Yeast Blows Up a Balloon
✨ A spoonful of dried powder, fed nothing but sugar, inflates a balloon while you watch.
🧰 You need
- one teaspoon of dried yeast
- two teaspoons of sugar
- warm water
- a small bottle
- a balloon
- a piece of string to measure
⚠️ Use warm water, not hot, and never taste the mixture.
👀 What you will see
A creamy froth builds on the liquid within ten minutes and the balloon slowly swells. The measurements grow quickly at first and then more slowly as sugar runs out. The bottle smells of bread and a little of alcohol.
🧪 Do it
- Half fill the bottle with warm, not hot, water and stir in the sugar.
- Add the yeast and swirl until there are no lumps.
- Stretch the balloon over the neck of the bottle so no air can escape.
- Stand the bottle in a warm place and start a timer.
- Every ten minutes, measure the balloon around its widest part with the string.
- Record six measurements and note the smell at the end.
💡 Why it happens
Yeast is a living single-celled fungus, dried and dormant in the packet until warm water wakes it. It feeds on the sugar and, with little oxygen available, breaks it down to carbon dioxide gas and alcohol, a process called fermentation. The gas has nowhere to go but into the balloon, which is why it inflates. The same gas makes bread rise, and the same alcohol is why fermentation matters in industry.
🔁 Now try this
Set up three bottles with no sugar, one spoon and three spoons, keeping water, yeast and temperature the same, and plot balloon girth against time for each.
🤔 Think about it
Why does the same mixture do almost nothing in a fridge?
🧘 Ask the Acharya
“Why does the same mixture do almost nothing in a fridge?” — ask him and he will explain it from your own chapters.
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