Research on the alcohol content in fruits
by Luciano vd Veekens and Man Ho Chong
Zaanlands Lyceum, The Netherlands
Summary:
Ethanol is the name for what we call alcohol in daily life. The molecular formula for ethanol is
C2H5OH, you see this often as CH3CH2OH. Ethanol has a molar mass of 46.07 grams per mole and a
density of 0.7894 grams per cm3. The boiling point of ethanol is at 78.4ᵒC. Using fermentation,
destilation and titration in this study, we investigate from which kind of fruit you can retrieve the
highest percentage of alcohol. We have bought apples, pears, bananas and white grapes from the
supermarket for our project. The results from our research prove that bananas contain the highest
percentage of alcohol. We went through some problems too. The amount of mL acid changed during
the study. Because our teacher first told us to dilute the alcohol solution we got from destillation. But
a week after we done it, he told us it wasn’t necessary. So with these tiny mistakes we got negative
alcohol percentages.
Introduction:
Ethanol is used as fuel or blended fuel these
days. The Netherlands are on the ninth place in
the list of top fifteen producers of ethanol in the
European Union. Currently, the largest national
fuel ethanol industry is in Brazil. When ethanol is
used as fuel it is called bio-ethanol. Bio-ethanol
is the same ethanol as the alcohol in our drinks.
Due the way it is used, it has a different name.
Because almost everyone participates on the use
of ethanol, it is running short. That is why the
interest for the production from ethanol through
fermentation has grown. Bio-ethanol is
produced through fermentation of sugars with
micro-organisms. The micro-organisms are often
used yeast. Bio-ethanol is seen as an alternative
to fossil fuels and as an environmentally friendly
solution. CO2 emissions to the use of bioethanol is much lower than that of oil.
Yeast is a unicellular fungus. In this study we use
baker's yeast ( Saccharomyces cerevisiae ).These
yeasts can convert glucose into ethanol and CO2
by anaerobic dissimilation of glucose. The yeast
can only assimilate dissolved glucose from its
environment The purpose of dissimilation is
energy (in the form of ATP) release, necessary
for various processes. If there is enough oxygen,
aerobic dissimilation will occur because there so
much more energy. However, this doesn’t lead
to ethanol.
The reaction of aerobic dissimilation is as
follows:
6 H12O6 + 6 O2 6 CO2 + 6 H2O + energy
(enough for 38 ATP)
Only when there is little or no oxygen present,
there will be switched over to anaerobic
dissimilation.
The anaerobic dissimilation is as follows:
First, during glycolysis from glucose into Pyruvic
acid, several processes take place. This cost 2
ATP and 4 ATP is released. A profit of 2 ATP. This
also occurs in aerobic dissimilation.
Pyruvic acid will normally be burned aerobically,
here is another 36 ATP won. Pyruvic acid in
anaerobic dissimilation will however be
converted into ethanol and CO2.
And this shows us the reaction for anaerobic
dissimilation:
C6H12O6 (glucose)
2C2H5OH (ethanol) +
2CO2 + energy (enough for 2 ATP)
With all of this information we came to the
question: Which kind of fruit contains the highest
amount of glucose? ( and we investigate this via
the percentage of alcohol, glucose + yeast 
alcohol ). We got apples, bananas, pears and
white grapes from the supermarket.
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Our hypothesis is that the grapes contain the
most glucose. In other words, from grapes you
can receive the highest amount of ethanol. We
have this idea because wines are made from
grapes.
Experimental procedure and approach:
Before we could do the experiment, we first had
to bought some fruit. This is because we wanted
the fruit as fresh as possible.
We wanted the water to absorb as many glucose
as possible, so we needed to slice the fruit in
small pieces.
Of each fruit we used about 40 gram fruit and 4
gram yeast. We putted the 40 gram fruit in a
Erlenmeyer and added some water (till all pieces
of the fruit were drown). When we were ready,
we added the 4 gram yeast and putted a
plumbing on the top of the Erlenmeyer(we
fermentated the fruits so we could form
ethanol).
After a week we opened the Erlenmeyer and
filtrated what was in it. We used the filtration so
we could do the distillation method on the
filtrate (we used the distillation so we could split
the ethanol and water from the filtrate). We
tried to keep the temperature about 100 Celsius
and keep it for a while. After that we dilute the
alcohol solution 40 times. We did this by
appending 2.5 mL alcohol solution and 97.5
water together.
The only thing left was the titration(with this
titration we could get to the percentage of
alcohol in the distillate). When we were ready
we added 25 mL dilute solution with 5 mL 1,0 M
sulfuric acid and 5 mL 0,10 M Cr2O72− in a beaker
of 250 mL
3 CH3CH2OH + 3 H2O + 2 Cr2O72− + 28 H+ → 3
CH3COOH + 12 H+ + 4 Cr3+ + 14 H2O
2 Cr2O72− + 16 H+ + 3 C2H5OH → 4 Cr3+ + 11 H2O +
3 CH3COOH
Then we heated the beaker to 60 Celsius and
keep it on that temperature for like 5 minutes.
After that we appended 12.5 mL KI (Cr2O72− + 14
H+ + 6 I− → 2 Cr3+ + 3 I2 + 7 H2O) and titrated with
0,1 M thio (2 S2O32− + I2 → S4O62− + 2 I−) till the
solution is light yellow (before the titration was
the solution brown). Then we added some drops
of starch and titrated it again, but only this time
till the solution is light blue. At we looked how
many thio we used for both the titration and we
repeated the same method on the other fruit.
Results:
Table 1 presents the total amount of Thio we
had to use to get the alcoholic solution from
brown to light yellow, and from there on to
blue.
Kind of
fruit
Mass
used of
the fruit
(g)
Mass
used of
yeast
(g)
Thio
used
(mL)
White
grapes
Apple
Pear
Banana
41,616
4,094
38
40,675
40,864
41,383
4,006
4,165
4,300
33
36
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Table 1: Shows the amount of Thio used for each
fruit.
Data analysis:
Now we know how much Thio was used during
the titration progress. We can calculate back to
the percentage of alcohol from the solution.
I’ll take white grapes as example:
used thio 50,0 – 12,0 mL = 38,0 mL x 0,10 M = 3,8
mmol
3,8 mmol thio ↔ 1,9 mmol I2 ↔ 0,63 mmol
Cr2O72−
5, 0 x 0,10 M Cr2O72− = 0,5 mmol – 0,63 mmol =
-0,13 mmol that has reacted with C2H5OH
-0,13 mmol Cr2O72− ↔ -0,195 mmol C2H5OH in
25,0 mL solution = -0,0078 M
-0,0078 M x 46 g mol-1 = -0,3588 g L-1
-0,3588 g L-1 / 0,80 g mL-1 = -0,45 mL alcohol per
liter = (-0,45 mL / 1000 mL) x 100% = -0,045 vol%
White grapes
-0,045 % alcohol
Apple
-0,017 % alcohol
Pear
-0,035 % alcohol
Banana
-0,012 % alcohol
Table 2: The alcohol percentage from each fruit.
As you see here, a banana contains the highest
amount of glucose. By the study we did, it
concludes here that a Banana is good for -0,012
% alcohol.
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Conclusion and discussion:
With a diluted solution we got negative alcohol
percentages of each fruit. But if you take a look
at the banana, you see the negative percentage
is the closest one to 0. So we could say, of all
these fruits we chose for this experiment, a
banana is the most suitable for making bioethanol. We could easily say that without an
experiment. Because for making bio-ethanol we
needed glucose and yeast. So we used the fruits
for the glucose. That means the fruit with the
most glucose is the best suitable for making
ethanol. And from all the fruit we tasted banana
was the sweetest.
When we were busy with the experiment we
doubted that making bio-ethanol is a good
replacement of fossil fuels. After doing some
research on the internet. We found out bioethanol isn’t a good alternative after all. We
found a pretty recent clip of the news program
in the Netherlands, where they said bio-ethanol
is bad for the environment. They reason they
gave was : the world population still needs more
food. So there isn’t any place for cultivate bioethanol. So what they could do is deforest to
make place for building fruits that’s making bioethanol. But if you cut all the trees down, the
remaining trees produce less O2 and absorb less
CO2 then before.
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