Purple Palate Blog

The Column Still=Coffey Still, Patent Still and Continuous Still-innovations in distillation

Distillation is the process of physically separating/purifying component products from a liquid mixture by the use of evaporation and steam.

The process was (probably) first discovered by the Greeks, creating flammable, intoxicant substances from wine (fermented grapes).

It travelled throughout the known world through travels of monks (carrying alcohol medicines(tinctures)) and the invasion of Europe by the Moors (Ottoman empire).

The first stills were Pot Stills, which was a large single chambered Pot that boiled the fermented mixture(mash, wort etc) separating the components at different volatility (boiling points).

These liquids become gases and rise to the top of the still, where they cool (either on the neck of the still or at the condenser area), and reform into a liquid, which then runs to a tap.

While the basic method was (in concept) fine, different alcohols (Ethanol, Methanol,particularly) had very similar boiling points, so early distillation would have been dangerous (especially without systems for recognising boiling points of less toxic alcohols, and regulating temperature of the Still).

Also this means that the “wash” was distilled as a single batch, meaning it reduced the amount of potential alcohol production from it.  It also means that get higher alcohols requires multiple distillations.

For centuries this was the method of Distillation used world wide.

In 1822 Sir Anthony Perrier created and patented the first Continuous Still, to allow the mash to flow gradually and continuously over the heat though a maze of partitions.  This means that the small portions of the “wash” receive the greatest amount of heat freeing the most amount of potable alcohol available.

In 1828 Robert Stein developed a variation of Perrier’s Still by creating a Still that fed the “wash” through a column of partitions (Patent Still).

It was Aeneas Coffey, previously an Irish Excise Tax Inspector, who tweaked Stein’s idea (after he left the Tax Office) in 1830, to create the Coffey Still, which Coffey inserted two pipes into Stein’s column still that allowed a greater portion of the vapours to re-circulate into the still instead of flowing into the receiver with the spirit. This eliminated the need for multi-distillation and produced a spirit with a higher proof and lighter character. In 1830, he was granted the patent for his design, a two-column continuous still.

Nearly every liquor producer in Europe and the Americas embraced Coffey’s new continuous column still. Cuban rum, gin, vodka, blended Scotch whisky, and blended Irish whiskey all gained new stature as output went through the roof and the character of the spirit became smoother and generally more palatable.

Unfortunately Coffey received a pushback from his fellow Irishmen, saying that the whiskey produced was bland, and Pot Still method was promoted as True Irish Whiskey.  So Coffey looked to Scotland for potential for his Still.

coffey

The Coffey Still works by the first column (called the analyzer) still has steam rising and wash descending through several levels.

The second column (called the rectifier) carries the alcohol from the wash, where it circulates until it can condense at the required strength.

Column stills behave like a series of single pot stills, formed in a long vertical tube. The tube is filled with either porous packing or bubble plates. The rising vapor, which is low in alcohol, starts to condense in the cooler, higher level of the column. The temperature of each successively higher stage is slightly lower than the previous stage, so the vapor in equilibrium with the liquid at each stage is progressively more enriched with alcohol. Whereas a single pot still charged with wine might yield a vapor enriched to 40–50% alcohol, a column still can achieve a vapour alcohol content of 96%.

A continuous still can, as its name suggests, sustain a constant process of distillation. This, along with the ability to produce a higher concentration of alcohol in the final distillate, is its main advantage over a pot still, which can only work in batches. Continuous stills are charged with preheated feed liquor at some point in the column. Heat (usually in the form of steam) is supplied to the base of the column. Stripped (approximately alcohol-free) liquid is drawn off at the base, while alcoholic spirits are condensed after migrating to the top of the column.

Column stills are frequently used in the production of grain whisky and are the most commonly used type of still in the production of Bourbon and other American whiskeys. Distillation by column still is the traditional method for production of Armagnac, Vodka (and the derivative Gin) is generally Column Still in Manufacture.

Essentially the development of the Coffey Still was a massive leap in innovation for the distilling industry, allowing increased production, better extraction and making distillation less dangerous.

 

Cheers

Andrew Jones

 

 

 

 

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