In this activity students make yogurt. Next, they compare both the milk and yogurt under a microscope to see the huge number of bacteria present in the yogurt but absent in the milk. Before refrigeration was common, people used fermentation as a means of preservation. Here students study the process up close. 
 
Use this to learn and reinforce answers to questions such as:
❑  Individual bacteria can only be seen under a microscope
❑  Many bacteria are beneficial
❑  Microorganisms are a key component in fermentation
 
Once students try this activity, they can capture their observations using the included Lab Notes or probing questions included in the instructions. 
 
Concepts Addressed
♦  How did people preserve excess milk before refrigeration?
♦  Are all bacteria harmful?
♦  What do bacteria look like under a microscope?
 
Answer Keys and Teacher Notes address most questions and issues that might arise in this study—you shouldn’t have to do any outside research unless you want to.
 
Materials Needed  Milk, thermometer, hot plate, sauce pan, yogurt (spoonful), thermos, food coloring, microscope slide and coverslip, pipette, plastic cup, water
 
Prep Needed  Gather supplies
 
Teaching Time   2 days
 
Student Sheets   Scaffolded writing prompts & lab reporting 
 
Connect with me… If you have questions or problems, please let me know in the Q&A section and I’ll get back to you asap.
 
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