Capture wild microbes
and turn them into bread – for science!
To make your own sourdough starter, all you need is flour, water, and a little bit of time. Whether you are here because your favorite bakery is currently closed and you need your bread fix, or because you are eager to help make even the smallest progress in our understanding of the microbial world, we are glad you are here! Regardless, we hope you will follow-along, make your own sourdough starter captured from wild microbes, and share your experience.
The microbial world is still full of mysteries. Some of the answers might be lurking in your kitchen. We know more about the deep sea than we do about some of the bacteria and fungi that are most important to us, partially because they can be so difficult to study. The microbial communities in sourdough are comparatively easy to grow and study, so understanding sourdough can help us untangle some of the mysteries of the microbial world.
The Mystery
Humans have been baking bread for at least ten thousand years. If you mix flour and water, the community of organisms that colonize the resulting concoction is almost always composed of a small handful of organisms that are able to leaven bread, yielding a sourdough starter. Yet, how this happens is one of civilization’s great mysteries, a mystery at the heart of bread making (and, for that matter, traditional beer brewing). While bakers generally understand how to make starters, the underlying biology of the species in these starters remains mysterious. A couple of years ago we launched the Global Sourdough Project and studied hundreds of existing starters from all over the world. While we learned a lot from these starters, there were still lingering questions that we couldn’t decipher from the data: How does the type of flour you use and where you live affect the success or failure of a wild sourdough starter? Together we can reveal how these communities form over time and understand how factors such as flour type or geography impact these communities.
Wickerhamomyces yeast colonies grown in the lab from a wild sourdough starter (left) and a close up of the individual cells under a microscope (right). Images by Elizabeth Landis.
What you’ll do
We will guide you through creating a “wild” sourdough starter using only water and flour following a ten-day protocol. If you are curious (and a little ambitious), we are hoping to recruit some folks who want to make more than one starter using different flour types or using the same flour type but setting one outside and one inside your home.
Once you have made your starter we will ask you to observe it and record some observations about its aroma and how fast it rises. You will submit these data through a short online questionnaire.
We are going to let you—folks reading this—take the lead. If there is enough interest, we will likely create a new iteration in which we move on to asking questions about the bread making process itself!
How your data will be used
Your data will be compared with other folks’ from all over the world who have concurrently created wild starters. Together we can use these data to learn how geography and different flours affect microbial growth over time, and how those microbes affect the taste and texture of bread. If your starter fails—we hope it doesn’t, but sometimes microbes aren’t cooperative—we still want your data!! We can learn as much from the failures as we can from the successes. Perhaps there is something about geography and a specific flour type that are not compatible for making a starter.
Additional resources for teachers!
We have created several additional lesson modules that work well in combination with this activity. For example, “Which Variables Matter?” challenges students to consider what influences the growth of a sourdough starter, and to differentiate between independent and dependent variables. The “Graphing Student Data” activity allows students to explore the data they have collected, and in the “Who’s My ‘crobe?” activity, students learn about the most common bacteria and yeasts that live in sourdough starters. These and more activities can be found in the comprehensive Sourdough for Science packet.
Variations on the Basic Experiment
Indoor/Outdoor Experiment
While some of the microbes that colonize a sourdough starter might come from the flour or the water or even your own hands, it’s possible that some of the microbes are drifting in from the surrounding environment. From our work on microbes in houses we know that the microbes that are inside your house or school are likely different from those outside. We would love to recruit some folks who are willing to make sibling starters, one outside and one inside their home. “Outside” could be your front porch, on a planter box, or fire escape. The important part is to keep all other variables (e.g., the flour, the feeding schedule, the water) the same for the indoor and outdoor starter.
The Power of Flour
Some of our preliminary work suggests that whole grain flours may contribute different microbes (i.e., more fungi) compared to all-purpose flour. But how do differences in flour microbes impact the starter community? You can test this by concurrently making starters using different kinds of flour so that you can compare how the characteristics of the starter (height and smell) differ between flour types.
Characterize your starter!
Once you have refreshed/fed your starter at least fourteen times, you should have your very own wild sourdough starter(s)! Or, perhaps you won’t. We actually have very little data about how often sourdough starters fail. So regardless of whether you were successful or plan to throw this one out and try again (or give up on wild sourdough altogether) please help us by characterizing your starter (or failed starter) and submitting your data.
For some of you, you will finish refreshing/feeding your starter for the fourteenth time after fourteen days (one feeding every 24 hours). For those of you with particularly hungry starters that shifted to a twice-a-day feeding cycle, you will get to your fourteenth feeding sooner. Either way is OK! Just characterize your starter whenever you have refreshed/fed your starter fourteen times and are about to feed it for the fifteenth time.
Characterize rise time and height
We want to know how long it takes for your starter to reach its maximum rise, and the extent (i.e,. height) of this rise.
- When it is time to refresh your starter for the fifteenth time, rather than discarding a tablespoon of the starter as you usually do, transfer 2 Tbsp of your starter to a new jar. Depending on how much starter you have, this may be all of it. That is ok, you will still have it at the end. We just want to make sure that everyone is starting with the same amount.
- Add 3 Tbsp flour and 2 Tbsp water and mix thoroughly, scraping down the sides. The starter will be a little thicker than usual.
- Before setting it aside, draw a line with a sharpie on the jar to indicate the height of the starter.
- Using a ruler, measure the height of the starter from the base of the jar. This is your “Baseline” height.
- Every few hours, check on your starter and indicate the height with a new mark. Ideally, this would be every 3 hours. If you set it up in the evening, it is OK to leave it overnight. Just check on it first thing in the morning.
- Keep checking on your starter every few hours until it is no longer growing in size.
- Measure the height of the highest mark from the base of the jar. This is your “High Tide” mark.
Characterize aroma
After you measure its height, remove the paper towel lid and give your starter a good sniff. What does your sourdough starter smell like? Use the Sourdough Aroma Wheel to the right for reference.
Take two photos of your starter
- Photo #1: Take a photo of the side view of the starter in its jar against a solid background.
- Photo #2: Take a second photo from an aerial view, looking into the jar.
Who we are
We are a diverse group of scientists broadly interested in understanding the microbial science of sourdough. We have worked together, and with others, on sourdough microbial research for over four years. Visit our broader sourdough project page to learn about our other sourdough science projects and for a more complete list of collaborators and partners.
Erin McKenney, Ph.D. – a microbial ecologist, lecturer, and academic coordinator for the department of Applied Ecology at North Carolina State University.
Anne A. Madden, Ph.D. – a microbiologist, research affiliate in the Applied Ecology department of North Carolina State University, and Founder and President of The Microbe Institute.
Lauren Nichols – a research affiliate in the Applied Ecology department of North Carolina State University, data scientist, and manager of the Wild Sourdough Project.
Rob Dunn, Ph.D. – an ecology and evolutionary biologist, author, and professor in the Applied Ecology department of North Carolina State University.
