That’s the spirit! – Standard Procedure
1. Scope
This experiment is used to determine the effect of sugar concentration
on the rate of reaction of the fermentation of sugar by yeast.
2. Principle
Fermentation is a chemical process by which microorganisms such as
yeast break down sugars into alcohol, and carbon dioxide gas.
C6H12O6 →2C2H5OH + 2CO2
The rate at which fermentation occurs depends upon factors such as
temperature, pH and sugar concentration. In this experiment you will
measure the effect of changing sugar concentration on the rate of
fermentation.
3. Reagents

Distilled water

Glucose

Yeast powder (fast acting)
4. Apparatus

4 x 250 cm3 flat bottomed flasks

Delivery tube and gas syringe in clamp/stand

Water bath set to 32oC

Stopwatch

Electronic balance
5. Safety
A Risk Assessment must be developed and used before doing this
experiment.
Glucose Hazcard 40c
6. Procedure
1. Obtain four 250 cm3 flat-bottomed flasks and label them 1,2,3,
and 4.
2. Add to each of the four flasks 2.5 g of yeast, accurately weighed.
3. Weigh accurately 0.50 g of glucose for flask #2 and 1.50 g of
glucose for flask #3, 2.50 g of glucose for flask #4
4. Prepare 500 cm3 of distilled water, heated to 32°C in a water
bath. Add 100 cm3 of the water to flask #1. Swirl the contents
gently to mix.
5. Attach a delivery tube connected to a gas syringe (supported in a
clamp and stand) to the flask.
6. Place the flask into the water bath set to 32oC.
7. Record the volume of gas every minute for 15 minutes.
8. Repeat steps 4 to 7 for flasks #2; #3 and #4
9. Repeat the whole experiment obtaining two sets of data for each
flask.
7. Calculations
Calculate the average volume of gas produced by each flask for each
minute of the experiment. Plot graphs for each one, showing volume of
gas produced (y-axis) against time (x-axis).
Draw tangents to each graph every 2 minutes. Calculate the tangent –
this gives you a measure of the fermentation rate in cm3 min-1
Plot graphs of fermentation rate (y-axis) against time (x-axis) for each
concentration of glucose solution.
Plot a graph of fermentation rate after 2 minutes (y-axis) against mass
of glucose (x-axis).
8. Expression of results
Pattern statements of the trends in each graph are required.