The Fermentation of
Monosaccharides to make Ethanol
Sandra Reynolds
Dr Paul Grbin
University Senior College
Wine & Horticulture, University of Adelaide
The Fermentation of
Monosaccharides to make Ethanol
“This material has been developed as a part of
the Australian School Innovation in Science,
Technology and Mathematics Project funded by
the Australian Government Department of
Education, Science and Training as a part of the
Boosting Innovation in Science, Technology and
Mathematics Teaching (BISTMT) Programme.”
Fermentation of Monosaccharides
To make Ethanol
Subtopic 5.3
“ETHANOL IS DERIVED BY
FERMENTATION OF GLUCOSE WHICH
CAN BE DERIVED BY HYDROLYSIS OF
COMPLEX CARBOHYDRATES.”
The origins of
wine-making are
lost in history.
The earliest known
beers were brewed
6000 years ago in a
country called Sumer
on the plains
between the Tigris
and the Euphrates
which is now part of
Southern Iraq.
To pick grapes
at the right
pH is important
Too much
makes
the wine
undrinkable
Too little gives a
flat taste
Crushing
Seeds &
stems are
removed
Grape juice is
called must.
• Sulphur dioxide has been used in
winemaking for 100’s of years to control the
growth of unwanted microorganisms.
• Sodium sulphite, sodium hydrogen sulphite
and sodium metabisulphite are used.
• A wrong yeast strain can produce an aroma
described as wet horse blankets, cow
manure and plastic bandages!
Skins are
removed from
the must for
white wine.
The skins give
the red colour
to red wine!
C6H12O6(aq)  2CH3CH2OH + 2CO2
FERMENTATION of
monosaccharides
using enzymes in yeast
Conditions
1.
2.
3.
4.
5.
Anaerobic
Yeast to provide enzymes
Warmth, 20 to 30 deg. C
pH less than 7
Dilute aqueous
Saccharomyces cerevisiae – the yeast that
provides our bread, wine and beer.
Magnification X 13,800
Skilled
volumetric
analysis
determines the
acid content of
wine.
Fractional Distillation of
Wine to Produce Spirits
Maturation gives rise to new flavour
components by many chemical changes
and by extraction from oak casks.
Wine is Mostly Water & Has
Poor Keeping Qualities
• Fractional distillation of wine produces
up to 96% ethanol
• Spirits contain 52% – 95% ethanol and
these are not attacked by microbes.
• 100% ethanol is called absolute alcohol
– an excellent preservative!
Australian
brandy is
double
distilled
Cognac is triple distilled
Brandy & whisky are matured in oak casks.
Colour and flavour components are extracted
Some 400 flavour components have
been identified in whisky.
Copper rum pump
and rum measures
to dispense the
daily tot on
the Royal Yacht
Britannia until 1970
when the rum issue
was discontinued.
Her Majesty’s
proof spirit
Australian
wine ready
for drinking
Beer Making
Subtopic 5.3
“ETHANOL IS PRODUCED BY
FERMENTATION OF GLUCOSE WHICH
CAN BE DERIVED BY HYDROLYSIS OF
COMPLEX CARBOHYDRATES.”
To Make Ethanol in Beer
THE WORLD’S OLDEST RECIPE!
WATER, MALT, HOPS, YEAST
• Beer is made by SOAKING malted barley with
water, boiling it with hops; cooling it and then
letting the whole lot ferment and mature.
• This process was used at least 6000 years ago
in Iraq to make ale & bread.
Wine is usually made from fruits.
These contain simple sugars.
Beer is made from grain – barley is best.
Grains contain starch.
Simple sugars are called MONOSACCHARIDES e.g.
- Glucose (blood sugar, grape sugar)
- Fructose, (fruit sugar)
C6H12O6
Double sugars are called DISACCHARIDES E.g.
- Maltose
- Sucrose
- Lactose
C12H22O11
Complex sugars are called
POLYSACCHARIDES e.g.
- Starch
(C6H10O5)n
Barley Contains Enzymes to Convert
Starch into Fermentable Sugars
These are released when
the grain is soaked in water
& allowed to germinate for
several days at 18oC.
This is called BARLEY
MALT
The Sumerians baked this
into barley bread.
Ground barley malt is soaked in water.
This revives the barley enzymes which break
polysaccharides into disaccharide.
This reaction is called hydrolysis
H2O
(C6H10O5)n → C12H22O11
Boiling the Filtered Mixture
Kill Germs & Deactivates Enzymes
• Boiling extracts bitter
resin from the hops &
makes them soluble.
• Hops also act as a
preservative
Fermentation
Yeasts are added to the cooled wort
HYDROLYSIS
C12H22O11 + H2O → 2C6H12O6
OVERALL HYDROLYSIS
(C6H10O5)n + nH2O → nC6H12O6
FERMENTATION
C6H12O6 → 2C2H5OH + 2CO2
Note: Fermentation is an anaerobic process.
After maturing for
several weeks at
low several for
several weeks at
low
temperatures,
the amber liquid
is filtered, ready
for bottling or
kegging.
Making distilled
spirits:
The word comes
from the
latin ‘destillare’
meaning
‘to drip’
The Fate of Alcohol is Vinegar
‘Acidic Wine’ ‘Vin Aigre’ F
• Acetobacter – bacteria that can use O2 to metabolise
alcohol & extract energy from it.
CH3CH2OH + O2 → CH3COOH + H2O
• The ethanoic acid formed is a far more potent
antimicrobial than ethanol .
• Vinegar came to be one of the most effective food
preservatives of ancient and modern times.
Word List
CARBOHYDRATES
SIMPLE SUGAR
DOUBLE SUGAR
COMPLEX SUGAR
GLUCOSE
FRUCTOSE
SUCROSE
MALTOSE
STARCH
POLYSACCHARIDE
HYDROLYSIS
DISACCHARIDE
HYDROLYSIS
MONOSACCHARIDE
FERMENTATION
ANAEROBIC
ETHANOL
AEROBIC
ENZYMES
ETHANOIC ACID