Science Friday - Futuristic Freezing, Koji, Cheese Microbiome, Wine-Bottle Resonators. November 26, 2021, Part 1

Episode Date: November 26, 2021

New Cold Storage Method Solves Freezer Burn—And Saves Energy Have you ever pulled a long-anticipated pint of ice cream out of the freezer, only to find the strawberries crunchy and the normally creamy substance chalky and caked with ice? Freezer burn, a phenomenon caused by water in food crystallizing into ice inside the ice cream or fruit or meat during freezing, is a menace to taste buds, a driver of food waste, and even damages some of the nutritional benefits of food. And it’s always a risk as long as food preservation relies on very cold temperatures. Even flash-freezing, which works much faster, can still create small ice crystals. But United States Department of Agriculture (USDA) food scientists, working with a team at the University of California-Berkeley, have a method that could help solve this problem. Normal food freezing, called isobaric, keeps food at whatever pressure the surrounding air is. But what if you change that? Isochoric freezing, the new method, adds pressure to the food while lowering temperature, so the food becomes cold enough to preserve without its moisture turning into ice. No ice means no freezer burn. And, potentially, a much lower energy footprint for the commercial food industry: up to billions fewer kilowatt-hours, according to recent research. Ira talks to USDA food technologist Cristina Bilbao-Sainz and mechanical engineer Matthew Powell-Palm about how pressure and temperature can be manipulated to make food last longer, and hopefully taste better. Plus, the challenges of turning a good idea into a widespread technology. Koji: The Mold You Want In Your Kitchen When chef Jeremy Umansky grows a batch of Aspergillus oryzae, a cultured mold also known as koji, in a tray of rice, he says he’s “bewitched” by its fluffy white texture and tantalizing floral smells. When professional mechanical engineer and koji explorer Rich Shih thinks about the versatility of koji, from traditional Japanese sake to cured meats, he says, “It blows my mind.” Koji-inoculated starches are crucial in centuries-old Asian foods like soy sauce and miso—and, now, inspiring new and creative twists from modern culinary minds. And Shih and Umansky, the two food fanatics, have written a new book describing the near-magical workings of the fungus, which, like other molds, uses enzymes to break starches, fats, and proteins down into food for itself. It just so happens that, in the process, it’s making our food tastier.  You can grow koji on grains, vegetables, and other starchy foods, and make sauces, pastes, alcohols, and vinegars. Even cure meats. Umansky and Shih say the possibilities are endless—and they have the koji pastrami and umami popcorn to prove it.   The Bacteria Behind Your Favorite Blues, Bries, and More Cheese lovers, you can thank microbes for the flavorful funk of Camembert cheese and the perforated pattern of Swiss. According to microbiologist Rachel Dutton, one gram of cheese rind is home to 10 billion bacterial and fungal cells. Dutton describes our favorite cheese-microbe pairings and explains why the cheese rind is ripe for teaching us about the basic interactions of bacteria.   The World According To Sound: When Your Wine Bottle Sings A few years ago, Chris Hoff was making himself some plum wine. He had a nice big plum tree in the apartment he was renting in San Francisco, and it had been a plentiful year. During the process he came across a beautiful, simple sound that made him get out his recording gear. It came from his little metal funnel. Each time Hoff poured liquid through his funnel to fill a bottle, it made this pleasant rising arpeggio of bubbles. When the pitch reached its height, the bottle was filled, and Hoff moved on to the next one. He liked it so much that he grabbed his small handheld recorder and captured the sound. This simple, everyday sound is the result of a complex interaction of the liquid, bottle, air, and funnel. While water pours down through the funnel, air is being forced out of the bottle and up through the liquid, where it makes a bubble on the surface and then pops. As the level of liquid decreases in the funnel, the pitch of the popping bubbles rises. Read more at sciencefriday.com.     Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This is Science Friday. I'm Ira Flato. We've all had that moment. You've got that pint of ice cream in the freezer. Strawberry, maybe? I'll go with coffee. You've been looking forward to this treat all day. You open the carton, and it's covered in ice crystals. Freezer burn. Your ice cream is going to taste bad and feel chalky and strange in your mouth. Those little chunks of strawberry? Weirdly crunchy, bleh, as they say. That dreaded freezer burn happens when the water in your food forms ice crystals that destroy the cellular structure of the food itself. It's a common risk when we preserve food by exposing it to very cold air, right? And the result is bad taste, of course, but also some loss of the food's nutritional value. That's the bad news. The good news is USDA food scientists working with a team at the University of California, Berkeley,

have something that could solve that problem, a whole new method of chilling food to preserve it. This new method called isochoric freezing actually plays with pressure, so the food becomes cold without its moisture turning into ice. No ice? No freezer burn. And potentially a much lower energy footprint for the commercial food industry.

We're talking billions fewer kilowatt hours. Here first to explain more about why this is so exciting, Dr. Christina Bilbao, a food technologist with the USDA's Agricultural Research Service in Albany, California. Welcome, Christina. Hi, hi, I, thank you. Thank you for inviting me to the show. Always a pleasure. Maybe you were a little frozen there because you know we're going to talk about freezing, right? Yeah, yeah. I had no idea that we needed a new way to freeze food. Why is conventional food freezing flawed? So conventional freezing, it has the advantage that the temperature is very low.

It can slow down the deterioration processes such as respiration, oxidation, oxidation, microbial growth. However, ice formation during freezing can cause cellular damages that results in the product with poor quality. In terms of maybe texture, color, they might lose some nutrients. That's the reason we need to find out a new technology that can be used to preserve food as a freezing temperatures,

but without any ice formation inside the food product. Isocotic freezing, what it does, it takes advantage of preserving the food at suffreasing temperatures and therefore slowing down the deterioration reactions, but without any ice formation inside the food product. So what happens to foods you froze with the new method? What were they like after being frozen? We were pleasantly surprised at how similar these food products are to the fresh products.

In terms of the appearance, they don't lose volume, they don't lose mass, the texture, the color, even the nutrient content. So it's very, very similar to the food. the fresh products. Huh. So it even tastes the same way? We have only tested tomatoes and raw potatoes. And they tasted the same, yes. Not every fruit and vegetable is a good fit, right?

What kinds of food would this method be best for? I think this technology can be used to extend the self-life of fresh produce. Good candidates would be those fruit and vegetables. tables that are difficult to freeze using conventional freezing processes like tomatoes. We have also found out that minimally processed food such as cut potatoes can be also a good candidate. Cut potatoes when they are packing vacuum on in a modified atmosphere. The safe life is only five to seven days in the refrigerator.

So this technology can be used to extend the safe life of this cat products. Wow. Does food frozen this way retain its nutritional value also? Yes, we can do it in a way that it retained the nutritional value. So is this exciting to you? I mean, to have a new way to freeze food. This seems like something that doesn't come along very often. Yeah, we have also found out that this technology can improve the food safety and reduce the energy cost of refrigeration. Now we are going to investigate the potential juice of isochoric freezing for cold pasteurization and preservation of fluid foods such as milk, fruit juices and vegetable juices. There is an increased consumer demand for more fresh, authentic, fluid foods. The industry is offering pasteurized fruit foods,

the safe life of these products is very short. So we are now trying to to investigate the potential of using isocotic freezing to pasteurize and preserve these fluid foods in just one step. Wow, that sounds exciting. I want to thank you for taking time to be with us today. You're welcome. Thank you to you. Dr. Christina Bilbao is a food technologist with the USDA's Agricultural Research Service in Albany, California.

I want to turn out to another researcher on the team, Dr. Matthew Powell Palm, a mechanical engineer, and postdoctoral scholar at UC Berkeley. He is based in Bozeman, Montana. Welcome, Matt. Hi, Ira. Good to be here. Nice to have you. First of all, let's geek out a bit about this freezing myth, because I am a geek and I got to know all the details. I mentioned it involves keeping foods at a higher pressure than just sticking it in a freezer. So explain what we're doing exactly what the effects are of that.

Yeah, so isochoric, the word means constant volume. So what we're doing is we're taking foods and we're trapping them in a constant volume box, a constant volume container. And what this does thermodynamically speaking is it cuts them off from the atmosphere. And so what we find is that if we take food products that are, you know, mostly water and we cut them off from the atmosphere and we start to freeze them, cool them down in a confined volume, then ice, because it wants to expand relative to liquid water, ice will try and expand, but the container will push back against it, and this sort of tug-of-war will create an internal pressure in the system. And essentially, the confinement of the system prevents the ice from freezing the food. So just a little bit of ice grows at the sort of periphery of the container, and it drives this

hydrostatic pressure that stabilizes the whole system at sub-zero temperatures without allowing the foods to freeze solid. That was maybe a little more info than you were looking for, Ira. So we need a little bit of water inside the little freezing chamber in order for this to work then. Indeed, indeed. So we're swapping, if you think of conventional food freezing as happening in air, this mode of food freezing happens in water and takes advantage of the quote unquote incompressibility of liquids. You know, this seems like such a simple principle in some ways. It's sort of the opposite of the pressure cooker, instead of heating it up and keeping it cold, right? Exactly.

Quite interesting. You know, one of the things that Christina just mentioned was its potential for energy savings. Why is this a more efficient process than just sticking your strawberries in a cold box? A tomato is over 90% water, right? So a lot of the foods that we consume are mostly water. And the freezing of water is incredibly energy intensive. Right. So just the process of converting the liquid state of water into its crystalline icy state requires a huge input of energy. So at the core of this isochoric energy savings premise is the fact that we simply aren't allowing the food products themselves to freeze, to solidify.

We're keeping them at sub-freezing temperatures, but we're using this interesting constant volume, high-pressure relationship to keep the food products. themselves from freezing. And it saves us from having to pay, let's call it, the energetic toll of converting the water inside the food into ice. Yeah, that phase shift really draws a lot of energy. Food preservation in isochoric systems requires much milder cold, right? So we can hold, let's say, tomatoes for length scales of months at only minus two or minus three Celsius instead of minus 20 Celsius, right? And so asking your freezer to operate at minus two, requires of it much less energy than it operating at minus 20 or below. And this doesn't have to be a system for food. We can keep all kinds of things at cold temperatures.

And you've been doing work on finding applications for human tissue preservation and transplants. Tell us more about that. Yeah, I think one of the transplant medicine is one of the absolutely most fascinating applications here. Because, like for instance, if we look at heart transplant, right, which is particularly relevant in the U.S. where heart disease is one of the major annual killers, we get thousands and thousands of donor hearts that are made available every year, but we end up transplanting only about 30% of them. And the reason that so many go to waste is our simple inability to hold those hearts outside the body for sufficiently long periods of time to get them into someone who needs them, right?

So you imagine how complicated a heart transplant is. You only have four to six hours after the death of the donor to get that heart into a recipient. So it's an unbelievable logistical hurdle. And so we're looking at using the same fundamental thermodynamic premise, isochoric freezing, to enable preserving hearts outside the body for, let's say, 24 hours or two days instead of four to six hours. So really anywhere that the shelf life of biological matter is a problem, we can apply this technology. Wow. Wow.

What are some of the challenges you have to overcome? What about the container? We're talking about you have a very small experimental container, right? Don't you have to scale that up? I think of problems as a whole, technological problems, in two categories, science problems and engineering problems. So we've been working for the last several years to settle the science of isochoric freezing, right, the food science and the thermodynamics, you name it. And so the next sort of phase is tackling the

engineering, right? And the nice thing about it is that the building of large pressure-bearing containers is not new. It's something that the industry has already figured out for oil and gas, for the storage of various compressed liquids and gases, you name it. So now what we're looking at is taking knowledge that already exists out there in the engineering and mechanics world and using it to scale our, yes, our two-liter prototype systems up to 50 liters, 100 liters, 500 liters. So that's something that will happen likely outside of the university, but is top of mind here for the next couple of years. Well, I want to thank you for taking time to be with us today. I think I've learned a whole lot about food. Well, thank you, Ira. Dr. Matthew Powell Palm, postdoctoral scholar,

and mechanical engineer with the University of California at Berkeley. After the break, feasting with help from fungus, marinating with mold. Yes, we revisit a classic conversation about cooking with Koji. Stay with us. This is Science Friday. I'm I'm Irafledo. One of the silver linings of this long pandemic, if there is one, is that many people discovered or rediscovered their love of cooking.

Last year, at the height of the quarantine, these listeners called us to share their proud creations. Since the onset of the pandemic, I've brewed three big batches of kombucha using a variety of teas, chai, Assam, and white. I've grown oyster mushrooms from a mail-ordered bag of my salleal spawn and fermented two jars of sauerkraut. I've done a lot of bread baking and a lot of fermenting. I recently made a sauerkraut with red cabbage, beets, and carrots, and it was really, really good. and I have a whole bunch of ginger that I accidentally bought too much of. So now I'm going to make a fermented ginger paste and see how that works. So I made dandelion jam, pesto from the chickweed and dead nettle in my yard.

I've been brewing kombucha. I'm trying to make kvass. I've been using a mesophilic yogurt starter to make my own yogurt. It's really been great fun and a good way to pass time. Those were the voices of Morgan from Portland, Camille and Tanya from Arkansas. Thank you for your submissions to the Science Friday Fox Pop app. Maybe you've already done the sourdough or the pickles or the yogurt, right? My next guests have the perfect next step for you.

It's called Koji. It's a white, fuzzy mold, and it smells like fruit. And we can thank it for a splendid array of foods from East Asian cultures, including soy sauce, miso, and sake. And my next guest want you to join in to make culinary delights with the help of this magical mold, even beyond the traditional uses.

Think Koji Shikudery or miso peanut butter. Here to talk more about the transformation power of Aspergillus or Isay are my guests, the co-authors of the book Koji Alchemy. Rich Shee is a mechanical engineer by day and the exhibit engineer for NYC's Museum of Food and Drink, and Jeremy Umanski is a co-chef and co-owner of Larder Delacetessen and Bakery in Cleveland, Ohio. Welcome to Science Friday.

Thanks for having us on. Thank you. I know I've already given the overview that Koji is a mold and had it's been used for thousands of years, but please, you've got to sell me on the idea of using a mold to make food, Jeremy. Why is this so delicious? Well, one thing to keep in mind is you're already eating this mold in one way, shape, or form. I'm willing to bet that virtually every listener today has some soy sauce in their house, whether it's a bottle of it or a little packet from Chinese takeout.

And that soy sauce cannot be made without this mold. So we already have it in our lives. We already eat so many different fermented foods that rely on molds, things like cheeses and sharkoos. We can lump yeast into that. They're both types of fungi. So bread, it's already exists there. So using it to make foods more delicious is pretty simple and straightforward. And is it the rice that we're really cooking with it, right?

Exactly. You can't just take the spores of the mold and make something delicious. You have to get it to grow first. So you grow it on rice or barley or actually any starchy substrate. So it could be wheat berries. It could be rye. It could be harmony. Give me an idea what it looks like.

You know, I've seen photos. It looks very pretty growing there on the rice. I think pretty is a lackluster word, Ira. It is, it is sultry and stunning. I mean, it's sultry and stunning. It really is, you look at it and you get lost in it. it is just so white and fuzzy and fluffy it's inviting almost like you know you look at a picture of a sky with beautiful like cumulus clouds in it and you're like that just makes you relax and feel at

home and it just oh i could i could hug one of those clouds or i could lay down on it and take a nap cogi kind of has that same effect on you when you look at it and it's growing fresh and then you throw its aroma on top of that, which, you know, its aroma is, you know, green apple and champagne and honeysuckle, tropical fruit like mango and pineapple with a little bit of mushroominess there. Some people even say they pick up roasted chestnut. I mean, it's just absolutely bewitching and intoxicating from how it looks to how it smells to how it tastes. It's just absolutely incredible. You know, you sound like you're describing a fine wine. Does it do that for you, too, make you feel that way?

Yeah, I mean, I am not as externally excited about Kogi as Jeremy is, but internally, it just blows my mind. Koji is so simple. All you need is like a warm space with a little bit of humidity that can be achieved in an array of ways, very similar to setting up, you know, setting up for breadproofing. And you just basically boil some water or you set up a steamer and you mix these ingredients in, dust on some spores, and you mix every 12 hours. And who can't do that over the course of two days?

I mean, you can go to work, come back home and do your mix. And at the end of the day, it's done and ready to go. And then all you have to do is add some water to it and some cooked grains. And you can make this amazing sweet porridge that you can always make this amazing sweet porridge that you can also use as a marinade that's a perfect like the perfect marinade for any piece of meat or a protein you put it on because we often go through the exercises of making a marinade such that you enhance the flavor of the core component itself. Koji does that by default by taking the enzymes to break down the constituent parts of this food and creates, you know, basically what I like to

refer to as, you know, an automatic barbecue sauce that has nothing, that is made with everything that's part of the food that you create it with. And Jeremy, does it have a taste of its own? If I put it on rice, for example, and I'm growing it on rice, I know what rice tastes like. Well, well, then the other flavor there be that of the mold. Yeah, so it's actually going to transform the rice itself. So oftentimes we talk about one of the molds, Aspergillus Lucensis, that produces citric acid as it grows, not as a byproduct, but actually produces it as it grows. And if you were to eat some rice that had this mold growing on it, it would taste like sour patch kids.

And we're talking just plain old rice here. And Rich, are there different strains of Koji that produce different flavors? There are specific cogees that create different flavors based on their enzyme engines. SoJ has this an enzymatic engine that is more on the protease side to break down proteins into amino acids. As these enzymes become active in terms of breaking down the base food substances, you get all sorts of, you know, interesting and funky flavors. I recall, you know, every time that I grow it on rye or even taff, I get these, you know, mushroomy aromas as well as flavors. We're all familiar with soy sauce, for example, which is one of the many things Koji is used to make, as you said before. How does that process work?

I mean, how do you start from a mold and get to a tasty soy sauce, Rich? Yeah, so to make soy sauce, you basically cook some soybeans, whether you soak them and steam them or you boil them such that in the state where they're cooked all the way through. So that's one part of it. The other part is you have toasted cracked wheat. So what you do is you basically have a one-to-one ratio of these two ingredients. You mix the ingredients together. You allow it to cool to a temperature that's pretty much to your body temp. And that's how a lot of Japanese makers gauge when you can actually inoculate it with the spores.

Then you basically sprinkle it lightly with spores. Once you grow the Koji, you put it in basically a saltwater brine. and you allow it to ferment. And then you have a specific mixing schedule based on the temperature conditions and the stages of making it. So that's how it happens. Yeah. And, you know, the only difference between miso or an amino paste, as we call them, because they're pasts and they're rich in amino acids and an amino sauce like soy sauce is water content. So whether you decide you want to make a miso or gojejean or any of these pasts or you want to make an amino.

sauce, it's just varying degrees of water that they contain. So you can go in either direction just as easily. And sake, can you get alcohol? Oh, my God, can you? You know, it's really interesting because of the breath, the types of sugars, like the oglios sugars and the glucose that's formed in an amazaki, which is a mixture of a cooked starch, the code. The code, inoculated starch and water, you can get a lot of alcohol. I mean, you can get upwards towards a 12% ABV without doing anything extraordinary, literally just putting some yeast in and letting it sit and be happy. So you can get some fantastic alcohols. And some of the cojis that produce these different flavors and aromas and some that produce citric acid can just add infinite layers of complexity

to any of the alcohols you make. I understand. and you can make popcorn. Rich, how did you come up with that? So I was kind of just looking around in my pantry to figure out, hey, what could I really play around with to create this accessible starch that could have these gaps such that the mold would grow in between because you need a level of air in between the grains? And I just saw this popcorn.

And I said, well, when you pop popcorn, you're basically, you know, it's basically a pressure cooker for each kernel. And when it blows up, it uses the internal steam to blow it up to create a puffed condition such that the starch is very accessible. As we all know, when we eat it, it dissolves in our mouths. So I just decided that, hey, I don't have to cook it. I can make it explode and create this accessible starch. And all I needed to do was not to make it too wet is just to mist it with a little bit of water. And there I had my accessible starch.

I had plenty of air for the mold to grow. And I just, you know, to assure that it would grow well, I just dusted it with a little bit of flour in the spores. And it took off like gangbusters. And for somebody who doesn't necessarily want to sit and wait for, you know, your grains to soak or your beans to soak and you just want to try something, it's a pretty cool starting point. Can you use Koji as, you know, as a quarantine experiment for all of us now? You most definitely can. Whatever level you want to plug in with, you can. So for example, traditionally throughout Japan, they use a product called Shio Koji, which is this porridge of the molded rice or barley with salt added to it. And that is used as a general all-purpose seasoning. So you can easily find that online and you can order a little package of it. It'll show up at your doorstep.

You can rub it on some chicken or some steak or saute some vegetables with it and see instantly the short-term drasticness that Koji brings to amazing flavor as you're working with it. So while it is straightforward, should you not want to grow the mold, there's several great companies out there. Most of them are really small, family-owned businesses like Cold Mountain Koji, and you can buy pre-inoculated rice or barley from them. So if you wanted to go ahead and make an amino paste, like a miso or a gojejean, you could simply buy the inoculated grains, mix them with a little water to hydrate them,

open up a can of beans, mix those together with the inoculated grain, and a little bit of salt. We use 3% of its weight as a very minimum on the base, but you can go 5%, 7%, 10%, and let it sit, and you will have your own amino paste, something like a miso. Or you could simply order spores and just go all in and start growing the mold on everything like we do. There really are no barriers to entry for working with Koji. I'm Ira Plato, and this is Science Friday from WNYC Studios. Does Richard, does playing with molds give you a new dimension about creativity with food? Would you know we're talking about jams and pickles and pestos and vinegars?

Now you have something new to play with? I think it's just the fact that Koji allows you to do so many multi-faceted things. A lot of us focus on very specific fermented products like crowd or kimchi or, you know, yogurt or a very specific beer from a very specific region with all these, you know, incredible malts and hops and specific. and specific water and a specific alcohol content, what we have to think about is they got to that point because somebody just left something out for a period of time such that it can be consumed at a specific time for survival. And people got tied into this idea of, hey, I really love that.

I want to keep making it the same exact way because not only is it safe to consume, but it's delicious. But our idea is to think about this in much larger, scheme in terms of that specific discovery can be with any food that you apply it to. I mean, granted, things can go wrong, but it's the adventure of all these possibilities that we have access to, whether it be the ingredients, technology, ideas, you know, or even, you know, past products that we know and love that we can kind of change up and play around with. And that's the nature of what we love to do.

How does it go with pastrami? Oh, man. If I describe it, I'll be bragging. So I'll let Rich who's eaten my pastrom me describe it. So I think one of the things to understand about it is that, you know, through these, you know, through usage of, you know, creating these amino acids through the, you know, through the enzymes and these sugars, you get this, this amazing flavor like that, that bounds, you know, that's above and beyond what you could do in a traditional method. With a traditional method, you know, you have the slow process of heating such that you can create the food that is quite unctuous by breaking down the connective tissue and it makes it moist and it makes it very pleasing. And then you also have a brine to create this, you know, the salinity. But with a Koji, you can actually create like this level of tenderness and depth of flavor without doing any sort of manipulation. and it's just bringing it up a level of what it already is. I'm coming over.

We'll save a seat on the patio for you. Thank you both. This was quite fascinating. I hope we have inspired a lot of people to try some new cooking ideas. Rich Shee is a mechanical engineer by day and the exhibit engineer for NYC's Museum of Food and Drink. And Jeremy Umanski is a chef and owner of Larder Delicatessen and Bakery in Cleveland, Ohio, and their co-authors of the book Koji Alchemy, Rediscovering the Magic of Mold-Based Fermentation.

Thank you guys for enlightening us and giving us something more to do as we stay home. You're welcome. Ira, thank you so much. This has been a dream come true. Yeah, this is a pleasure. Yeah, thank you so much. That conversation was from 2020.

We've got more mold on the menu. Coming up, how mold and bacteria make those funky flavors you love on your cheese. Penicillium, Camemberte. which, as you can probably tell, was named after Camembert cheese. Gives the cheese some of these sort of mushroomy flavors. Stay with us. This is Science Friday. I'm Myra Flato.

If you love cheese like I do, you know that pairing cheese with the perfect wine or beer can really enhance the flavors of your frommage. You know that a Merlot may bring out the mushroominess of a nice guta or an amber ale with a sharp cheddar. I'm getting very hungry right now. But if you're a cheese geek and you really want to understand what makes those cheese tastes and textures, you need to match your cheese with its microbes. Yes, microbes.

Back in 2016, we talked to a scientist who says that 10 billion, you heard me right, 10 billion microbial cells live on just the rind alone. Talk about flavor enhancers. She's even sequenced the colonies on the rind of 160 different cheeses. And our callers had a lot of cheesy questions for her. Rachel Dutton is Associate Professor at UC San Diego and Director of Microbial Sciences at Arcadia Science. Welcome to Science Friday. Hi, Ira. Thanks for having me.

You know, I'm not sure a lot of people realize that there are bacteria involved in all parts of cheese and cheese making. But you specifically focus on the rind. Why the rind? Yeah, well, bacteria actually important for pretty much every delicious food that we eat. So whether we're thinking about cheese or beer or wine, these microbes actually have an important role. And we're really interested in cheese because it is an example of a simple ecosystem that we can really pull apart and put back together in the lab and understand how microbes actually build communities and fight with each other, help each other communicate. And the rind of cheese has this amazing biofilm-like structure. So it's actually a completely separate community of microbes that grows on the surface of cheese during the aging process.

And in the cheesemaking, you purposely put the microbes to make the rind? So in some cheeses you do. So if you think about a brie or a camember, those cheeses, you actually add specific types of fungi and sometimes bacteria to make the rind of the cheese. So if you look at those cheeses, you see this fluffy white surface on the cheese. And so that's actually all microbes. So the fluffiness is the penicillium camemberti, which, as you can probably tell, was named after camembert cheese. And penicillium gives the cheese some of these sort of mushroomy flavors. And then you also have two other really interesting microbes.

One is a fungus called geotricum, and one is a bacterium called hafnia. and together they produce a lot of the sort of cauliflowery kind of smells and taste that you get in these really ripe camemberes. Hmm. That penicillin is, is it an antibiotic too when we eat it? It's not, but it is sort of a cousin of the fungus that produces the antibiotic penic penicillin. Now, there are bacteria inside the cheese versus the stuff that's on the rind. Does that mean that the inside of the cheese is going to have a different? flavor given by those microbes and the ones that are closer to the rind?

Yeah, exactly. So there's the lactic acid bacteria inside the cheese. So those are the species that were used to acidify the milk and produce the fresh curds. And so the sort of closer you get to the rind, the more intense a flavor is often in the cheese. So if you, again, think about something like a brie, you often have the cheese starting to get really gooey just underneath the rind, so it's ripening. And that's because the activity of the microbes growing on the surface, they're actually producing a lot of the molecules that cause the cheese to ripen. So it's sort of ripening from the outside in. Yeah, no, there are people who are afraid to eat the rind. Are they missing the whole part of the cheese if you don't eat the rind?

Absolutely, yeah. So those microbes are incredibly tasty. So I encourage people to at least give it a nibble and see what they think. How many kinds of rinds are there? There are, well, if you think of different kinds of cheeses, there's hundreds, if not thousands, of different cheeses. And we can kind of classify rinds into maybe three major groups. So we have the first group would be these bloomy rind cheese is what we call them, so the brie and camembert-style ones. And then we have the rinds, which during the aging process, the cheesemakers will actually wash the surface of the cheese with a saltwater solution. And those create this really stinky, funky flavors in the cheese.

And so those are called the washed rinds. And then the third variety of rind that we think about is the natural rind. So this is where you make the cheese of something like a cheddar and you put it into a cave and you just let it be. Let the microbes colonize. Don't really mess with it. And you have a completely different type of microbial community that forms on these three different types of rinds. Let's go to the phones because lots of people love cheese and they are interested. First, let's go to Moscow, Idaho.

And Hannah, hi, welcome to Science Friday. Hey, Ira, thanks. Go ahead, sure. Okay, so I had a question. My mom, growing up, whenever we got mold or some dish or just or any fuzzies on the cheese in our home or in our fridge, she would always cut that part off and then we could use it. She would always say, oh, it's just mold, it's not going to hurt you. And so she would cut it off.

I didn't know where that came from. Does that come from the cheese itself, or would that happen in the packaging facility, or where would that come from? Yeah, good question. Yeah, so there's mold all around us, and there's sort of wild species of mold that are often closely related to the ones we find in cheeses that are just in your home, say, floating around your kitchen. And so once you slice into the cheese, you create this open environment that any micro floating around might want to grow on. So often when you cut into the cheese and you put in your refrigerator, some of those microbes might start growing on there. And they actually like cool temperatures like your refrigerator. So it's sort of like a cheese cave.

And so that's probably where they're coming from. Is it safe to eat that mold that's growing on there? I probably wouldn't recommend eating. But yeah, if you sort of cut it away, it seems to be fine. So, Rachel, what makes a hard cheese versus a soft cheese? What's going on there that turns it soft or keeps it hard? Yeah, so a lot of that has to do with what the cheese maker is doing to the milk and the curds when they first make the cheese. So if you heat the curds to a higher temperature, that will help get rid of moisture. If you press the curds, once you've made the first wheel, that will also get rid of moisture.

So the more moisture you remove at the beginning of the cheese making process, the firmer the cheese will be, and the longer you can age that cheese. So things like the cloth-bound cheddars, you can age them for a year or more. And that's because they have a low moisture, which actually slows down the growth of microbes. So you can kind of control how quickly the microbes grow and how quickly your cheese ripens by how much moisture is in the cheese. And all that's, the veins running through Gorgonzola, whatever, were they put in there or did the cheese make them? Yeah, so those are really fascinating. So those are due to a microbe. It's a fungus.

Again, it's a penicillium species, but this penicillium is called penicillin Roqueforti, so named after Roquefort cheese in France. And this particular species of penicillium produces this blue pigment, and it only grows in, low oxygen environments. So when cheesemakers make this cheese, they actually take the spores of the fungus and mix it into the milk. So it's all over throughout the milk and throughout the cheese. And then after they've made the wheel of cheese, they actually take a metal spike and punch holes into the cheese to make these little cracks throughout the wheel. And oxygen can get into these cracks. And that little bit of oxygen is what stimulates the growth of penicillium rook 4T. And it starts to grow.

It produces these beautiful blue-green pigments as it's growing. And the other interesting thing it does is not just producing this color is actually doing a lot to the flavor of these cheeses. So anytime you eat a blue cheese, you recognize that you've eaten a blue cheese, right? It's a very sort of distinctive flavor. And that's because this mold, Penicillium Roque 4-T, is breaking down the fat and milk. And it's releasing these free fatty acids. So some of these free fatty acids have the spicy peppery flavor that you associate with blue cheese. So the more blue mold you have in the cheese, the spicier the cheese will be.

And then it actually can break those down further and produce these volatile molecules, so very small molecules that we can smell. And so there's one of these molecules that it produces called two heptanone. And that's one of the key aromas of blue cheese. So when you're smelling blue cheese, you're actually smelling the byproducts of this fungus as it's growing. Wow. What is complex stuff going on.

And I understand that you have even found marine bacteria on some cheeses. How did it get there? Yeah, we don't know. So on these wash-drine cheeses that I mentioned, so where the cheesmakers will wash the surface with a salty solution of water, we actually find many organisms, many bacteria that we normally would find in the ocean, which is sort of perplexing. And so we still don't know exactly where they're coming from, but we think it's probably from the sea salt that's being used in cheese making. Or it could be due to the fact that cheese itself is a very salty environment, and these microbes are used to growing in salty environments.

So they just happen to find an environment that they really love. Do you ever get tired of talking about cheese? No, I feel like I have the best job in the world. I get to talk about cheese. I get to study cheese in my lab. It's wonderful. Let's go to a Portland, Oregon with Michael. Hi, Michael.

Hi, there. My question is about storage of cheese. I have put, I've always been taught to wrap it in plastic to keep the oxygen out. And then I just was in a fancy kitchen store that had something called a cheese vault, where it said air was important to be around the cheese when you're storing it. Yeah, so because cheese is alive and the microbes in it, if you want to keep those microbes alive and happy, you want to allow them to have a little bit of oxygen.

So if you wrap it in plastic wrap, you're suffocating the microbes on the cheese. That's kind of interesting. And thanks for the call. That brings up the question, And can every cheese batch or however you call it be the same? I mean, if there are microbes and bacteria and different kinds of stuff floating in the air, isn't every, what's the wheel or whatever, what do you call a batch of cheese?

A batch of cheese. A batch of cheese. And they can all be different, really? Yeah, so you can have differences depending on the season, where the milk is coming, from. But it's sort of amazing to me how reproducible cheese can be. And so that's part of why we're interested in studying these microbial communities that form on the surface, because it's sort of, you can think about it as humans over thousands of years have figured out ways to very precisely manipulate how microbial communities form. And we sort of know exactly the

conditions to create on the cheese, and those conditions will sort of allow the growth of a certain type of cheese rind versus another. So you can have sort of subtle variations, but if you zoom out a little bit, it's kind of amazing how reproducible they are. This is Science Friday from WNYC Studios, talking about the microbiology of cheese with Rachel Dutton, an associate professor at UC San Diego. Rachel, I have to ask, and I know it's a tough question, but what's your favorite cheese? Yeah, I get asked that a lot. One of the things I love the most about cheese is how much diversity there is. So you can go to a cheese shop, and there's hundreds of varieties, and every time you can experience a new set of flavors.

One of my favorite cheeses sort of is a cheese that we actually study a lot in my lab. So we collect samples from all over the world. And a cheesemaker that we work with a lot is Jasper Hill Farm in Vermont. And they make a blue cheese called Bailey Hazen Blue, which I love. And it's sort of our lab rat. We're very interested in the microbes there. And it's just a delicious cheese besides being very interesting from a scientific perspective. Yeah, I'd go get some of that research too.

All right. Here's my last question is, what is your holy grail for cheese? What do you need to know? Yeah, well, we're really trying to understand how a microbial community is organized. So what I would love to be able to do is figure out how all of these microbes are communicating with each other. Are they fighting? Are they helping? So what are all the molecules that are being shared amongst the community and how are the species interacting?

Yeah. With all these microbes, do we know how it might interact with our own microbiome? All these cheese you're eating. Yeah, so we actually had a study a couple years ago where we fed human subjects cheese and followed the microbes. And actually, many of the microbes can survive the gastrointestinal tract. So we're becoming more and more interested in the interaction of microbes from fermented foods with the human gut microbiome.

Rachel, you're welcome back any time to talk about cheese. Thanks so much for having me. Rachel Dutton, Associate Professor at UC San Diego, and Director of Microbial Sciences at Arcadia Science. And if you haven't had enough cheese, you can go over to our website, ScienceFriday.com slash cheese, and find a whole archive, a cheese sampler, if you will.

Before we head out this hour, here's a sci-fry soundscape that we think will pair very nicely with our conversational. It's from Chris Hoff and Sam Harnett of The World According to Sound podcast. This is wine draining through a funnel. Chris off is making himself some homemade plum wine. When the wine passes through the funnel and into the bottle, air escapes, creating this little bubbly crescendo. The more liquid that empties from the funnel, the higher the pitch.

That's what happens with a Helm-Holtz resonator, any vessel with a small opening. These sounds are part of a communal listening series. the World According to Sound is hosting this winter. For more information about their 80-minute binoral events, visit the World According to Sound.org. And that's about all the time we have this hour, and we're very thankful for all the people who make the show possible.

Here's Ariel Zich. Thanks, Ira. Nadia Ortelt is our chief content officer. John Degoski is our director of news and radio projects. Zociel Garcia is our K-12 education program manager. Luke Groskin is our video producer. And I'm education director, Ariel Zitch. Thanks for listening. Thank you, Ariel. B.J. Leideman composed our theme music. And of course, if you missed any part of this program or you would like to hear it again, subscribe to our

podcasts or ask your smart speaker to play Science Friday. Have a great, safe holiday weekend. I'm Ira Flato.