Yeast and Fermentation: How hard can it be?
16/4/2010
de Vries, D., Klaver, S.
st. Ignatiusgymnasium Amsterdam, The Netherlands
- Yeast
Introduction
- Calcium chloride crystals
- Sucrose
Ethanol is normally produced by the reaction
- A measure
𝐶2 𝐻4 + 𝐻2 𝑂 → C2 H5 OH at 300°C. This
- A few beakers
gives problems as the oil needed for the
- A scale
reaction is a bit running short nowadays. So
6 Wet lutes
there was searched for a new technique to
- A funnel
make ethanol, and one of mankind’s oldest
For our experiment, we wanted to know if the
chemical processes was found out to be
hardness in water had any effect on the ethanol
perfect: to produce ethanol from sugars by
production of the yeast. Since we wanted to
fermentation. For the fermentation are monoexclude the effects of the acidity of the water
sugars as D-glucose and D-fructose needed.
for instance, we used purified water to make
The reaction which happens at the
our sucrose solution. We dissolved our
fermentation:
𝐶6 𝐻12 𝑂6 → 2𝐶𝐻3 𝐶𝐻2 +
sucrose, after weighing out 30,00 grams of
2𝐶𝑂2 . It happens in an oxygen free
sucrose for every bottle, in 200 centiliters of
purified water and poured our solution with a
environment, so the S. cerevisiae cells extract
funnel in a plastic bottle. We repeated this 6
more energy from the sugar than with oxygen.
times, so that we had 6 bottles filled with 200
centiliters
of
our
sucrose
solution.
As we used Sucrose, 𝐶12 𝐻22 𝑂11 , it is
hydrolyzed to D-glucose and D-fructose by
invertase, an enzyme found in yeast:
𝐶12 𝐻22 𝑂11 + 𝐻2 𝑂 → 𝐶6 𝐻12 𝑂6 + 𝐶6 𝐻12 𝑂6
Sucrose
Water
D-Glucose D-Fructose.
We used 𝐶𝑎𝐶𝑙2 to create a variety of the hard
water in various bottles. After putting it into
the bottles, it falls apart to calcium and
chloride: 𝐶𝑎𝐶𝑙2 → 𝐶𝑎2+ 2𝐶𝑙− . As there are
more molecules in the mix now, the change of
invertase interacting with sucrose is lowered.
The calcium is hindering the reaction this way,
so there should be produced less ethanol and
carbonate dioxide. Thinking of this, the best
way the reaction should happen is without
calcium, so the water is soft. This gives the
question: Does hard water stop the
fermentation of glucose with yeast? Our
hypothesis is that the more calcium is added,
the less ethanol is produced, but the calcium
can’t stop the reaction completely.
Experimental design
Items needed:
- 6 Plastic bottles
- A barrel of purified water
After this, we
wanted to raise the hardness of our water by
adding calcium chloride crystals to our
solution. The calcium ions would raise the
water hardness. So, first of all, we labeled our
bottles: The bottles would have a molar
concentration of calcium ions of 0 mol/dm³,
0,25 mol/dm³, 0,5 mol/dm³, 0,75 mol/dm³,
1,00 mol/dm³ and the last bottle would have a
molar concentration of calcium ions of 1,25
mol/dm³. To get these molar concentrations,
we had to use the following chemical equation:
CaCl₂ (s) → Ca²⁺ (aq) + 2 Cl⁻
This means that we had to dissolve 5,55 grams,
11,10 grams, 16,65 grams, 22,20 grams and
We can conclude from our results that more
ethanol is produced when the water is soft. As
seen in table 1, the higher the molarity of 𝐶𝑎2+
in the bottle, the lower the mass 𝐶𝑂2 that is
produced.
If we look back at our experiment, one may
find some flaws. For example, we haven’t
done our experiment in duplicate and as we
can see, with a molarity of 1,25 mol/L the CO₂
production seems to rise. Is this a mistake or is
there really more ethanol produced with a
higher Ca²⁺ (aq) concentration? We think it’s a
mistake, but we should try to repeat the
experiment, maybe with higher Ca²⁺ (aq)
concentrations and in duplicate. At second, the
weight of the bottles also varies a lot. the bottle
with 0,25 Molarity does have the most weight,
while it is expected that the more 𝐶𝑎2+ is
added, the more weight it should have. We’ve
tried to keep the variables constant, like the
temperature and we’ve excluded the effects of
the acidity of the water. All in all, we think it
was a great experiment that needs more finetuning to be perfectly reliable.
27,75 grams of CaCl₂ respectively in our
sugar solutions. At last we added 1,00 grams of
yeast in every bottle. After sealing the bottles
with a water trap filled with water, we
oscillated the bottles to make sure everything
was dissolved. We weighed every bottle and
placed them for 6 days in a room where
temperature was kept constant. When the 6th
day had ended, we weighed our bottles again
and noted down the results.
Results
The following table presents the released
amount of CO₂ in grams.
Weight of the bottles
Mass
CO₂
[𝐶𝑎2+ ]
Before After
Molarity
(g)
(g)
(g)
0
270,4
256,7
13,7
0,25
310,6
302,4
8,2
0,75
271,2
266,1
5,1
1
292,5
288,8
3,7
1,25
297,9
293,6
4,3
Table 1: Release of CO₂. The difference in
weight of the bottles is the released amount of
CO₂ (g).
16
14
12
Mass CO₂ (g)
10
8
6
4
2
0
0
0.25
0.5
0.75
1
1.25
Molarity (mol/L)
Chart 1: Mass CO₂ (g) versus molarity (mol/L)
As we can see, there aren’t any results of the
bottle with the molarity of 0,5. This is because
we’ve lost the bottle during the experiment,
someone must have emptied this bottle.
Conclusion and discussion
1.5