Editors note: This publication contains the video of the talk from the Fermentology webinar series, as well as a lightly edited transcript of the lecture.

Abstract

Should you add raisins to your starter? What is the best feeding schedule? When is it “ripe?” What can you do with excess starter waste? Join Francisco Migoya, head chef at Modernist Cuisine and co-author of the award-winning Modernist Bread, as he answers these questions and provides findings from research conducted by his team over four years that dispel many long-standing baking myths. Fermentation transforms dough into bread with a complexity of flavors, aromas, and a tender crumb from the moment the yeast is mixed with flour, water, and salt to the time it’s baked. Understanding fermentation’s critical role in the stages of the bread making process enables you to bake better bread.

Header image: Flours by Mudd1 (CC BY-SA 3.0)

Watch the talk

Introduction

At Modernist Cuisine we're in charge, every day, of doing the research and development for the books that we write. We try to do practical science without dumbing down the information, but also be as informative as possible so that the information that comes in our books is readily available to all. That's basically our day in and day out.

We have a modestly sized kitchen. I know it's my kitchen, but this is one of the best, most well-equipped kitchens I've ever worked in. We've been in this particular lab/kitchen for the close to five years—actually five years this August. It's a combination of a professional kitchen/bakery, but there's a science lab environment as well because we have some scientific equipment in there. We have a rotary evaporator. We have a spray dryer. We have a rotor-stator homogenizer. We have various types of equipment that are utilized more in scientific lab environments.

But we also have a lot of home baking equipment. That's one of our important goals: to make sure that all of our books also have practical applications for home cooks and home bakers. If anybody needs more of that, it's people who try to do this at home, and so we really make a huge effort to have that information available in our books. Our book came out in 2017, and at the end of 2019 it came out in the French, German, and Spanish translations. So this is basically where we're coming from with our bread project.

The first thing I wanted to do was introduce you to one of our best friends in this book: yeast cells. We took a picture here at our lab with a scanning electron microscope, or SEM. It allowed us to take a really close look at yeast. And you can see in the picture how it looks like it has little eyes. But obviously those aren't eyes. What those are are basically scars from when the yeast buds, meaning yeast doesn't reproduce. What it does is it buds, and you can see the budding scars from the yeast cell. So I thought it was a very interesting thing to show, up close and personal, what a yeast cell would look like.

Levain

I'm going to talk about starting a levain. Some people call it sourdough, some people call it a sourdough starter. There's many different names for it. But we decided to stay with ‘levain’ because it was a little bit clearer, simply because when you just say ‘sourdough’ it could imply that you're talking about the bread or you're talking about the starter. So we decided to keep the French term for a wild yeast bread starter.

Recipe

This recipe is available as a PDF. A basic process for starting a levain is to just combine water and flour. In your flour, you're going to have a lot of what is needed for the levain to get going, which is the wild yeast. But you also have the lactic acid bacteria in the wheat flour that is going to be doing all of the fermentation work.

Timing

You're going to need a few days once you mix your water and flour to get the whole process going. But around the end of the first week or by the middle of the second week, you'll be able to start making bread with it. One of the biggest things, once you have it, is to actually maintain it and keep it going.

Once your levain, your sourdough starter, has already become active it goes through a cycle of fermentation, and that fermentation really depends on what temperature you keep it at and what time it's going to get fed. It's a very interesting culture because yeast is one of the organisms that is most adaptable on our planet. And it learns; if it's fed every 24 hours, it pretty much learns to adapt to that. So it goes through its feeding cycle, and it knows when it's going to be slowing down because it knows that more food is coming. So it's a very interesting culture that you create when you start a sourdough starter.

The pH levels will drop and become more acidic as time goes by. It really depends on how acidic you want your bread to be. That's what determines when you're going to start using your sourdough starter. It also depends on what temperature you leave it at. Certain lactic acid bacteria prefer to be in warmer temperatures, and there's certain lactic acid bacteria that prefer to be in colder temperatures. What temperature you're going to leave it at really depends on what flavor outcome you want. You're in control of the lifespan of your levain.

Lactic acid bacteria

I mentioned lactic acid bacteria, or LAB, and I also mentioned yeast in the same sentence. That is because it's very important to understand—and I really want to make sure that everybody is going to get this as a big takeaway from my talk—that if we're talking about a levain or wild yeast starter, a lot of people really focus on the yeast part. And while that is important, I would almost say that the lactic acid bacteria in this levain is more important.

The reason for that is because lactic acid bacteria microorganisms outnumber yeast about 100 to one. So if we're talking about numbers, the number of lactic acid bacteria in the sourdough starter is much more important than the amount of yeast. The yeast strains, the cells that you're going to get in your starter, are going to be pretty much the same. Saccharomyces cerevisiae is about 80% of the yeast that is in a starter. The other 20% can be a mix of different strains of yeast, but the dominant strain in most sourdough starters is going to be Saccharomyces cerevisiae.

Lactic acid bacteria are what give your levain its own character and personality. And why is that? It's because the mix of the different strains of lactic acid bacteria is different in every environment that it's kept in. So it'll vary from one home to another. If you share your levain with your neighbor next door, eventually that starter's going to take on its own characteristics, its own flavor profile, because the lactic acid bacteria mix is going to change once it moves from one place to the other, even as close by as your neighbor next door.

That's why we have such appreciation for our own sourdough starters and we may have such appreciation for a bakery we've been going to because the taste of it is just so unique, and it cannot be replicated anywhere else. That's one of the most important things that we need to take away from understanding our sourdough starter.

Stages: Young, Ripe & Mature Levain

There are three very distinct stages of our levain through this fermentation curve.

1. First is what we would call a young levain, meaning it's been mixed. It's been a few hours and you're going to start to see some activity. In the actual tub, you might see some bubbles that are starting to form as well, so there is some activity happening here.

2. In the middle is what we would call a ripe levain. That's when I like to use it, although some bakers like to use it when it's young. I like to use it when it's ripe because I do like some of that acidity, that personality of acidity in my sourdough bread. But some bakers prefer to have it a little bit less sour, and so they use it when it's in its younger stages, in the first hours after it's been fed. And that's totally fine, too. It's a matter of personal preference.

3. Finally, we're going to have what is called a mature levain, which is still active. There's still going to be some fermentation activity. It's already reached its peak. After that, it's going to start going downhill and it won't have as much fermenting strength once it reaches that point.

At this third point is when we're not using it anymore. We're going to perhaps feed it. It's not at a point where I would actually use it to make a dough.

Through the passage of time it will increase in volume, just from fermenting in the tub. You’ll be able to see what stage it’s at by how it grows in the tub, but you can also judge by what it looks like on top. In a young levain we might see some CO₂ bubbles forming within it. But then we start to see, as it gets more and more mature, how that CO₂ production becomes a lot more intense, and we have a lot more bubble formation. That is, in part, what is responsible for all of the crumb and the air pockets that you're going to see inside your baked loaf of bread, that in combination with production of steam and the expansion of the bubbles during the baking process.

If you don't have a clear container, you can also see from the top what sort of stage your levain is on. When I take a look inside it and I can see when it iswhat I consider to be an ideal pH for the actual starter for when I want to mix it into the rest of the ingredients to make a dough. So I've learned to not always have to use a pH meter, because when I look at it and it looks like this, I know that it's ready to be used.

If you do have a pH meter, at this point I would say it's between 4.1 and 4.4 pH. To me, it's at its peak of fermentation. It's when it's going to make a really nice bread. Once you do it enough, you can go by what it looks like. You might even be able to set your watch to it because it's so adaptable that it goes through its fermentation curve on a pretty consistent basis if you feed it more or less at the same time every day and if you keep it more or less at the same temperature.

Consistency

That is something that I want to emphasize: in order to maintain a levain that is going to be consistent for you, that is going to be reliable, what I would really recommend is feeding it at more or less the same time every day. You don't necessarily need to set your alarm. If you feed it more or less between 22 and 24 hours after its last feeding, it's going to go through a very predictable fermentation curve.

Temperature

Additionally, I would say keep it more or less at the same temperature if you can, because drastic temperature changes are going to change the lactic acid bacteria mix. Some bacteria prefer warmer temperatures; some bacteria prefer colder temperatures. The dominant temperature is what's going to establish what that lactic acid bacteria mix is going to be.

And just in general terms, the warmer you keep your sourdough starter, the less acetic acid the lactic acid is bacteria is going to produce. If I keep my sourdough starter at 70 degrees Fahrenheit, the bacteria that is going to dominate produces a flavor that is acidic, but it's more like a yogurt acidity. So it's a very mellow acidity.

The colder I keep my levain, the more vinegar acidic flavors it's going to produce. So it's a matter of personal preference what mix you want. I like somewhere in between. And that's why I keep mine at 55 degrees Fahrenheit, which is 13 degrees Celsius.

You might be wondering, well, how do you keep it right at that temperature? One of the things that we discovered that works great for keeping a levain is a wine refrigerator. There's many different shapes and sizes, but we were testing this in a very small wine cooler, which holds about 10 bottles of wine. It also holds our tub of sourdough starter or levain perfectly, and we can keep it at exactly the same temperature regardless of what the temperature outside of it is. So it's a really good piece of equipment to have if you want to have a sourdough starter that's going to be consistently reliable—is to keep it in that sort of environment. That would be one of my suggestions for maintaining your sourdough starter.

Gauging readiness

So how do you know when your sourdough starter is ready? Earlier, I said it goes through a fermentation curve, meaning it goes through a process of starting the fermentation, and it starts to expand, and you can see it actually expanding in whatever tub you keep it in. You may not have a pH meter. And I can't blame you because it's not a very common piece of equipment and good pH meters can be slightly costly.

Float test

One surefire way to know if your sourdough starter is ready for making bread is to do what is called the float test. The way we suggest doing it—and this is something that has existed for as long as people have been making bread—is this particular test. It consists of taking some of your levain and just putting it in a cup with water. If it floats, it means that there's still bubbles inside of it. And those bubbles are the CO₂—the results of the fermentation of the yeast that are going to keep the sourdough starter afloat.

Once a sourdough starter starts to decay and reach the end of its active lifespan, those bubbles are going to start to pop, and it's going to make it so that it doesn't float. It'll start to sink. So when you have something that is alive and active, it's going to be floating to the top of the water. If it's starting to age out, it's going to start to sink to the bottom.

And this is why I suggest, whenever you're making a sourdough bread, that you measure out your water into whatever you're mixing it in, and the second ingredient to go in should be your starter. And that is so that you do two things. You kill two birds with one stone.

1. You make sure that your sourdough starter's actually active and it's ready to go.

2. You're not having to measure it into different bowls or different containers where you can lose a little bit every time you scrape it out. It's a very practical thing to do, to try and measure everything out into the same container that it's going to be mixed in. It's just practical.

Some levains take a little bit longer to float. For example, if you have something that is pretty dense—like if it's a rye levain—it tends to take it a minute to reach to float to the top, but eventually it does. This float test also works if you're doing gluten-free starters, for gluten-free bread.

Additives: raisins and beyond

There are many different ways that people have used through time to basically inject life into their levains. One of those is culturing water with raisins. On their surface, raisins have yeast. So when we mix raisins with water, what we're doing is we're inoculating that water with all of that yeast that is on the surface of the raisins. That takes about three to four days to happen, and then we'll take that water and use that to get our sourdough started.

So we thought, “Well, let's see what happens if we take those raisins and that water—and then, after inoculating them, what if we pressure cook them?” Why would we pressure cook them? Well, anything that you put in a pressure cooker that is alive is not going to come out alive after pressure cooking, because it reaches a very high temperature and deprives it of oxygen. Pressure cooking brings the liquid within the pressure cooker to about 240° F, which is about 112° C.

It also creates an environment that's essentially a vacuum. That's why it's used for preserving. If you're going to make marmalades, sometimes they're canned this way, in pressure cookers. It's basically to kill anything off that might be harmful to us.

So after pressure cooking the inoculated raisin water we mixed it with flour, and it created a very active sourdough starter. So what is happening here if the yeast is dead? By having cooked the raisin water like this, we made more simple sugars available to the yeast that was already in the flour. It had nothing to do with the yeast that was in the raisins. It had more to do with making simple sugars more readily available to the yeast that is already in the flour.

I would recommend just flour and water as your best course of action, just in general. Why is this? Because what we're doing with the raisin water is creating something that's called a false positive. It works the one time but it doesn't mean that it's going to continue to work in the same way after that, unless you continue to give it raisin water, whether it's inoculated or not.

This could be a very expensive way of maintaining a sourdough starter. If we're adding raisin water every day to it, it's possible you can do it, but you're going to be going through a lot of raisins to do that. If you do the simplest way, which is just combining water and flour, all you have to do is be patient and let time do all the work that it has to do. It's the tale of the tortoise and the hare. Flour and water is something that's going to take a little bit longer, but in the end, we're acclimating the yeast that is in the flour to just require water for it to go through its fermentation cycle.

We've heard of people that add yogurt to the sourdough starter. And that's making a connection that isn't 100% accurate, which is that yogurt has lactic acid bacteria. But the thing is, the lactic acid bacteria in yogurt is not the same as the lactic acid bacteria that you find in flour. There are many different kinds of lactic acid bacteria, and the kind that you find in yogurt is not necessarily going to work on flour. So keep it simple. Water and flour is really all you need to get your sourdough starter going.

For me, personally, a sourdough starter going to full fermentation within six hours is too fast. It's too much, and it's not going to give us the complexity of flavors that we're looking for in a sourdough starter. There is such a thing as going too fast. It's almost as fast as if you were using straight-up commercial yeast.

There's nothing wrong with using commercial yeast. In fact, it's the same strains as you find in your sourdough starter. It's just a more purified form of that yeast. But what it allows you to do is make breads a lot faster. Those breads that are a lot faster, as you may know, have a completely different set of characteristics than a fully sourdough bread does. So it's a matter of personal preference. I prefer to have a sourdough starter that's going to have a longer fermentation curve time and produce more complexity of flavor and aroma in my bread, if I'm looking for a sourdough type of bread.

Water

That brings us to the water. This is one of the things that we really wanted to test out—does the type of water really matter?

We have sourdough starters that were all fed with different types of water. Hard water has a high mineral content. Filtered water is basically just water that you would drink straight-up. Tap water is water from your sink. Distilled water is water that has been completely purified. It contains no minerals at all. So it's just water. That's all there is in it. And then chlorinated water, which is water with a little bit of chlorine. Actually, what we did is we replicated the amount of chlorine that is typically used in pools, I think it's four parts per million, or 0.4 per million. We didn't go into somebody's pool and get water from their pool, we replicated what that mix of water and chlorine is.

In all four of these, the yeast couldn't care less what type of water was part of the mix. Now, this is important because there are a lot of attributes that are sometimes given to water that are not completely accurate. Now, there is such a thing as too hard of a water, water that has too many minerals. And this creates a hostile environment for many types of microorganisms. So we wouldn't recommend that.

The quickest gauge for whether your water is good enough for bread or not is, ask yourself this. Would you drink that water? If that water is clear and it doesn't have any aroma and it's not slimy, it's water you would drink. That water is perfectly good to use for your bread and for your sourdough, for your levain, without any problems whatsoever.

I say this because we did a lot of experiments with water, particularly for bagels, mostly because we all hear that the only good bagels are bagels in New York City. That is a problematic assessment for many reasons. And very importantly because it's not true, because New York City doesn't have a single source of water. New York City gets its water from five different sources, and all those five different sources have very different types of water.

I've also had plenty of bad bagels in New York City, so how do you explain that? If they had the water, why did these bagels not turn out so good? So there's some mythology to that and some, I guess, stubbornness attached to it. You can make a perfectly good bagel anywhere in the planet as long as you have drinkable water and a good recipe. And we just happen to have a really fantastic recipe in our book. So do not be discouraged about making bagels wherever you might find yourself. You can make a perfectly good bagel anywhere.

Waking up your levain

You might find that your levain is sluggish. You might find that maybe it's not as active as you'd like it to be. There are a few things that you could do to it to kind of wake it up. It turns out that a little bit of chickpea flour or a little bit of rye flour or even whole wheat flour is fantastic. It's like giving it a vitamin B shot, if your starter is sluggish. I would suggest substituting 2%, 3%, 4%, or 5% maximum of that different kind of flour.

Of course, you might have a whole wheat flour starter, which is 100% whole wheat, and that's fine. You probably won't have any problems if with it becoming sluggish if you're doing a whole wheat starter. But if it's a white flour, like a bread flour starter, and it's sluggish, adding chickpea flour or rice flour or whole wheat flour really, really wakes it up. And why is this? Because there are substrates or nutrients in these types of flours that yeast loves. You could do it every day, or you could do it for just a few days while your sourdough starter starts to wake up. But it's a great way to basically get it back to life, just with a little bit of these flours.

So you might ask yourself, “OK, so I don't make bread every day. Do I have to feed my sourdough starter every day?” The short answer is no, not every day. But don't leave it in your fridge for weeks and weeks and hope that it's going to be fine two or three months later. You try to wake it up, and it takes it three, four or five days to come back to life—in reality, what you're doing is actually starting a brand new starter. Whatever was left in that jar is not really alive anymore. Yeast is a living thing, and if we deprive it of food it's going to die.

There is a state of dormancy, sort of. But for the most part, when we try to wake it up with new flour, essentially what we're doing is we're starting a new starter. So I would recommend that, if you're not making bread every day, there's different things that you could do with whatever you're discarding.

Preserving levain

Just to put it in context, if you feed 1 cup of levain for one year, you're basically utilizing 50 pounds of flour. That's a lot of flour. So it's good to make sure that you're actually going to be making some bread with it. And if you made 1 kilo of sourdough starter a year, you essentially would need 200 pounds, or 100 kilos, of flour just for feeding. So it definitely can go through a lot of flour.

I would say that it's not a good idea to throw out the extra, mostly because it's very wasteful. There's a few things you can do, a lot of people have solutions for it. Some people use it to make cookies. Some people use it to make pancakes or waffles. I don't know if I would make waffles with my sourdough starter, simply because it has too strong of a flavor and I don't care for waffles that are going to be tough. I prefer to have them be softer.

Dehydration

What I would do is I would try to find a way to preserve it, and dehydration is a very easy way to to that. What we do is we take it; we spread it very thin on a mat; and then we put it in a dehydrator at a very low temperature. If you do too high of a temperature, you're going to have increased yeast activity. It's basically going to go through its fermentation curve and die. What we're trying to do is just remove the water.

So this might take a little bit of time, but we're removing the water and keeping the dry matter. There's going to be still a lot of yeast cells that could become active once we bring it back to life. After we put it in a dehydrator it becomes brittle and cracker-like. We then grind it in a spice grinder and we keep it like that in refrigeration.

When we're ready to use it again, we mix it with water, and within a day or two we're going to see that it has come back to life. I would suggest doing this over keeping that jar in your fridge for months, because this way instead of having to wait three, four, or five days for the sourdough starter to come back to life, you only have to wait a day or two. It's almost like having an instant yeast, but it's a sourdough starter that will hold very well as long as it's kept pulverized in your refrigerator.

Freezing

Another thing that you can do is freeze it. We weigh out how much we're putting into the bag to freeze, and then we let it freeze flat, because flat things will freeze a lot better and occupy less space in your freezer. Another way to freeze it is in an ice cube tray, and this way you can basically pull out what you need for whatever amount of bread that you're going to make.

A sourdough starter is probably going to stay in a freezer and still be active for a couple of weeks. Yeast, like any living thing, doesn't like freezing temperatures. After a couple of weeks, it's not going to be very active anymore. But within those two weeks, you can easily freeze it, thaw it, and use it to make bread. It's another way of not wasting a sourdough starter.

Second-chance sourdough

The other option is to do what we call second-chance sourdough. Instead of throwing that old starter away, think about this: that starter has two very good things going for it.

1. It already has the flavor from having gone through the fermentation.

2. It already has hydrated flour.

Why is hydrated flour important? Because it's going to reduce your mixing time once you mix it into a dough. Hydrated flour will already have some gluten development happening, just by the passage of time. So it reduces mixing time and it also has a lot of flavor.

The problem is that your old sourdough starter is not going to have much active yeast anymore. So what we do is we utilize it just like we would a sourdough starter, but we're going to add a little bit of commercial yeast to our dough. And that commercial yeast is standing in for the yeast that used to be in our sourdough starter. We're getting all the flavor, all the aroma, and all the complexity of our sourdough starter without the quandary of having wasted it. It's going to be put to use. All we have to do is add a little bit of commercial yeast to it, and it comes back to life.

The other piece of good news is that if this is old sourdough starter, you can also save it in Ziploc bags in your freezer, use it as you need it. We just mix in 0.5% of the weight of the flour in commercial yeast, and it gives us a bread that has the same aroma and complexity of the sourdough bread has. And we're reducing our amount of waste.

Naming your levain

One thing that we learned here while we were doing research for this book and how to get people to care for their sourdough starters was to actually name your levain. It's a little bit of a quirky thing, but it helps to think of your levain as a pet. I have four pets in my house, and I know that they all know when it's dinner time. Your levain is not that different. You have to make sure that you feed your pets so that they stay healthy and alive and nourished, and your levain is very similar.

So we came up with naming your levain. Everybody here who works at the lab that had their own levain—they actually gave names to theirs. Mine is Levain James. He's still going strong almost seven years later. And we have Sir Yeast-a-Lot, Ryan SeaCrust, and Clint Yeastwood. Who could forget Clint Yeastwood?

It's cutesy, but if you give something a name, it's almost like you're giving it some sort of personality, and I feel like it's a great way to keep up your levain and make sure that you're feeding it and taking care of it.

Other resources

If you want to dig more into the world of bread that we've created, there's a fantastic podcast called Modernist BreadCrumbs. It's 16 episodes long. It's really good. There's a bunch of different people that are talking about bread in this podcast, not just us. I highly recommend it. If you like our photography, we have various galleries across the United States where our photography is displayed. There's one in Las Vegas, New Orleans, Seattle, and La Jolla, California, and also online.

We have our upcoming project, our three-volume book on pizza, which we're getting close to wrapping up. It’s also very connected to the world of bread, so look out for that next year at some point. I mean, who doesn't like pizza? I'm sure somebody out there doesn't, but very few people. So that's the next project, and that's what we'll be looking at in the future.