c

Yeast is added to a sugar solution and is left for several days in the absence of air, this anaerobic conditions cause zymase enzymes in the yeast to convert the glucose into ethanol and carbon dioxide

The optimum temperature for fermentation is 37 o c as yeast grows best at this temperature. A PH near 7 also gives the yeast the best conditions for growing.

Through alcohol fermentation ethanol can be no purer than 15%, this is because greater concentration of ethanol denature. The enzymes in the yeast and the reaction stops.

Alcoholic beverages Ethanol fuel Rising of bread dough.

c More than 330, 000 tonnes of pure ethanol (which is a type of alcohol) are produced each year in this country, it is used for fuel, feedstock for other chemical process such as manufacture of fibres are esters but is mainly used during the process of fermentation.

Pure ethanol can be produced by reacting ethene with steam, a process called hydration. The ethene and steam are passed continuously over a catalyst of phosphoric acid The temperature needed for this reaction is 300 o c at a pressure of atmospheres.

An alternative and very new method of making ethanol involves the use of genetically modified E. Coli bacteria. These bacteria have a gene introduced into them that it is capable of converting all types of carbohydrates found in plant cells into ethanol.

Beer is the world's oldest and most widely consumed, It is produced by the brewing and fermentation of starches, mainly derived from cereal grains, most commonly malted barley, although wheat, maize (corn), and rice are widely used. Most beer is flavoured with hops, which add bitterness and act as a natural preservative, though other flavourings such as herbs or fruit may occasionally be included.