Yeast Balloons
Your Activity
Inflate a balloon using yeast
Materials
Glass or Plastic Water Bottle
One large balloon
Active Dry Yeast (4-oz jar)
Sugar
1-tsp measuring spoon
Funnel
Create
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Fill the bottle about 1/3 full with warm water.
Add about 3 tsp of sugar (the exact amount is not important) using a funnel.
Add 2 tsp of yeast using a funnel.
Cap the flask or bottle and shake it well to mix and dissolve the yeast and the sugar.
Remove the cap and stretch the mouth of the balloon over the mouth of the bottle. In 5-10
minutes, the yeast will produce some foam and enough gas to start inflating the balloon. Over a
long period of time, the balloon will inflate significantly.
6. Set the bottle on the counter, behind a Plexiglas shield or in a warm area. If you cannot find an
area that is warmer than room temperature you can place it in a bowl of warm water.
Science Topics
Fermentation, Biochemistry, Chemical Reactions, Properties of Gases
What’s going on?
The bottle contains yeast, sugar, and water. Yeast are tiny living organisms. Yeast use the sugar for food. They use a
biochemical reaction called fermentation to break down the sugar into ethyl alcohol and carbon dioxide gas. The gas produced
by this reaction creates the foam and inflates the balloon. Brewers use fermentation to make the alcohol and carbon dioxide
bubbles in beer. The gas bubbles produced by fermenting yeast also make bread rise. Just like any living thing, in order for
yeast to stay active it needs source of energy or food. That is why we added sugar. Sugar served as its food, letting the
yeast eat it.
The scientific name for the yeast that baker's use is Saccharomyces Cerevisiae, or "sugar-eating fungus". A very long name for
such a tiny organism!
Yeast Balloons
Activity Lead Notes
Introduction
In this activity, students learn how Yeast produces Carbon Dioxide which then inflates the balloon. Yeast is a living
organism responsible for alcohol fermentation and dough leavening.
Background
What happens when you blow the balloon with your own mouth? When you breathe out (or exhale), your lungs push
carbon dioxide out, along with a few other gases, which is how you are able to blow up a balloon.
How can we produce carbon dioxide? Using yeast!
Ask students where holes in bread come from. Yeast are living organisms that multiply quickly and as they grow they
produce carbon dioxide. Because of this, yeast is important in baking and fermenting – we would not have bread
without it! In this activity, yeast reacts with sugar water and produces carbon dioxide, which fills up the balloon.
A tiny organism with a long name: The scientific name for the yeast that baker's use is Saccharomyces Cerevisiae, or
"sugar-eating fungus". A very long name for such a tiny organism! This species of yeast is very strong and capable of
fermentation, the process that causes bread dough to rise.
A fungus with a sweet tooth: Yeast cells digest food to obtain energy for growth. Their favorite food is sugar in its
various forms: sucrose (beet or cane sugar), fructose and glucose (found in honey, molasses, maple syrup and fruit), and
maltose (derived from starch in flour).
Fermentation in nature: Fermentation occurs naturally in nature. For instance, many berries break open in late fall
when they are overripe and full of sugar. Natural yeast organisms, so small they cannot be seen with the naked eye,
lodge on the surface of these berries, which then become fermented and alcoholic.
Materials
The materials are required for each student. You can also make it a completion, so the child with the most inflated
balloon at the end of the class wins a prize.
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One clear, narrow-necked, glass or plastic bottle
One large balloon
Active dry yeast
Sugar
One 1-tsp measuring spoon
Marker
Procedure
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Give out material to each child (can be done in a sequence). Mark the bottle with child’s name, so we can
identify it for prize at the end of the class.
Put activity instructions in the sign holder.
Ask kids to follow the steps in the activity instruction.
During the Activity
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Make sure yeast/sugar liquid is not seeping out of the bottle.
Keep an eye on the children. They should not lift and shake the exhibit or the yeast solution will leak.
Takedown
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Check the balloon for holes. If none is found, it can be washed out and reused.
Clean the bottle, if it is reusable
Discuss Student Observations
The warm water made the yeast "wake up" and it immediately started to have a chemical reaction with the sugar. Two
substances, yeast and sugar, reacted to each other and together they made a new substance - a gas called carbon
dioxide. Carbon dioxide is the same gas that makes soda pop fizzy, and one of the many gases in the air we breathe in
and out. The carbon dioxide from the reaction filled up all the space in the plastic bottle and kept rising to fill up the
balloon. At first, the yeast should have looked puffy or bubbly on the surface of the water as it was beginning to react
with the warmth of the water. Then, you probably noticed that the balloon was standing straight up instead of being
flopped over the mouth of the bottle! That was the first sign that the yeast was reacting with the sugar and that carbon
dioxide gas was being made. Soon after that, the balloon should have started to inflate. Since the balloon was made of
stretchy rubber (and you helped stretch it out), it kept expanding to hold the carbon dioxide.
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What is happening to the balloon?
What color is the liquid in the bottom of the bottle?
What else do you see in the bottle?
Does room temperature affect how much gas is created by the yeast?
Does the size of the container affect how much gas is created?
What water/room temperature helps the yeast create the most gas?
What "yeast food" helps the yeast create the most gas? (try sugar, syrup, honey, etc.)
Source
Experiencing Chemistry, Museum Manual Part 1, Oregon Museum of Science and Industry.