Wild Sourdough Project

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.

About the experiment

Video introduction

How to make a starter

Variations on the basic experiment

Characterize your starter

Basic sourdough recipe

Who we are

FAQs

Resources for educators

Our other sourdough projects

Follow along on Instagram!

Follow along on Facebook!

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 anomalus

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!

Sourdough starter

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.

Slice of sourdough

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.

Get the teacher’s guide!

How to make a wild sourdough starter

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Ingredients:

  • Flour (Any type you like! Rye, whole wheat, all-purpose, etc.)
  • Dechlorinated water (filtered water or tap water that has been left in a clear glass overnight)
All you need is tap water that has been left out for at least 8 hours. Is there, perhaps, a half-finished glass of water from yesterday laying about? Perhaps next to your bed? All you need are two tablespoons. If not, no problem. Just remember to leave a glass of tap water out on purpose for tomorrow!

Materials:

  • Mason jar or other glass jar
  • Cloth or paper napkins to use as jar covers
  • Rubberband
  • Ruler
  • Measuring spoons
  • Spoon for mixing

Preparing the starter:

  • Add 2 Tbsp* of flour and 2 Tbsp of water into a jar and mix to make a paste
  • Mix thoroughly, scraping down the sides of the jar with your spoon.

*Note: These measurements are in US Tablespoons (~14.8mL). If you live in Canada, Australia, or another region that uses a different interpretation of Tablespoon, you will have to adjust your volume. 

Scraping down the sides is useful for a number of reasons. Starter on the sides of the jar is more likely to grow mold. Additionally, it allows you to see more clearly whether or not  your starter is rising after you feed it.
  • Cover the mouth of the jar with a paper towel and secure it with a rubber band. This keeps out any large debris or insects, but microbes do filter in from the environment.
  • Place your jar in a warm location out of direct sunlight for 24 hours before moving on to the next step.

Refreshing/feeding your starter:

  • Time to feed your starter! Remove the paper towel and use a spoon to mix your starter thoroughly.
  • Smell your starter. This may sound odd, but by giving your starter a good sniff each day, you are training your nose for the subtle shifts happening in the microbial community. Use our Sourdough Aroma Wheel as a reference.
  • Remove 1 Tbsp of the starter and dump it into the trash or compost.
If you didn’t, your starter would grow exponentially – and so would it’s appetite! Within a week you would have over a gallon of starter that would require more than a bag of flour per feeding.
  • Add 4 teaspoons (11/3 Tbsp) of flour and 1 Tbsp of water and mix well, scraping down the sides of the jar.
  • Cover the jar with a paper towel.
  • Set aside for 24 hours. 
  • Continue to repeat the refreshing/feeding every 24 hours until you have refreshed the starter at least 14 times.

*Note: After 4 or 5 days, you may notice that your starter reliably rises but then falls again and develops a layer of liquid on the surface within the 24 hour period after feeding. This layer is called “hooch” and, combined with the reliable rising and falling of the starter, indicates that your starter is hungry. It is time to switch up the schedule! Instead of refreshing your starter every 24 hours, you will need to refresh it every 12 hours instead. Not everyone’s starter will need this. Starters all have unique schedules and metabolisms. You are getting to know yours.

Frequently Asked Questions!

Variations on the Basic Experiment

Indoor / outdoor starters

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.

Flour

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.

  1. 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 jarDepending 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.
  2. Add 3 Tbsp flour and 2 Tbsp water and mix thoroughly, scraping down the sides. The starter will be a little thicker than usual.
  3. Before setting it aside, draw a line with a sharpie on the jar to indicate the height of the starter.
  4. Using a ruler, measure the height of the starter from the base of the jar. This is your “Baseline” height.
  5. 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.
  6. Keep checking on your starter every few hours until it is no longer growing in size.
  7. 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.
Sourdough aroma wheel
Submit your data!

Basic sourdough bread recipe

Once you have created a starter and submitted your data, it is time to settle into the next two phases of wild sourdough guardianship: baking and maintaining your starter!

There are many different ways to maintain and bake with your starter, and lots of schools of thoughts around “best practices.” Rather than be intimidated, we hope that this is just further permission to experiment, to explore and to ultimately choose the maintenance and baking techniques that work best for you—and your unique wild starter!

If you are following along with our Fermentology mini-seminar series, this is the recipe that we will be using as a “baseline” for discussing bread aroma. By baking a standard recipe, we can compare and contrast the flavors and aromas we detect in our bread. But this is just a starting place! We will actually be posting many more recipes as we go along, as every baker has their favorite tips and techniques.

Ingredients:

  • 3 ⅔ cups all-purpose flour (regardless of what flour you used for making your starter!)
  • 1 ¾ teaspoons salt
  • 1 ½ cups plus 4 teaspoons water, room temperature
  • ⅓ cup mature sourdough starter (fed 8-12 hours beforehand)

Directions

(I usually mix the dough 24 hours before baking.)

  • Mix the flour and salt in a large mixing bowl. Mix the sourdough starter and water in a separate bowl. Pour wet ingredients into dry ingredients, mix for 10 minutes (until the dough is smooth-looking).
  • Turn the dough onto the counter and form the dough into a ball. Coat the bowl with oil and put the dough ball back into the bowl, rolling it in the oil to coat the entire surface of the dough ball. Cover the bowl with a lid and let it sit on the counter for 12 hours.
  • Transfer the covered bowl to the fridge, to continue fermenting overnight.
  • When you are ready to bake: Preheat oven to 500°F, with a baking sheet or cast iron skillet inside (to get nice and hot).
  • When oven has preheated, take the bowl of chilled dough out of the fridge. Gently run a spatula around the edge of the dough ball, to separate it from the wall of the bowl. Sprinkle rice flour or cornmeal on the top surface of the dough ball.
  • Remove the hot baking sheet from the oven, then turn the bowl upside-down over the pan so that the dough ball falls out (flour-side down) onto the hot pan. Using a sharp knife, quickly score the top of the loaf.
  • Place the pan (now with the scored loaf on it) into the oven on the middle rack. Close the oven door and re-set the temperature to 475°F.
  • Bake 20 minutes at 475°F. Lower the temperature to 350°F and bake another 20 minutes.

Maintaining your starter

Link to maintenance tutorial!

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

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

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.

Collaborators and Partners

Sourdough Projects

Wild Sourdough

Sourdough for Science

Global Sourdough Project

The Belgian Experiment

More sourdough

Sourdough sonification

String of Yeasts

Fermentology

Lecture series

Sourdough photos

Media toolkit

Interactive map

Microbial species

Sourdough lesson plan

Making a starter

A guide

Wild Sourdough

Mini-seminar

Get to know your sourdough yeast

Liz Landis photos