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4-H Sourdough Science

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Bread mixLoaf of sourdough bread

Humans have been baking bread all over the world for thousands of years, yet we know almost nothing about the microbes that make a loaf of traditional sourdough bread.

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. (2020 The Public Science Lab | Department of Applied Ecology | North Carolina State University)

By participating in a real science project, you can help us solve the mysteries of bread. Your data will be compared with data from other participants, all over the world, who have completed the same experiment. Together we can use these data to learn how different flours affect microbial growth over time – and how those microbes affect the taste and texture of bread. (Copyright 2017 | All Rights Reserved)

You will even be able to bake your own bread!

Follow These Steps

(more information)

  1. Set Up Experiment

      • 2 Tablespoons of flour 

      You can use any type you like except coconut (gets too greasy). Rye, whole wheat, all-purpose, etc. all work fine.

      • 2 Tablespoons of dechlorinated water 

      You can use filtered water or tap water. Leave it in a clear glass overnight to dechlorinate it.

        • Mason-style glass jar or similar (half-pint or pint-sized jar; measure the diameter in centimeters)
        • Cloth or paper napkins to use as jar covers


    1. Rubber band
    2. Ruler
    3. Measuring spoons
    4. Spoon for mixing
  2. Create Starter

    • Add the 2 Tbs of flour and 2 Tbs of dechlorinated water to the jar.
    • Mix together thoroughly.
    • Make sure you scrape down the sides of the jar.
    • Cover the mouth of the jar with a paper towel or cloth and secure it using a rubber band.
    • Place the jar in a warm (but not sunny!) place where it can be left alone for 24 hours.

    Note: The top of a refrigerator works well!

  3. Care for Your Sourdough

    1. Give it a name. 
    2. Feed it.
      1. Remove the paper towel and use a spoon to mix your starter thoroughly.
      2. Smell your starter. Use our aroma wheel for sourdough as a reference.
      3. Remove 1 Tbsp of the starter and dump it into the trash or compost.
      4. Add 4 teaspoons (11/3 Tbsp) of flour and 1 Tbsp of water and mix well, scraping down the sides of the jar.
      5. Cover the jar with a paper towel.
      6. Put it back in its warm spot for 24 hours.
      7. Feed your starter once every 24 hours until you have fed it at least 14 times.
    3. After 4-5 days, you may notice that your starter reliably rises but then falls again and develops a layer of liquid on the surface before 24 hours have passed. This means your starter is hungry. Start feeding it once every 12 hours instead of once every 24 hours.
  4. Collect Data

    1. Characterizing height
      1. When it is time to feed your starter for the fifteenth time, do NOT discard it. Instead, transfer 2 Tbsp of your starter to a new jar
        • Add 3 Tbsp flour and 2 Tbsp water and mix thoroughly, scraping down the sides. The starter will be a little thicker than usual.
        • Draw a line on the jar with a marker to indicate the height of the starter. 
        • Use a ruler to measure the height of the starter from the base of the jar. This is your “Baseline” height.
        • Set aside like normal. Every 3 hours, check on your starter and indicate the height with a new mark. 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.
        • 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 in centimeters of the highest mark from the base of the jar. This is your “High Tide” mark.
    2. Characterizing aroma
      1. After you measure its height, remove the paper towel lid and give your starter a good sniff
      2. What does your sourdough starter smell like? Use the Sourdough Aroma Wheel for reference.
    3. Take photos of starter
      1. Photo #1: Take a photo of the side view of the starter in its jar against a solid background.
        1. Tip: Use a sheet of plain white construction paper to make a background for your sourdough.
      2. Photo #2: Take a second photo from an aerial view, looking into the jar.
  5. Report Data

    1. Go to
    2. In the “Address” field, type your zip code.
    3. In the “Other Observations” field, type NC 4-H and the name of your county.
      • Example: NC 4-H Northampton County
    4. Complete the rest of the form as you normally would.

More information and how to submit your findings.

Helpful Worksheets

All information is from Rob Dunn Lab.