Aeneas Coffey (1780 – 1852), the inventor of the Coffey or columnar still, was an Irish (born in Dublin) excise man and inventor who worked for the British government in Scotland. During his long tenure as an inspector, he had plenty of time to inspect and study a range of mostly illegal and some legal stills. Over time his astute observation talent and engineering knowledge led him to invent a very efficient and fast still that accomplished three consecutive distilling operations in one step. It is less expensive to operate than any alembic still and much faster. The invention was patented in Dublin (1831).
The principle of distillation is simple. The important aspect remains the means of separating alcohol from an alcohol containing liquid. Alcohol starts to evaporate at 78.3 C at sea level, hence when an alcohol-containing liquid is heated to that temperature the alcohol starts to vaporize. A simple devise composed of metal container connected to another by means of a swan neck can be employed as a still. In fact such crude devices have been and are still being used illegally in many countries to manufacture potent distillates, many unfit for human consumption due to their high fusel oil and methanol content
Arab scientists trying to convert base metals to gold accidentally discovered the principle of distilalton in the west. Al-cool an Arabic word is the root of the word alcohol.
Some researchers claim that Chinese employed a similar process to distil 3000 years ago, but so far, there is no conclusive evidence to prove this theory.
The Coffey still (a k a columnar still) consists of three interconnected towers equipped with perforated trays stacked at intervals of approximately 20 – 30 centimetres. Each tower has to inlets; one for the alcohol-containing liquid the other for pressurized steam. The ferment is fed through the top inlet and the steam from the bottom. As the liquid trickles down the steam rises and literally strips the alcohol from it at a high temperature and speed. The vaporized alcohol travels to the top of the tower and to the next tower to undergo the same process. The third tower usually shorter distils a smaller quantity, as the volume is now much smaller than at the beginning of the process.
At the end of the run, a highly purified (90 percent ABV) alcohol is obtained which is, regardless of the base material, tastes the same -colourless, and tasteless much like vodka or industrial food-grade alcohol. This alcohol consists mainly of ethyl alcohol and very little, lethal methyl alcohol.
Gin is redistilled alcohol in the presence of botanicals; vodka can be obtained quite simply by running pure alcohol through charcoal filters and diluting it to the desired level of ABV.
Using pure alcohol manufacturers produce liqueurs, by blending sugar, flavouring agents and colouring matter.
Blended whiskies contain both grain whisky from Coffey stills and whisky from alembic or pot stills.
A pot still consists of a copper container, connected to a receptacle by means of a metal swan neck. Pot still is fired by wood, or coal or gas.
The still master has a much better control of the pot still temperature and can regulate the strength of the distillate to fit his objective. Generally, pot still distillates contain 70 percent or lower ABV. The rest is composed of phenolics of the base ingredient; thus the final product carries a distinct taste. A low alcohol wine will end up at 60 percent ABV distillate and similarly a fermented corn mash will taste of corn before aging in barrels.
Pot still distillates contain small amounts of fusel oils which are chemically “corrected” by barrel aging whereas the Coffey still discharges a pure distillate with negligible amounts of fusel oil, but also little taste.
Single malt Scotch whisky producers, a few rum manufacturers, Armagnac and Cognac distillers, employ pot stills.
Bourbon distillers use both stills and blend according to their philosophy and market needs.
Alembic stills yield better taste and more characteristic distillates, but are slow, and require more labour.
In addition the “head” and “tails” of each batch must be separated and redistilled. As you can appreciate alembic stills lack the efficiency and purity of Coffey stills. Still masters and manufacturers must choose either one to suit their marketing strategy and quality standards.
Small quality-oriented distillers everywhere, including ultra-premium vodka manufacturers use alembic stills.
In the U S A more and more small distilleries are coming on stream using alembic stills and marketing their products to niches prepared to pay for these high end products and appreciate their subtle, refined taste.