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Rates of Reaction

Enzymes  -  Yeast  -  Fermentation  -  Alcoholic Drinks.

How is Fermentation used to make Alcoholic Drinks?

Fermentation is used in a batch process (see below) 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).

Fermentation will work at temperatures between 18 and 35 °C.
Too cold and the enzyme in yeast is inactive, too hot and
the enzyme denatures. The best wines are generally made
at the lower end of this temperature range although at
lower temperatures fermentation is slower and takes longer.

When the alcohol concentration in wine reaches about
10 to 14%, the alcohol damages the yeast and stops the
fermentation. Ethanol can be separated from the
mixture of water and alcohol by fractional distillation and
this process can be used to make alcoholic drinks with
a higher alcohol concentration such as brandy and whisky.

Is Drinking Alcohol Harmful?

It can be. Different alcoholic drinks contain different amounts
of alcohol. Some people drink alcohol for pleasure, some
drink to excess and some people become addicted to drinking
alcohol. The harmful effects (physical and social) of drinking
excess alcohol are widespread and reach all parts of society.

What is a Batch Process?

In a batch process the reaction vessel must be emptied
and cleaned when the reaction is complete and then refilled
with the new starting materials. A batch process takes
more time and is more expensive than a continuous process.

Other Examples of Fermentation.


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.

and Cheese.

Bacteria can be added to milk to make yoghurt.
An enzyme in the bacteria reacts with a sugar in the milk
(called lactose) and converts it into lactic acid. As the
amount of lactic acid increases, proteins that are present in
the milk begin to change and form 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.

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