The student researchers studied how varying the pH level of glucose solutions affected the anaerobic respiration rate of yeast. They tested solutions with pH levels of 4, 7, and 10 and found that pH 4 had the fastest respiration rate, while pH 10 was slowest. This suggests that yeast fermentation works best under more acidic conditions and higher pH may inhibit the enzymes involved in the process. However, the researchers noted some limitations in their methods and materials that could have impacted the results.

1. The Effect of Changing pH in
Yeast Fermentation
Debbie Sasges
Kelsey Sunderland
Lauren Rizzo

2. Experiment
• We studied the anaerobic respiration
capabilities of yeast with varying pH levels
in the glucose solutions.
• We wanted to know how acids and bases
affect the respiration of yeast and what pH
would be the optimized pH for this
reaction.

3. What is the Effect of varying the pH level
of the environment on the rate of the
reaction (anaerobic respiration)?
•We wanted to know how acids and bases affect the
respiration of yeast and what pH would be the optimized
pH for this reaction. Is optimal pH 7?
•Possibility that pH when increased or decreased
dramatically will denature the enzyme that helps fuel the
reaction, and will in effect, decrease the rate at which
the reaction occurs.

4. Methods and Materials
• Original directions were followed, but
instead of changing glucose
concentration, 5 ml of 10% glucose
solutions of pH 4, 7, and 10 were added to
the 5 ml of yeast.

5. Results
• pH 10 had the slowest rate of respiration. The
graph has a line with a slope of only about
1unit/min, which means a reaction rate of about
.007 mL/min.
• pH 7 had a much steeper slope than that of pH
10 (about 6.75 units/min), with a reaction rate
of about .44 mL/min
• pH 4 had the steepest slope (about 7.67
units/min) and was closest to the control trial.
We believe that pH 4 is the optimal pH level for
yeast respiration.

6. Reaction Rate of Yeast Fermentation
0
0.01
0.02
0.03
0.04
0.05
0.06
4 7 10
pH of Glucose Solution
ReactionRate(mL/min)

7. What This Means
• Since the reaction was slower at pH 10
and pH 7 than it was in the control trial, it
is safe to estimate that pH 4 is the optimal
pH for the fermentation of yeast, or that
yeast fermentation is aided by a more
acidic than basic environment.
• Higher pH levels may well have aided in
the denaturing of the enzyme that help
yeast to ferment.

8. What this Means (cont.)
• Supports the hypothesis that the optimal
pH would have a faster rate of reaction.
• pH 10 and pH 7 in fact slow down the
reaction.

9. But. . .
• Possible that experimenters mixed pH
solutions in the wrong way, or made
mistakes measuring out glucose solutions
or yeast, thusly affecting the rate of
reaction.
• Machine recorder may not be working
perfectly.
• Timing was not always exact, some extra
time was sometimes given.

10. For the Future
• Because the experimenters only had
access to 3 pH levels, possible research
could be done on all levels of the pH
scale. Try working with pH and
concentration or with pH and enzymes at
extremes.
• What exactly is the pH of the original
glucose solution?

11. Yeast is Fun!