The Effect of Different Levels of
pH on the Fermentation of Yeast
By Rachel Koch
Hypothesis and Problem Statement
Problem:
How do different levels of pH in the
environment around yeast effect its
fermentation?
Hypothesis:
If the environment around the yeast has a
higher pH, then the yeast will create more
CO2.
Background Research

Yeast: microorganism, Eukaryotic domain and
the Fungi kingdom

Baker’s yeast: digests sugar

Fermentation: release carbon dioxide

Energy and warmth for fermentation

Dough rising is result of fermentation
Design Diagram
Title: The Effect of Different Levels of PH
on the Fermentation of Yeast
 Hypothesis: If the environment around
the yeast has a higher pH, then the yeast
will create more CO2.

Levels
pH of 5
pH of 6
pH of 7
(control)
pH of 8
Trials
5
5
5
5
Design Diagram cont.
IV: pH level
 DV: Height of dough(cm)
 Constants: Ingredients in dough (besides
IV), the measurements of each ingredient,
temperature at which the dough is placed
to ferment and the amount of time the
yeast ferments.

Materials










Flour
Sugar
Instant yeast
Warm water/solution
Oil
Salt
Ruler
HCl
NaOH
Oven
Procedure
•
Prepare pH solutions in lab with the
instructor using NaOH for basic solutions
and HCl for acidic solutions.
1.
Heat water/solution to 35 degrees C.
2. Add flour, sugar, oil, yeast and salt to
the warmed water/solution.
Procedure cont.
3. Knead dough for about 8 minutes.
4.
Measure the height of the dough.
5. Store dough in a warm place for 45
minutes to allow yeast to ferment.
Procedure cont. 2

Put dough in the oven set to 54
degrees C and turn the oven off
6. Measure the final height that the
dough raises with a ruler.
Photodocumentation
Data
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Averages
pH 5
pH 6
4.5 cm
5 cm
5 cm
5 cm
4.5 cm
4.8 cm
2 cm
3 cm
3 cm
3.5 cm
2.5 cm
2.8 cm
pH 7
(control)
4.5 cm
4 cm
4 cm
4.5 cm
4 cm
4.2 cm
pH 8
3.5 cm
3 cm
3.5 cm
3 cm
3 cm
3.2 cm
Averages
PH 5: 4.8 cm
 PH 6: 2.8 cm
 PH 7 (control): 4.2 cm
 PH 8: 3.2 cm

Graph
Height of dough in cm.
6
The Effect of Different Levels of pH
on the Fermentation of Yeast
5
4
3
2
1
0
pH 5
pH 6
Level of pH
pH 7
pH 8
Statistical Analysis
ANOVA
Source Sum of
of
squares
Variati
on
Between 13.14
Degrees Mean
F
of
Squares
Freedom
Signifi
cance
3
4.379
0.000
Error
2.1
16
0.1313
Total
15.24
19
33.37
Conclusions

Hypothesis did not support data

Ideal environment is pH 4-6

Yeast ferments better in acidic substances

Data is inaccurate
Possible Errors

Oven temp. wasn’t exactly the same every
time

Measurements might not have been exact

Measured every half centimeter
Improvements

Could buy an alternative heating devise

Measure ingredients more carefully

Measure the height to a tenth of a cm
Reasoning

Like to bake

Thought it was interesting that yeast
makes dough rise
Extensions

Test other factors that effect yeast
fermentation, like:
oTemperature
oAmount of sugar
Acknowledgements
Mrs. P
o Preparing solutions
o Helping

Parents
o Bought ingredients

Bibliography
"Basic Bread." PrismNet : Austin TX VOIP, Broadband Colocation, Web Hosting. Web. 05 Oct.
2010. <http://www.io.com/~sjohn/bread.htm>.
"Fermentation." Utah State University: Intermountain Herbarium. Web. 04 Oct. 2010.
<http://herbarium.usu.edu/fungi/funfacts/Fermentation.htm>.
"What Are Yeasts?" Saccharomyces Genome Database. Web. 05 Oct. 2010.
<http://www.yeastgenome.org/VL-what_are_yeast.html>.
Campbell, Neil A., Jane B. Reece, Lawrence G. Mitchell, and Martha R. Taylor. Biology
Concepts & Connections. San Francisco: Benjamin Cummings, 2003. Print.
"Factors Effecting Fermentation." Web. 19 Dec. 2010.
<http://home.earthlink.net/~ggda/factors_effecting_fermentation.htm>.
"Yeast Fermentation in Baked Goods." Dakota Yeast. Web. 20 Dec. 2010.
<http://www.dakotayeast.com/help-fermentation.html>.