Instant Genius - The fascinating chemistry of fermentation, with Andrea Sella

Episode Date: June 18, 2023

From kimchi to kombucha to kefir, you’ve probably noticed that fermented foods are trendy right now. They appeal to the daring, but also to people who may not even know they are eating fermented foods when they enjoy their beer, bread, and cheese. In fact, these fermented goodies have actually been around for hundreds of years – but what actually are they, and why do we like them?   This week, I’m joined by Andrea Sella – a professor of chemistry at University College London and a keen fermenter. Speaking to Andrea behind the scenes of the Cheltenham Science Festival, we discussed the importance of sugars to creating and digesting food, why and how we overcome disgust responses to get pleasure out of fermented foods, and how new fermentation techniques could help us lower our greenhouse gas emissions – along with some chemist’s tips for creating delicious fermented meals.   Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Visit name audio.com to learn more. BBC Science Focus, this is Instant Genius, a bite-size masterclass in podcast form. I'm Noah Leach, news editor at BBC Science Focus magazine. From kimchi to kombucha to kaffir, You've probably noticed that fermented foods are trendy right now. They appealed to the daring, intrigued by swelling tins and stinky smells, right down to people who may not even know they are eating fermented foods when they enjoy their beer, bread and cheese.

In fact, these fermented goodies have actually been around for hundreds of years. But what actually are they? And why do we like them? This week I'm joined by Andrea Seller, who's a chemist at University College London and a keen fermenter. Speaking to Andrea behind the scenes of the Cheltenham Science, Festival, we explored the importance of sugars to creating and digesting food, why and how we overcome disgust responses to get pleasure out of fermented foods, and how new fermentation

techniques could help us lower our greenhouse gas emissions, along with some chemist tips for creating fermented meals at home. Right, Andrea, could you kick off by telling us what exactly are fermented foods? So fermented foods are a really big sort of fan. family of foods and where there is a kind of, let's call it a natural processing which take place where you take some kind of raw ingredient. And then what you do is you just get the conditions right so that some microorganism or other goes and develops it. And it transforms it in some way. And what it does is on the one hand, it hugely enhances it both nutritionally,

but especially in terms of flavor. And the side benefit is that what it does is typically it will allow you to store that food for much longer. So there's a kind of preservative side to it as well. So when we taste fermented foods, what are we actually tasting in them? What's been changed? Are we tasting the bacterias or the sugars? Fermentation is typically done either by bacteria or by yeasts. and yeast are this funny group of organisms that sort of sit close to fungi, right, and somewhere

between fungi and bacteria. And what these organisms do is they live typically on sugars. And what they then do is kind of partially process them. And as they do so, they produce a whole pile of flavor components. And in particular, what they're doing is they're effectively metabolizing. they're burning through the sugars. But then they will often produce acids on the side as well. And so what you tend to find with fermented foods is that you start out with a food at whatever

a kind of normalish pH. Now, people might think that's seven, right? Mutual, not necessarily. An awful lot of the food that we eat is actually slightly acidic. But what happens during the fermentation process is that typically that will go a lot, a lot lower than that. and the lower it goes, I mean, that's fine. Also, the more alcohol is produced, that's fine too.

But you get to a point where your bacteria or your yeast actually can no longer propagate. And so at that point, the whole thing tapers off. The classic example of this, for example, is wine, where what you do is you press grapes, and you get some kind of natural yeast which comes from the skins of the grapes or whatever. And, you know, hey, these are ripe grapes. They're absolutely chock full of sugars. And so they go completely crazy. And they start chewing through that sugar, producing alcohol as they go CO2.

The whole thing frosts and boils. And then eventually it peaks, right? There isn't enough sugar left for all the fun to continue. The alcohol level has got to some point. and then everything stops. And at that point, you've got something which will last for, I mean, days, weeks, years, centuries in some cases. And so wine is a really interesting example and one I think that people will be quite surprised about. I mean, what actually counts as fermented food?

And are there some examples of foods and drinks that people might be surprised to learn has been produced through a process of fermentation? So, yeah, I mean, fermentation we often think about as being the process of making wine and beer. But, you know, you can't really think about beer without thinking about bread because bread is effectively fermented. I mean, you know, we use a yeast. We typically deliberately put it in there. That will be a brewer's yeast, right? And what it's going to do, again, eat the sugar, produce carbon dioxide. And that's the thing which inflates and produces the bubbles in the bread.

Now, interestingly, this idea of using brewer's yeast is actually perhaps, you know, it goes hand in hand with a different kind of fermentation, which is, you know, now we would call it sour dough, which is a different set of microorganisms, which give really quite a different set of flavors. And sour dough, its name is telling us, right, that what you're doing is to produce. these acids, which give it that tang, which has now become very fashionable, right? But all of these things are really old. They're ancient. And brewing and making booze, they're two of the things that really made us human. So they're incredibly old. They go back thousands of years. So you've touched on a few things there that I really want to ask you about, and I'll come back to human civilizations a bit later. But you talk about these things being on the rise, fashionable. Things like kimchi and sourcrow and kaffir, we're seeing more and more in

supermarkets. So why do you think that is? Why are people becoming more aware of them? So it's interesting. I mean, you know, one of the big problems with milk, for example, is that milk doesn't keep. You know, all of us at some point, you know, I've poured ourselves or pours, you know, we've had some milk and the milk has gone off. And most of us go, ew, yuck. And, you know, we pour it down the sink because milk is actually, at the moment, very, very cheap for all the price rises and so on, we wouldn't think twice about pouring away a glass of milk. Of course, in an age before refrigerators, before the easy availability of ice, of that kind of thing, milk was incredibly perishable. And so, you know, your cows are going to

produce loads and loads of milk in the summertime when there's lots of grass and and that sort of thing, what happens in the wintertime? What are you going to do with all the excess milk that you can't drink? And so that's where the idea of taking the milk and actually making it go off deliberately, right? And presumably the way in which this would have started was, oh, my God, my milk's gone off. Well, I'm not going to throw it away. I mean, this is incredibly precious stuff. So I'm going to eat it all the same.

And so, you know, for many of us now, this would seem disgusting. But actually, that is really what we're having when we eat yogurt, when we eat kefir, when we eat, you know, all of those kinds of milky-based, you know, they're the more proprietary ones. You know, there's a whole pile of these milk-based drinks, which are therefore extremely nutritious, which then lasts for a long time. Beyond that, of course, you have cheese. Again, you've got this fermentation process initially followed by aging. And here, you have to ask the question, where does fermentation kind of end and other processes begin?

Because, for example, a cheese like Stilton, you have the fermentation, the kind of curdling part in a sense. I mean, you might use an enzyme like Renet or you might be able to to, to, to, to, to, make the cheese using yeast or whatever. But you might inoculate it deliberately with some kind of culture, which will get it to go.

But you can then further change the flavor by letting air into it. And so you will deliberately spike it with a needle. And that causes a fungus to grow that gives you, A, the blue color, but B, that fantastic smell that you have associated. It's still

which interestingly, I'm a chemist, right, turns out to be a very specific molecule, which is two hexanone. It's a ketone, which has this bizarre sweet smell. In fact, I've got someone in the green room if you want to have a sniff afterwards. I'm sorry to listeners that haven't been provided with scratch and sniff cards for this podcast. I wish we could do that. So these are delicious smells to some people, but to some people they're incredibly disgusting. And there are some fermented foods that I think objectively are disgusting. Femented fish that kind of gets sealed away for many years or eggs or whatever it is

might produce this feeling of disgust in some people as a response. And that is understandable scientifically because these are kind of rotting really chemically. Is that correct? You know, I think I would differ. Disgust is built into our wiring very, very deeply. and the disgust response, which is when the corners of your mouth turn down and you scrunch up your face a bit, you know, that's something that when sees in, you know, deaf, blind children, you know, at very young age, in a sense, yes, that disgust is built in, but an awful lot of it is cultural, right?

An awful lot of it is what you were brought up with. And so, you know, it is, it used to be that one would say, ah, the people from China who were not used to drinking milk, who had not grown up with cheese, would say, you know, cheese, rotten milk, how disgusting. The rest of us actually love it. And so, yes, of course, I mean, you know, some of us have likes and dislikes. But many of these likes and dislikes are actually kind of programmed in very, very early. You know, you mention the idea of rotting fish. You know, one of the most famous or perhaps notorious of these is a fermented fish called hacarl that is eaten in Iceland. And many years ago, when I still took airplanes and traveled around the world, I went on a cycling trip to Iceland.

and one evening in a restaurant, there it was on the menu. And I thought, I have to try this, right? You have to try in your life. You have to try every food once. And if you don't like it, you have to try it again five years later, right? Because your tastes change through your life. And it's quite interesting, particularly fermented things. It was very strange.

There were these little white cubes, which had a slightly rubbery texture, that gave. It was, I can't quite, maybe it's a little bit harder than tofu, perhaps. But the flavor was just bonkers. I mean, there was something rather fishy with quite a lot of what I would call amine, very sort of, you might think of it almost like a bit like pee. And I know, I can, I can just sense listeners with their disgust response. their mouths are turning down at the thought. It was completely fascinating. Quite, you know, it reached parts of me that others don't.

And it was not very pleasant. But you know what? I wish I could go back to Iceland and try it again now out of curiosity. Now, what is this stuff? This is Greenland shark. These are these incredible, slow-moving sharks that live in very, very cold water around the Arctic there. One shouldn't really eat them.

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So what is the relationship here between health and decay really? I mean, you've spoken about it just then, but what are the actual benefits to us of eating these foods? I mean, I think the principal benefit is the pleasure of it. It's just that these are wonderful, wonderful foods that hugely expand the, if you think of it, like a painter using colors, the palette of different flavors, textures and so on that are available to us. And I think we're in an age where we're constantly trying to medicalize food. That said, one of the things which is quite interesting in the history of science, is that fermentation lies at the heart of our understanding of disease.

And it was Louis Buster's work in France in the mid-19th century, which helped with others, Robert Cough, in particular, to cement the idea that illness came through what they called germs. In other words, microorganisms that carried disease. And so before that, there was what was called the idea of miasma. The idea that somehow through the air, through smells, disease was transmitted. And that idea, of course, is completely wrong. it's interesting that the word malaria, in Italian, malaria, bad air, right?

It really harks back to that idea. And it was Pasteur who looked at fermentation and wanted to understand how wine was made, how bread was made, who actually realized that microorganisms were involved. And from there came what came to be known as the germ theory of disease. And the germ theory of disease is really important because, you know, we've been able, to deal with cholera, we've been able to partly deal with malaria. But I mean, it's an incredibly important paradigm in our thinking about health and well-being because of these terrible diseases. And yet one of the things that it has done, I think, is to blind us to the fact that we are

integrally and intimately connected with the microbial, viral and other world. and that we actually live together with them. So our guts, as we have discovered in the last sort of 20 years, are absolutely heaving. There are a whole ecosystem of bacteria. We refer to that now as the microbiome. And it turns out that what mix of microorganisms that are in there has a big impact on our health. We don't fully understand it, but there seem to be connections with allergies. there seem to be connections with cancer.

There seem to be connections with autoimmune diseases. You know, there are all sorts of things there. There are even suggestions that certain psychiatric conditions, depression, and so on, are related to that. And it's something we don't know about. We don't know enough about. And fermented foods seem to be a part of that. When you ferment things, one of the things you're doing,

you're doing something a little bit like cooking. cooking remember is essentially having an external stomach you're doing predigestion right which means that then your body can actually derive more nutritional benefit from stuff that if you ate it raw would either clog you up or not you know come out the other end unchanged and so you know cooking and this fermentation process are both ways of kind of pre-processing things but of course the fermentation one may actually bring additional nutrients on the one hand and potentially additional microorganisms may be good for us. So in the US there is a nun, Mother Noella, Marcellino. Your pronunciation of that is probably much better than mine. Marcellino. So this nun makes

cheese. And she was told by the kind of food safety standards that her wooden barrels didn't cut it. and she willingly moved to stainless steel, the sake of food safety. But in fact, in that environment, E. coli developed because it's the kind of good bacteria living in the wood of these barrels that helps to kind of fight off the bad bacteria. There seems to be this fine line between safety. I know we've spoken about rotten food and it actually, you know, that being something that we perhaps overthink. So how do we find that line?

I mean, that's a really, really interesting point and one that is actually quite hard to answer. Because on the one hand, there's no question that there are certain pathogens out there. There are certain bacteria which are incredibly harmful and which have to be kept in check. On the other hand, we know that there are a whole pile more which are responsible for bringing out the flavors. and in some cases for combating or for keeping in check the more harmful ones. And it's very, very difficult to sort of balance these things, particularly when your legislation is very rigid. And one of the things is that as the industrialization of food, the fact that people moved off the land and ended up in cities and were therefore disconnected. There had to be a food supply chain coming through,

and food needed to be produced in larger quantities and in much more sort of uniform, reliable ways. There was this progressive process of industrialization. And, you know, as you scale things up, you then also need to look very carefully to make sure that pathogens don't grow. And so everything has to be sterile and so on. The fact that we can confidently go into a shop and take a sandwich off the shelf comes down to all of those food hygiene rules and regulations, which might seem a bit arbitrary, but actually are there to keep us safe. The difficulty comes, right, when you're looking at these more artisanal, in a sense, foods,

these things that rely much more on the local conditions. You know, the French have this wonderful word, der Wares, which means, you know, the soil, the local air, the local vegetation, and so on, the grass that the cows have eaten and so on, which means that a particular agricultural product really tastes of the place that it comes from. And so they will also distinguish between something that's made on a farm and something that's made industrially.

So, you know, we tend to codify things based on our fears and saying, oh, sterilizing everything is best. But in some cases, on the one hand, you can start getting microorganisms that you didn't expect growing. And on the other hand, you know, step. away from all of the medicalization and the germification and so on, is you risk losing the wonderful individuality of those things that are made in an old-fashioned way, let's say, with less steel, maybe, and more wood. So as a chemist, what would be your tips for people

wanting to make their own fermented or distilled or pickled foods at home? So, you know, I mean, I think as a chemist, I have had to kind of re-educate myself. I make sourdough bread at home, and I find that completely fascinating because you get fermentation from nothing. You are taking natural organisms, right, which come from rye flour or whatever, and a miracle happens and the whole thing goes bubbly, and then you can make bread. I mean, I think that the rule has got to be trying. Try it. Go and do it. Experiment. Do something because one of the things is that you can derive extraordinary pleasure from just the process of making something. And, you know, I talked earlier about this idea that we moved from the countryside to the cities in the 19th century, in Europe, at least, in Europe and North America, where, our supply chains got longer.

And at the moment, we're seeing a very, a kind of corresponding shift. And, you know, here I am speaking as an old person, okay. But one of the things that really strikes me when I look at my students and so on, and actually some of my neighbors, is how much takeaway food is being brought in. And that now the connection between the kitchen and the cooking and the cooking, the eating is being lost. And for me, I think one of the great benefits of doing your own fermentation, pickling, you know, all those kinds of things. Distillation, you want to be a little careful because you can set fire to your house, but it can be quite cool too. And that is a

properly chemical process, right? But one of the great pleasures is the fact that you've done it yourself, that you have that kind of control. And you know what? It will go wrong. You'll probably muck it up. And I cannot tell you how many times I have made things that were really pretty rubbish, right? And yes, maybe I could have gotten a better quality takeaway. But on the other hand, the idea of saying, this is my bread. Will you share it with me? Right? Is one of the real great pleasures. And it takes you back thousands of years. Do we know about when this would have started? And again, was this a question of safety? You know, why did this begin? This is a very ancient process, right? And it really comes with a time when people move from being hunter-gatherers

to actually being stably agricultural. They have agricultural settlements. They start growing crops rather than foraging around. And so in many ways, you know, we can think of the Middle East, the fertile crescent as it used to be before the climate shifted and made things much more arid. It will almost certainly have been an accident, the idea that if you left, you know, moist ground flour and so on together, that you would get something bubbly with an interesting taste.

From there, it doesn't take long for you to start developing a taste for it and realizing that actually it's kind of fun because it makes you giggly, talkative, more sociable, whatever. And I think that there is this very tight connection. You know, you would need to really talk to more of a food historian or even an archaeologist about this. But, you know, we find traces of people, you know, fermenting stuff across the globe. Everyone, it was discovered multiple times in different places because it was fun. And in some cases, this actually took on a kind of sacred element because perhaps you, you know, certain kinds of fermentation and alongside them the consumption.

certain plants might take you into trans like states and so on, which would then have religious significance. But just that very fact of the social element that you now had of foods that was tasty and nutritious that came along with a beverage that was, you know, first of all, safer than the water. You know, in Britain, of course, you know, until really the start of the 20th century, small beer was something that you would drink. Very, very weak beer, but you weren't drinking nasties either out of the tap, but especially out of the well, right? Because a lot of people didn't have running water. Then actually, getting, there was a safety aspect of it, but on top of it, it was fun. And I think that that element of fun and that importance of fermentation is actually

probably more prevalent than people are aware. I mean, just doing a bit of research for speaking to you today, I discovered that chocolate apparently involves the processes of fermentation. So, I mean, are there any other foods that we might be surprised to learn as involved that process? So it really kind of almost everything. You know, virtually anything can be fermented, right? I mean, anything biological.

And the fact is that, you know, our entire world runs on sugar. And so every organism on the planet is basically desperately trying to grab sugar. Why? Because sugar is sunbeams, right? It's captured sunbeams. And so every organism out there is trying to get its hand on units of glucose in some way. And therefore, pretty well, anything that has carbohydrate in it will be fermentable.

The moment it's fermentable, guess what? first of all, different plants, organisms, or whatever, will ferment in different ways because they will favor different microorganisms. And they produce side products. There are co-benefits, co-flavers, which come out. And so, yes, I mean, the, you know, in the, in the production of, of, of chocolate, right, taking the co-co pods, right? What you do is essentially you allow them to ferment. And what's really being eaten, right, are the sugars on the outside of the pod, but that actually transmits flavors sort of further in. And so fermentation is pretty hard to run away from. And I think, you know, given in our supermarkets, you know, we have access to

an extraordinary range of foods by comparison with two or three generations ago. You know, I think everyone should from time to time go, hey, I've never had sourcrow. Let's try it and see what happens. And if anybody wants a good recipe for a sauerkraut soup, I've got one for you. Sourcrow soup, I haven't heard of that before. Sourcrowd is interesting because sauerkraut is one of these sort of Eastern European and kind of Russian ways of storing cabbage. And cabbage, very easy to grow in cold climates and so on. But of course, if you just leave a cabbage lying around, it's going to run.

rot. So what you can do is chop it up very finely, add salt. One of the things salt does is it pulls the moisture out of it, and then you leave it to ferment quite cold. And what happens is that it gradually goes acidic. So this is not pickled or itself pickled in a sense. It produces this this acidic glop around it. Well, you will find a sauerkraut, which of course comes from the German, sour and kraut being cabbage. You will find it all the way through, you know, the former Austro-Hungarian Empire, you find it in Italy, you find it in Germany, Poland, and you can go east, Ukraine, of course. But in Trieste, Trieste is a city which is the very top of the Adriatic Sea. It's on the border between Italy and Slovenia. And it is really the

gateway through which for 200 years, all of the trade from Central Europe found its outlet to the sea. So it's an incredibly kind of cosmopolitan mixed up. You hear people speaking German, Slovenian, Italian. And there is a soup called Yalta. And Yalta is amazing. And you, if you're vegetarian, you can leave out the sort of chunks of bacon. And nowadays, as I'm almost vegetarian, I do, but chunks of bacon, which you fry up with some, with some onion. And then what you do is you drop into the mix, Italian burlotti beans. You can buy them in tin so you don't have to cook in advance. You then add loads of sauerkraut. Again, very few people make their own. You buy a big glass jars. And then potatoes cut into cubes.

and you cook the whole thing up. And it is absolute, it's thick, it's viscous, it's slightly sour, it's very soft in the mouth with the sauerkraut strands. And it is utterly delicious, very filling on a cold winter's night. That sounds amazing. I'm definitely going to try that, but possibly not in this weather. And so we're talking about things, you know, ingredients, recipes that have existed for thousands of years. Are there foods which are, are there trials for kind of new fermented foods or are there new technologies, new techniques that are kind of cutting edge that are being developed in this area?

As we, you know, realize just the enormity of climate change and the challenge that it represents, you know, it is absolutely critical that we think about our food system. And, you know, our insatiable demand for beef, remember that every kilogram, of beef is equivalent to about 70 kilograms of CO2. I mean, you know, beef is about as, as heavy as you can think of. And other meats as well, you know, looking at what one might call synthetic meat is an interesting prospect. And, of course, when you say synthetic, people have to disgust response, right? Their mouth goes down.

But actually, what you're really talking about is saying, okay, what I'm going to do is I'm going to take the starting materials, typically from plants. And what I'm going to do is I'm going to add a microorganism of some kind. It might be a fungus. It might be bacteria. And what I'm going to do is I'm going to do a fermentation process to essentially process that protein and any associated carbohydrate into something that I can eat and which can become a meat replacement. And of course, the challenge is that while it's possible to match the nutritional kind of properties, let's say,

in other words, how many calories and how much amino acid and fat, you know, all of that kind of technical stuff. The thing that's missing, right, and the reason why people come back to meat, the combination of two things. one are, of course, the smells, the flavors, and so on. And the second thing is the mouthfeel. And so that is one of the challenges is how do you take this process, which will have a much lower carbon footprint, much lower energy footprint, much lower environmental footprint. In other words, we cut down fewer forests to convert them into plants that we will feed to cattle, the chicken, or whatever.

How do we then transform this fermented stuff into something which will give us the same kind of pleasures that we derive from the burgers, the steaks, whatever, that we have come to love? That's where I think the challenge is. That was chemist Andrea Seller speaking to BBC Science Focus at the Cheltenham Science Festival about the science of fermentation. you for listening to this episode of Instant Genius, brought to you by the team behind BBC Science Focus magazine. The latest issue of Science Focus is on sale now in supermarkets and newsagents, or through your favourite app store. You can also visit us online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal.

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