Yeast Lab

Problem: What effect does sugar have on the growth rate of yeast?


  • measuring spoons/cups and funnel
  • Four clean, dry glass or plastic bottles (Ex: 16oz water bottles)
  • Four packets (or 9 teaspoons) of active dry yeast – not quick-rising
  • Six teaspoons of sugar
  • Four cups warm water
  • Four balloons

Key Terms
Fermentation – A metabolic process that converts sugars to acid, gasses, and/or alcohol. It occurs in yeast, bacteria, and other microorganisms as well as oxygen-starved muscle cells.


  • Add one packet (or 2 1/4 teaspoons) of yeast to each bottle.
  • Label your bottles 1-4.
  • Add sugar to the bottles:
    • Bottle 1 – no sugar
    • Bottle 2 – 1 teaspoon
    • Bottle 3 – 2 teaspoons
    • Bottle 4 – 3 teaspoons
  • Add one cup of warm water to each bottle.
  • Gently mix each bottle. (Cover the bottle with your thumb or put the lid back on.)
  • Uncover the bottles and stretch a balloon over the mouth of each bottle.
  • Leave the bottles some place warm to sit for an hour.
  • Create a table to record your data: the diameter of the balloon, the time passed, and any observations. Starting at one hour after the balloons are placed onto the bottles, measure every 12 hours for two days (4 entries of data).
  • Create a graph to compare your results.

Watch this video for more discussion.

Write a conclusion. State your question, your findings, and your answer  to the question – how did you see sugar affecting the growth rate of yeast?