Fermentation of glucose using yeast
Beer and wine are produced by fermenting glucose with yeast. Yeast contains enzymes that catalyse the breakdown of glucose to ethanol and carbon dioxide. In this experiment, a glucose solution is left to ferment. Students then test for fermentation products.
Read our standard health & safety guidance
Lesson organisation
This experiment takes time. The solution needs to ferment between lessons, especially if you are distilling the final solution to produce ethanol.
Apparatus and chemicals
Eye protection
Each pair of students requires:
Conical flask (100 cm3)
Boiling tube
Measuring cylinder (50 cm3)
Access to a balance (1 dp)
Cotton wool
Sticky labels
Warm water 30–40 °C (see note 1)
Glucose (Low Hazard), 5 g
Yeast (as fast acting as possible), 1 g
Limewater
Technical notes
Glucose (Low hazard) Refer to CLEAPSS Hazcard 40C
1 A source of warm water is required. Larger conical flasks can be used, but this dilutes the carbon dioxide concentration, and makes testing for carbon dioxide with limewater more difficult.
Procedure
HEALTH & SAFETY: Wear eye protection
Lesson 1
a Put 5 g of glucose in the conical flask and add 50 cm3 of warm water. Swirl the flask to dissolve the glucose.
b Add 1 g of yeast to the solution and loosely plug the top of the flask with cotton wool.
c Wait while fermentation takes place.
d Remove the cotton wool and pour the invisible gas into the boiling tube containing limewater. Take care not to pour in any liquid as well.
e Gently swirl the limewater in the boiling tube and note what happens.
f Replace the cotton wool in the top of the flask.
Lesson 2
a Remove the cotton wool and note the smell of the solution.
b The solution may be retained for a teacher demonstration of distillation.
Teaching notes
Class results can be pooled to demonstrate distillation.
If you want to do this, carefully decant or filter the solution into your distillation flask. (Significant quantities of yeast will produce foaming and this can be carried over into the product.)
Collect the fraction between 77–82 °C. (Ethanol boils at 78 °C.) This fraction should burn easily compared with the non-flammable original solution.
The ethanol must be burnt or poured away immediately. It must not be kept or used.
If fermentation is not rapid because of the yeast used, then the whole experiment can be carried over to the second lesson.
Yeast has an enzyme called zymase and this catalyses the fermentation process.
Glucose zymase → Ethanol + carbon dioxide
C6H12O6 (aq) → 2C2H5OH(aq) + 2CO2(g)
Student questions
Here are some possible questions to ask students:
How do you know fermentation is taking place? Which gas does limewater test for? Suggest other methods for measuring the speed of this reaction.
Health and Safety checked, September 2007
Web Links
General information on glucose fermentation.
www.gcsechemistry.com/rc16.htm
(Website accessed March 2009)
Updated 25 Mar 2009Average rating: 
3 out of 5
Your reviews
Please mention how to make dilutions.
Submitted by: priya on 10 November 2008
It is good, but why do you use glucose instead of starch? I am a student of Olabisi Onabanjo University in Nigeria and I am working on biodiesel as my final year project. I first extract ethanol and it was 95% pure from starch material (maize).
Submitted by: sulaimon olaleye on 18 December 2008
Make it better.
Submitted by: Nick on 18 December 2008
boring...
Submitted by: Jordan on 27 November 2008
1.Why is it important to boil the water?
2.What new substancewould you expect to find in the sugar sln containing living yeast?
3.What is the use of liquid paraffin?
4.Why must the sugar solution be cooled before adding the yeast?
5.What happened to the lime water?
Submitted by: qadir muradali on 18 March 2009
Sulaimon Olaleye -- why wouldn't you use glucose? Starch is a homopolysaccharide of glucose molecules.... sure starch would be fine but add the enzyme amylase and it just breaks down into glucose.... glucose is a sugar and is perfectly fine for this experiment. Fructose, sucrose and maltose are also sugars and can be used...
Submitted by: caleb machin on 8 April 2009
I liked the experiment because it gave me a better thing to do rather than spoonfeed my fish sugar.... However I found that the yeast did not last when I put it in the microwave to get the heat up. Please explain?
Submitted by: Martin Webster on 23 April 2009
It's really helpful.
Submitted by: sherona williams on 11 May 2009
Hmm..the experiment was useful. At least now I'm already aware that beer and wine are produced by fermenting glucose. Good work!!
Submitted by: clave cyrine joy s. cadiz on 17 June 2009
I want to know more about the inhibitors used during these experiments and for what reasons as the process should be continous as it's life sustaining to all living matter....................
Submitted by: HLAYISEKA WALTER NKWINIKA on 4 August 2009
In what ways are the starting materials and end products in three processes similar, different?
Submitted by: erica on 11 August 2009
Great, but any errors occurred?
What's your conclusion for this experiment?
Submitted by: HM on 13 August 2009
I was looking for this experiment which forms a part of the B.Sc. Life Science syllabus of Delhi University, being taught a Zakir Husain College. It not only solves my problem but gives an insight into many required details. We will be now doing fermentation better than we attempted in last week's class.
Submitted by: Dr. M.K. Gupta on 3 October 2009
It needs improvement as I am studying at Birmingham Uni and I neeed BETTER guides.
Submitted by: Ahsan Ghafoor on 20 January 2010
I want to know the observations for the practical activity.
Submitted by: Akeem on 7 February 2010
This helps me with my work. Thank you
Submitted by: zain zafar on 9 March 2010
I was curious as to the optimum amount of yeast/nutrients that needs to be added to the sugar water such that no yeast is wasted at the end of the fermentation process. This is assuming a 3 day fermentation process.
Submitted by: Andrew Bawn on 19 March 2010
The glucose solution in the flask was boiled and then cooled to 38°C. Give me some reasons why the glucose solution was boiled before use. (fermentation)
Submitted by: mary on 14 April 2010
Submitted by: Patricia Poolface on 20 April 2010
Really this is very helpful to all of biotechnology students. I understood so many things that I was missing.
Submitted by: Ahmed abdalla on 13 July 2010
This is very good and helpful. I am a student of biotechnology (integrated).
Submitted by: Rahul Poonia on 26 June 2008