The purpose of the distillation is to concentrate the alcohol and remove unwanted components by using the simple fact that ethanol boils at a lower temperature than water. The Scottish distilleries use a very basic process compared to modern technology, in fact it is done in the same way as it has been done for the last several hundreds of years. But this is also a key factor for making whisky, the spirit must not be too pure. There are a large number of flavour components originating from the fermentation, called congeners, that contribute to the taste and aroma and they should not be eliminated completely.
The distillation is usually done twice, even if there are a few distilleries that triple distill their whiskies or perform some home-made two-and-a-half distillation. Either way works but results in different whiskies.
In the first distillation the aim is to vaporise and condense as much alcohol as possible while retaining water and left-overs from the fermentation. The distillate is called low wines and has a alcohol content of about 25%.
The second distillation is where the skill of the still man comes in handy, this time he must remove congeners that will affect the final whisky in a negative way but still keep a sufficient amount that will shape its character. The first fraction is called foreshots or the head, it is harsh and oily and is collected to be redistilled together with the next batch of low wines. The second fraction starts at 72-74% alcohol and is known as the middle cut or the heart. As the name implies here is where the soul of the future whisky is found. There are notably fruity and pleasant esters in the beginning but they decrease after a while and the feints will arise. The stillman can now choose to stop and create a light, clean whisky or go on for a while and create a more robust, heavy whisky as the feints increases. Since some distilleries interrupt the collection already at 69% alcohol while other continue until 60%, this is clearly a factor that plays a great part in creating different whiskies.
The third and final fraction is called the feints or the tail. It is collected as long as there is still alcohol left and is redistilled together with the foreshots.
The spirit received has an alcohol content of 65-70% and is now transferred to the filling vat.
A distillery has at least two pot stills, often more. Tomatin has got 23, the greatest number in Scotland. They consist of a copper pot with a narrow neck attached on top which curves into a lyne arm and ends in a condenser. The still is heated indirectly using steam coils in the bottom of the pot. The old way which some distilleries used until recently, was to have an open fire beneath the pot. Health and Safety regulations have now put a stop to that.
There are two types of stills: the wash still is used for the first distillation and the spirit still for the second. The former range from 4 000 to 30 000 L, with the latter being 50-75% of that size. They are always made of copper for different reasons, the most important being that nothing else works. Nobody has the full explanation but it may have something to do with the removal of heavy sulphurous impurities or as being a catalyst for chemical reactions during maturation. What we do know is that each pot still releases considerable amounts every year to the spirit produced. And into the drain which has to be taken care of.
The shape of the stills has a great impact on the end product. A high neck will partially condensate the spirit vapours and cause it to be boiled again, creating a lighter, cleaner spirit. This can also be achieved by the angle of the lyne arm, cooling of the swan neck, a pipe leading from the lyne arm back to the still or a boil ball which is a bulge between the pot and the neck. The ingenuity knows no limit and each distillery has their own design which they stick to. A new pot still is always made in the same fashion as the old.
THE SPIRIT SAFE
Due to tax reasons, whisky production is a closed process from the moment the wash enters the first still. It must be ensured that no spirit disappears, but the still man must at the same time be able to supervise the process and to direct the fluids into different vessels. To solve this the spirit safe was introduced. It is a brass box to where the pipes from the condensers are connected. The still man can draw off a sample to check the alcohol concentration with a hydrometer or test for purity by mixing it with water and see if it gets cloudy. When the mix is clear he diverts the flow to the receiving vessel.
The spirit safe is always kept locked during production. In older days it was only the excise man who had the key, but today the distilleries are entrusted with it.
Some distilleries have reduced the importance of the still man and are only using a time-based collection. There are also a few distilleries which have automated their distillation, controlling the collection with in-line meters and automated valves. In this case the spirit safe is kept as not more than a showpiece.
The wash is distilled twice in order to increase the alcohol strength.