Yeast Fermentation Lab
Name:
Biology 6.0
Date:
Period:
Introduction
In this lab study, you will investigate alcoholic fermentation in yeast (a single-celled fungus), Saccharomyces
cerevisiae, or “baker’s yeast.” When oxygen is low, some fungi, including yeast and most plants, switch from
cellular respiration to alcoholic fermentation. In bread making, starch in the flour is converted to glucose and
fructose, which serve as the starting compounds for fermentation. The resulting carbon dioxide is trapped in the
dough, causing it to rise. Ethanol is also produced in bread making but evaporates during baking.
In this laboratory experiment, the carbon dioxide
(CO2) produced, being a gas, bubbles out of the
solution and can be used as an indication of the
relative rate of fermentation taking place. The rate of fermentation, a series of enzymatic reactions, can be
affected by several factors, for example, concentration of yeast, concentration of glucose, or temperature. In
this lab study you will investigate the effects of carbohydrates on the rate of fermentation.
Hypothesis: Write a hypothesis to explain the effect of different carbohydrates on the rate of fermentation.
Materials
test tubes
test tube rack
pipettes
sugar solutions
yeast solution
Procedure
1. Obtain four clean test tubes, and label them 1 through 4. Fill the test tubes with the following:
Tube 1: 5 mL of distilled water and 5 mL of yeast solution
Tube 2: 5 mL of glucose and 5 mL of yeast solution
Tube 3: 5 mL of sucrose and 5 mL of yeast solution
Tube 4: 5 mL of starch and 5 mL of yeast solution
2. Fill a beaker ¾ full with hot water (~37-40°C). Place all test tubes in the beaker. You must maintain the
warm water temperature. Constantly replenish the beaker with warm water.
3. You should observe tiny bubbles being released within the test tube forming a froth above the liquid. See
the picture below of yeast froth.
4. Measure the amount of froth above the liquid every five minutes for a total of 30 minutes.
5. Record your results.
6. Clean all test tubes with soap and water before returning glassware to the lab drawer.
Yeast Froth 
Data and Observations:
Time Elapsed
(min)
Measured amount of froth
Tube 1
Water
Tube 2
Glucose
Tube 3
Sucrose
Tube 4
Starch
5
10
15
20
25
30
Glucose
Sucrose
Analysis Questions:
1. Using graph paper construct a line graph of your results. Use different colors for each yeast solution. Be
sure to include a key.
2. Explain the results shown in your graph.
3. What molecule is split in the fermentation process that produces CO2?
4. Identify which of the tubes represents the control for the experiment. Briefly explain why this is a valid
control for this experiment.
5. Based on your knowledge of cellular respiration and carbohydrates, attempt to explain why some of the
substrates gave faster fermentation rates than others.
6. When a carbohydrate is fermented by yeast cells, only one third of the carbons are released as CO2. The rest
of the carbon atoms are released as a molecule of what?
7. Explain how measuring the froth is a way of measuring the rate of fermentation.
Use the following website to review the lab and to help answer the questions.
http://emp.byui.edu/wellerg/Cell%20Respiration/introduction.html