Becoming a Microbiologist with Yeast Balloons!

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Let your little microbiologist experiment with yeast to inflate a balloon!


What you need:

  • Clear empty bottle00100lrPORTRAIT_00100_BURST20200406113249841_COVER.jpg
  • A small funnel
  • A tablespoon to measure the ingredients
  • 1 balloon
  • 2 Tablespoons of dry yeast
  • 1 Tablespoon of sugar (any sugar should work)
  • 3 Tablespoons of warm water
  • Mug filled 1/3 of the way with warm water


  1. Add 2 tablespoons of yeast to an empty bottle.
  2. Add 1 tablespoon of sugar to the bottle.
  3. Add 3 tablespoons of warm water.
  4. Swirl the ingredients around in the bottle.
  5. Quickly place the balloon on top of the bottle.
  6. Place the bottle in a mug of warm water. (This helps activate the yeast even more.)
  7. Wait and watch what happens. (My balloon started inflating within 5 minutes!)

What is happening?

Yeast is a microorganism that LOVES sugar and moist warm environments. The yeast is activated by the warm water and begins to eat the sugar. As it eats the sugars, it expels a gas – carbon dioxide. This process is called fermentation. If your child likes to talk about ‘flatulence’, this is a great experiment for them! Haha!


Let your child measure the ingredients – If your child is old enough, let them measure out the ingredients into the bottle. Ask them questions like, which ingredient is the greatest and which is the smallest in the bottle.

Check over your balloons before getting started – We found out that our pink balloon had a hole on top. This caused the carbon dioxide to leak out the hole and so the balloon did not rise.

Be careful of aggressively mixing the ingredients – One of our mixtures was aggressively mixed. Some of the yeast ended up on the sides of the container and others inside the the balloon. Since the yeast was dispersed throughout the balloon and not where the majority of the sugar and moisture was, that (red) balloon took longer to rise than our first balloon.

Other Topics to Discuss with your Children:

What is a microbiologist?

Microbiologists are scientists that study microorganisms and their processes – like how they grow and interact with their environment. There are trillions of microorganisms in the world – fungi, algae, bacteria and some parasites. According to a 2016 article by the New York Times, 99.999% of them are still yet to be discovered!

What is a microorganism?

It is an organism is usually too small to be seen with the human eye – it must be seen with a microscope.

What is yeast?

Yeast is a species of fungus (a type of microorganism). Humans have been benefitting from yeast since (at least) the time of the Egyptians. “Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeast-raised bread, as well as drawings of 4,000-year-old bakeries and breweries”.

Use your smart phone, a microscope or an endoscope to take a look at the dried yeast up close. Let your child describe its shape or what else they might see.

Dry yeast magnified 7x.

We thoroughly enjoyed this experiment because it was quick and mess free. The kids loved watching the balloons and taking guesses on which balloon would inflate first. They also thought the smell of the fermented yeast was interesting to smell afterwards.

If you try this at home, let me know on my social media pages or at




New York Times –

Wikipedia –

WebMD –

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