The distillation is the process used to separate alcohol from water and other substances contained in the wash.
This is a classical operation, and it is the base of each spirit round the world. It is used in perfumery too. Distillation is made in stills. The principle is very easy: water evaporates at 100% while alcohol does from 80%.
Alcohol will thus be transformed in vapour and raises into the still before water itself begins evaporating.
Pot stills are used in Scotland.
The size of the stills is fixed by the law. This is due to historical reasons, related to excise rights.
Edradour has the smallest legal stills of Scotland. If the stills were a bit smaller, the distillery would lose its licence. There is however an exception to that rule. Loch Ewe found a gap in the law and could start distilling legally in very small stills. But of course, the production is confidential...
Stills are in copper, because this material has a great influence on the physical process of separation of the waters and the spirits. The quality of the dram we will enjoy a few years later depends partially on the copper surface being in contact with the liquids during the distillation process. Other things are important, like the shape, the height, the length of the lyne arm are also very important in the making of the taste of the future whisky. If a distillery has to add or replace a still, it will always try to get a still with the same capacity and the same shape, in order to guarantee a constant quality to the whisky.
Because of the extreme diversity of the stills used throughout Scotland, it is not possible to display some pictures on this page. I created a special page with pictures of various stills from several Scottish distilleries. To get there, just click on the still icon on the left. By the way, this is a still of Glenfarclas distillery.
Traditionally, the stills were heated with coal or peat, depending on the areas and possibilities. Currently, nearly all of them are heated with vapour, because this method gives more control on the process.
The fuel used to heat the vapour is generally petrol, but it can happen that coal is still used.
The huge quantity of heat produced by distilleries is sometimes recycled. For instance, the municipal swimming pool of Bowmore is warmed with recuperation heat from the distillery.
Scotch whisky is double distilled, with some exceptions to this rule, like Auchentoshan which is distilled three times, just like Irish whiskey.
The distillation process occurs in two stages in two still with different capacity and shape.
The first distillation occurs in the wash still whose capacity can be between 25 and 30.000 litres and transforms the wash in "low wine", at about 21 % of alcohol. If the stills were originally heated with a naked fire, generally from coal or gas, the current stills are heated by a serpentine within the still, where the vapour is circulating.
The alcohol vapours are cooled outside the still by condensers. The traditional condensers were serpentines immerged in a great open wooden back, containing cold water.Currently, most of the distilleries use vertical tubular condensers, because the output is better. Waste of the first distillation is called "pot ale" or "burnt ale", and is transformed to feed cattle too.
The low wines resulting from this first distillation are kept in the "low wine receiver and will be used as ground for the second distillation.
The second distillation occurs in a spirit still which is generally smaller than the wash still, as there is less liquid to process.
During the second distillation, only the "distillation heart", the part which has between 63 and 72% of alcohol will be casked. The heads and tails, also called feints, will go to the feint receiver, and reused mixed with the low wines of the next distillation.
To separate the feints from the distillation heart, a spirit safe is used. This spirit safe (was) used for the determination of the quantity of alcohol produced , to calculate the taxes due by the distillery