'Malt distillery', 1754.
© Science Museum / Science & Society Picture Library
Engraving from a supplement to the 'New and Universal Dictionary of Arts and Sciences' by J Barrow, published in London in 1754, showing the proceses of distilling malt. The malt (dried, malted barley) is ground and soaked in water which disolves the sugar and produces wort (a sugary liquid). Yeast is then added and the wort is allowed to ferment. At this stage the wort is called wash and contains around five percent alcohol. The wash is moved into pots for the first of several distillations. Once all the distillations are complete, the spirit, which now has an alcohol content of around 60 per cent, is allowed to age, usually in used sherry or bourbon barrels. The spirit must age for at least three years before it can be called Scotch whisky.