Alcohols are organic compounds of carbon, hydrogen and oxygen with the general formula CnH(2n+1)OH
The lower alcohols, with a few carbon atoms, are flammable liquids, and the higher ones, with many carbon atoms, are waxy solids. Cholesterol is one of the higher alcohols
“Alcoholic drinks” contain ethanol - when we talk about alcohol rather than an alcohol we almost always mean ethanol. Alcoholic drinks are made by fermenting natural sugar solutions.
Fermentation is carried out by microscopic fungi called yeasts. The yeast grows by turning sugar into ethanol and carbon dioxide. However, ethanol is a poison for yeast and once the concentration of ethanol reaches 10% to 15% (depending on the strain of yeast) the ethanol will kill the yeast and no further fermentation can occur, no matter how much more yeast or sugar we add. Alcoholic drinks stronger than this cannot be made by fermentation alone. Fermentation is further discussed in the page on respiration - to read this page please click
The boiling point of ethanol is about 78oC, compared to 100oC for water, so if any alcoholic drink is left in an unsealed container the ethanol will evaporate at a higher rate than the water, and the alcoholic strength of the solution will fall - the higher the temperature the more rapid and the greater the fall.
Mulled wine is a very warming drink in cold weather. It is made by adding spices to heated red wine. If the wine is not drunk straight away most of the ethanol will evaporate and what is left tastes very different: it is as though the life has gone out of it. The Ancient Greeks used the word spirit to describe what was lost from the wine when it was heated. Later people discovered how to capture the spirit (that is, the ethanol) by distillation (evaporation followed by condensation) and today alcoholic drinks made by distillation are called spirits. Common spirits are
Spirits usually have an ethanol content of from 25% to 60%.
By analogy many other substances made by distillation are called spirits.
Fortified wines, such as madeira, sherry and port, are made by fermenting grape juice and then, at exactly the right point adding exactly the right amount of brandy. This raises the ethanol content of the mixture to a level at which the yeast is killed, and fermentation stops. The timing of the addition of the brandy, and the amount added, have a critical effect on the quality of the end product and require very careful judgement.
Fortified wines usually have an ethanol content of about 20% to 25%.
Ethanol is absorbed into the bloodstream very rapidly, not only through the stomach but also through the lungs and nasal passages - thus drinking alcoholic drinks through a straw, where the fumes are inhaled, greatly increases the rate of absorption. Ethanol affects the central nervous system, and although different people are affected in different ways, for all people even small amounts of ethanol in the bloodstream can affect reaction times and judgement to the point at which driving becomes unwise or dangerous. In larger quantities it causes drunkenness and eventually death.
Ethanol in the bloodstream is broken down by the liver. Small quantities, for example a glass of wine with a meal once or twice a week, are unlikely to be harmful to healthy adults, but larger quantities, whether taken at one time or over a longer period, may cause long-term liver and brain damage and other health problems.
Methanol is very poisonous and causes blindness and death. It can be made by distilling wood, hence its common name wood spirit.
Apart from being present in alcoholic drinks ethanol has other important uses, as a fuel and as a solvent and in many other ways. But there is an excise duty (tax) on alcoholic drinks based upon their ethanol content, and pure ethanol would have such a high rate of duty that it would be far too expensive to use in these ways. To avoid the tax it is mixed with a small amount (about 5%) of methanol to make it poisonous. This is called methylating it, and because this mixture is poisonous it is not taxed. A mixture of ethanol and methanol is called industrial methylated spirits, or IMS. IMS is a clear colourless liquid. Methanol and ethanol are very similar and for almost all purposes (other than drinking of course!) IMS can be used instead of ethanol. In school science laboratories bottles labelled “ethanol” are almost invariably IMS.
It is however possible (if you know how) to separate the methanol from the ethanol in IMS and for this reason you cannot buy IMS without a special permit from the Customs and Excise - most secondary schools have such a permit. Mineralized methylated spirits (ordinary meths) is a mixture of ethanol and methanol, with the addition of a blue dye to make it easily recognizable, another substance to give it a revolting taste, and a third substance to make it more difficult to separate the ethanol from the mixture. This can be bought by anyone over sixteen. These extra substances do not prevent meths from being used as a fuel but do make it unsuitable for many other purposes including use as a solvent in school science experiments.
Even though meths tastes revolting and is very poisonous it is more than 90% ethanol and some alcohol-dependent people on the very edges of society do drink it - meths drinkers usually go blind within a few weeks and die within a few months.
© Barry Gray November 2005
Alcohols were once called by names which included the word alcohol, for example methyl alcohol for methanol, ethyl alcohol for ethanol.
Alcoholic drinks
By international agreement, the word wine by itself may be used only to describe wine made from grapes. It is possible to make alcoholic drinks from many different plants but these must be called, for example, dandelion wine or, collectively, country wines. Most country wines are home-made.
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Vinegar
Many micro-organisms other than yeasts can also cause chemical changes to grape juice, and one of them, a bacterium carried by fruit flies, can cause a chemical change leading to the production not of ethanol but of ethanoic acid. (Ethanoic acid used to be called acetic acid.) Grape juice that has been affected in this way tastes sour and is called vinegar (from the French for sour wine). For obvious reasons, in wine-making countries fruit flies are more commonly called vinegar flies.
Vinegar can also be made from malt, cider and many other substances. In Britain most vinegar is made from malt and is brown.
Methylated spirits
