Distillation is the process by which the alcohol is separated from the water, possible because alcohol has a lower boiling point than water (80°C compared to 100°C).

In practice, distillation is done using copper pot stills. Scotch whisky is usually distilled twice, using one wash still and one spirit still, whereas Irish whiskeys are generally distilled three times. The stills are made from copper as it is a material that is easy to work with, doesn’t rust, and conducts heat efficiently. Unfortunately copper also wears down slightly during each distillation, and the thickness of the stills is therefore monitored carefully. Each still lasts for about 15 to 30 years, depending on usage.

The wash is first pumped into the wash still, the larger of the pair of stills. Inside, the liquid is heated, either directly by coal or gas or indirectly via steam coils in the bottom of the stills. As the alcohol boils, its vapours rise up, through the swan neck of the still and the lyne arm (the horizontal(ish) pipe extending from the still) and into the condenser, where they return to a liquid form.

The output from the wash still is referred to as low wines and it has an alcohol content of about 20% to 25%. This liquid is then sent on to the spirit still, where the process is repeated.

You may have noticed that the stills at each distillery differ in size and shape – some are more bulbous, others have very long and graceful necks, others more dumpy. This is not merely an aesthetic design issue. The shape of the stills has a definite effect on the taste and aroma of the whisky they produce. Those with short necks, for example, produce heavier whiskies than those with long high necks.

It is because of this distinctive contribution to the end-result that distilleries take a great deal of care to replace their stills with exact copies when they eventually wear out. The attention to detail in this regard is amazing, with distilleries replicating stills right down to individual dings and dents!

The output from the spirit still is monitored very carefully by the stillman. It is a procedure that to me is reminiscent of Goldilocks picking and choosing her way through the Three Bears’ house… the start of the run from the spirit still, called the foreshots, is too high in alcohol content, whereas the end of the run, called the feints, is too weak. The middle bit, however, known as the heart of the run or the middle cut, is “just right”.

In order to get this bit that is “just right”, the stillman uses hydrometers to check the alcohol content of the liquid. He “cuts” the run when the alcohol content reaches about 75% and stops the run when the alcohol content has fallen to just over 60%. The foreshots and feints are mixed with the next batch of low wines and redistilled, and the middle cut is collected in the spirit receiver. It is this middle cut that will be put into casks and matured.

The process of selecting the middle cut all takes place within the spirit safe. This is an impressive looking highly polished container with large glass panels, external controls, and great big ugly padlocks. Okay, not necessarily so big and ugly. But padlocked nevertheless. You see, as soon as the spirit emerges from the spirit still, it comes under the control of Customs & Excise. And, as we all know… death and taxes, and all that.

The spirit safe was first developed in the 1820s to allow the government to keep tabs on the amount of whisky produced at each distillery. Its purpose was to prevent anyone from siphoning off some of the precious product as it emerged from the still. Until 1983, only the local Customs & Excise Officer had the keys to the spirit safe. However, after that, the government decided to trust the manager of each distillery and give him or her the responsibility of holding the keys. This trust, though, is not perfect – the manager still has to submit copious reports (probably in triplicate) to prove that they haven’t allowed anyone access to the spirit safe. Oh, the joys of bureaucracy.

This is Part 3 of 4 in a series on the whisky production process:
Part 1 – Malting
Part 2 – Brewing
Part 3 – Distillation
Part 4 – Maturation

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