A Sourdough Saga, From Starter To Slice

17:08 minutes

two loaves of sourdough bread with nice brown crust on a stove top
Two sourdough loaves, freshly baked by Ira! Credit: Ira Flatow
a loaf of sourdough bread sliced in the middle to see its rich density
One of Ira’s sourdough experiments. Credit: Ira Flatow

What makes sourdough taste sour? Was the first bread invented, or discovered? How did scientists eventually figure out that yeast and bacteria were the true master bakers? Will commercial bread ever be as good as that hand-baked loaf? 

Ira releases his inner breadmaking nerd in this conversation with Eric Pallant, author of the forthcoming book Sourdough Culture: A History of Breadmaking From Ancient to Modern Bakers

Read an excerpt from the Pallant’s book about the surprising history of yeast.

Segment Guests

Eric Pallant

Eric Pallant is a professor of Environmental Science and Sustainability at Allegheny College and author of Sourdough Culture: A History of Bread Making from Ancient to Modern Bakers. He’s based in Meadville, Pennsylvania.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira FlatoWw. What new hobby did you take up during the long COVID isolation period last year? For me, it was baking sourdough bread. I must have watched hundreds of videos on how to make sourdough, spent countless hours waiting for the bread to rise and proof.

In fact, COVID has been the perfect time to practice waiting. It takes two or three days to make sourdough bread. And as one instructor said, it’s 15 minutes of work, 3 days of watching. But you know what? It’s all worth it. There is nothing quite like the crunch, the smell, the flavor of homemade sourdough.

And the geek in me– and there is a lot of that– enjoys understanding the chemistry and biology, the ongoing battle between yeast and bacteria in the ferment. That’s why when I heard about a new book called Sourdough Culture– A History of Bread Making From Ancient to Modern Bakers, that book spoke to me. So I invited the author to break bread, so to speak, on the radio.

Dr. Eric Pallant is a professor of environmental science and sustainability at Allegheny College in Meadville, Pennsylvania. Welcome, Eric.

ERIC PALLANT: Hey, great to be here, Ira.

IRA FLATOW: Nice to have you. So why this book?

ERIC PALLANT: Well, let’s geek out, OK? So it comes from curiosity about living with a batch of glop in my home for a couple of decades and then realizing, this is older than anything else I own, and it’s alive. And it’s not just one thing. It’s this whole ecosystem of bacteria and yeast. And I got it from somebody who I met once. And where did it come from originally?

And that started a search to see how far back I could push the origins of my sourdough starter, which turned out to be the Cripple Creek gold rush of Colorado from 1893, as far back as I think I could push it. But then the question is, how did it get there? How did it get to Colorado? And then I had to start at the very beginning. Who invented bread? Who invented sourdough?

IRA FLATOW: So sourdough starter, just for people who don’t know what that is, that’s something you need to have, make, beg, or borrow to get your sourdough bread started.

ERIC PALLANT: Sure. But anybody can do it, and you can do it by accident. All you need is some flour and some water and as you said, at the beginning, about three days. If you put it out on your countertop– and it doesn’t matter if you’re in Arizona or Seattle or Stamford, Connecticut– it will, after three or four days– wild bacteria and wild yeast will start to consume, essentially, predigest that yeast. And you’ll get little bubbles of carbon dioxide, and off you go.

IRA FLATOW: Now, people who bake bread, just regular bread, they go to the store. They buy that yeast in that flat package. But you’re saying the yeast in sourdough does not come from that package.

ERIC PALLANT: Oh, no. So it’s actually the other way around, where the yeast in the package came from a wild variety of yeast, and it was selected to put in the package. Whereas wild bacteria and wild yeast, which are around all of us, are what’s going to land and grow in your mash that you’ve just put out on your countertop or your windowsill. But that’s going to be a whole suite of organisms. It’s going to be a little ecosystem as opposed to, think of it as, a monoculture, is what you’re buying. You’re buying monocultural agriculture when you buy that single package from the store.

IRA FLATOW: So why is wild yeast better than the store bought? Why is that? Is that what gives it its unique flavor?

ERIC PALLANT: It’s better because you have multiple species of yeast at work. And even more importantly, you have multiple species of bacteria in the microbial competition to consume the food, essentially, in that dough. Those bacteria are competing like pigs at a trough. But they’re doing it by exuding acids and microscopic compounds that are toxic to other bacteria and other yeast. It has its benefits, which is a sourdough bread won’t molt because it’s got this acidity in it.

But they are also– to us humans, they provide flavor and variety and aroma and so forth. Whereas if you go out and buy Red Star or Fleischmann’s yeast, you’ve just bought a single species of yeast, completely absent of all other microorganisms, no bacteria. And you will get a single flavor, which is pretty flat, pretty boring, in my opinion.

IRA FLATOW: Where does the sour flavor in sourdough come from?

ERIC PALLANT: So that’s the bacteria, right? So bacteria excrete either lactic acid, which is the same acid you would find in yogurt. And so some breads that are made with sourdough will have kind of a creamy yogurt kind of acidity. And then there are others that are using acetic acid to– again, their purpose is not to make bread tastes good, but it’s to keep all those other microorganisms from getting into the bread. And they’re excreting acetic acid, which is vinegar. And there are sourdough bread that taste sort of vinegary and have a little bit more bite to them.

And the great bakers are the ones who can reliably manipulate their starters, their sourdough cultures, to aim the flavor in one direction or the other or get some combination of creaminess and tanginess and acidity that are partly a function of low pH. You can make a sourdough bread and watch the pH drop as those bacteria do their work. But it’s the bacteria that get most of the flavor and the wild yeast that give most of the leaven, which caused the bread to rise.

IRA FLATOW: Let’s talk about the history of bread. And you spend so much time in your book talking about it. It’s very fascinating because I was never quite sure whether bread was invented or discovered. Which one was it?

ERIC PALLANT: Yeah, well, so there’s a problem there. I hand it to archeologists for the work that they are doing in sort of pushing back the date for when the first breads were made. But the problem is that when the first bread was either discovered or invented, there wasn’t Instagram. So we don’t really know for sure who did the work.

We can speculate. And the archeologists do so by finding remnants of the grain and the flour and finding that next to a stone, then a flat stone that has been fired. It’s next to a big campfire from which you could fairly safely assume that at least a flatbread was made here. And if that bread had wheat in it, which is really rich with gluten, then chances are that there was some leavening agent there.

And then it’s speculation, which is somebody made this thing probably by accident. They had a porridge. We know they were eating porridge probably. But, OK, now we have to figure somebody forgets about that porridge for a day or two or three, and they’re in the Fertile Crescent. And it’s really warm, and that thing starts to bubble away. And they say, heck with it. I’m going to cook it anyway.

And it rises. And then it springs in the oven. And then all the kids say, whoa, mom, that’s great! Can you do that again? We can only speculate that probably happens across the Fertile Crescent between 6,000 and 8,000 years ago, discovery or intentional or an accident, some combination of all the above. But it’s really a function of the human brain to recognize it’s this particular grain, wheat, which is really good for making bread. And it’s this process of waiting a few days for the thing to bubble.

And then, OK, let’s do this intentionally. Let’s plant the seeds of wheat. Let’s harvest them. Let’s mash them into a flour. Let’s soak them in water, maybe knead them a little bit. Add a little bit of salt because that really makes it tastes great. Now we have bread.

IRA FLATOW: Let’s talk about bread and culture because you make a good point of showing how it’s involved in so many cultures. For example, in Christianity, you say that there are many references to Jesus’ symbolism with bread.

ERIC PALLANT: Yeah. So Jesus at the Last Supper says to his 12 disciples, among the last things he says is, my body is bread, and my blood is wine. And what are those both? They’re products of fermentation. Nobody knows that at the time. But there’s something spiritual about both bread and wine, that they’re transformed, in some ways, magically, spiritually. And now we know scientifically exactly what’s happening from the time that they’re dough or a mash of grape juice to the time they become something rather sublime, which is baked bread and wine.

And for 2,000 years, the sacrament is to take both bread and wine. And so I don’t know that it starts there. But you can’t help but notice that connection between all Western religions and– and bread.

IRA FLATOW: Mm-hmm. When did we begin to understand that it’s the microbes in the bread, the starter, the yeast, that it is necessary for bread to rise? You mentioned in the book it was the invention of the microscope that made this possible. And then it went on from there.

ERIC PALLANT: Yeah, so Antonie van Leeuwenhoek is the first guy to actually see things that are invisible to the naked eye that are tiny, right? We have Galileo looking up into the heavens. And at the same time, we’re taking those same lenses, in some ways, and reversing them. And van Leeuwenhoek sees these little tiny, tiny things that he calls cells. But he has no idea what he’s looking at. He calls them animalcules, part animal, part molecule.

And at that point, nobody knows what a molecule is. It takes 200 years of really interesting experimentation before they can sort of wrestle those cells back and forth between chemistry. Are they just molecules that cause grape juice to turn into wine and barley malt and water to turn into beer and bread to leaven? Back to biology, are they cells that are living? And if they’re living, do they reproduce? And do they actually consume nourishment?

It doesn’t really end until– we start in the 1650s– until the 1850s, more or less, when Louis Pasteur finally puts the whole puzzle together and says, you know what? Yeast are living organisms. They consume sugars. They excrete carbon dioxide and alcohol. And they reproduce. They’re the organisms responsible for fermentation.

IRA FLATOW: If bread is so simple, why fundamentally do we see so much variation culturally with different kinds of breads? And you talk about going around the world and tasting all these different breads in these different cultures. I wish I had been along on that trip with you.

ERIC PALLANT: Yeah. I think that has been a wonderful part of this journey, is that to make bread really only takes four– I would argue five– ingredients. You need flour, preferably wheat flour if you want the bread to rise. But it doesn’t have to be wheat flour. You need water, salt. It’s absolutely essential that it tastes better. And then the hidden ingredient you alluded to at the very beginning is time.

I hope you had this experience. Anybody who starts making bread can’t help but do a little experimentation, which is like, what if I added in a little bit of rye flour? What if I had it in some sesame seeds?

IRA FLATOW: Yeah. I did that. Guilty as charged.


IRA FLATOW: Absolutely.

ERIC PALLANT: What are the local products? And some of these think, ooh, this is a nice combination, a little bit of cocoa powder and dried cherries. Now we’re talking, right? And that becomes part of the local culture. And then it’s further advanced by local geography. So wheat is a really finicky crop. It needs a lot of attention. It needs the right climate and so forth.

It’s fairly limited where it will grow. And so by the time you’re, for example, in Northern Europe, if you’re in Germany or Scandinavia or Scotland, wheat doesn’t grow. But you still like bread. And so what do you do? The local crop there are oats and rye. And so if you go buy a bread in Denmark, it’s going to be a dense, heavy, rye bread. And if you buy bread in Scotland, where what won’t grow well because it’s just too wet and damp, you’re going to get a an oat cake. They’re all breads.

IRA FLATOW: This is Science Friday from WNYC Studios. We’re talking to Eric Pallant about the history and culture of sourdough bread. Until 150 years ago, you said that all bread was sourdough. And then we got little loaves you get in the packages in the store, right?


IRA FLATOW: How did that happen?

ERIC PALLANT: So that’s not so complicated. That’s an American– well, it’s not American, per se, but we did it better than anybody else. If sourdough, as you said at the outset, is a three-day process, and commercial yeast that you buy in the store is so vigorous and reliable that you can make a recipe that says, after one hour of putting in your yeast to your dough, that bread is so inflated you have to punch it down– sourdough bakers don’t usually have to– their wild yeast aren’t that strong. And so they don’t have to punch their bread.

But bread that can be given enough yeast that it will inflate like a balloon is a really reliable product. If you want to make a profit as a baker, you had a choice. Am I going to spend three days futzing with this bread every few hours, trying to add a little bit, turning it, all that? Or can I make a lot of breads very quickly and reliably every couple of hours with commercial yeast? So it’s about profit.

IRA FLATOW: Do you have any vision for making good bread and maybe sourdough more widely accessible?

ERIC PALLANT: Most of us who are living even in urban areas, most of us can now, in an urban area, walk to a handful of artisanal bakeries. They’re making really good quality bread, a large portion of which is sourdough. And what makes it so good is the time and the attention they’re giving to it.

The big manufacturers are paying attention. And so the big manufacturers are thinking, OK, the market growth in sourdough is just exploding. We’ve got to get in on that. And they’re doing everything they can to try and figure out how to do that quickly, including– and you and I can debate whether this is legit or not. They’re growing, like, Olympic-swimming-pool-size vats of sourdough in just huge quantities, drying it, autoclaving it– there’s nothing alive in that– turning it into powder and adding that to their bread, marketing it a sourdough bread.

It does have sour note in it. But it is not leavened by sourdough, by any stretch of the imagination. But it doesn’t take a lot of imagination to picture in the next couple of years how many loaves of bread are going to say sourdough on them that also say yeast on them. And the sourdough is just dead, dry powder. And so there is a kind of competition going on there over which way bread is going to go. The part I wish would happen, sort of the next thing I’m starting to think about and think about how to work on, is that really good bread is expensive. And there’s a justice issue if only wealthy people can afford good bread.

IRA FLATOW: Yeah, because you’re talking $10 a loaf when I look for it.

ERIC PALLANT: Yeah, that’s crazy. Yeah. And if you make it yourself, it’s about time poverty and who has the time to be at home. The average working stiff doesn’t have the time to put into just making all of their own bread. And so there is still a problem among the artisanal community, I think, in trying to figure out how to make good bread, like all good food, accessible.

IRA FLATOW: Well, Eric, we bread geeks could go on talking forever. It’s a great book, Eric. I want to thank you for taking time to be with us today.

ERIC PALLANT: Thank you, Ira.

IRA FLATOW: Eric Pallant, author of Sourdough Culture– A History of Bread Making From Ancient to Modern Bakers. And if we have whetted your appetite for sourdough culture, we’ve posted an excerpt from the book on our website at sciencefriday.com/culture.

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