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Planning a Halloween party this year and need some spooky activities to do? Or just looking for some light-hearted Halloween science experiments to do with the kids? I’ve got one to add to your list.

We call this witches’ brew at our house. You’ll create a sticky, brown, bubbly potion that will magically inflate a balloon. Draw a pumpkin or a bat on the balloon for added Halloween science fun!

Kick your Halloween science up a notch with witches

This activity was inspired by 100 Science Experiments, a book that also inspired the ever-popular rainbow paper!

Materials You Need:
2 Tbsp dried yeast
1 Tbsp sugar
2 Tbsp lukewarm water
Glass bottle
Bowl half-full of lukewarm water

Make Witches’ Brew

  • Mix together the yeast, sugar, and water in your bottle.
  • Quickly stretch the balloon over the mouth of the bottle.
  • Set your bottle in the bowl of warm water and wait! It usually takes about an hour for this chemical reaction to finish. I set a timer for every 10 minutes so we could check on its progress and watch the balloon get bigger and bigger!

Halloween Science

The mixture should start to bubble within the first few minutes. These bubbles are the result of the chemical reaction we are interested in here. Yeast is a microbe that “eats” sugar when it is wet and warm. As it “eats” it gives off carbon dioxide, which are the bubble you see. This carbon dioxide gets trapped in the balloon over the top of the bottle, which makes it inflate. As the minutes tick by you should also start to see the mixture bubble up and grow higher and higher in the bottle. After about an hour it is done reacting (we call this equilibrium) and the mixture recedes back to the bottom of the bottle. However, the balloon stays inflated as long as the seal is in tact with the bottle.

Kick your Halloween science up a notch with witches
Print Instructions

This is the exact same reaction that happens whenever someone makes bread, rolls, breadsticks, pizza crust, or cinnamon rolls. As the dough rises (AKA as this yeast reaction occurs) it produces carbon dioxide bubbles, but they get trapped inside the dough. This makes the dough expand, so when you bake it, you have a fluffy, soft texture to bite into. YUM!

Looking for even more Halloween science, math, and engineering activities to do? Check these out!

STEM Saturday

Magic Leak-Proof Bag Experiment from P is for Preschooler

Frozen Halloween Bubbles from Preschool Powol Packets

By | 2017-04-22T15:27:39+00:00 September 26th, 2015|Halloween, Science, STEM Saturday|5 Comments


  1. Carla September 26, 2015 at 1:11 pm - Reply

    Fun! I love how you used yeast too!

  2. Alison September 29, 2015 at 6:52 pm - Reply

    What a cool project! 🙂

  3. Kim October 2, 2015 at 11:53 am - Reply

    Fun project! My oldest loves experiments! We have not used yeast before!

  4. Mrs. AOK October 4, 2015 at 8:28 am - Reply

    Awesome! Thanks for sharing with us at Mommy Monday 🙂

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