Materials
- A small amount of plain yogurt (unflavored, with live cultures)
- Microscope
- Glass slide and coverslip
- Dropper or pipette
- Distilled water
Instructions
- Use a dropper to collect a tiny amount of yogurt. Place it in the center of a clean glass slide.
- Add one small drop of water to thin the sample.Mix gently with the toothpick.
- Lower a coverslip slowly at a 45° angle to avoid trapping air bubbles.
- Observe under the microscope.
- You’ll see many tiny moving shapes. These are live lactic acid bacteria, the microorganisms that ferment milk into yogurt!
What’s going on?
- Yogurt is made by lactic acid bacteria, such as Lactobacillus bulgaricus and Streptococcus thermophilus.These bacteria feed on milk sugar (lactose) and produce lactic acid, which thickens milk and gives yogurt its tangy taste.
- Under the microscope, the tiny moving cells you see are the live bacteria still active in the yogurt.Their movement (called Brownian motion) shows that the yogurt is alive with microorganisms that make fermentation possible.
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