Bourbon - Distillation
All American distilleries (except Labrot & Graham) use column stills for distillation. They were invented by Robert Stein (Haig Co.) in Scotland in 1826 and their pillar-like shape makes a continuous distillation process possible. The basic operation principle is simple: You set up an upright pipe with a height of 5m to 20m and a diameter of 70cm to 150cm. You insert floors with holes into the pipe so there is a connection from the bottom to the top. The edges of the holes are slightly bent upwards so no liquids can flow down through them. Then you insert small tubes so the liquid that accumulates on the floors can flow down to the next floor.
The column is filled with beer in a middle position and heated from the lower end. Thus two opposite flows are created. The liquid beer runs down through the tubes, while the gaseous particles (alcohol vapours) flow upwards through the holes.
The temperature of the column is regulated in such a way that the alcohol is gaseous at the top (78 - 85°C / 172° - 185°F) and the beer is cooking at the bottom (95 - 100°C / 202° - 212°F).
This process can run forever as long as there's enough supply of new beer. While the alcohol is extracted at the top, the water with the fibres and remnants of the grain accumulates at the bottom. This product is called 'stillage' and is processed into animal feed and 'sour mash', which is reintroduced into the fermentation process.
In small column stills an alcohol content of approximately 120 American Proof (60% abv) can be reached at the top. If the columns are taller the alcohol content can be raised up to 80% and more.
After the alcohol has been extracted from the still, the steam is led through the doubler, a copper pot, where a catalytic conversion takes place which improves the taste of the whiskey. Many column stills need such a doubler since the column floors aren't made of copper. In copper pot stills, as can be found in Scotland, a continuous catalytic conversion takes place. With column stills that lack copper parts, the distillate must be brought into contact with copper externally. That's what the doublers are for.
The vapour is then led into the condenser where it liquefies again and has now become raw whiskey, which the Americans call 'white dog'.
From the condenser the whiskey is led through a spirit safe into vats, from which either the barrels are filled or trucks are loaded for transport.
The white dog is regularly tasted directly after production, for which it is diluted to approximately 20% abv. In this state the aromatic substances can be judged best.
Per bushel of grain (35.24 litres) about 5 US gallons of 100 Proof Spirit are produced (9.5 litres of pure alcohol). Translated to the weight of the grain, approximately 400-450 litres of pure alcohol can be produced from one ton of grain.