introductory fermentation bag


what materials are needed


  1. Dry active yeast (one 4 oz. jar contains approximately 36 teaspoons of yeast, which will make 36 bags)
  2. Warm water source
  3. Small graduated cylinders (100mL)
  4. Measuring spoons (one teaspoon for each feedstock source and the yeast to avoid cross-contamination)
  5. Feedstock(s): sugar, cornmeal, corn stover, sawdust, etc.
  6. Resealable zipper bags (“snack" size) with fill-in labels (see Supplementary Materials for label template).


  1. Rulers to measure bag inflation. See Supplementary Materials for instructions.
  2. Classroom-grade ethanol probe (Vernier or PASCO) or breathalyzer for detecting ethanol levels. See Supplementary Materials for instructions.
  3. 2-4 liter thermos (with spout) for dispensing warm tap water
  4. Paper towels
  5. print this data collection sheet

Pre-experiment questions

  1. What food source will you give to your yeast?

  1. What changes, if any, do you expect to observe with your bag over time?Explain.

  1. Do you expect to see any differences in observations between food sources that your class is comparing? Explain.

During experiment questions

During the experiment: Record your observations and measurements.

Yeast food source: _______________________

Start time:__________  End time:__________  Total time (min):___________

Observations & Measurements: Before After
Record scientific observations & measurements
(changes in appearance, smell, etc)

what are the steps

1. In a snack-size resealable zipper bag, combine 1 teaspoon of sugar (or another feedstock) and 1 teaspoon of yeast.

2. Add 50 mL (1/4 cup) of warm tap water (approx 40° C) and seal bag closed, removing as much air as possible.

3. Mix gently. Lay bag on a flat surface and watch for results – fastest results should be achieved in 15 minutes.**

4. Optional: Measure and compare ethanol and/or CO2 production using ethanol probes, breathalyzers, rulers, etc. Discuss and interpret results.

break point: 45 minute lesson plan

After experiment questions

After the experiment: Analyze and interpret your results.

Summarize what you know about substances in the bag before and after the experiment using this table:

Questions Start of experiment After experiment
What's in the bag?
What evidence do you have?

Propose an explanation for the changes you observed.

Compare your results with the class. What differences did you observe between food sources made of sugar, starch or cellulose?

Propose an explanation for those differences.