanical engineer in the Department of Engineering and Biology at Georgia Tech in Atlanta on Science Friday from PRI, Public Radio International. We’re talking about everything you wanted to know about the fluid dynamics of cheese.

Now let’s talk about queso. Why not, because we’re now into that world. How do you test the properties of queso in your lab? It’s got to be more complicated than just putting some in a bowl and dipping a chip in it, right?

DR. DAVID HU: That’s actually almost how they do it. So they actually have these–

IRA FLATOW: Very cheap equipment.

DR. DAVID HU: Well, these devices called rheometers. They are basically like $50000 blenders. And you just put a very small dollop of this fluid in. And they’re so expensive because they sit on air bearings. So they basically are totally frictionless. And they have these– imagine it looks like two Oreo cookies. And they rub the cookies back and forth like you were taking a chip and sort of twisting it back and forth.

And they measure basically how the queso responds to you twisting, twisting the chip. And in certain cases, for example, if the queso starts cooling down, it will start acting very springy. So you’ll twist the chip and it will twist your hand right back. But if you heat up the queso, it will act more like a fluid. And it will just smoothly turn as you twist the chip.

IRA FLATOW: We’re talking about cheese. If you want to get in on this, there’s a lot of fun stuff going on. 844-724-8255 is our number, if you’d like to call. Let’s see if we can get a call in before we go to the break. Mike in Inverness, Florida– hi, welcome to Science Friday.

MIKE: Hey, how you doing?

IRA FLATOW: Hi there.

MIKE: I was wondering when you were talking about the string cheese and you said, you pulled it apart and it’s like in strips. But if you were to melt it, and then it would lose its memory after you melted it. If you let it solidify again and pulled it apart, would still come in the string lines, the strips like that before? Or would it have a new design to it?

IRA FLATOW: He’s got a project for this evening, I can see here.

DR. DAVID HU: Oh, yeah. The interesting thing about cheese is that basically it’s liquid when it’s hot, and then the molecules are just random. They’re just all– and in fact, when you’re boiling it, the molecules are just literally running around.

And as soon as you cool it down, you want to make it in some kind of configuration. And so while it’s cooling, right before it become solid, you can stretch it and then people put it into these long sticks. And that will help align these long, stringy molecules so that they’re facing the same direction.

IRA FLATOW: Knowing what you know about the fluid dynamics of cheese, is there a right way and a wrong way to eat it?

DR. DAVID HU: I think the right way is you really want to stretch it a lot. You really want–

IRA FLATOW: All cheese, you want to stretch it? Cheddar or gouda–

DR. DAVID HU: At least pizza cheese. I like stretching it. I mean, when you pull the pizza off the pizza slice from the rest of it, you see these cheese actually stretches. So that’s not a typical fluid. That’s these long, springy molecules really absorbing the energy as you’re pulling this away.

And if you look carefully as you’re stretching it, the cheese will sort of spring back, like little springs. That really shows that it’s the nature of these really long filaments.

IRA FLATOW: It’s getting it off of everything that it stretches onto that is the challenge. It makes that giant loop.

DR. DAVID HU: And nature really takes advantage of these things. I mean, they don’t make cheese, but they make sort of the equivalent. Because I would say cheese is sort of everywhere in American cuisine. And in nature, the equivalent of cheese is mucus. I mean, they put this thing into everything.

IRA FLATOW: OK, good place to take a break. Come back. I want to follow up on this, in nature it’s mucus– mucus equal to cheese. There’s a takeaway for Science Friday, this show. We’re going to come back and talk more with David Hu about cheese. Our number 844-724-8255. We’ll explore this further when we get back. Stay with us.

This is Science Friday. I’m Ira Flatow. We’re talking with David Hu, a mechanical engineer professor at Georgia Tech in Atlanta. We’re talking about the fluid dynamics of cheese. Of course, when you tune in to Science Friday, you know that’s what we’re going to be talking about– an engineer talking about cheese.

And the most fascinating part which I said I would follow up on before the break is that David, you said that the closest thing in nature to cheese is saliva. Mucus– I’m sorry– mucus, not saliva. I can’t let you get away with that without explaining that a little bit more.

DR. DAVID HU: Well, the interesting thing about cheese and these other non-Newtonian fluids is that you just add a little bit of this special ingredient and you can totally change its properties. So mucus is one thing that almost everything in nature makes. So it’s similar to cheese.

Imagine if you had a big vat of cheese, something like a swimming pool, and you got stuck in it. How would you get out? Well, this is exactly the problem that is faced by little flies when they fall into these horrible traps called pitcher plants. There are these plants in the rain forest that literally look like pitchers. And they exude some kind of sweet scent, and the flies want to come and check it out.

And the pitcher plants fill with rain water. And they add a little bit of extra ingredient. And they basically mix the rainwater in the pitcher plant, and it makes it essentially like cheese. And so this little fly goes for a swim, goes for a dip in the pitcher plant. And flies are actually pretty good at swimming. But the problem is, it’s really hard to swim through cheese.

Because every time– you imagine this fly’s flailing about. Every time it lifts one of its little legs, instead of forming drops like we do in a swimming pool, you pull up this big string of cheese. And it does this with one leg. And problem is, it’s got six legs.

So they’ll take all these six legs and whale them around. And sooner or later, it’s sort of twisted and turned itself into a rope of cheese. It’s really twisted itself and tied itself up with the mucus and then is trapped there.

IRA FLATOW: You know, the Smothers brothers used to have a song they did, “I Fell Into a Vat of Chocolate,” about swimming around, trying to get out. This is sort of the same thing.

DR. DAVID HU: Yeah, and it’s the ability of these, for example, cheese and mucus and these other kinds of special fluids– they can generate long, stringy things. I mean, that’s not typical. If you were to pour water out of a pitcher, when you stop pouring, it wouldn’t have this long string that you’d have to separate. But that’s the problem with these. Or, in the pitcher plant’s case, that’s the solution.

IRA FLATOW: Yeah. You sound like a geeky guy who loves to talk about cheese. And fluid dynamics– how did you get so involved? What captures your imagination about fluids? When did you first learn that you were interested in fluids?

DR. DAVID HU: When did I first learn? I think when I started realizing that fluids are everywhere. And we’ve basically figured out how to, like I said, these non-Newtonian fluids have personalities. We’ve figured out how to change their personalities to just do what we want.

So I’ll give you another example. So paint is a nice example of a cheese-like substance, of a non-Newtonian fluid. For example, paint, we want to basically be able to take a brush and a paint can and mix it around with a brush. And we want to be able to coat the brush with it. But then we want to be able to throw it on the walls and we want it to not fall off the wall.

So that’s one of the properties of– similar, cheese-like property. Basically acts like a fluid when you mix it really fast. But then once you put on the wall and it’s dripping slowly, it solidifies. And we don’t have to do anything special. We just sort of change the personality of the fluid so it just sticks to the wall, without falling down.

IRA FLATOW: Is ketchup non-Newtonian?

DR. DAVID HU: Oh, yeah. Ketchup is non-Newtonian. And that’s why it’s generated this whole craze of people trying to figure out how to get it out of the bottle. It’s just like paint, that basically if you push it really fast, it’ll be fluid-like. But if you push it too slowly, for example, when there’s just a little bit left in the bottle, it doesn’t weigh enough.

Then you sort have to just bang at it. And then once you exceed this critical amount of force, it just flies out. It’s just like this person that just seems like they’re calm and steady and then suddenly, when you push them too hard, they just sort of go explosive. That’s what ketchup’s like.

IRA FLATOW: So if you’re a school teacher and you want to do a demonstration in your class of non-Newtonian fluids, cheese would be a good thing to use.

DR. DAVID HU: Yeah, cheese would be great, because it really– you could pour it. It can fill in molds. And then you can stretch it. And you can see it really is– basically you can stretch it and it can really absorb some energy. But then you can basically melt it down again. You can’t do that with too many things that taste good.

IRA FLATOW: Do you have your own favorite cheese? [INAUDIBLE] use in your lab or just to eat?

DR. DAVID HU: I actually really like bleu cheese, the kind that looks like it has mold in it. But then every time– so I’m Chinese. Every time my mom comes over and she sees the fridge and there’s this bleu cheese in it, she thinks it’s totally rotten and she’ll just throw it away. I’ll say, no, it’s supposed to be like that. It’s actually kind of expensive.

IRA FLATOW: I can’t top that, so I’m going to say goodbye. Say hello to your mom for us, next time you see when we talk about cheese. Thank you, David. Fascinating. David Hu is a mechanical engineer and associate professor in the Departments of Mechanical Engineering and Biology, a rambling wreck from Georgia Tech in Atlanta. Thanks for joining us. And for more cheese science, check out our spotlight at sciencefriday.com/cheese. And our gooey, salty saga is going to continue next week– more cheese on this show also.

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