Sourdough for Science
This project is appropriate for participants of all ages, and can be completed at home or in a classroom.
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
Photos by Lauren Nichols
Submit your data at Sourdough for Science on SciStarter.org
Sourdough for Science downloads at a glance
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
About the scientists

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

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

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