Chemistry only
Unfortunately most alcohols are toxic and are definitely
not suitable as drinks. The one alcohol
which is less harmful is ethanol, although it still causes many people to do very silly things when
taken in excess! Ethanol has been made for thousands of years as an alcoholic drink. Traditionally
beer was made in large copper tanks or vats as shown in the image.
Barley or sometimes oats grains are allowed to
germinated in water. The germinated grains are then dried in a process to produce a substance
called
malt. The malt is soaked in hot water which activated enzymes present in the barley grains to
break down
the starch in the barley grains into simple sugars. After about a hour the liquid is drained
off and
hops are added. Hops give the beer its bitter taste. This watery solution is then added to
a copper
vat where fermentation happens. The fermentation process is slow and can take days or even weeks.
Fermentation is a natural process, it is a form of anaerobic respiration. In brewing a fungus called
yeast is added to the sugary solution and the yeast will convert the simple sugar glucose into ethanol.
glucose(aq) → ethanol(aq) + carbon dioxide(g)
C6H12O6(g) → C2H5OH(aq) + 2CO2(g)
Making alcohol using yeast is very simple. All you need is a source of sugar, it could be any fruit e.g. apples, pears,
strawberries, blackberries, grapes. The fruit is squashed, added to lukewarm water and placed in a bucket with a lid
or air lock somewhere hot, like an airing cupboard or beside a radiator. Once the yeast is added fermentation will begin.
After about 2 weeks filter the mixture to remove the yeast and any other solids present. That is it.... Easy, you have made ethanol!
Yeast is a fungus, a living organism, and it will produces enzymes that turn glucose into ethanol. This is a form
of anaerobic respiration which work best around 370C. If the fermenting solution gets to hot then the yeast
will be killed and fermentation will stop. If the solution is kept too cold then obviously fermentation will be very slow. Air needs to be excluded since bacteria and oxygen present in the air will oxidise the ethanol into ethanoic acid (vinegar).
One of the uses for alcohol is as an agent to kill bacteria and fungi. Once the concentration of alcohol in the fermenting container reaches around 15% alcohol fermentation stops- this is because the alcohol has killed the yeast. For alcoholic spirits such as whisky or vodka
which may contain up to 40% alcohol, the alcoholic solution from fermentation needs to be distilled
Direct hydration
Alcohol (ethanol) used in alcholic drinks such as beer, wine and spirits is made by fermentation. However
alcohol can also be made a method called direct hydration. Using this method produces
alcohol very quickly and being
the only substance made there is no waste and no costs needed in separating out unwanted substance.
Alcohol
used for industrail purposes e.g. solvents and in sanitisers will more than likely be made by the direct hydration method rather than fermentation.
Here steam is added across the C=C in an alkene as shown below. A catalyst and some heat are both needed to get this reaction to occur smoothly.
Equations for this reaction are:
ethene(g) + steam(g) → ethanol(g)
C2H4(g) + H2O(g) → C2H5OH(g)
Key Points
- The alcohol ethanol can be made in a process called fermentation.Fermentation is a form of anaerobic respiration where enzymes
produce by the fungus yeast convert glucose sugar into ethanol and carbon dioxide gas.
- Fermentation occurs quickest around 370C. This is the optimum temperature for the enzymes produced by
yeast to work most efficiently at..
- Alcohols can be made by a process called direct hydration. Here steam adds across a C=C in an unsaturated alkene in the
presence of a catalyst and under a fairly high pressure.
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