The Current

Growing a sourdough starter? This microbiology researcher wants to know about it

With more and more people cooped up in their homes baking bread, the Wild Sourdough Project is crowdsourcing an experiment in hopes of learning more about the science behind the 'microbial gardens' in their kitchens.

'We'd love to get everyone's help by growing starters all from scratch,' says Erin McKenney

Erin McKenney is an associate professor of ecology at North Carolina State University. She's part of the Wild Sourdough Project, an experiment gathering data about how geopgraphy affects sourdough starters. (Submitted by Erin McKenney)
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Microbial researcher Erin McKenney wants you to grow a sourdough starter — for science.

With more and more people cooped up in their homes baking bread, the North Carolina State University ecology professor is crowdsourcing an experiment in the hope of learning more about the science behind the "microbial gardens" in their kitchens.

The Wild Sourdough Project is an online community where both novice and professional bakers can share data about their sourdough starters.

Starters are made from a mixture of flour and water left at room temperature so bacteria can grow, and they give the bread its signature tangy flavour.

Researchers are gathering data about how the yeasty concoctions vary around the world, and what effects geography has on the rise and flavour of a freshly baked loaf.

Here's part of McKenney's conversation with The Current's Matt Galloway.

Humans have been making bread for a long, long time. But … there's still a lot that we don't know about the science behind it. Why is that the case? 

There are a lot of discussions we could have about power dynamics in science — of what gets studied and funded and why. But I think for us, [the recent rise in interest] mostly just made this [experiment] a tremendous potential of low-hanging fruit.

This microbial phenomenon, these microbial gardens are grown in jars across the world and they're relatively simple microbial ecosystems.

So whereas in a pinch of soil, you get thousands, or tens of thousands, of different types of microbes — and you have all these different contributing factors that can affect the content and the behaviour of those communities — the sour dough starter microbiome is very simple and has very simple inputs … it's flour and water. 

So we have this great opportunity to engage the public in the creation of a microbial masterpiece that's unique to you in all the world. 

With physical distancing measures keeping people at home, bakers — both seasoned and novice — are trying their hands at baking sourdough bread. (Julie Van Rosendaal)

There are people who I mean, they've heard of their neighbours and friends creating a sourdough starter while they're locked in their homes, and they may have no idea what it is. Just very briefly, why is the starter so important in the making of sourdough bread? 

So flour and water on its own is a glorified papier-mâché paste, right? If you try to bake bread with that, you'll come out with a rock cake. 

Not particularly appetizing. 

It always reminds me of Hagrid from Harry Potter, right? So when, over time, as you allow and enable the colonization of that flour and water paste with bacteria and with yeasts, the bacteria produce acids and the acids contribute that sour tang that we tend to characterize sour dough bread — that unique flavour. 

But the acid also prevents moulds and potential pathogens from growing in that community. So these bacteria are little ecosystem engineers and they actually favour the growth of very specific yeasts that are acid tolerant. 

And those yeasts are what churn out the carbon dioxide that makes the bread actually rise, and also a lot of other volatile gases that actually have flavour and smell that contribute those lovely aromas to bread that actually make us salivate because our body recognizes it as food. 

And the starters are unique. I mean, my starter is different than your starter. Even if we lived in the same city, we would have different starters, right? 

Absolutely, and that's due in part what we know from previous projects but haven't really been able to get a good handle on is that yeast tend to vary depending on where you live.

But bacteria tends to follow rules, not depending on geography so much as depending on your home. So what flour are you using? What microbes are growing on your body? 

And so what's the question ... that you want to answer with this wild sourdough project? 

So we're focusing on function and not so much on which specific microbes are growing there, because you don't all have sequencing labs in your kitchens. Completely understandable. 

But you do have rulers, right? You do have a jar and you have a sense of how high things are rising over time. So we'd love to get everyone's help by growing starters all from scratch. They're all going to be babies. They'll all be the same age. 

By being housebound at this point in our lives, we are taking the migration out of the question. So they'll all be new starters and they'll all be staying in your homes. 

So now we can ask very specific questions about how does the grain type and how does where you live in the world geography affected the leavening or the rise, and how much do those same factors influence aroma? 

Once we see some extremes … we can start to ask what creates those really unusual starters with really unusual aromas or leavening properties. 

The Wild Sourdough Project is asking participants to grow a new starter from scratch so researchers can measure the effect geography has on the ingredient's microbiome. (Josee St-Onge/CBC)

Sourdough is a pretty intimidating thing. And people will look at recipes from bakeries and it's a 37-page recipe and they'll think, 'Oh, my goodness, I couldn't possibly do this.' What sort of support are you offering people who are entering into the world of sourdough baking? 

I would offer solidarity. I'm a microbial ecologist. I've been studying the tiny bugs in fancy labs for over a decade, and it was intimidating and humbling to me, too, to enter the world of fermented foods. 

The reason that those recipes become 37 pages long is that there is so much variation. Each sourdough is unique and behave differently in different conditions. 

Instead of feeling like there's no single right way or there's no direction, think of it as as artistic licence to really learn the specific nature of your particular microbial garden and how it behaves in your home and your hands. 


Written by Jason Vermes. Produced by Richard Raycraft.

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