This quick and simple science experiment has plenty of wow factor.  With just a few household items, kids will see how the tiny fungi work to create those pockets of air that make bread so delightfully squishy.

Follow the simple step-by-step below and then grab 30 more easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop!

Simple Kids Science - How Yeast Works

Getting Ready

To prep, I gathered a few supplies:

  • Active dry yeast
  • 2 bottles {ones with narrow openings like water bottles work best}
  • 2 balloons
  • Sugar
  • Warm water

Feeding the Yeast

To begin, I had my 5 year old, A, pour 1/4 cup of very warm water in each bottle.

Science of Yeast

Next, she added a 1/2 teaspoon of table sugar to each jar. She poured one packet of active dry yeast into one container, while leaving the other without yeast as our control.

Science of Yeast

I placed a balloon over each jar, which was quite an ordeal with these wide mouth baby food jars.  In hindsight, we should have used bottles with a narrow opening.

I asked A what she thought was going to happen.  She predicted the balloon with yeast would inflate and get really big.  She also thought the control with water and sugar would fizz but then changed her mind after she thought about how my coffee didn’t do that when she added sugar.

It only took minutes to see if she was right.

Science of Yeast

When A put her ear on the balloon, she could hear the bubbles as they formed and grew out of the jar and into the balloon.  Soon the balloon got so big we were worried it was going to pop off from the pressure so we moved the experiment outside.

Science of Yeast

Eventually, the yeast stopped bubbling and, thankfully, the balloon didn’t pop off after all!

The Science Behind Yeast

Yeast is a tiny single celled fungi that feeds off of sugars.  As the yeast eats the sugar, it releases a gas called carbon dioxide. The gas fills the jar and, as more and more gas is produced, it fills the balloon.

In bread dough, the carbon dioxide from the yeast gets trapped in the gluten from the flour.  The yeast dies in the hot oven leaving and the gluten solidifies leaving us with wonderfully soft bread!

More Kids’ Science

Grab 30 more easy-to-follow (super inspiring!) science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop!

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  1. I am currently in ECED education classes. And am always interested in simple science projects for 3-5 yr. olds. This is just up my alley, Thanks!

  2. Olá
    Sou educadora de infância em Portugal, dedico bastante tempo às experiências na minha sala de atividades com crianças entre os 3 e 5 anos. Nestas idades o conhecimento é sobretudo feito através da experimentação, “Só se aprende experimentando, caso contrário é apenas informação” . Apreciei as suas experiências porque leva a criança a questionar, colocar hipóteses e tirar conclusões, não é apenas um simples observador. Parabéns.

  3. Hi, Noirin, my 7-year-old son and I did this experiment twice this weekend. We used plastic water bottles and followed your instructions. The first time, the balloon over the yeast bottle barely inflated. I later found out (from another resource) that we should have blown up the balloon to stretch out the latex a bit. We were better prepared for our second experiment, and saw a better outcome, but, based on pictures, not as impressive as your inflated balloon. Any advice?

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