Yeast Lab

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


  • teaspoon
  • Active dry yeast – not quick-rising
  • 2-liter soda (shake and open) – Let it go flat. (two of these)
  • Water in a clean 2-liter bottle  (two of these)
  • Identical round, thin, regular balloons



  • Write on your bottles or place labels on them for control and experiment. (Don’t just assume you’ll remember. The appearance of your soda can change.)
  • Put a teaspoon of dried yeast in all bottles. Be careful to make them all the same.
  • Close the bottles and shake them the same in order to dissolve the yeast.
  • Open the bottles and stretch a balloon over the mouth of each bottle. Do one at a time to avoid gas leaking.
  • Find a warm place where they can be undisturbed. Don’t place it in the sunlight.
  • Create a table to record your data: the diameter of the balloon, the time passed, and any observations. You can squeeze the balloon flat at the widest point to measure across for the diameter. Measure every 12 hours for two days (4 entries of data).
  • Create a graph to compare your results.

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?