carbon dioxide +
ethanol.Catalysts - Enzymes.
What is Fermentation?
Yeast
is a microorganism containing an
enzyme
which will convert a sugar
(glucose) solution
into carbon dioxide and alcohol (ethanol).
This process is called fermentation.
The word equation for fermentation is
glucose + yeast
carbon dioxide +
ethanol.
Carbon dioxide
gas bubbles out
of the solution
into
the air leaving a mixture of ethanol and water.
Ethanol can be separated from the mixture by
fractional distillation.
Fermentation must be carried
out
in
the absence of air to make
alcohol.
If air is present, ethanoic acid is made instead of alcohol.
Fermentation works best at a neutral
or slightly acidic pH.
What is a Batch Process?
In a batch process the reaction
vessel must be
emptied and
cleaned and then refilled with
the
new starting materials. A batch process takes more time
and is
more expensive than a continuous
process.
Yeast
is used in a batch process to make alcohol in beer
and
wine.
An enzyme in yeast acts
on the natural sugar
in
malt (to make beer) and grapes (to
make wine).
When the alcohol concentration reaches about 10 - 14%,
the
alcohol damages the yeast and
fermentation stops.
Is Drinking Alcohol Harmful?
Different alcoholic
drinks contain different
amounts of
alcohol.
Some people drink alcohol for
enjoyment, some
drink to excess and some people become
addicted to
alcohol.
The harmful effects (physical and social) of drinking
excess alcohol are widespread and reach all parts of
society.
How is Ethanol made on a Large Scale?
Ethanol is made from both renewable
and non-renewable
resources. Ethanol can be made on a large scale for use as a
fuel or
solvent by the
hydration of
ethene (non-renewable)
or by the fermentation (see above) of sugar
cane (renewable).
What does Renewable mean?
Renewable means that the resource can be replaced.
For example more sugar cane can be grown for
fermentation. Compare
this with using fossil fuels
which are the non-renewable
source of ethene.
Bread.
Yeast
is used in the baking of bread.
The carbon dioxide produced causes the
bread to rise
and fills the bread full of bubbles.
The alcohol evaporates during the baking
process.
Yoghurt and Cheese.
Bacteria can be added
to milk to make yoghurt.
An enzyme in the bacteria reacts with
sugar in the milk
(called lactose) and converts it into lactic acid.
Lactic acid changes milk proteins and forms the thicker yoghurt.
Cheese is made by adding an enzyme called rennet
after bacteria have produced
lactic acid in milk.
Rennet makes
milk proteins turn solid and this is the basis for cheese.
Rates of
Reaction Enzymes Search Questions 
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