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← Summer Solo-Science

Week 4Releases July 13

Grow yogurt and watch microbes work

Use a spoon of store yogurt to turn warm milk into new yogurt overnight — proof that living microbes are doing the work.

For you to do

You'll warm some milk, stir in a spoon of yogurt (which is full of living bacteria), and keep it cozy overnight. By morning the microbes will have turned the milk thick and tangy.

Grown-up help

Ask a grown-up to help warm the milk to just-warm (not hot). After that, it's your experiment to watch.

Set it up

  1. Warm the milk until it feels like a warm bath — not hot. A grown-up can help here.
  2. Stir in one spoon of plain live yogurt. Pour into the clean jar and put the lid on.
  3. Keep it warm and undisturbed for 8–12 hours (wrap it in a towel in a warm spot).

Observe

Make it a fair test

Try two jars — one warm, one in the fridge — changing only the **variable** of temperature. Which microbes were busier?

Write down what it looks like at the start, then again in the morning. How thick is it? How does it smell?

What's happening

The yogurt spoon adds living **microbes** (bacteria). In the warmth they eat the milk sugar and release acid, which thickens the milk into new yogurt. Your careful **observation** notes are how scientists track invisible living things.