Distillers can buy ‘standard design’ pot stills which are available off the shelf in several different sizes. The usual route is commissioning one of several specialists such as Forsyths, Vendome or Kothe Consulting, to design individual pot stills for each distillery’s specific requirements.
“The first thing to establish is the production capacity and how many litres of alcohol you want to produce in a year, then we size the stills accordingly.
“Sometimes we are also asked to factor in the potential to increase production capacity, which may be projected in five years time, to avoid having to buy a whole new set of stills,” says Richard Forsyth, chairman of Forsyths, based in Rothes, Scotland.
Another key decision is the shape of the still as taller, slimmer stills typically produce lighter spirit while shorter, rounder stills produce a richer spirit.
This is because richer flavour compounds have a higher boiling point than lighter flavour compounds, and when flavour compounds rise up the still the temperature becomes progressively cooler.
Consequently, the longer the neck the greater the reduction in temperature, which results in a greater proportion of richer flavour compounds condensing and returning to the base of the still. Meanwhile, the temperature (even with a longer neck) is sufficient for lighter flavour compounds to remain in a vapour form and continue to the condenser.
Once the size and shape of the stills is agreed, detailed drawings are produced on a computer.
“Engineers develop a blueprint for our coppersmiths, detailing the dimensions of every part of the still. The engineers enter these dimensions into a computer, and sections of the still are then cut from copper plate using a computer controlled plasma torch, which uses high amperage arc to cut through the metal,” says Rob Sherman, vice president, Vendome Copper and Brass Works Inc, based in Louisville, USA.
Once the sections have been cut they are shaped to form each component of the still, including the base of the still, the shoulders, and the ogee, which links the shoulders to the neck of the still.
Copper plates can be shaped manually or mechanically. In a process known as spinning a machine takes a flat copper sheet and feeds it around a central cylinder, slowly forming the required shape. Alternatively, the copper can be hammered by hand, or by using vast, mechanically operated hammers.
Once the component parts of a still have been shaped they can be welded together. A welding rod is placed along the junction of the copper plates, which provides the additional metal required to join the edges.
The weld is subsequently hammered on the exterior side, while holding an anvil against the interior side, which has a profound effect on the copper. Prior to hammering, the structure of the copper comprises a series of individual molecules, whereas hammering causes these molecules to become ‘integrated’ with each other, which strengthens the copper.
Welding is standard practice being the least expensive and quickest option. However, this method has only been used since the mid-20th century. The historic way of joining copper plates was by riveting.
“There’s no difference in terms of strength or vulnerability to leaks between welding and riveting,” says Richard Forsyth.
With so many options to consider, the time scale from initial discussions to installation of a new still can be lengthy.
“It usually takes around five to six weeks to settle the size and shape of the stills, it may take 12 to 16 weeks to make the stills, depending on the size, though we’re often talking to a new client for several years before a decision is made to move forward,” says Richard Forsyth.
A recent ‘test case’ is Roseisle distillery. Mike Fraser, engineering director responsible for Diageo Abercrombie coppersmiths says: “I was requested to develop preliminary costings for a new distillery in October 2006, and we soon assigned engineering and technical resources to begin detailed design work. The project was authorised in August 2007, site works commenced in September 2007, and the distillery was operational in April 2009. Abercrombie fabricated and installed various production equipment, including 14 stills.”
A vital part of the package when ordering a still is the control system (ie. computer system), which operates a consistent distillation regime. However, distillation relies on natural ingredients and is not always consistant. Separate batches of malted barley can behave differently, for example when a distillery moves from one barley variety or one harvest to another (as the average size of the grains can differ). Similarly, fermentation times can vary, as can the alcoholic strength of the resulting wash, and any change in any detail can require the stillman to step in.
Technology is continually advancing, with more enhanced systems available every few years.
“Computer systems is where the greatest developments are right now. We have a department working on this, but most innovation is done using customer feedback and requests, and we have a test distillery where we can work with distillers who would like to try something new. Currently a computer system is able to do 90 per cent of what a human can do, and in a few years time a computer will be able to match human ability. It’s a very interesting time,” says Robert Birnecker, ceo, Kothe Distilling Technologies, USA.