Secrets of Sourdough (encore)

Once upon a time, not too long ago, Nikki and I went on a trip together to Belgium, and I ate more bread in a couple of days than I have ever eaten at any one time.

It was a glorious time and one of our favorite episodes.

And that's why we're bringing it back again because it's too delicious not to.

This is an Encore presentation of our sourdough episode.

Enjoy.

It's really good.

It's really good.

Okay, I'm going to have to turn it on.

I know I need to have some more tea.

Just one more piece.

I'll join you in that.

How can I not?

It's so good.

It's so warm and yummy.

I'm gonna taste some of this.

Oh,

Nikki,

hot puddle with garlic butter.

Welcome to an episode of Carb Lovers Anonymous.

Not so anonymous, Nikki.

They know who we are.

I'm Cynthia Graeber, and I'm Nicola Twilley.

And this is actually Gastropod, the podcast that looks at food through the lens of science and history.

And Cynthia and I are the not-so-anonymous carb lovers.

We spent three days in Belgium with two scientists and more than a dozen bakers.

We were, in theory, investigating a deep scientific question about bread, but actually...

We were eating our body weight in bread and Belgian waffles.

Nikki, I'm still not sure I can forgive you for encouraging me to eat that second hot lige waffle.

I felt a little sick afterwards, but it was frigging amazing.

Listeners, I ask you, was that a bad thing that I did?

No.

When in Belgium, eat the lige waffles.

But you're not here to find out how many pieces and what what type of bread we gorged ourselves on in a 72-hour period.

You want to know what we wanted to know, all about sourdough.

In fact, many of you have written us emails asking us to do this very episode.

For instance, listener Alex Friedman, who lives nearby in Somerville but grew up in San Francisco, wanted to know about the history of sourdough.

Alex, we're on it.

Listener Denae Goriga in Northern Illinois requested an episode devoted to sourdough starters.

As a baker, she'd read about wild yeasts and how the environment the starter is made in affects the microbes in it, and she wanted to know if she gave some of her sourdough starcher to a friend, would the microbes in the starcher change?

Denae, exciting news.

That is exactly what we went to Belgium to figure out in the world's most delicious science experiment.

In fact, we have the world exclusive scoop on this brand new research.

It's true, we tagged along with scientists at the cutting edge of sourdough.

The question they were trying to answer is, those microbes that make up your wild sourdough starter, where do they come from?

Is it from the water, like so many people, especially in San Francisco, believe?

Is it from the baker or the bakery?

Is it from the flour?

This was a gigantic scientific mystery.

Up till now, we are going to take you along to Belgium with us on this path of scientific sourdough discovery.

But a quick note: if you're a regular listener, you know we have a gastropod drinking game.

We say microbes, you yell drink, and then you, you know, do so.

If you do that this episode, you'll be drunk really fast.

Fair warning.

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This summer, Nikki and I traveled to a remote corner of Belgium.

We were visiting the headquarters of Poratos, one of the world's biggest bakery ingredients companies.

They'd invited more than a dozen bakers from more than a dozen different countries to participate in a science experiment.

Hi, my name's Paul Barker, and I'm from the UK.

My name is Christopher Volking.

I'm from Germany.

My name is Josie Baker.

And I'm from America.

Hello.

My name is Tavros.

I speak not.

My English is not good.

I am Hakan.

I'm from Turkey.

I am from Mexico.

I am a baker too.

And then there were also two scientists, Anne Madden and Rob Dunn.

They worked together in Rob's lab at North Carolina State University, and they were also meeting all these bakers for the first time too, to introduce the experiment.

We know that when you make a sourdough, the species and strains of microbes in that starter, they influence the nutrition of the bread, they influence the flavor of the bread, they influence every part of the bread.

And yet it's still pretty mysterious what determines which of those microbes are originally in your starter.

Rob and Ann are microbiologists.

They've been studying communities of microbes in all sorts of places, your belly button, your shower head.

And we've worked on microbes for a long time, and often the response is repulsion, like, oh, gross, there are microbes in my house.

When you talk to people about bacteria that might be in their bathroom, it's, oh, please stop talking.

Please don't tell me anymore.

I don't want to know.

But when you talk to people about the microorganisms and their sourdough,

it's like, what did my children do?

This is lovely.

Like, can we put it on the refrigerator?

Are there pictures?

I love the response.

And this was this one little niche where people

seemed seemed to gather around the idea that this was a beautiful kind of microbe, that there was something wondrous about them.

And there really is something wondrous about a sourdough starter.

It's a community of wild microbes that somehow miraculously makes bread rise.

And you need something to make the bread rise, because otherwise, if you mix flour and water and bake it together, you get matzah, or, you know, a cracker, hard and flat.

Today, if I'm a baker and I want to make my bread rise, I can just go to the store and buy some baker's yeast.

Baker's yeast is precisely one microbe, Saccharomyces cerevisiae.

But it does the trick.

But bakers have been making leavened bread in an oven, bread that poofed up and got soft like ours does today.

People have been baking that for thousands of years.

The ancient Egyptians made bread.

So our question was: okay, so where did the Egyptians bought their yeast?

Because to make bread, you need flour, water, salt, yeast.

So where did they bought their yeast?

They didn't.

It was there.

This is Carl Desmet.

He's the communications and training manager at Paratos, and for this experiment, he was the one in charge of wrangling the bakers.

And before we got started on the science, he dropped some sourdough history on the group.

Nobody knows exactly where and when sourdough bread was first invented.

The earliest evidence we have for making bread comes from a site in Africa.

Archaeologists have dated the remains of that bread to 100,000 years ago.

It was probably made from pounded sorghum and water and baked on a hot stone.

We're not sure whether that was a sourdough or not, but it may have been something like the injera that Ethiopians still eat today.

That's sort of spongy and bubbly, and those bubbles are created by a community of wild microbes, just like today's sourdough.

Basically, if you combine ground-up grain, something like wheat, with water, and you forget about it and leave it alone, eventually it starts bubbling.

And that's because a bunch of different microbes, usually a combination of fungi like yeast and bacteria like lactobacillus, they colonize the mixture and feed on the flour, and that is both the start of beer and a sourdough starter.

There is hot debate among historians about whether humans first figured this out because they were making booze or making bread.

I'm on team beer to be honest, but short of Cynthia finally inventing her time machine, we will probably never know.

Either way, humans figured that this wild, bubbly mix made their flatbreads into breads, the non-flat kind.

These loaves of bread would have all been sourdoughs.

There was no other way to make bread rice.

So for thousands of years, sourdough was being used by each and every baker or person that would bake bread.

And even before people knew what microbes were, they were already caring for these wild communities of bubbling beige gloop, feeding them with more flour and water to keep them alive and happy.

They figured out that you only need to add a dollop of starter to your dough to leaven it, which means you can keep the same starter going for years and years, decades even, just by feeding it with flour and water and using a little bit of it every time you bake.

It becomes like your own personalized wild leavening leavening mix that you can keep alive and use it again and again and again.

Other people developed variations on this approach.

In ancient Greece, for example, Pliny the Elder describes people saving a piece of their dough from the previous day to raise their bread the next day.

Pliny also reported that people in Gaul and Iberia, otherwise known as France and Spain, they'd use the foam they'd skimmed from beer to produce what he called a lighter kind of bread than other people's.

It's the beer bread question again.

Either way, it's communities of microbes that grow on mashed up grain and water and that have the power to both both leaven bread and ferment sugar into alcohol.

Over time, we figured out how to curate and stabilize these communities so that they worked as expected most of the time.

Still, they were all a little different and a little finicky.

My sour culture might make bread rise faster, yours might produce a better crumb, mine might all of a sudden stop working.

But these sour cultures were the only tool we had to bake leavened bread, and then everything changed.

And we discovered that with the discovery of the microscope, with some research done by scientists, that everything resulted actually with Louis Pasteur, who wrote his memoir Sur la Fermentation Alcolique, who opened actually the production of commercial baker's yeast.

It was two Hungarian-born brothers, Charles and Max Fleischmann, who first commercialized Pasteur's insight.

They started selling baker's yeast, fresh yeast, sold in little cakes.

And it was such a convenient product that bakers embraced it with open arms.

They all started to switch from that very inconsistent, complicated,

long process that is sourdough towards something that was very precise,

very accurate, very fast, very reliable that called yeast.

And so in 150 years, bakers switched completely.

Like I said, commercial bakers' yeast is just one microbe, not a community, which has both pros and cons.

So a commercial yeast is super boring, right?

So nobody ever thought Saccharomyces service baker's yeast was the most flavorful, that it had the best effect on the bread.

We just thought you could make a ton of bread really quickly.

Because not only is it a single yeast that you can buy whenever you need some and that doesn't need feeding or watering or loving care, but it also makes your dough rise a lot faster than that sourdough starter you've been keeping alive.

By the 1960s, boring commercial baker's yeast was available as shelf-stable granules in little packets.

And by then, bakers had also invented industrial processes that sped up the whole rising and baking process to just over three hours.

This bread, the bread of the 1960s, the bread of our parents?

This was not good bread.

Carl says the 1960s was bread's nadir.

Sourdough all but disappeared.

The 1960s sucked for bread, commercially, but it was also the time of good bread's rebirth.

The country's first Zen Buddhist monastery was created in California in the late 60s.

It was called Tasahara.

The monks there baked bread slowly as part of their spirituality.

They saw bread as being alive.

And a young Zen student named Edward S.

B.

Brown, who lived and worked at Tassahara, he published a book, Collecting the Monks' Recipes in 1970.

It was super homemade and hippie.

The cover is made of brown paper.

It was published in a tiny edition by Shambhala Press, and Edward received the princely sum of a hundred bucks.

But it sold out immediately and it went into second and third and fourth printings.

Making your own sourdough bread at home became part of the counterculture and a way to eat healthier.

At the same time, there was another group of people who thought that commercial bread kind of tasted like crap.

They weren't inspired by spirituality or health, but by flavor.

Between them, these two groups helped create the sourdough revolution.

This revolution took a while to spread.

During Carl's own training as a baker, he never set eyes on a sourdough.

It wasn't till he started working at Paratos in 1994 that he first encountered it.

I've been to one of the better bakery schools in Belgium and we never learned how to make sourdough.

It's just not part of the educational program.

So it was a discovery.

I had to take out a bucket of the fridge.

It looked strange.

It smelled strange.

It was funny when you touched it, it was a bit sticky.

But Carl is thrilled to say things have been changing for sourdough.

And we see now the latest 20, 25 years, there is a revival of sourdough and we think we are now at the beginning of something very nice that will come uh the coming years where sourdough will again take its place in the bakeries that it deserves.

With that sourdough revival came a renewed appreciation for the diversity of microbes in sourdough starters and they are diverse as we discovered.

Come closer, come closer, because something very special is going to

happen.

You have to realize that what we have here is

probably

the most unique place in the bakery world.

Carl led the group up the stairs and to a closed door.

Ready?

Keep your eyes on the door.

Well, let's go for some magic.

Three,

two,

one.

And with that, we stepped inside the world's one and only sourdough starter library.

It's a library, yes, but instead of bookshelves, there are 12 illuminated refrigerators with glass doors so you can see the jars inside.

Carl's collected 93 different sourdough starters starters from 17 different countries and they look totally different from one another.

Some of them are liquid and some are stiff and then some are very dark, some are spickled, some are almost looking like crumble because they're so dry.

So there's a lot of colors, very dark ones to brownish ones to yellow ones and then the normal white ones.

Carl took some of the jars out and allowed us to smell the starters.

Some smelled fruity, some were acidic, some were biscuity, some were creamy.

The Chinese, for example, one of them is very meaty.

When I open the jar, it's like almost a sausage, very savory.

Some of them are really very pungent, that when I open the jar and I smell the first, that you really feel the

acids go into your nose and it's like if you would have a spoon of

very heavy mustard, so the Dijon mustard that you well, that reaction.

Carl's goal with this collection is to preserve the communities of microbes that make each sourdough unique.

But for Carl, it's also really fun.

Carl is the keeper of the sourdough library.

He can't sell these starters or even give them away.

Each unique microbial community still belongs to the baker who donated that starter in the first place.

But Carl feeds them and takes care of them, and sometimes he plays with them too.

I do take home.

some sourdoughs and I do some experiments at home.

So yes, I do bake with them and I, yeah, discover

other things.

Sometimes the fermentation power is totally different.

When Carl is feeding the starters, he puts them into small plastic buckets.

Some of them, they just blow away the lid of these things, and other ones are just like very, very slowly rising fermenting.

So, there's really differences in fermentation power, in flavor, in aroma,

in the way the dough is feeling.

When you touch the dough, it's different.

So,

yeah.

Carl's point is that these starters are all different from one another, and the library itself is also unique.

Nobody's ever tried to conserve communities of useful food microbes for the future.

Walking around the library, looking at these spotlit jars in their glass refrigerator vitrines, you really see each sourdough starter as a distinct, individual, precious thing.

But how different are they microbially, really?

Who's living in these jars?

Sourdough, in terms of the number of species we know how to grow, is toward the simple end.

Often, you'll have two to four culturable bacteria species and one yeast species.

It's very likely, although we don't know, that there are also things that are hard to culture in the lab that are in those sourdoughs that make it a little bit more complex, but it's toward the simpler end in terms of numbers of species.

It's not simple though, in as much as

different sourdoughs seem very different.

And so if you were to look around the world, how many different species could you find in all of the sourdoughs?

That's actually a much longer list.

And so an individual sourdough is simpler.

This big picture of sourdough is far more complex.

As Rob is explaining, a sourdough starter is an interesting creature, or really creatures.

You can have a community of just a handful of different microbes that works perfectly together.

As Rob says, maybe two to four species of bacteria, maybe one kind of yeast, and it'll work.

It'll make sourdough.

But what's also probably true is that your sourdough starter could contain an entirely different community than mine, and they'd both still make sourdough.

And it's that diversity, that huge world of bacteria and fungi that can collaborate to raise bread.

That's what Carl is trying to collect.

His library, as unique and impressive as it is, it's probably just the tip of the iceberg.

And maintaining this library is a lot of work.

It's not just collecting samples and putting them behind glass.

Any baker can tell you what a commitment it is to keep a sourdough starter alive.

I always describe it if you have a sour culture.

It's like having a pet or a child.

Paul Barker owns a bakery just outside London called Cinnamon Square and he has many sourdough pets.

You have to look after it if you don't feed it, keep it warm or whatever.

So unless you look after it, it will spoil, it will eventually die on you.

So it's a commitment to having a sour culture.

In fact, there are even specialized sourdough hotels where you can send your sourdough starter to be looked after if you're going on a super long long trip.

A sourdough starter is really much higher maintenance than commercial yeast, so why do bakers use it?

We asked Paul.

Firstly, because the sourdough gives you a much different type of bread, different textures, more digestible bread, more nutritional breads.

So I like the fact that you can get a totally different product and you can be so creative with a sourdough more so than a yeasted bread.

So you can actually do a lot more with the shaping, the baking, the decorations.

I think because you can get more from it.

Whereas a yeasted bread, a commercial yeasted bread, you're just expanding your dough and baking it.

Commercial yeast, as Paul explained, it makes the bread puff up, but that's it.

Paul knows that the microbes in his starter are giving him a different dough.

It often has the right type of texture to allow him to play around more with the shape of his loaves.

But what are those microbes actually doing to create these differences, and how are they doing it?

So the microbes in the starter are starting to break down some some of the hard to break down things in the grain that you've given them to eat.

And they are beginning to produce these gases that we think of as some of the really important flavors in the bread.

But as they metabolize the grains, they're also altering the structure of the carbohydrates that are present, which then is going to alter the nutrition of the carbohydrates.

It's going to alter the outside of the bread.

As Paul has noticed, and as Rob just explained, microbes improve the texture and the nutrition and even the look of the final loaf.

They can even produce extra vitamins, but they also shape its final flavor.

You can literally taste the difference between bread from different starter communities.

And so butteriness, a lot of butteriness comes from which microbes are in your starter.

The kind of sourness you have, how lactic it is versus how acetic it is that comes from which microbes are in the starter.

Rob told us that some sourdough bread has a particular gooey melt-in-your-mouth feel that comes from a chemical called dextran, which is produced by a bacteria called Wicella.

Wicella lives in some sourdough starters, but not in others.

So, microbes are munching away on the flour, excreting things like buttery-flavored lactic acid and yeasty farts that puff up bread.

That much we know.

But Rob and his fellow microbiologists don't understand how all this microbial munching and excreting creates the differences between different finished loaves of sourdough.

And the further you you get down that chain of events, the less we understand about the mechanics of how all of that is happening.

But what we do know is that all of the things that could influence those final flavors, final texture, final nutrition, are things that we think of as predominantly microbial.

So we don't know.

We really don't know how the microbes are working their magic.

We don't even know where they come from in the first place.

But Rob wants to know, and so did we.

And hence this giant three-day experiment in Belgium.

We have the exclusive first results after the break.

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Back to Belgium, where we are about to conduct an epic baking experiment in order to figure out where the microbes that are in a sourdough starter actually come from in the first place.

In order to make a starter, you take a simple set of ingredients and you expose them to open air and to your body and to your home, and it starts to grow.

It's like making a garden without ever planting the actual seeds.

And so the mystery to me is what determines which life forms are growing in that garden.

And so that's the fundamental mystery.

Why is your garden different from my garden when we use the same things to start with?

Many bakers think they know the answer to this mystery.

I think it's a flower.

But the hands of the bakery is very important to the results.

I think it's probably a combination of all of the variables.

It's mostly, in my opinion, this has to be the reactionary within the flour and water.

That's where it starts.

I would assume the environment is going to play a part to it as well.

Because there's going to be a lot of cross-contamination in a bakery from different flours anyway, and you can end up with different types of sours.

I feel like every baker we talk to has a different assertion about where the microorganisms from that sourdough starter came from.

Some people are very clear.

It's likely coming from the flour.

If I use a different flour, I'll have a different sourdough starter and a different sourdough starter must be different microorganisms.

Some people have suggested that it's the water.

That's why I use San Francisco sourdough.

It's San Francisco sourdough, and you can never make it in New York.

There are claims about it being in the wood of buildings.

What I like about this project is that as scientists, we have not had to come up with our hypotheses because the community of sourdough makers has provided us with the longest possible list of what they might be.

From that long list, there are four main hypotheses that the microbes that make each sourdough starter unique and individual come from A.

The wheat, B, the water, C, the environment, and D, the bakers themselves.

Rob says we know that there are different microbes on different grains.

Even within the same grain, there are different microbes on different strains of wheat, different heritage varieties, for example, or wheat that's grown in different ways like organic wheat.

And then even on the same plant, you can find different microbes in the germ of the grain versus the endosperm.

The endosperm is what Millers used to make white flour.

So this means that whole wheat flour has different microbes than white flour does.

Rob says all these variables in the flour itself could certainly be influencing the sourdough starters.

Then there's hypothesis B, the water.

Water can conceivably kill things in the starter.

It's unlikely to be adding things to the starter because we have a pretty good list of what lives in water and it's I think people are surprised often that all water they ever drink, even bottled water, has microbes in it, but they're not the kinds of microbes we characteristically see in sourdough.

In other words, Rob is saying that the water might prune particular microbes out of a sourdough starter garden, but it's unlikely to be contributing any new microbes itself.

The other thing though that can then contribute to the starter is what falls from the air into the starter.

This is hypothesis C, the environment around you as you make the starter.

Rob says that plants might have a particularly strong impact because of the insects they attract and the microbes on those insects.

And then there's just the bacteria that are swirling around in the dust and air.

Some of those come from pets.

If you have pets, the majority of them usually come from your own skin and the skin of the people you live with.

And finally, hypothesis D, the baker.

Specifically, the microbes living on the baker's skin.

We can think of many ways that microbes differ from one person to another person.

For example, there's that gene that determines whether you have sticky or dry ear wax.

And depending on which version of that gene you have, your skin microbes in your armpits, but also around your body more generally, are super different.

There are also microbes on your skin that don't live on your skin.

They get there when you touch parts of your body that have other microbial communities, like your gut microbes.

And then we know that human women and human men differ greatly in microbes because of vaginal microbes.

And so women have way more lactobacillus in general, but especially in vaginal communities.

And those sort of travel around through the day-to-day business of being a human.

These vaginal microbes are particularly interesting because lactobacillus is a key part of most sourdough starter communities.

So in some cultures, sourdough is mostly or exclusively something that women bake.

And to me, it's really intriguing to think about does that have something to do about the unique sourdough community that emerges when women make sourdough versus when men make sourdough.

This three-day Belgium adventure at the experiment we're watching unfold, it's designed to try to tease out where the microbes in the sourdough come from, A, B, C, or D.

To be precise, it's designed to isolate two variables from these four possible sources for the microbes in sourdough.

The microbes on the different bakers' hands and in their environment, those are the variables.

They were shipped the ingredients.

They were given the same protocol, the same recipe.

That is, these bakers were shipped exactly the same flour.

Not the water, because based on the existing research, Anne and Rob don't think the microbes and water play a big role.

Anne and Rob cultured the microbes out of that flour, so they already have a list of the microbes that are being contributed to the starter from the wheat.

Like Anne said, the bakers were given very specific instructions about exactly how much flour and water to use and exactly how long to ferment their starters.

The goal is to make this all as controlled as possible.

So all of these bakers, men and women in different parts of the world, they all made their sourdough starter using the same flour according to the same protocol.

And then they put their starters in a baggie and they brought it with them to Belgium.

And that was a really fun part when we got to open them all up and they're

coming in and some of them smell like vinegar and some of them smell more like yogurt and some of them smell creamy.

As soon as the bakers arrived, Anne and Rob opened packages of sterile swabs like super long q-tips to get samples of those rich microbial communities.

One double swab per.

Then we took a break from the science.

We all introduced ourselves and met each other and everyone talked bread.

The final part of the experiment that day was refreshing the starters according to the protocol.

I'm gonna put my starter in this bowl and then I'm gonna mix it with the water.

First of all, dilute it with the water

and then add the flour on top.

Mix it,

put it back in here,

and then we'll wait until tomorrow.

And that's it.

That's it.

And then we all ate dinner together accompanied by lots of bread, and day one of the experiment was over.

First up, day two, after breakfast featuring lots of bread, we got to everyone's not-so-favorite part,

getting swabbed to find out what microbes live on their skin.

Paul from London was up first.

I'm going to be swabbing your hands.

And I'm going to ask that you put your hands out just in a way that I can apply some pressure.

And I'm going to spend kind of a few seconds just going over the front, and then I'm going to ask you to flip, and then I'll do the back.

And if we could not talk over the swab when it's out so that we can not introduce some of our oral microbes.

Sure.

Thank you.

Anne was swabbing the baker's hands because if any microbes are going from a baker's body into their sourdough starter, they're probably getting in there via their hands.

It would be wonderful in some future version to top to bottom swab all these bakers and really start to tease out, you know, which body part is really contributing.

But we had to start somewhere, and so we start with the hand connection.

In case you're getting a little grossed out, don't worry.

The bakers do wash their hands, and they should wash their hands and made sure to emphasize that.

Even after you wash your hands, though, there are still microbes on them.

They're everywhere.

So, next step.

After their hands were swabbed, the bakers were allowed back into the test kitchen to be reunited with their starters, which they could hardly wait.

It was like parents at the kindergarten gate.

But before they could be fully reunited, the starters all had to be tested with some cool science gear to find out their pH and their organic acid content.

Once again, the sourdough starters all looked and smelled surprisingly different.

My sourdough was called Danish Dynamite.

That's right, Danish Dynamite.

So it has a lot of activity inside.

So, as you can see, upside off the class here.

It was like looking at baby photos.

I'm not kidding.

Everyone thought theirs was just the prettiest of all.

You're smelling your sourdough?

Smell is the

butter milk

smell taste,

aroma.

Can I smell?

Yeah, it's kind of a little sweet.

The bakers made their bread and left it to proof overnight.

And as that official science experiment bread was rising, the bakers were set free in the test kitchen to let their pent-up creativity run wild.

And they went to town.

Hakan made this crazy Turkish bread that had lots of melted cheese and a cracked egg on it.

Leticia, the Mexican baker, she was putting cocoa and raisins into a sourdough loaf.

Someone made pita bread.

I'm gonna taste some of this.

Oh.

Nikki?

Hot squeezo with garlic butter?

It's really good.

It's really good.

So look,

let me do this.

Mmm.

I'm squeezing the bread like it's a bellows on an accordion or something.

Or I'm trying to light a fire.

This is what I'm doing.

The smell.

Isn't that amazing?

It's like as you squeeze the dough, the scents in the air pockets just like get blown right at your face.

So I stood here.

Stavros like pumped the bread in my nose.

And Vasilis was like,

this is sourdough.

We sniffed bread and we ate bread and then we ate more bread.

And then we ate dinner, which also had some bread.

And then we rose bright and early on the third day, had some bread for breakfast, and went back into the kitchen to bake the science experiment bread.

But there was some tension.

Tommaso, for one, he's from Italy, he didn't want to put his bread in the oven when everyone told him it was oven time.

He said that the dough wasn't ready for baking, it hadn't risen enough.

Rob whispered to us that he and Anne were having a hard time making sure that all the bakers kept to the scientific protocol.

Yeah, so we're thinking about it right now.

There's the tension between like what people view as counting as a bread

and

what we want.

Tommaso was overruled in the nicest possible way, and all the baker's dough went into the oven at the same time.

And the same way that their starters had looked and smelled really different, despite having been made from the same flour using the same instructions, the dough looked really different as it went into the oven, too.

You could see some really big air bubbles in some and none in others.

Some rose a third of the way up to the tops of the baskets, some rose all the way to the top, some were super bubbly on top, some were shiny and smooth.

And then the bread came out of the oven.

Oh, those are pretty.

Some of the bakers were happy and some were not.

Mom, see you like the microphone?

Because when it's cracking open, you see black line.

And Carol calls it eyeliner.

So we have to bake it like eyeliner on the bread.

And eyeliner is a good thing, right?

Yeah, yeah.

I learned something new.

I never knew bread should have eyeliner on it.

It's basically the nice dark cracked edge you see at the top of the loaf.

Tom's loaf had really lovely eyeliner.

This has a lot of nice fish eyes or blisters.

Little bubbly blisters on the cooked crust are another sign of a great sourdough, but some loaves didn't look as good like Paul's.

This one doesn't look like it did very much over here.

It didn't even crack.

The ones that are looking very sad at the back, the two behind this one here.

Yeah, the loaves.

They're not very good.

And then, as soon as it was cool enough, all of the loaves were sliced in giant bread slicing machines.

And the bakers were asked to evaluate a slice from each loaf.

They had to assess its appearance, its smell, and of course the way it tasted.

So we got kind of two different colours I see already.

One which is a bit greyer and one which is a bit more yellowy, creamy colour.

And is that reflected in differences of smell too?

Yeah, so the grayer ones, the grayer ones have less of an acidic aroma.

Some are

creamier, some have gone kind of more reddy, kind of browny, sort of.

So So, there was a distinct difference in the colour, which is quite interesting.

I wouldn't have expected that, considering we're all using the same flour, the same ratios of ingredients.

Like the one of Guillermo is

dense and

stronger, and from Tom it's very fragile and very open, but

the taste and smell is about the same.

For example, Hanken is very, very similar to Casper.

I think it's the same bread.

Incredible.

Paul

is the same than Guillermo.

It smells more like wheat, not so fruity.

Yes, right.

Haken and Tom.

It tastes more

acid taste than Tatiana and Giuliemio.

And so in this case, we know that all those differences from bread to bread are really microbial.

But it might not actually be because the starter contained different microbes.

The exact same microbes can create different smells and tastes just based on the temperature that they grow in, for instance.

So these results, that the breads smell and taste different, could just be because the temperature in London is different from Guadalajara.

Sensory evaluation was not enough to answer this question.

Instead, Rob and Ann had to take their swab samples back to the lab and analyze them.

A few months later, we called Rob up to find out how it all went.

That's coming up after the break.

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You're basking on a beach in the Bahamas.

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Hey, Rob, so Belgium ended.

You packed up to go home.

How did you feel?

Um, I felt super full.

I felt really full, too, just so you know.

I was never gonna eat bread again.

And then I did.

No, I'm ready for more bread, to be honest.

There's been time.

Science takes time, but this science took a little bit longer than Rob wanted because his samples, the swabs from the baker's hands and the sourdough starters, they got held hostage in Belgium.

Trying to get these kinds of biological materials across borders can be tricky.

Rob is a patient man, but even he was getting a little frustrated.

And then, amazingly, just

last week, we got the first results from that decoding of the DNA.

Rob Ann and their whole team spent a day just marveling at the data and poking around.

They were trying to figure out if they could make any sense of the data just by looking at it, which of course they couldn't.

But then eventually, we start to formally analyze what's going on with the patterns of the data.

And that's where it starts to get interesting.

And so the first one of those analyses happened on Friday and the second one happened about two hours ago.

So tell us, what did you find?

Well, so the first thing last week was a result we totally didn't, we weren't looking for, we didn't anticipate, and I had no idea it was even possible.

It's about the baker's hands.

Normal hands usually have Staphylococcus and some armpit microbes, some bacteria that are the same as acne bacteria, maybe some random bacteria from things you've touched recently.

When we looked at the baker's hands, their skin bacteria on their hands was about half sourdough bacteria.

And so they like have sourdough paws.

Sourdough paws?

But like we've looked at zillions of hands.

We've never seen anything like this.

And so the first result is that the bakers themselves have changed in response to their occupation.

Normal hands like mine and Cynthia's and Rob's, they're something like 2 to 4% lactobacillus.

On the hands of the bakers, it's the star of the show.

It's wild.

I mean, if it's right, you should be able to put flour and water on a baker's hand and it should start to ferment immediately and become acidic.

Working with sourdough has entirely changed the microbial environment on the baker's skin.

They've been colonized by their pets.

Rob wonders if the bakers spend so much time with their hands in acidic dough that the sourdough lactobacillus microbes end up with a competitive advantage over normal skin microbes.

So that is weird.

But it's not what Rob and Anne set out to find.

What they were trying to understand from this three-day Belgian breadfest is whether the microbes in the sourdough starter come from bakers' hands.

Not whether bakers' hands are somehow different from normal hands.

So what we saw two hours ago was that there's a group of bakers that has very different sourdoughs and the unusual microbes in those sourdoughs are also on their hands.

One question answered.

The bakers who have weird bacteria on their hands have the same weird bacteria in their sourdough.

There is a connection.

Individual bakers do indeed seem to influence their starters.

But so does this difference influence the flavor of the resulting bread?

Rob doesn't know.

He hasn't done that research yet, but he has a hunch.

I predict that second group has more unusual flavors, and we should be able to capture that.

But we'll see.

Stay tuned.

Meanwhile, what Rob and Ann have done is sit down and compare the list of microbes that were in the flour, and the list of microbes that were on the hands, and the list of microbes that were in the starters.

We get a total of about 193 kinds of bacteria in the sourdose, which is a lot more than the bakers tend to think is there, which is interesting in and of itself.

Something like 80 of those are also found on hands, and roughly the same number seems to be found in the flour.

And there's overlap between the flour and the hands.

We saw almost nothing in the water, so they're probably not coming from the water.

But they did see some microbes that weren't accounted for, that were not from the hands or the flour.

They were maybe microbes that were just floating around in an individual baker's kitchen.

You know, they could come from a leaf outside the bakery.

It could come from a bowl, a spoon.

But it's not so surprising that we haven't found where all those microbes are coming from.

And in some ways, it leaves the baker some magic, right?

Where does the stuff we've not measured yet coming from?

Wow, it's just magic.

You guys can keep that.

Rob also told us another new finding that totally contradicts what he told us back in Belgium earlier this episode.

Remember how he said that sourdough starters have three or four species of bacteria and maybe one species of yeast?

Rob says, based on these new samples, he's seeing 10 species of bacteria in the average sourdough starter and maybe three species of yeast.

We now have enough data to say that I was wrong when I was describing the simplicity of these starters, which also means the whole literature is wrong.

Folks, this is science in action.

We think we know things, like about how many species of microbes live in a sourdough starter, and then we do some research and discover we don't.

But Rob pointed out that sourdough starters are still not particularly complex in microbe terms.

And so part of the story that's super fascinating to me is you put out flour and water all around the world, and somehow you can create this very similar ecosystem out of what for bacteria and fungi is a relatively small number of species.

If you put out sterile soil in as many sites globally, you'd be looking at 20,000 species.

And so on the one hand, that individual start are more diverse than we tend to think.

On the other hand, that global picture is actually a lot simpler.

So that was really interesting.

Robin Ann and their collaborators have really only just begun analyzing this data.

Over the next six months, they're going to be figuring out what types of compounds each species of bacteria can produce.

Not necessarily that they're actually making those compounds in the starters, but that they can.

And then they're going to match those compounds to their possible effects in bread.

Different flavors, different textures, different nutritional values.

The other part is we've barely touched the fungal data, and so that will be, I mean, we'll be spending a fair amount of time on that even this coming week.

So there's much still to be done with just the data from our great Belgian bake-off.

But there's also just more sourdough research to be done in general.

Our Belgian Breadfest was only one of the sourdough experiments Rob and Ann have got going on in their lab right now.

They've already gotten about a thousand people from around the world to send in their sourdough starters.

Rob and Ann want to get a big picture of sourdough diversity.

They're hoping to see patterns like whether some species are more common in some areas of the world and they're already starting to see some results.

Rob told us that in terms of bacteria, there seems to be a shared sort of pool that colonizes grain and water mixtures all around the globe.

In other words, the same bacteria are pretty much everywhere, and then which end up in which starters seems to depend mostly on the flour and the baker, as we just learned.

But they are seeing a little bit of geographic variation with bacteria.

Some bacteria tend to live in more northerly Scandinavian countries, for instance.

That's not the only anomaly.

There's a little bit of a hint so far that maybe France is kind of special.

France is special.

But the fungi we're seeing globally have a lot of geography.

And so there's one kind of yeast, a kind of fungus that we've basically only seen in Australian starters.

We know that the yeast can do a lot in terms of flavors and aromas.

And if that unusual yeast is playing a big role, then there could be a flavor that you could only actually savor when you're in Australia.

And we don't know that yet, but that's a...

It's a fun idea.

Sourdough tourism is going to become a thing.

Just wait and see.

One of the things Rob and Anne are going to do over the next year is bake some bread from these thousand starters that that they received.

That way they can start to assess flavor while controlling for the other ingredients.

The ultimate goal is to arrive at microbial recipes for sourdough deliciousness.

Once we do that, that would be the hope, is that there's some mix that really gives you the perfect butteriness or the

sourest souriness.

Is souriness a word?

I don't know.

Rob and Ann are also working with colleagues to tease out the evolutionary history of sourdough.

They're going to be working out how microbes and starters change over time.

So eventually they'll be able to tell you, if you're using your great-grandma's starter, are those your great-grandma's microbes?

Or, as listener Denae asked, if she gives her sourdough starter to a friend, will it change?

And if it does, how quickly?

So, there is still tons to figure out about sourdough.

But Rob is on it and we'll keep you posted as his results come in.

It's super exciting research.

Not just because we love microbes.

A round of applause if you haven't killed over yet from taking a shot every time we say microbes.

We do love microbes, but we also love this research because it points the way to a future of even more delicious bread.

And so I think the question is the next step, which is what microorganisms create what flavors and aromas and traits in bread that we want.

And then we can start tracking down what microorganisms might be leading to those traits.

And so you can imagine a future where you could think about the kind of bread you want.

Maybe I want it to be crusty and kind of chewy with fruity notes.

And by having that choice of bread, there'll be a list of species that will work together to create that.

So you'll have a designer sourdough.

Thanks this episode to the Burroughs Welcome Fund for supporting our reporting on biomedical research.

And a big thank you to Paratos who hosted this experiment but also hosted Cynthia and me in Belgium.

We have photos and links to Carl's magical sourdough library on our website, gastropod.com.

Thanks so much to Rob Dunn and Ann Madden for letting us follow them around for three days and try not to get in the way of all their swabs.

And thanks also to the lovely bakers who couldn't have been more of a fun gang to hang out with while doing some cutting-edge science and some competitive level eating.

We'll be back with a brand new episode in a couple of weeks.

Till then.

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This month on Explain It To Me, we're talking about all things wellness.

We spend nearly $2 trillion on things that are supposed to make us well.

Collagen smoothies and cold plunges, Pilates classes, and fitness trackers.

But what does it actually mean to be well?

Why do we want that so badly?

And is all this money really making us healthier and happier?

That's this month on Explain It To Me, presented by Pureleaf.