Tuesday the 13th of April, 2010
Yeast and fermentation: research into variables
Berger, C.D. & Scholtes, A.J.G.T.
Philips van Horne SG, Weert, Netherlands
Introduction
Experimental procedure and approach
When glucose is fermented by S.
Cerevisiae the amount of CO2 produced
depends on several variables. In the
research of Slaa, Gnode & Else all variables
except for temperature are kept constant,
and the amount of CO2 produced at
different temperatures is measured.
However, temperature is not the only
variable that can have a crucial effect on
the amount of CO2 produced. After some
research into the subject, it becomes
apparent that the pH-level is also a very
important factor.
Another variable in the fermentation of
sugar are the enzymes in yeast. Yeasts of
different species do not all contain the
same enzymes, and hence different yeasts
behave differently towards the various
sugars. A particular yeast may ferment
one sugar but not another.
This raises the question how the yeast
cells will behave at different pH-levels and
how different species of yeast ferment
one sort of sugar.
Our hypothesis is that the optimal pHlevel for yeast cells will be around 5-6. This
is typical for Saccharomyces Cerevisiae.
Our second hypothesis is that the high
temperature Saccharomyces Cerevisiae
will have the best results, because our
research is conducted at a high
temperature.
Research into optimal pH-level
In order to find out what the optimal pHlevel for fermentation was we made 4
different pH-buffer solutions with Sodium
acetate and acetic acid.
A 0,2M acetic acid solution was made
using this calculation:
0,20 mol x 60,05 g/mol = 12,01
ρ = 1,048 g/ml
12,01 / 1,048 = 11,46
This means 11,5 ml concentrated acetic
acid on 1L of water.
A 0,2M sodium acetate solution was made
solving 27,20 grammes of sodium acetate
in 1L of water.
0,2M Sodium
Acetate [ml]
63
40
21
9,5
0,2M Acetic
Acid [ml]
37
60
79
90,5
pH
4,471
4,820
5,224
5,611
The pH levels were checked with a pHmeter (WTW).
Four portions of 10,00g of sugar and just
as many portions of 2,50g of
Saccharomyces Cerevisiae were measured
with analytic scales. From each was added
one portion to each buffer solution.
In order to measure the amount of CO2
that would be produced during the
process of fermentation we constructed
the following setup:
Picture 1.1
Results
Research into optimal pH-level
Our experiments aimed to give us the
optimal pH for Saccharomyces Cerevisiae.
This gave the following results:
Table 1.1
pH
4,471
4,820
5,224
5,611
CO2 [mL]
0,00
3,47
4,80
4,70
Picture 1.2
In this setup the burette was filled with
CO2 saturated water, so all CO2 that comes
out of the erlenmeyer flask will result in a
change to the waterlevel in the burette,
exactly as much as CO2 as left the
erlenmeyer. The amount of liquid that was
in the burette was noted at the beginning
and after a fixed period of time (1 hour)
the amount of liquid in the burette was
again noted. The difference between
these numbers was the amount of CO2
produced.
The Erlenmeyer flask was put into a
waterbath set at 36,5oC to keep the
solution at a constant temperature.
Research into different yeast species
For our research, four different species of
yeast were acquired. The same set up was
used as described above and shown in
picture 1.1. Each of the species was put
into an erlenmeyer flask , with 10
grammes of sugar and 100 mL of destilled
water with a pH of 5,960. The reaction
was started and was allowed to ferment
for 15 minutes. All research was done at a
constant temperature of 36,5oC.
Research into different yeast species
Our experiments aimed to give us the
fastest growing species of yeast at a
temperature of 36,5oC. This gave the
following results:
Table 2.1
Yeast species
Saccharomyces
Cerevisiae (high temp.)
Saccharomyces
Cerevisiae (low temp.)
Saccharomyces
Bayanus
Fresh bakers yeast
CO2 [mL]
> 48,80
47,26
47,98
6,10
Data analysis
Conclusion and discussion
Research into optimal pH-level:
ρCO2 = 1,98 g/L
Molecular mass CO2 = 44,01
The amount of CO2 in mol was calculated
using the following formula:
[ρCO2] x 10-3 x [mL CO2] = [grammes CO2]
[grammes CO2] x [molecular mass CO2] =
[mol CO2]
Research into optimal pH-level
From these prelimenary results can be
concluded that a mildly acidic pH level is
the best environment for fermentation.
Table 1.2
pH
CO2 [mL]
4,471 0,00
4,820 3,47
5,224 4,80
5,611 4,70
CO2 [g]
0,00
0,00687
0,00950
0,00931
CO2 [mol]
0,00
0,302
0,418
0,410
The
chemical
equation
of
the
fermentation of sugar is:
C6H12O6  2 CH3CH2OH + 2 CO2
The amount of CO2 in mol is equal to the
amount of ethanol (in mol) produced. The
amount of ethanol in mL was calculated
with the following formula:
[mol C2H6O] x [molecular mass C2H6O] / [ρ
C2H6O] = [mL C2H6O]
ρ C2H6O = 790 g/L
Molecular mass C2H6O = 46,0688 g/mol
This means that the following amounts of
ethanol were produced:
Table 1.3
pH
4,471
4,820
5,224
5,611
Ethanol [L]
0
0,0176
0,0243
0,0239
Research into different yeast species
/
However, our results show that there is
room for even a higher pH to be the
optimal level for fermentation. During our
research there was no time to check this
new hypothesis, but a follow-up research
is planned in the near future.
Research into different yeast species
Our results show that our hypothesis is
confirmed because the high temperature
S. Cerevisiae produced the most CO2. It
produced even above our expectations so
the exact amount of CO2 could not be
measured.
To acquire more accurate results our way
of reading the amount of CO2 has to be
improved. However, the set up in general
was very succesfull and an accurate way, if
used correctly, to measure the amount of
CO2 produced.
Bibliography
1. Binas, 5e druk, 288 pagina’s, ISBN
978-90-01-89380-4,
uitgeverij
Noordhoff
2. Chemical specialists Jan van
Hunsel, Martin Waals, Susanne
Trommelen