Scotch sales rise as the pound falls

Sales of Scotch whisky are their highest levels for decades…but why? Roger Jewsbury, Head of Department of Chemical and Biological Sciences at the University of Huddersfield explains how the spirit is emerging as a winner of the credit crunch.

These may be days of economic gloom but they are also times of 'Whisky Galore', with sales of Scotch whisky at their highest level for decades and old capacity being brought back into use.

George Bernard Shaw may have called it "liquid sunshine", but to the discerning Chemist whisky is much more, with over 100 chemicals all determining flavour and distinguishing one whisky from another.

The law limits whisky made in Scotland to a few ingredients - malted barley and water, fermented only by yeast with just one permitted additive - caramel for colouring.

Despite this, the diversity of flavours is a feature of Scotch whisky and it arises from differences in production and particularly maturation.

Malting is the process in which the grain is germinated by soaking in water briefly before drying.

This releases natural enzymes which convert starch into the soluble sugars, such as maltose, that will be fermented to alcohol. Historically, the malted barley was dried over peat fires and some distilleries, notably those from Islay, still smoke their malt to incorporate phenolic compounds from the peat to give a characteristic smoky taste.

Phenols are interesting compounds; phenol itself is a disinfectant which older readers may remember as the ingredient in carbolic acid soap, which incidentally is now banned.

Levels of phenols in drinking water are tested to ensure that they are very low – at least 10,000 times lower than found in some whiskies.

From a mash of malt and water, the solution is taken and yeast is added for fermentation. After about three days, the sugar will have been converted to alcohol.

The next step is distillation - heating the mixture to separate it into different fractions. Distillation is used to remove the most volatile and least volatile fractions. The distillation is usually in copper vessels, which is thought to help the removal of foul smelling sulphurous compounds.

The next step, again defined in law, is maturation in oak casks not exceeding 700 litres for at least three years. The limit to the size of the casks is an indication of the importance of this step and the need for the whisky to be in contact with the wood.

Like many other spirits and wines, aging takes place in oak casks. It is rare to use new oak. The vanillin in oak, the same compound found in vanilla pods, imparts a strong vanilla flavour, so casks previously used for American whiskey (Bourbon) or sherry are preferred, as much of the vanillin has already been removed.

Other processes also occur during maturation. Pungent sulphur compounds diffuse out through the wood and air diffuses in starting a series of reactions which leads to the formation of esters - a significant contribution to the aroma.

Esters have pleasant odour – they contribute to the characteristic smells of fruit. The colour also develops during this time from the compounds in the wood.

Once a whisky has matured, it is blended and diluted to its final bottle concentration of 40 per cent alcohol. Single malts are usually blended from several casks - all from the same distillery - to establish just the right flavour, the age on the bottle indicating the youngest whisky in that blend.

The flavour of the whisky comes from the taste and the aroma from the volatile compounds. Connoisseurs describe whisky by categories such as colour, nose, body, palate and finish. These are mostly understood in terms of the chemical composition, although it would be a brave chemist who tried to tell an expert which malt he should drink. The chemical analysis does have another use; it can be used to identify counterfeit whiskies.

If the chemistry is understood, what is the best way to drink whisky?

Again this is really a matter of taste - there is no simple answer. If you add water, you reduce the solubility of compounds such as the esters and increase their volatility.

So do this, if you like the fruity aroma. In contrast, the phenolics are water-soluble and the volatility of these is reduced, so if you like the smoky peaty aroma, drink your malt whisky neat.

If you add ice, all the compounds will be less volatile – so the aroma will be reduced with less effect on the taste.

And the expert verdict? Well, the chemist can explain the differences, but how you drink your whisky should depend upon your personal preference.

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