The "alcohol" that is found in various alcoholic beverages is ETHANOL, also known as ETHYL ALCOHOL, CH3CH2OH. It is a volatile liquid boiling at 78.5 ºC, freely miscible with water, with which it forms a CONSTANT BOILING MIXTURE containing 95.6% CH3CH2OH, boiling at 78.1ºC. Ethanol with a purity above 99% is known as ABSOLUTE ALCOHOL.
Ethanol is produced naturally by the fermentation of sugars in fruit juices of from the starch of cereals. Without going into the biochemical details, the alcoholic fermentation process may be summarised as:
Fermented liquors come in various types. BEERS are typically produced by the fermentation of barley or other grains, and contain normally 4-6% ethanol. It is known that beer has been produced for over 7000 years. WINE is fermented grape juice. A typical wine will have about 10-14% ethanol. As with beer, the technology is very ancient, as there is evidence that grape juice was fermented (and consumed!) in the Middle East as early as 8000 years ago. Other fruit juices can be fermented to give beverages such as cider, from apples, or perry, from pears.
Classical still design. |
A 19th Century French distiller hard at work. |
Stills in a Scottish whisky distillery |
The technology of distillation has a long history, dating from the ancient Egyptians some 5000 years ago, who invented a crude form of still which they used for the preparation of cosmetics and perfumes. The Arabs perfected the still, and gave us, through the word "al-kuhl", the term "alcohol" used today. After the Arab conquest of Spain in the Middle Ages, the technology spread to Europe, and distilling became a well regarded profession, producing "spirits" from whatever fermented liquors were readily available locally.
Various countries developed their own distinctive spirits. In France, distillation of wine gives rise to "Cognac" and "Armagnac" (in South Africa, we know these spirits as "brandy"), in Ireland and Scotland, fermented barley mash produces whiskies, in the Caribbean, distillation of fermented molasses results in rum, in Mexico, fermented agave juice is distilled to produce tequila. Almost any fermented fruit or grain will give a liquid containing ethanol amenable to distillation.
Typically, bottled distilled spirits are water-ethanol mixtures containg 40-45% ethanol by volume. The distinctive tastes of the various spirits are due to small quantities of substances that are "carried over" during the distillation process, or extracted from the wood from the barrels used for storing the spirits. In most countries, the distillation, storage, and distribution of spirits are strictly controlled by legislation, and tax on the ethanol content is an important source of revenue.
During the distillation process of wine, the fraction which comes over below 78 ºC contains aldehydes and is discarded. The ethanol-containing fraction boils between 78 and 85 ºC and , while the higher boiling fractions is known as "fusel oil", and contains mainly alkanols with 5 carbon atoms. These are processed to make useful solvents.
Ethanol is toxic. While enzymes in the liver can remove alcohol from the system, this is not an instantaneous process, and the more alcohol is consumed, the longer it takes to remove ethanol from the bloodstream. The removal of alcohol from the blood takes place firstly by oxidizing the ethanol to ethanal (more toxic than ethanol, and the source of hangovers!) using the liver enzyme ALCOHOL DEHYDROGENASE, with subsequent oxidation of the ethanal to acetyl coenzyme A, again using a liver enzyme, ETHANAL DEHYDROGENASE. Acetyl coenzyme A (a sulphur ester of ethanoic acid) is a normal metabolite which is not toxic. These steps are outlined below.
Ethanol is a depressant, which, if it reaches a level of about 0.5% in the blood, can cause death. Intoxication, characterised by loss of coordination, sets in at levels that depend on the individual. A person will be severely intoxicated if the blood alcohol level reaches 0.15-0.20%. In South Africa, the legal limit is 0.05% (50 mg ethanol per litre of blood), above which an individual is considered to be unfit to drive a motor vehicle. Various techniques are employed to determine blood alcohol on the spot (the "breathalizer" is an example), but for accurate values, blood has to be drawn and sent for analysis to a laboratory. The "legal limit" may be reached after even moderate consumption, say two or three beers, a couple of tots of brandy or 2 glasses of wine. As a rule, it takes about one hour to metabolize 20 g of ethanol. This is about the mass of alcohol found in one 375 ml can of beer or one 200 ml glass of wine.
It is a tragic consequence of alcohol abuse that a great number of fatal traffic accidents occur as a result of the intoxication of the driver (or, to be fair, as a result of the intoxication of pedestrians). Young people are particularly at risk due to their inexperience in consuming alcohol, and their generally lower body mass. The best advice that one can give is
If you must drink, do NOT drive!
While moderate "social drinking" is largely innocuous, and may even have some health benefits, many individuals develop a dependence to ethanol, in other words, they become addicted to it. This is a great social evil, found in all income groups. The effects of alcoholism are most keenly felt in lower income groups, who cannot afford liquor, and whose dependence frequently results in loss of employment and consequent malnutrition for themselves and their families. In addition prolonged abuse of alcohol leads to a condition known as "cirrhosis of the liver", leading to death.
Women who abuse alcohol during pregnancy may cause harm to the unborn foetus. This is known as FOETAL ALCOHOL SYNDROME, FAS. Children who are born with this syndrome have various levels of brain damage, and most are intellectually impaired. FAS is a serious problem in poor communities with easy access to cheap liquor. For this reason, women should avoid all alcohol consumption during pregnancy.
