The ones doing work we want
Show on a big screenWarm milk, one spoon of curd, and a night. By morning, the milk has set. Here, set means the milk has turned thick and firm.
- Warm the milk.
- Add a spoon of yesterday's curd.
- Wrap it. Keep it warm.
- By morning, it has set: curd!
The rule
To ferment is to let microbes change food. Something new is made.
Yeast is a fungus made of one cell. Lime water is a clear liquid. It turns milky when carbon dioxide mixes with it.
Yeast needs sugar, water and warmth. Then it makes carbon dioxide gas. The gas fills a balloon. It turns lime water milky. The gas, not the yeast, does this. Yeast breaks down sugar to make this gas.
Plants need nitrogen to grow. Rhizobium is a bacterium in the roots of bean plants. It traps nitrogen from the air for the plant. Lactobacillus is also a bacterium. Manure is rotted waste that gives plants food.
| The job | The microbe |
|---|---|
| Dough rises | Yeast, a fungus. Its gas makes bubbles |
| Milk sets into curd | Lactobacillus, a bacterium |
| Peels turn into manure | Bacteria and fungi |
| Bean plants get nitrogen | Rhizobium, in the roots |
Idli and dosa batter also ferment.
Watch out!
Hot milk kills the curd bacteria. Add the spoon only to lukewarm (slightly warm) milk.
Switch things on and off. When does the balloon fill?
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Try the lab to finish this lesson.