Blow up a balloon using yeast

Do it yourself

Imagine baker’s yeast would occasionally go to parties with other types of fungi. Maybe the porcini mushroom, the stinkhorn and the mold might find themselves on the guest list for such a fungal get-together. Before the party starts, the yeast would have to prepare a few things for its guests, of course. As you might already know, baking pizza and cakes is not a problem for yeast. But can it also blow up balloons?

Sure, fungi rarely celebrate parties (except maybe the mold in the lunch box that was forgotten in your backpack over the summer holidays), but a yeast cube from the grocery store can actually inflate balloons! Don't believe us? With the following experiment you can easily put this to the test. Also, find out why fungi don’t belong to the kingdom of plants.

What are mushrooms and what else can you do with yeast?

What happens during our little experiment? How can yeast be used in the kitchen and is it still alive after baking? And why are mushrooms no plants? Here you can go directly to our background knowledge and learn more about these topics!


  • Suitable for age group: children at the age of 6 to 12 under adult supervision

  • Especially interesting for: friends of fungi, young researchers and budding chefs

  • Duration: 1 hour


  • You need:

  • A cube of yeast or two 2 packets of dried yeast

  • A party balloon

  • A glass bottle (250 - 500ml) with a narrow neck

  • One teaspoon of sugar

  • Warm water

  • A teaspoon

  • A funnel (optional)


Step 1:
Prepare the balloon

Blow up the balloon once and let the air out again so that the balloon is stretched a little.

Step 2:
Put yeast and sugar into the bottle

If you have a cube of yeast, crumble it with your fingers and put the yeast crumbs into the bottle. If you have packets of dried yeast you can simply pour it from the sachet into the bottle.

Now add a teaspoon of sugar to the yeast. Using a funnel makes it easier to fill the bottle.

Step 3:
Add warm water and swirl

Next, add lukewarm water into the bottle until it is filled to one third of its height. Yeast doesn't like hot water. As a rule of thumb, the water should be about the same temperature that you would use when bathing or washing your hands.
Carefully swirl the bottle with the lid open in order to dissolve the yeast and sugar.

Step 4:
Put the balloon on the bottle

Now all you have to do is to pull the balloon over the bottleneck. The balloon opening should tightly cover the opening.

Step 5:
Wait and watch

From now on you just have to wait a little while (approx. 30 - 45 minutes) until the balloon fills up.


The yeast will feel particularly comfortable and speed up the process if you put it close to a heater.

Have fun

Learn more!

It is exciting to see how the yeast manages to inflate the balloon. But how does it do that anyway? We explain it to you here!
In addition we have some interesting facts about fungi and yeast!

What is going on?

The yeast digests the sugar and creates a gas as waste product. This gas is called carbon dioxide (CO2) - it’s the same gas that is responsible for the fizzy bubbles in your lemonade. Since the gas carbon dioxide takes up more space in the bottle than the solid sugar, the balloon expands.

You might be wondering where this carbon dioxide is coming from. The gas originated from the sugar and parts of the oxygen. Oxygen is in the air around you and every human needs it to breathe.

However, since there was only little oxygen in the bottle, the yeast formed carbon dioxide mainly by fermentation instead of forming it by respiration. Yeast is pretty good at fermentation - much better than us humans. This special ability of yeast is used in the process of brewing beer, as alcohol is a waste product of fermentation.

Yeast has two survival strategies: either it lives with oxygen (aerobic) or without oxygen through fermentation (anaerobic). Carbon dioxide is produced during both processes.


Fungi don’t belong to the kingdom of plants

Plants need carbon dioxide, water, nutrients and sunlight (energy) to grow. So they use the gas, which humans, animals and also fungi constantly emit, as food. This creates a cycle consisting of plants producing oxygen and animals and fungi producing carbon dioxide. Therefore, the diet of fungi is more comparable to that of animals. Fungi  are neither animals nor plants and form their own incredibly diverse kingdom in nature.

Perhaps it’s easier to realize if you think of the following: Plants are mostly green as they harvest solar energy with the help of the green pigment chlorophyll. Green fungi are rare as fungi don't have the ability to use sunlight as a source of energy. Plants have to do this job for them - just like for animals, too. However, one should not exclusively  rely on the characteristic “green color” as a criteria for the ability of using sunlight as a source of energy. There are for example green animals (tree frogs, grasshoppers ...), which -despite of their green color -  do not belong to the kingdom of plants.


Research questions:

  • Under which conditions is baker’s yeast particularly active?
  • Take a look at a recipe for dough made with yeast and think about the purpose of the single steps. What’s the balloon envelope in a yeast dough? Why is it important to knead the dough for quite a while and why should it become elastic? Why do you always add a little sugar to the dough? And why is it important to place the kneaded dough at a warm place?
  • Is the yeast still alive after he baking process?
  • How could you prove that carbon dioxide was produced  during the experimet- and not for example oxygen?A little hint: not only organisms need oxygen ...

Created by our Lab Pilot Monika

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80638 München, Germany


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