Editors note: This publication contains a lightly edited transcript of the question and answer portion of the corresponding lecture.

Header image: Bread pyramid by McClay Manufacturing Company (public domain).

Q + A :

Question: With the Quest for Sourdough website, folks can enter their information. You then use that information to potentially find candidates to move into your fridge. What is that process? What does it take to make it into the Sourdough Library?

Karl: Yes, that's a good question. There is one basic rule: to become a candidate to enter in the library, the starter has to be made from a spontaneous fermentation, meaning that it cannot contain any commercial starter culture that is used. Because we know what is in these commercial starter cultures, and these do not contribute to the biodiversity of sourdough.

Besides that we have a list of parameters that we check. For example, what kind of flour is used? Where does the sourdough come from? Is there a story linked to the sourdough? How old is the sourdough? These parameters are not hierarchical. We use them in order to evaluate each and every sourdough.

I'll give an example. So we have a total of 39 starters from Italy. If tomorrow an Italian baker contacts us and says, “Whoa, I have this amazing sourdough and I would like to have it in the Sourdough Library,” we will ask what kind of flour is used. If he's using wheat flour, the chances to get another Italian wheat sourdough in the collection are small because we have already 39. If that baker uses a whole wheat or a rye, his chances increase.

If tomorrow, someone from Panama tells me that he or she has a starter based on wheat flour, well, the chances are higher to get into the library than if it's coming from a country where we already have a collection. So the more sourdoughs we have from one region, the pickier we become.

Question: How you can tell if these starters are mature? I'm sure that it falls into the categories you were just talking about.

Karl: Well, we have this unwritten rule, actually, that a starter should be at least five years old before entering in the library. And we also want a minimum guarantee that it's not a starter that has been created like, last year or, still, during COVID, many starters have been created by people who suddenly have time to discover sourdough, but who probably will not continue once everything is getting—I'm not going to say back to normal—but when the situation becomes more like it was before. So we are looking for these starters that we know will be there for the coming 10, 20, 50 years.

Question: Have you ever taken starters out and baked with them to compare flavor?

Karl: Yes. To be honest, I haven't done it with all of them. I picked 133 starters, that if you want to bake with that? Feh. It's already a huge task when we feed these 130. In the past, when we had 120, we were feeding them all at the same time, and that was four days of feeding three times, because every starter is fed three times before we put it back in the fridge. So that's a lot of work. And I guarantee you that when you finish mixing the last one, the only thing you want to do is to go home, to relax, and to think about something other than baking.

But sometimes I took a couple of buckets home and I baked with it. We have also done some comparative trials with sourdoughs. When we look at the analysis and say, oh, this one has a different yeast. This one is nice with the consortium of lactic acid bacteria. We did some baking trials and yes, we've seen differences. Sometimes you see big differences. You can place them in different flavor groups: some are fruity, some are cereals, some are acidic, some are electric. Some are fermented. So yes, we do it, but not on a regular basis, and not in a consistent way.

Question: Do you find that there's a relationship with some starters as being better used with rye, or other grains, or et cetera? Quite a few people are asking about rye, actually. If you have any thoughts about rye, go nuts.

Karl: Well, to be honest, no. I am allergic to rye flour. In the beginning of 2019, they had to call an ambulance here. They had to drive me to the hospital because I was giving a workshop and some of my colleagues—who had no idea I was allergic to rye—I was teaching them how to work with sourdough. And in the evening when we had to shape the breads, some people started to use a lot of dusting flour—to dust like, through a sieve. With rye, rye is very volatile. And yeah, I got an asthma attack. I thought I was going to die that night. But everything worked out alright.

So I'm avoiding rye a little bit, but it's interesting to see. Rye bread is a completely different world than the wheat breads. When you make rye bread, the rules that you use when you make wheat bread are not valid at all. You don’t have to develop a gluten network because you can’t—there are not enough proteins, and not the right proteins, to make that gluten network that makes kind of this balloon in the bread that retains the gas which make your bread rise nicely.

With rye, you don't have that, so you don't have to mix for a long time. You don't have to do long build fermentations. The only thing you need to make sure is that you have enough acidity in rye bread. If someone has already experimented with rye bread, you probably know that one of the biggest issues is that the rye bread tends to stick together after you cut it. And that is for the simple reason that the dough was not acidified enough.

That's why the Germans have studied sourdough for so many years in order to acidify their sourdough as much as possible so that they can use as little as possible in their production, and still be sure that the bread is getting baked properly.

When it comes to rye sourdough, there are all these little tips and tricks. When you have the starter, you don't need to feed it constantly with the same flour. It's like us. If you had to eat spaghetti and meatballs every day, I think that after five days you will be fed up and you want something else. These microorganisms, I don't think they think that—they do not think—but they react the same. When you see that a starter is losing fermentation power, that it's not behaving the way it was, you can feed it with a different kind of flour from time to time. And rye flour is something that revives and increases the fermentation power of a starter tremendously in the short term. I'm not saying in the long term because the same thing will happen when you keep on feeding it only rye flour.

That's the thing with sourdoughs: making a sourdough is easy, but maintaining one in a stable way is very complex, because you have all these microorganisms. They behave differently depending on the temperature. They produce lactic acid, they produce acetic acid, they fight with the yeasts. So it's always very complex to control that, and rye is a completely different ballgame that needs different rules.

Question: Well speaking about different rules and really complex starters, can you tell us more about the starter you mentioned that was started with manure?

Karl: There is not one—it's not written in stone. There is no transmission of why and how people did it, but there is a tradition in Italy where they use—you call it manure. I said cow shit. I'm not a native English speaker, so I use what I learned from Bruce Willis.

So yes, they use it. They collect dried manure after the winter that they soak in water. It's filtered so there is no shit actually going in the mix with the flour. It's very well filtered. So they use the water, which is full of bacteria.

Now I have a theory. I don't know if it is correct, but it is my theory. If we look in nature, there's only two animals that can digest grains: cows and goats. So it could be that our ancestors noticed that, and that they started using their manure.

Because they said, well, if they can eat grains they might have-—I don't know if they were aware of microorganisms, but we have those microorganisms in our intestine as well. It is lactic acid bacteria that take care of the digestion. The only thing is that when you eat a grain, the amount of time it is in our body is too short to be digested.

So in sourdough you start that digestion early, and that could be one of the reasons. So that water coming from the manure, the dried manure, is used to make sourdough. Now when you make sourdough you mix the flour and water, the lactic acid bacteria, they start to turn the sugars into lactic acid and acetic acid, and those acids are lowering the pH. And we know that Mother Nature has decided that when the pH gets below 4.2 that all pathogens are probably killed. That's the beauty of fermentation.

Once you have that low pH, well, it doesn't matter if you used—well the Italians use cow manure, the French use honey, or a grated apple, or fermented raisins. The Greeks use basil leaves. The Japanese use rice. So there's so many ways to make sourdough. And no two sourdoughs that we have here in the library have the same composition. They are all unique. A bit like humans.

The type of flour, where they come from, the weather, the climate, the soil where the grain was coming from, all that has an influence on the final result of that sourdough. And, depending on how the sourdough is dealt with, it can still change.

A bit like us, OK? We are humans. But if you are well-fed and if you are OK, you are happy. If you are hungry and you live in an area where it's too cold, you are going to get unhappy and you will be completely different. It’s the same thing with the sourdough. A shift in environment can have all these different effects on the variables that all come together to make this thing. It's incredible.