Alcoholic Fermentation in Yeast

In the lab, Alcoholic Fermentation in Yeast, students learn about the basics of aerobic cellular respiration and alcoholic fermentation and design and carry out experiments to test how variables such as sugar concentration influence the rate of alcoholic fermentation in yeast. In an optional extension activity students can use their yeast mixture to make a small roll of bread.

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

We invite comments on this Hands-On Activity and the accompanying Teacher Preparation Notes, including suggestions for other teachers who are planning to use the activity, useful preparatory or follow-up activities, additional resources or any questions you have related to the activity, or a brief description of any problem you might have encountered. If you have a relevant Word document you would like to have posted on this comments page, such as a version of the protocol you have used in your classroom, or if you would prefer to send your comments or questions in a private message, please write Ingrid Waldron at

See also a complete list of activities:
Hands-on Activities for Teaching Biology to High School and Middle School Students



Serendip Visitor's picture

Optimal Sucrose concentration

I apologize if this answer is found somewhere in the teacher prep material, I have not found it. When preforming this experiment I expected to see an increase in the carbon dioxide production as the sucrose concentration increased. For example, the 10% sucrose would result in the most carbon dioxide production. Instead, several lab groups saw the most carbon dioxide production with the 1% solution. Is this due to experimental error or is this the expected result? I am curious if too much sugar is detrimental to the yeast.

iwaldron's picture

Relationship of sucrose concentration to CO2 production

We would expect to see an increase in CO2 production as sucrose concentration increased, at least up to 10% sucrose. There is some evidence that very high concentrations of sucrose can result in decreased CO2 production, perhaps due to osmotic effects resulting in dehydration of the yeast cells. However, we would not expect to observe this effect in the range of 1-10% sucrose concentrations. As you suggest, there may have been experimental error such as differences in temperature that produced the anomalous results.

Serendip Visitor's picture

the lab

Why did the bubbles happen? why did they come up from the yeast?

iwaldron's picture

bubbles due to carbon dioxide production

The bubbles are due to the carbon dioxide produced by anaerobic fermentation (see the next to the last section of the Teacher Preparation Notes).

iwaldron's picture

October, 2011 Revision

The Teacher Preparation Notes have an improved section of Instructional Suggestions.  The revised instructions on the top of page 3 of the Student Handout will help to ensure student success with the experiment.  

iwaldron's picture

May, 2011 revision

This activity has been revised to clarify and streamline the first experiment and the discussion of aerobic cellular respiration and alcoholic fermentation.

iwaldron's picture

December 2010 update

The main change is an updated, reorganized description of aerobic cellular respiration and alcoholic fermentation.

Anonymous's picture

Effect of salt, egg and flavoring agent (i.e. raisin) in bread

What is effect of adding salt, egg or raisin in fluffiness of bread?

Jennifer Doherty's picture

Hi, We don't know the answer


We don't know the answer to this question. The baking site we have provided in the prep notes ( says salt and fat cause bread not too rise as much. My own experience in performing the lab is that salt (and cinnamon) slows down the rate of cellular respiration in baker's yeast.

This sounds like it could be a good investigation for your students.

I hope this helps!


Anonymous's picture

Answer Key

Dear Mrs. Ingrid.

Is it possible that you have the answers to the questions for this lab?

iwaldron's picture

Answers for Questions


We do not have teacher answer keys for our activities. However, most of the questions for this activity can be answered based on information presented in the Student Handout and Teacher Preparation Notes or general knowledge of principles of experimental design (which are particularly important for this activity since it is an inquiry activity in which students design their own experiments). If you would like more background concerning the biological processes discussed, we recommend that you read relevant sections in a good college-level introductory biology textbook or a biology textbook for a high school AP course, e.g. Campbell, Reece, et al., Biology, eighth edition (Pearson/Benjamin Cummings). If you have a specific question or two that you are uncertain about, please let me know.

 Ingrid Waldron, Ph.D.


Neff's picture

Respiration Lab

We did this lab on a Friday and left it for the weekend.

We got foaming and some gas produced after 20 minutes. By the end of the day the 10% and 5% solutions had produced enough gas to measure but the students never saw it.

By Monday morning the gas was all gone due to the fact that the building is not heated on the weekends.

I suggest doing the lab on a weekday and looking at results after 24 hours.

We also added BTB solution to each one for a color change which showed the production of carbon dioxide gas.

iwaldron's picture

Getting results within one class period


It should be possible to complete Part I of this activity in one class period. To ensure that your students can observe results at 10 and 20 minutes, be sure to use rapid rise or fast acting yeast that is not near or past its expiration date and water that is between 80°F and 115°F.


Barb Tharp's picture

What was the grade level of

What was the grade level of the students who completed this lab? Do you think middle schoolers (7th & 8th graders) would be able to complete this lab? Any guidance about aspects of the lab with which students struggled?

iwaldron's picture

suggestion for middle school students


We have used Cellular Respiration in Yeast with high school students, typically ninth graders. For seventh and eighth graders we recommend Is Yeast Alive? ( This activity provides a simpler approach to yeast metabolism which is more appropriate for most middle school students. You could use pages 1-3 of the student handout for Is Yeast Alive? and omit the part on growth of yeast if you want to focus just on metabolism.


Ingrid Waldron


Jason Crewe's picture

Yeast & Celluar Resp.

Just a comment about the yeast used. I used baker's yeast which claims to be Saccharomyces cerevisiae.

This yeast did nothing after 10 minutes, 20 minutes, after 30 min there was some action. This is not useful for a 90 minute period as there is no visible buildup of CO2 and 'measure the bubbles' means nothing if there aren't any, or they are not in the same area (after overnight they were distributed throughout the tube).

Just wondering what I did wrong? I used water heated to 38degC and the 0%,1%,5%,10% solutions. However nothing there something wrong with my yeast? Does it go off? Should I not be using baker's yeast?

As an addendum, I wanted to view the comments for this activity to see if someone had already answered this question but only this form came up, no prior comments area. Maybe it would be easier if I could just see the comments and then I might be able to work this out without posting!

Thanks for the lab, I think it's good but I couldn't get it working.....any advice?

iwaldron's picture

advice to ensure that your yeast will grow

We are sorry you had problems getting the yeast respiration lab to work in your classroom.  Simply mixing yeast, sugar, and warm water (80-115 F) into a homogeneous solution will cause the yeast to start respiring.  If yeast do not respire (release gas and make bubbles) when mixed with warm water and sugar there is either something wrong with the 1) yeast or 2) water. 

Problems with the yeast could be that it is too old or was exposed to extreme heat or cold.  Problems with water could be that it was too cold (below 80 F) or too hot (above 120 F) or has too many impurities (this would be very rare and would probably only be the reason if you used non-potable water).  If you start with water that is too hot and it cools to warm water, the yeast may still have been killed while the water was too hot. 

The speed at which the yeast respire will depend on how fast the warm water cools off in your classroom (how warm or cold your classroom is), however as your yeast mixtures didn't produce any bubbles I suspect that was something off with your yeast or water.

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