Distilled genius that kick-started the whisky industry

 

Mary Mulvihill reports on the Irishman whose invention of the heat exchanger dealt an unexpected blow to Irish distillers.

It has to be the ultimate tale of the gamekeeper turned poacher. Aeneas Coffey, a Dublin-born customs and excise inspector, spent years hunting illicit whiskey makers only to switch in 1824 and open his own distillery.

But there's more: Coffey then invented a new, more efficient whiskey still. It kick-started the Scotch whisky industry and, in so doing, effectively destroyed Irish distilleries, succeeding where his armed militia had failed.

And it almost never happened. In 1810, during a raid on poteen makers in Donegal, Coffey was stabbed and left for dead. Fortunately for the distillery and chemical industries, he lived to tell the tale.

At the time distillers used pot stills, or alembics, unchanged since Arab alchemists invented them around 700. This large copper kettle, topped with a bent condensing tube, or worm, exploited the fact that different liquids have different boiling points: control the temperature and you can separate alcohol from water. Arab alchemists attributed this amazing phenomenon to "spirits", the term that survives. Enterprising Irish missionaries brought the technique home from Arabia and, in the eighth century, made the world's first whiskey.

To make whiskey, fermented barley "wash" is put in the pot and heated; the alcohol vapour rises into the worm, condenses and drips into a collecting vessel. To produce concentrated spirit, however, the process has to be repeated several times. It's slow and consumes vast amounts of fuel; cooling and cleaning the pot between batches also takes time.

Coffey's apparatus, patented in 1830, was radically different. It consisted of two tall columns - the analyser and the rectifier - connected by pipes and filled with stacks of perforated metal plates. Steam could rise, and liquid fall, through the perforations, each plate acting as a small distillation chamber.

Significantly, Coffey used the heat from the outgoing vapour to warm the incoming liquid, making this the first known heat exchanger; the principles he developed are still used in the chemical industry and refineries.

To start, cold wash entered the top of the rectifier, flowing down in pipes that were warmed by the rising outgoing alcoholic vapour. The warmed wash was then pumped to the top of the analyser column and let fall through the plates while steam was pumped in from below; the rising steam extracted the alcohol from the falling wash.

The resulting steam-alcohol mix was then pumped to the bottom of the rectifier. As it rose it hit the cold pipes containing the incoming wash and began to condense. The lower condensate contained too much water and was returned to the analyser for a second pass; the middle fraction contained heavy, toxic alcohols that could be used by the chemical industry; and at the top came spirit that was about 90 per cent ethanol.

Coffey's apparatus was highly efficient, easy to maintain, could be run continuously, used less fuel than a pot still and produced a near-pure spirit. It could produce 2,000 gallons of strong alcohol a day and would have saved distilleries a fortune in fuel alone.

But the liquid it produced was so pure that it lacked flavour, so Irish distillers continued using pot stills. Coffey's apparatus was ideal for the chemical industry and English gin makers, however. It also suited Scottish distillers, who were happy to blend in a little malt to flavour their whisky. Thanks to Coffey's industrial-scale still they won the world whisky market - a blow from which Irish distillers are still recovering.

Aeneas Coffey features in Ingenious Ireland, Mary Mulvihill's award-winning book on Ireland's scientific heritage.