Yeast Blows Up a Balloon

An adult must prepare the warm water and stay present throughout: this uses a live yeast culture, warm water and balloons. The water should feel warm, not hot, on the inside of your wrist; very hot water kills yeast and can scald. Children under eight can choke or suffocate on uninflated or broken balloons. Do not drink the mixture, and point the bottle away from faces when removing the balloon.

Protective equipment and “do not substitute” warnings have not been recorded for this experiment yet. They are added when its safety review is completed; until then, follow the supervision notes above.

Disposal: Pour the mixture down the sink with plenty of running water, rinse and recycle the bottles, and put the balloons in general waste.

Do not start this experiment until an adult who has read the supervision notes above is present.

An adult needs to be here first

The materials (7) and steps (5) for this experiment are hidden until an adult who has read the safety information above is present.

What you should see

• The bottle with sugar fills with froth and bubbles and its balloon slowly inflates.
• The bottle without sugar shows little froth and its balloon stays almost flat.

Why it works

Yeast is a living single-celled fungus. It breaks down sugar to release energy. With little oxygen available, yeast carries out alcohol fermentation, which turns sugar into ethanol and carbon dioxide gas.

The carbon dioxide bubbles out of the liquid and fills the balloon. Without sugar the yeast has almost nothing to break down, so very little gas is made. Temperature matters: warmth speeds the yeast up, but yeast is killed at about 57 °C, which is why the water must be warm rather than hot.

Learn the ideas behind it

• Cell
• Chemical Reactions
• Respiration

Explore it further

The same ideas, as something you can change and watch on screen:

• Cell Explorer (3D)

Sources

• Biology 2e, 7.5 Metabolism without Oxygen — OpenStax
• Key Breadmaking Temperatures — Kansas State University Research and Extension
• EU does not ban children from blowing up balloons — European Commission