• Visit
    • Calendar
    • After Dark Thursdays
    • Buy Tickets
    • Exhibits
    • Museum Galleries
    • Artworks on View
    • Hours
    • Getting Here
    • Visitor FAQ
    • Event Rentals
    • Field Trips
  • Education
    • Professional Development Programs
    • Free Educator Workshops
    • Tools for Teaching and Learning
    • Learning About Learning
    • Community Programs
    • Educator Newsletter
  • Explore
    • Browse by Subject
    • Activities
    • Video
    • Exhibits
    • Apps
    • Blogs
    • Websites
  • About Us
    • Our Story
    • Partnerships
    • Global Collaborations
    • Explore Our Reach
    • Arts at the Exploratorium
    • Contact Us
  • Join + Support
    • Donate Today!
    • Membership
    • Join Our Donor Community
    • Engage Your Business
    • Attend a Fundraiser
    • Explore Our Reach
    • Thank You to Our Supporters
    • Donor & Corporate Member FAQ
    • Host Your Event
    • Volunteer
  • Store
  • Visit
    • Frequently Asked Questions
    • Calendar
      • Today
      • This Week
      • Online
      • After Dark Thursday Nights
      • Arts
      • Conferences
      • Cinema Arts
      • Free + Community Events
      • Fundraising Events
      • Kids + Families
      • Members
      • Special Hours
      • Private Event Closures
    • Prices
    • Hours
    • Getting Here
    • Museum Map
    • Free Admission and Reduced Admission
    • Accessibility
    • Tips for Visiting with Kids
    • How to Exploratorium
    • Exhibits
    • Tactile Dome
    • Artworks on View
    • Cinema Arts
    • Kanbar Forum
    • Black Box
    • Museum Galleries
      • Bernard and Barbro Osher Gallery 1: Human Phenomena
        • Tactile Dome
          • 1971 Press Release
        • Black Box
        • Curator Statement
      • Gallery 2: Tinkering
        • Curator Statement
      • Bechtel Gallery 3: Seeing & Reflections
        • Curator Statement
      • Gordon and Betty Moore Gallery 4: Living Systems
        • Curator Statement
      • Gallery 5: Outdoor Exhibits
        • Curator Statement
      • Fisher Bay Observatory Gallery 6: Observing Landscapes
        • Wired Pier Environmental Field Station
        • Curator Statement
    • Restaurant & Café
    • School Field Trips
      • Getting Here
        • Bus Routes for Field Trips and Other Groups
      • Admission and Tickets
      • Planning Guide
      • Reservations
        • Field Trip Request Form
      • Resources
    • Event Rentals
      • Full Facility & Gallery Bundles
      • Fisher Bay Observatory Gallery & Terrace
      • Moore East Gallery
      • Bechtel Central Gallery & Outdoor Gallery
      • Osher West Gallery
      • Kanbar Forum

      • Weddings
      • Proms and School Events
      • Daytime Meetings, Events, & Filmings

      • Rentals FAQ
      • Event Planning Resources
      • Rental Request Form
      • Download Brochure (pdf)
    • Groups / Tour Operators
      • Group Visit Request Form
    • Exploratorium Store
    • Contact Us
  • Education
    • Black Teachers and Students Matter
    • Professional Development Programs
      • Free Educator Workshops
      • Professional Learning Partnerships
      • Teacher Institute
        • About the Teacher Institute
        • Summer Institute for Teachers
        • Teacher Induction Program
        • Leadership Program
        • Teacher Institute Research
        • CA NGSS STEM Conferences
          • NGSS STEM Conference 2020
        • Science Snacks
          • Browse by Subject
          • Special Collections
          • Science Snacks A-Z
          • NGSS Planning Tools
          • Frequently Asked Questions
        • Digital Teaching Boxes
        • Meet the Teacher Institute Staff
        • Resources for Supporting Science Teachers
      • Institute for Inquiry
        • What Is Inquiry?
        • Watch and Do Science
        • Inquiry-based Science and English Language Development
          • Educators Guide
            • Conceptual Overview
              • Science Talk
              • Science Writing
            • Classroom Video Gallery
              • Magnet Investigation
              • Snail Investigation
            • Teacher Professional Development
            • Project Studies
            • Acknowledgments
          • Conference: Exploring Science and English Language Development
            • Interviews with Participants
            • Plenary Sessions
            • Synthesis, Documentation, and Resources
        • Workshops
          • Participant Portal
          • Fundamentals of Inquiry
            • Summary Schedule
          • BaySci Science Champions Academy
          • Facilitators Guides
          • Commissioned Workshops
        • Resource Library
        • Meet the IFI Staff
      • Resources for California Educators
      • K-12 Science Leader Network
      • Resources for Supporting Science Teachers
      • Field Trip Explainer Program
      • Cambio
    • Tools for Teaching and Learning
      • Learning Toolbox
      • Science Snacks
      • Digital Teaching Boxes
      • Science Activities
      • Tinkering Projects
      • Recursos gratuitos para aprender ciencias
      • Videos
      • Exhibits
      • Publications
      • Apps
      • Educator Newsletter
      • Exploratorium Websites
    • Educator Newsletter
    • Advancing Ideas about Learning
      • Visitor Research and Evaluation
        • What we do
        • Reports & Publications
        • Projects
        • Who we are
      • Center for Informal Learning in Schools
    • Community Programs
      • High School Explainer Program
      • Xtech
      • Community Educational Engagement
      • California Tinkering Afterschool Network
        • About
        • Partners
        • Resources
        • News & Updates
        • Further Reading
  • Explore
    • Browse by Subject
      • Arts
      • Astronomy & Space Sciences
        • Planetary Science
        • Space Exploration
      • Biology
        • Anatomy & Physiology
        • Ecology
        • Evolution
        • Genetics
        • Molecular & Cellular Biology
        • Neuroscience
      • Chemistry
        • Combining Matter
        • Food & Cooking
        • Materials & Matter
        • States of Matter
      • Data
        • Data Collection & Analysis
        • Modeling & Simulations
        • Visualization
      • Earth Science
        • Atmosphere
        • Geology
        • Oceans & Water
      • Engineering & Technology
        • Design & Tinkering
        • Real-World Problems & Solutions
      • Environmental Science
        • Global Systems & Cycles
        • Human Impacts
      • History
      • Mathematics
      • Nature of Science
        • Measurement
        • Science as a Process
        • Size & Scale
        • Time
      • Perception
        • Light, Color & Seeing
        • Listening & Hearing
        • Optical Illusions
        • Scent, Smell & Taste
        • Tactile & Touch
      • Physics
        • Electricity & Magnetism
        • Energy
        • Heat & Temperature
        • Light
        • Mechanics
        • Quantum
        • Sound
        • Waves
      • Social Science
        • Culture
        • Language
        • Psychology
        • Sociology
    • Browse by Content Type
      • Activities
      • Blogs
        • Spectrum
          • Arts
          • Behind the Scenes
          • News
          • Education
          • Community & Collaborations
          • Science
        • Eclipse
        • Studio for Public Spaces
        • Tangents
        • Resonance See & Hear Blog
        • Fabricated Realities
        • Tinkering Studio: Sketchpad
        • Exploratorium on Tumblr
      • Exhibits
      • Video
      • Websites
      • Apps
        • Total Solar Eclipse
  • About Us
    • Our Story
    • Land Acknowledgment
    • Explore Our Reach
    • Impact Report
    • Awards
    • Our History
      • 50 Years 1969–2019

    • Senior Leadership
    • Board of Trustees
    • Board of Trustees Alumni
    • Staff Scientists
    • Staff Artists

    • Arts at the Exploratorium
      • Artworks on View
      • Artist-in-Residence Program
      • Cinema Arts
        • History and Collection
        • Cinema Artists-in-Residence
        • Resources and Collaborating Organizations
        • Kanbar Forum
      • Center for Art & Inquiry
        • Begin Here
          • Lessons
            • Bob Miller/Light Walk
            • Ruth Asawa/Milk Carton Sculpture
          • Workshops
      • Resonance
        • About the Series
        • See & Hear
        • Past Seasons
      • Over the Water
      • Black Box
      • Upcoming Events
      • Temporary Exhibitions
      • Arts Program Staff
    • Teacher Institute
    • Institute for Inquiry
    • Explainer Programs
    • Studio for Public Spaces
    • Exhibit Making
    • Partnerships
      • Building Global Connections
        • Global Collaborations
          • Projects
          • Approach
          • People
          • Impact
      • Partnering with Science Agencies
        • NASA
        • NOAA
      • Partnering with Educational Institutions
      • Osher Fellows

    • Job Opportunities
    • Become a Volunteer

    • Contact Info
    • Newsletter
    • Educator Newsletter
    • Blogs
    • Follow & Share
    • Press Office

    • FY21 Audit Report
    • 990 FY20 Tax Return
    • Use Policy
      • Privacy Policy
      • Intellectual Property Policy
  • Join + Support
    • Donate Today!
    • Membership
      • Membership FAQ
      • Member Benefits
      • After Dark Membership
      • Member Events
      • May Is for Members
    • Join Our Donor Community
    • Engage Your Business
      • Corporate Membership
      • Luminary Partnerships
    • Attend a Fundraiser
      • Wonder Funday
      • Science of Cocktails
      • Party at the Piers
        • Event Leadership and Host Committee
    • Explore Our Reach
    • Thank You to Our Supporters
    • Donor & Corporate Member FAQ
    • Volunteer
      • How to Apply
      • Application for Internships
      • Our Contract
      • Application for Individuals
  • Press Office
    • Press Releases
    • News Coverage
    • Events Calendar
    • Photographs
    • Press Video
    • Press Kits
    • Press Visits
    • Exploratorium Logos
    • Recent Awards
    • Praise for the Exploratorium
    • Join Our Press List
  • Store

Masks and vaccinations are recommended. Plan your visit  

Visitor FAQ Buy Tickets Donate Today
Exploratorium
Exploratorium
  • Visit
    • Calendar
    • After Dark Thursdays
    • Buy Tickets
    • Exhibits
    • Museum Galleries
    • Artworks on View
    • Hours
    • Getting Here
    • Visitor FAQ
    • Event Rentals
    • Field Trips
  • Education
    • Professional Development Programs
    • Free Educator Workshops
    • Tools for Teaching and Learning
    • Learning About Learning
    • Community Programs
    • Educator Newsletter
  • Explore
    • Browse by Subject
    • Activities
    • Video
    • Exhibits
    • Apps
    • Blogs
    • Websites
  • About Us
    • Our Story
    • Partnerships
    • Global Collaborations
    • Explore Our Reach
    • Arts at the Exploratorium
    • Contact Us
  • Join + Support
    • Donate Today!
    • Membership
    • Join Our Donor Community
    • Engage Your Business
    • Attend a Fundraiser
    • Explore Our Reach
    • Thank You to Our Supporters
    • Donor & Corporate Member FAQ
    • Host Your Event
    • Volunteer
  • Store
Science Snacks
Science activity that explores how yogurt is made

Bacteria Culture Club

Make yogurt from yogurt.

Yogurt is the byproduct of hungry bacteria that digest the lactose in milk. You can make more yogurt just by feeding the bacteria more milk.


Grade Bands: 
3-5
6-8
9-12
Subject: 
Biology
Molecular & Cellular Biology
Chemistry
Food & Cooking
Perception
Scent, Smell & Taste
Social Science
Keywords: 
edible
bacteria
milk
protein
microorganism
NGSS and EP&Cs: 
LS
LS1
PS
PS1
ETS
ETS1
CCCs
Cause and Effect
Stability and Change

  • Facebook logo
  • Reddit logo
  • Twitter logo


Tools and Materials

  • One quart milk
  • Four tablespoons of yogurt (use a yogurt that has only milk and live active cultures as listed ingredients)
  • Spoon
  • Pot
  • Hot plate or stove
  • Cups (not shown)
  • Hot water bath. You can make a simple one by adding hot water to a cooler or plastic bin with a lid.
  • Thermometer
  • Optional: cheesecloth, strainer, compound microscope, slides

Assembly

None needed.


To Do and Notice

Heat the milk over medium heat until it reaches 180°F (82°C). Stir the milk as it heats to make sure it doesn’t scald the bottom of the pot.

Take the milk off the heat, and let it cool to 110–115°F (43–46°C). You can do this in a sink full of ice water to speed things up.

Thoroughly mix in the prepared yogurt.

Make a hot water bath in a cooler or plastic bin that will keep the yogurt insulated at 110–115°F (43–46°C).

Portion the milk/yogurt mixture into small cups and place them in the bath for 8–12 hours. If you don’t want individual servings, you can place the whole amount in a large container and make a giant batch.

Refrigerate the yogurt cups for at least two hours.

Optional: Strain through cheesecloth if you like thicker, Greek-style yogurt.

Eat and repeat.


What’s Going On?

Yogurt is the product that results from the bacterial fermentation of milk. When you buy yogurt that contains “live active cultures,” it means there are still living bacteria present inside. By feeding these bacteria and keeping them at their optimal temperature, they will eat and divide and process the milk into yogurt. These cultures are made up of a general class of bacteria called lactic acid bacteria. The ones used in yogurt-making metabolize lactose, a form of sugar present almost exclusively in milk, for energy, and create lactic acid as a waste product. This acid helps give yogurt its texture and tangy flavor.

Milk is made of proteins, carbohydrates (in the form of lactose), fat, and water. When you heat it up in the first step, the proteins denature from their tightly coiled state into relaxed chains. The temperature needed for this is too high for many bacteria to survive, so this has the added benefit of sterilizing your milk. The milk is then cooled to the optimal temperature for the yogurt bacteria to undergo metabolism. Adding a lot of acid at once would cause the protein chains to precipitate out of the milk into clumps, but since the bacteria produce lactic acid gradually, proteins gradually turn into solids and gently coagulate into a network of chains. This network is able to trap liquid inside, and the end product is a smooth gel that gets firmer over time. Even though the bacteria divide fairly quickly, it takes several hours for them to work through the entire quantity of milk. Longer fermentation times will yield a tangier and stronger-flavored yogurt since more metabolism occurs. Straining the final gel results in an even denser yogurt as it physically separates the solid curds from the liquid whey. The amount of fat in the milk doesn’t really participate in this process, but will affect the overall texture and flavor of the final product.


Going Further

If you have access to a compound microscope, it’s fun to look at yogurt bacteria at high magnification.

Make a wet mount with a tiny toothpick amount of yogurt and a drop of water. Under 400x, you can see individual bacteria swimming around. Store-bought yogurt often contains these species: Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus, Bifidobacterium, and Lactobacillus casei.

The first two are the main yogurt-makers and work in synergy to digest lactose and produce lactic acid. They work so well together because they each make a waste product that the other uses for metabolism and are both thermophilic (survive at relatively high temperatures) bacteria that grow best at 105–113°F (40–45°C). The other three strains work better at temperatures closer to the human body temperature of 98.6°F(37°C). They are often added as probiotics since they are already present in different parts of your body. As the temperature and pH of the yogurt changes, different species are able to metabolize at better or worse rates, and the end result is a unique flavor profile of everyone’s waste.

In general, these bacteria come in two main shapes, with the Lactobacillus having an oblong rod shape and the Streptococcus, which is Greek for “twisted berry,” like little spheres. After they divide they can still be attached to each other; they sometimes look like beads in a chain.


Resources

Check out this episode of Hungry for Science to see what the yogurt looks like at different stages.



Related Snacks

Science activity that demonstrates lactose digestion by lactase
Milk Makes Me Sick

Explore the basis of lactose intolerance.

Science activity that investigates deodorant's effects on skin bacteria
Salty Pits

Explore how different deodorants affect the bacteria in your armpit.

Science acitivity that explores decomposition with worms
Productive Poop

Turn your kitchen trash into garden treasure.



Creative Commons License



This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Attribution: Exploratorium Teacher Institute

  • Education
    • Teacher Institute
    • Tools for Teaching and Learning
      • Science Snacks
        • Browse by Subject
        • Special Collections
        • Science Snacks A-Z
        • NGSS Planning Tools
        • Frequently Asked Questions



Connect with us!



  •   Sign up for our educator newsletter

  •   Follow #ExploEDU

  •   Teacher Institute YouTube

  •   Teacher Institute Facebook

  •  teacherinstitute @exploratorium.edu

Exploratorium
Visit
Join
Give

Pier 15
(Embarcadero at Green Street)
San Francisco, CA 94111
415.528.4444

Contact Us

  • Plan Your Visit
  • Calendar
  • Buy Tickets
  • Getting Here
  • Store
  • Event Rentals
  • About Us
  • Become a Member
  • Donate
  • Jobs
  • Volunteer
  • Press Office
  • Land Acknowledgment

Get at-home activities and learning tools delivered straight to your inbox

The Exploratorium is a 501(c)(3) nonprofit organization. Our tax ID #: 94-1696494
© 2023 Exploratorium | Terms of Service | Privacy Policy | Your California Privacy Rights |