Lab 7: Alcoholic Fermentation

Objectives:
• Demonstrate an understanding of and apply the scientific method

• Develop appropriate statistical and biological hypotheses

• Observe CO2 production due to alcoholic fermentation

• Increase the rate of alcoholic fermentation

• Use data to analyze results and draw appropriate conclusions in relation rate of fermentation

• Demonstrate ability to effectively communicate through scientific writing

Note to Students:
If at any point you are unsure about how to identify variables or write your hypotheses, please remember that this
information is available in Module 1.

It is strongly recommended that you complete labs several days in advance, so you will have time to ask for help if
you need it. Remember, you can reach me via Remind, through the classroom "get help" discussion boards, or
email.

Remember to include your name card in all photographs!

Prelab/Background Research
This week you will NOT be submitting answers to the prelab questions - but you will need to use these questions to
help guide you as you develop your experiment and the information from the prelab should be used to write your
introduction for your lab report.

Today you will be investigating the process of anaerobic fermentation using baker’s yeast as your test subject.
Yeast is a fungus and it is what provides bread with its fluffy texture and can be used to carbonate beer. These
changes occur because of the way yeast breaks down carbohydrates. Yeast takes a simple sugar, such as glucose,
and breaks it down without using oxygen in an anaerobic process called alcoholic fermentation. (Other types of
fermentation also occur)
Background Questions to Consider:

• You will be counting bubbles produced by alcoholic fermentation - what are these bubbles?

• What is the formula for aerobic respiration? Alcoholic fermentation?

• What happens when yest uses alcoholic fermentation? What are the benefits to the yeast? What problems can

arise?

• Why would we be interested in increasing the rate of alcoholic fermentation in yeast? (In what situations would

people want this to occur?)

• You will pick 1 variable to manipulate in an effort to increase the rate of fermentation - you will need to justify

why you chose the variable that you select.

• Remember to include the "why" in your biological hypotheses - your hypotheses will be worked into your

introduction and do not receive their own heading. They will be used again during the discussion/conclusion

Materials Needed for "Kitchen Lab"

• Sugar - possible independent variable: other types of sugar/energy sources

• Glasses/cup

• Small Water bottles (8 oz)

• "bendy" straws

• Funnel (Recommended - can be made out of paper)

• Water

• Thermometer - inexpensive meat thermometer will work

• Balloons/Plastic Wrap

• Vaseline/Petroleum Jelly

• Timer
Assignment: Alcoholic Fermentation in Yeast
Summary:

In this experiment you will use the scientific method to help you learn about alcoholic fermentation. Keep in mind
that in order for fermentation rates to be high, oxygen availability in the system should be minimized - avoid
exposing your yeast mixtures to extra air once the experiment has begun.

You will conduct a demonstration first - this will serve as your baseline data. Your goal will be to increase the rate of
alcoholic fermentation in the yeast as indicated by the number of bubbles produced by the process.

Part I: Demonstration

Be certain to follow the directions precisely and collect data as you are instructed. This data will be used as the
“base-line” for the rest of your experiment.
Once you complete the demonstration, you will select a variable to manipulate.

Potential Independent Variables (Recommended):

• Sugar/Energy Source - you should use different sources of food for the yeast, powdered sugar, honey, brown

sugar, pancake syrup, powdered peanut butter, etc

• Amount of Yeast - increase and decrease amount of yeast while leaving energy source unchanged

• Amount of Sugar - increase and decrease the amount of sugar while leaving the type of energy and the yeast

amount unchanged

• Temperature of the water is NOT recommended as an independent variables as temperatures that are too high

will kill the yeast cells - temperature should be considered a controlled variable
Demonstration Procedure

• Put 3/4 C of water in a cup

• Put 3/4 C of warm water (40 - 42°C) in a 16 oz water bottle

• Add 1 tsp of white granulated sugar to the warm water in the water bottle, swirl until sugar dissolves

• Add 1 tsp dry active baker’s yeast to the warm water and sugar in the water bottle, swirl until mixture is

homogenous

• Place a balloon over the opening at the top of the bottle - secure with a rubber band if it is not flat across the top

(see photograph)

• Place end of straw through the balloon, apply petroleum jelly around the balloon/plastic wrap to make an air

tight seal

• Place the other end of the straw in water contained in the glass - be certain tip of tube is completely submerged

in water

• Allow solution to sit undisturbed for 3 minutes to allow the reaction to saturate the water with the gas being

released

• Take “bubble counts” for 60 second intervals beginning at minute 3, 4, and 5. (How many bubbles are released

over each 60 second period, starting at minute 3?)

• During each replication of the experiment be certain to place fresh water in the glass used for the bubble count

Figure 1: Fermentation Demonstration Set-up

Very little guidance will be provided to you for this portion. You should develop your own experiment - changing only
ONE of the variables recommended above, and then write a lab report with all required sections. Please take the
time to read the information on writing a lab report that is provided in this Lab Module. Let me know if you have any
questions and make sure you talk to your group members if you need help!

What to turn in:

o Introduction: background information and hypotheses, include intext citations using APA style

o Materials and Methods: written in outline/step-by-step format - do NOT write a separate materials list -

this should be for the EXPERIMENT you conducted, use the demonstrations instructions to help you get

started

o Data and Analysis: opening statement of overall data trend, table with data, graph representing data

with correctly labeled axes

o Conclusion: reject or fail to reject statistical and biological nulls - use data for support, relate treatment

of biological null to background information, describe mistakes made and potential impacts, describe

ways to improve experiment and potential future experiments to learn more about alcoholic

fermentation

o Citations page - using APA style - check out the Purdue OWL if you need help (Opens in a new

window)

o Attach a final page with photographs of the experiment that include your name card - you should include

one picture for change in the independent variable and an image showing the materials that were used