Watching Yeast Make Bubbles

This demonstration shows how bread yeast ferments sugar to release carbon dioxide, which can inflate a balloon, and allows students to observe live yeast cells under a microscope.

1. Place a packet of active dry yeast into a bowl.
2. Add warm water and about two tablespoons of sugar, then stir to mix.
3. Transfer the yeast mixture into a bottle.
4. Stretch a balloon over the neck of the bottle and wait about 10 minutes. The balloon should begin to inflate as yeast releases carbon dioxide.
5. To observe the yeast, place a drop of the mixture on a glass slide (diluting if necessary).
6. Cover with a plastic coverslip and examine under a compound microscope at increasing magnifications.

Yeast Fermentation Under the Microscope - Sci- Inspi:

📄 Watching bread yeast make bubbles - MRC Laboratory of Molecular Biology: https://www2.mrc-lmb.cam.ac.uk/microscopes4schools/yeast.php

• Try using different sugar sources (e.g., honey, fruit juice, or corn syrup) to see if fermentation varies.
• Compare the rate of balloon inflation at different temperatures.
• Observe yeast cells at intervals (e.g., 5 minutes, 30 minutes, 1 hour) to notice budding or growth.

• Use warm water, not hot, to avoid killing the yeast.
• Handle glass slides and coverslips carefully to prevent cuts.
• Do not consume the yeast mixture.
• Wash hands thoroughly after handling yeast and materials.

• Why does the balloon inflate when yeast ferments sugar? (Because carbon dioxide gas is released during fermentation.)
• What role does yeast play in bread-making? (It ferments sugars in flour, releasing carbon dioxide that makes dough rise.)
• What happens to the ethanol produced in bread dough? (It evaporates during baking.)
• How do yeast cells reproduce? (By budding in asexual reproduction, and by producing spores under stress.)
• Why are yeasts useful in scientific research? (They are simple, fast-growing eukaryotic cells used to study fundamental cellular processes.)