Sourdough for Science

This project is appropriate for participants of all ages, and can be completed at home or in a classroom.

Download Teacher Guide!

About this activity

Humans have baked bread for over 10,000 years. All over the world, different cultures bake their own unique breads – and have for centuries – and yet we know almost nothing about the microbes that truly make a traditional sourdough bread. In this project, you will grow your own sourdough starter from scratch just by mixing flour and water. For two weeks, you will measure the height and pH of your starter to track the growth of your “microbial zoo” over time, and share your data with a scientist.

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.

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.

Curriculum alignment:

NGSS Middle School Standards

  • MS-LS1-5
    Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms.

  • MS-LS2-5
    Evaluate competing design solutions for maintaining biodiversity and ecosystem services.

    • Students design the sourdough ecosystem with different types of flour to see which types has a greater diversity of microbes. Students can also develop their own experiment by changing materials, or the amount of materials used, and can track their data to see growth.
  • MS-LS2-4
    Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.

    • Students can draw conclusions about how the changes they made to their design affected the populations of microorganisms by using the starter’s growth as the empirical evidence.

NC Essential Standards

  • 6.L.2.1
    Food provides molecules that serve as fuel and building material for all organisms.
  • 6.L.1.2
    Photosynthesis and cellular respiration are complementary processes. Plants carry on photosynthesis and cellular respiration where food is broken down into energy. The requirements of one process are the products of the other…….

  • 7.L.1
    Understand the processes, structures and functions of living organisms that enable them to survive, reproduce and carry out the basic functions of life.

  • 7.L.1.1
    Within cells, many of the basic functions of organisms—such as extracting energy from food, getting rid of waste, movement and secreting waste—are carried out. The way in which cells function is similar in all living organisms. Even the simplest organisms have parts which enable them to move, take in food, to reproduce and to detect the environment they are in.

  • 8.L.1
    Understand the properties of matter and change that occur when matter interacts in an open and closed container.

  • Clarifying Objective 8.P.1.3
    Compare physical changes such as size, shape and state to chemical changes that are the result of a chemical reaction to include changes in temperature, color, formation of a gas or precipitate.

  • 8.L.2
    Understand how biotechnology is used to affect living organisms.

  • Clarifying Objective 8.L.2.1
    Know: Biotechnology has created benefits and concerns in the areas of medicine, agriculture, genetics, and
    food science.
    Understand: The microbial world has led to the emerging field of biotechnology which has given us many advances and new careers in medicine, agriculture, genetics, and food science.

Materials list

  • Flours (Rye, whole wheat, all-purpose, etc.). Half-pint jar requires 1 cup for a 10-day experiment. Quart jar requires 12 cups for a 10-day experiment. This amount will feed 1 experimental sourdough starter + 1 control.

  • Dechlorinated water (could be filtered or tap water that has been left in a clear bottle overnight). Amount varies per day (see directions).
  • Non-reactive jars of the same size (we recommend either half-pint or quart sized wide mouth mason jars). Minimum one per flour type, plus one extra for the control (freezer) sample. Here is one option you can buy on Amazon.

  • Cloth or paper napkins to use as jar covers.
  • Sharpie or tape to mark the jars.
  • Ruler.

  • pH paper 0.0-6.0 and 5.5-8.0: (any pH paper that will detect from 3.5-8.0 at the accuracy of at least one decimal place). You can find these on Amazon here.
  • Thermometer.
  • Measuring spoon or cups for liquid and solids.

  • Whisk or long spoon for mixing in the jars.

How to participate

Step 1
Step 1

Step 1

Add 2 tablespoons of flour and 2 tablespoons of dechlorinated water to a wide-mouth half-pint glass jar. Label the jar with the type of flour you are using (i.e., "Rye"). Repeat for each flour type you wish to test; make sure to clean tablespoon well between flours.

Step 2
Step 2

Step 2

Mix each jar with a spoon until well combined. (Make sure to clean mixing utensil well in between flour types.) Consistency should be that of toothpaste or apple sauce.

Step 3
Step 3

Step 3

Scoop a small amount of your starter into a spoon, and touch one side of a strip of pH paper to the starter. (This allows the starter to soak into the pH paper, but keeps the other side of the paper clean and easy to read.)

Step 4
Step 4

Step 4

To measure the pH, match the color of the paper to the color key on the package.

Step 6
Step 6

Step 6

Measure the height of the flour and water mixture in the jar. Measure the radius (half the diameter) of the jar. Record on data sheet.

Step 8
Step 8

Step 8

Smell your starter, and record a description on the data sheet (i.e. biscuity, fruity, floral, musty, rotten eggs, sour, no smell, etc.)

Step 9
Step 9

Step 9

Place napkin or cloth cover on jar(s); secure with lid ring or rubber band. Place jar(s) in a warm location, out of direct sunlight. Record temperature of the area and your geographic address. After 24 hours, measure and record height of each sourdough starter. Also record any additional observations: for example, is there a layer of liquid on top of the starter? Remove the cover and record aroma. Then mix starter and measure pH (before feeding).

Step 10
Step 10

Step 10

Remove 1 tablespoon of the starter. This can be discarded or composted.

Step 11
Step 11

Step 11

Add 1 tablespoon dechlorinated water and 1 tablespoon of the same flour that was used in that jar, mixing well. This is the ‘feeding’ step of making a sourdough starter. Cover. Return to location where the jar was stored previously. Repeat measurements and feeding every 24 hours for 14 days.

Step 12
Step 12

Step 12

At the end of the 14 days, enter your data into our online database hosted on SciStarter.

Step 12

Photos by Lauren Nichols

Enter Your Data!

Sourdough for Science downloads at a glance

Activity Overview
Data Sheet
Step-by-step teacher instructions

Opportunities for Extension

  • Bake bread: Use Lea Shell’s Sourdough Recipe, and follow the steps in our New Year, New Bread activity.Compare the microbial community of a sourdough starter with just the starting microbial community in flour and water by making bread with the rye starter and the rye starter that was kept in the freezer.  Note how the dough rises, or doesn’t rise. Note flavor and aroma differences.

  • Compare flour types: Test the effect of flour type on sourdough starter activity. Follow the procedure, but using extra jars each with a different flour type (whole wheat, spelt, millet, buckwheat, amaranth, etc.) Fill out a data sheet for each flour.

  • Data Visualization: As data comes in, you can plot different variables to compare dynamics over time. (Erin has doodled an example below.)

  • Calculations: You can calculate the change in volume of the starter, not just the change in height. Use this formula:
    Volume =pi*(radius of jar)^2*(height of total starter)
    On what day did the volume start to double?

  • Experimental optimization: Help us determine how small a sourdough starter can be to still form: Using the ratios we have provided, trying making mini and micro starters (¼ c. flour? 1 tablespoon flour?) Compare your results with the protocol we have provided. What size makes the fastest sourdough starter, as measured by the fewest days to get a starter that is doubling in size? You can modify the container to be appropriate for smaller sizes- perhaps small plastic water cups. Email us your findings!

About the research

The Dunn lab wants to learn the microbial mysteries behind bread. We have already collected over 500 sourdough starters from participants in 17 countries, as part of the global citizen science Sourdough Project.

By growing the bacteria and yeasts that live in each starter, and sequencing their DNA, we have learned a lot about how where you live, and what you feed your starter, affects the microbes that live in your starter.

Here’s where you come in: now that we know the “global trends”, we want you to grow your own starter from a specific type of flour and measure its growth and acidity over time. Your data will help us to figure out how specific flours affect the microbial growth and flavor of sourdough.

About the scientists

Erin McKenney

Dr. Erin McKenney is a microbial ecologist in the Department of Applied Ecology at North Carolina State University. Learn more on her website.

Anne Madden

Dr. Anne Madden is a microbiologist in the Department of Applied Ecology at North Carolina State University.

Lea Shell

Lea Shell, M.Ed. is a Digital Learning Specialist for the North Carolina Museum of Natural Sciences.

Collaborators and Partners

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