The Effect of Different Levels of pH on the Fermentation of Yeast

By Rachel Koch

Hypothesis and Problem StatementProblem: 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

Levels pH of 5 pH of 6 pH of 7(control)

pH of 8

Trials 5 5 5 5

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.

Design Diagram cont.IV: pH levelDV: 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.

MaterialsFlourSugarInstant yeastWarm water/solutionOilSaltRulerHClNaOHOven

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

  pH 5 pH 6 pH 7 (control)

pH 8

Trial 1 4.5 cm 2 cm 4.5 cm 3.5 cm

Trial 2 5 cm 3 cm 4 cm 3 cm

Trial 3 5 cm 3 cm 4 cm 3.5 cm

Trial 4 5 cm 3.5 cm 4.5 cm 3 cm

Trial 5 4.5 cm 2.5 cm 4 cm 3 cm

Averages 4.8 cm 2.8 cm 4.2 cm 3.2 cm

AveragesPH 5: 4.8 cmPH 6: 2.8 cmPH 7 (control): 4.2 cmPH 8: 3.2 cm

Graph

pH 5 pH 6 pH 7 pH 80

1

2

3

4

5

6

Level of pH

Heig

ht

of

dou

gh

in

cm

.The Effect of Different Levels of pH on the Fermentation of

Yeast

Statistical Analysis

Source of Variation

Sum of squares

Degrees of Freedom

Mean Squares

F Significance

Between 13.14 3 4.379 33.37 0.000

Error 2.1 16 0.1313    

Total 15.24 19      

ANOVA

Conclusions

Hypothesis did not support data

Ideal environment is pH 4-6

Yeast ferments better in acidic

substances

Data is inaccurate

Possible ErrorsOven 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

ReasoningLike to bake

Thought it was interesting that yeast makes dough rise

ExtensionsTest other factors that effect

yeast fermentation, like:

oTemperature

oAmount of sugar

Acknowledgements Mrs. Po Preparing solutionso Helping

Parentso Bought ingredients

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2010. <http://www.io.com/~sjohn/bread.htm>.

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<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>.

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<http://www.dakotayeast.com/help-fermentation.html>.