Types of Whisky Stills
There are many different types of stills in use around the world. From the vast to the strangely small, long-necked, multi-story, column stills, hybrid stills, and Lomond stills, indirect or direct fired. One of the most important distinctions, however, is the one between batch pot stills and continuous column or coffey stills.
Those looking a little deeper into the processes of distillation, quickly realise that the process has changed little over the centuries. Admittedly, the stills used today are significantly larger than those of the compared to the 18th or 19th centuries. Nonetheless the essential making whisky remains as it has always been. In the simplest language, a distillery transforms a rather flat, moderately strong and unhopped beer (commonly known as wash) into a new make spirit. By exploiting the dffering boiling points of liquid the wash is heated, vapourised, re-condensed and collecting again.
The system works because the components of the wash, the fatty oils, the stronger and weaker, and sometimes poisonous alcohols all have different boiling points. Ethanol alcohol, the potable alcohol the distillery wants extract has a boiling point of 78.2˚C. water and the other, less tasty and often harmful congeners have boiling points that are either slightly lower, or slightly higher than Ethanol. Through careful control of the heat, they can be seperated. As each turns into steam and rises up the neck of the still, the stillman can collect the vapors after condensation that are ready to be matured, and discard the rest. The feints and tail of the second distillation are added to the next batch to be passed into the still for distillation again. The exact cut between these alcohols, the speed of distillation and the method used to recondense them all play a part and determine the ratio of aromatic and foul-smelling odorants and flavours that make it into the final product.
Everyone who has ever visited a Scottish, Irish or Japanese whisky distillery has encountered a pot still, some are tiny such as those at Edradour or vast towering giraffes such as those at Glenmorangie. At some distilleries these are regularly polished glinting copper, at others these are dark stained stills. Malt whisky, traditional Irish Pot Still and even grain whiskies are distilled either twice or thrice in them. These pot stills narrows into a swan neck carrying the whisky into a lyne arm (tapered or lye pipe) leading to the condensor unit.
Wash, Spirit and Intermediate Stills
At most distilleries, with a few exceptions such as Glengoyne, or Macallan, pot still generally operate in pairs, with a larger wash still and a spirit still working together. In the case of tripple distillation a third intermediate or ‘low wines still’ may also be used such as at Auchentoshan.
The distillation process in a pot still is known as batch or discontinuous distillation, as only one batch at a time can be distilled at a time. At the end of the distillation, the copper still must be emptied and carefully cleaned before it can be refilled with the next batch of wash or low wines.
During the first distillation in the wash still, chemical compounds and flavors including alcohols, acids and esters are seperated from the remaining mix of yeast residue, water and other impurities. The process begins when the temperature in the still approaches 78 ° C, the boiling point of the drinking alcohol, ethanol, the main component of the wash alongside water. As this fermented liquid is heated, the alcohols and other compounds evaporate, rise up to the neck of the pot still, pass the swan neck and the subsequent lyne arm and finally reach the condenser. This achieves a concentration of the fermented liquid from an initiall about 7-8% ABV to an average of between 20% and 25% ABV now known as low wines. The spirit is collected in the appropriately named low wines receiver.
The pale yellow, golden liquid left behind in the still, is effectively a slurry comprised of of dead yeast and barley derived proteins at around 0.1% ABV. The remaining alcohol requiring too much energy to be commercially viable to extract. Use of pot ale varies, in some cases it is treated to remove any toxic levels of copper and other substances, then re-released into a large body of water, others use it as a form of fertilised but in recent years some distilleries have turned their draff and pot ale to power anaerobic digester (AD) plants, creating bio-gas that is then turned into steam energy.
Recycling the Heart and Tail
The first and last runnings from the previous second distillation commonly known as the foreshots and feints are then added to the low wines in a feints charger. Thus recycling any trapped ethanol and bringing the low wines alcohol content up to around 28-30% ABV. This combination is then added to the second ‘spirit’ still and distilled again.
Here, in contrast to the wash still, where all distillate is collected, the spirit still collects in fractions. The highly alcoholic and partly toxic first distillate called the head or foreshots are directed, via means of a spirit safe into a feints and foreshots receiver. The next run of the still the middle cut or heart is the new make which will become whisky. As this ends and ABV starts to lower again the final cut is made and the feints or tail are directed once again into the into the feints and foreshots receiver, ready to be added to the next batch of low wines. An intermediate still would be used in the case of triple distilation, with a virtually identical process.
Spirit and Wash Still Ratio
The spirit still, having far less water and other unwanted compounds to seperate in the low wines, is usually significantly smaller than the wash still. The size, and absence of a glass level compared to the wash stills are usually immediately recognizable to the distillery visitor, there are exceptions however. At Glenrothes in Speyside, the proportions are exactly the opposite. Five spirit stills, each with a capacity of 25,400 liters, are actually around 10 percent larger than the five wash stills, each with a capacity of 22,990 liters. The spirit stills at Dailuaine are also around 10 percent larger than the wash stills that feed them. In practice however the size of spirit still is different from the actual filling volume, as this is generally only between two thirds to three quarters of maximum capacity.
Common Pot Still Shapes
In general there are three different styles of pot stills:
- Onion-shaped stills (among the most common derived from the Alembic still)
All three types of stills may come with or without a spherical bulge in the lower part of the neck, the addition of which increases surface area and the heat emission to the outside with the effect increaseing reflux and creating the lighter new make. Despite this seeming similarity the shape and size of a pot still have a decisive influence on the character of the New Make Spirit.
Importance of Still Shape
While the lower part of the still is little more than a container to heat the the liquid and leaves the resulting distillate largely unaffected, the upper area of the still, the so-called reflux area, has a massive influence on takes the character of the spirit. Larger stills lead to more reflux, smaller squat stills will carry more of the heavy oils, esthers, and sulphurous notes into the condensor. It is the peculiarities of shape, specific to each distillery, that gives each single malt its character - its DNA. Therefore the rule is to Never change a running system!. No manager or stillman would dare to play around with the design of the stills less it change the unique character of the whisky produced. The original shape of a still almost certainly came about by chance, but the coppersmith ensures each replication is true to the original, and unchanged when it is repaired over the course of years through wear and tear.
Some distilleries go so far as to claim that when a still requires replacing every dent and bump from the old pot still is replicated in its successor. While this is certainly an exaggeration, it does illustrate the importance of the shape of a pot still. In spite of this attempt to replicate perfectly the process is still far from exact. Two distilleries using identical ingredients, equipment, and process can result in entirely different new make spirit being produced. Lagavulin distillery came into existence through an attempt to recreate the whisky style produced at Laphroaig.
Pot Still Variation Within A Distillery
At most distilleries uniformity across there stills is the rule, with each additional still added being if not identical, very similarly shaped. This is not always the case however a number of distilleries such as Aberlour, Glen Elgin or Glenrothes use different shaped stills, blending onsite to create a signature style. Mortlach distillery is also noteworthy as it use a dizzying array of still sizes and shapes in unusual ratio, what Diageo has coined the ‘Byzantine form of triple distillation’.
Other Flavour Factors
Beyond merely the shape and size of a still, other influential factors such the heating method the speed of distillation, and the type of condenser used influence the final spirit produced. The heating of the still can be eitehr by indirect methods such as steam heated coils, or direct using coal or gas, though in practice direct heating is now less common. The amount of copper contact is also determined by the use of either shell and tube condensors, or more traditional wormtubs.
The Lomond Still
An often forgotten and overlooked variation on the pot still was the Lomond Still. Developed in 1955 by Alistair Cunnigham and Arthur Warren, the neck of the still, consisted of movable cylindrical copper plates and moveable line arm that allow for manipulation of the reflux. However, the cleaning and maintenance costs were higher and it’s largely abandoned. Today it is still used in the Loch Lomond and Incdairne distilleries. Scapa continues to use a labotomised Lomond still as it’s wash still. The most famous Lomond still now dubbed ‘Ugly Betty’ is used for the production of the Botanist Gin. You can find our more in our article about the rise and fall of the Lomond whisky still.
The Lomond still has a cylindrical shape and inside there are copper plates with which the backflow can be regulated. However, this procedure could not prevail. The only distillery that still distills with a traditional Lomond still today is the SCAPA distillery on the island of Orkney .
In contrast to batch distillation using pot stills, most alcohol whether it be for tequila in Mexico, Gin in England or for worldwide vodka production is distilled using a Patent still. The vast columnar Patent, or Coffey stills, are reminiscent of an oil refinery in appearance and incredibly efficient. Their production need only halt periodically for cleaning and the method enables a higher alcohol yield of up to 94.8& ABV. These are also used in America for whisky production and in Scotland and Ireland for grain whisky.
The Stein Still
In order to meet the increasing demand for whisky in the 19th century, and to meet increasing competition refinements and advancements were made on the previously used batch distillation process. Although very high quality spirits could be produced using the traditional method, the production process, took too long often several days or weeks depending on the volume needed. Robert Stein, then owner of Kilbagie Distillery in Clackmannanshire, Scotland, developed a system in which the spirit was produced in a continuous flow, inspired by a previous model by the Irishman Sir Anthony Perrier of Cork in the 1820s. The only prerequisite was that sufficient mash was constantly being supplied. This new invention was patented as the Stein Stilland was officially put into operation for the first time in 1830 at John Haig’s Cameron Bridge Distillery.
The Coffey Still
Just a few years after the invention of the Stein still, the Irishman and former excise officer, Aeneas Coffey discovered a disadvantage in the new distillation process. To produce high-proof spirits, collecting containers had to be repeatedly changed to prevent the alcohol from mixing with too much steam in the event of multiple distillation. To solve the problem, Coffey attached two pipes to the fuel columns previously used. This enabled a larger amount of water vapor to circulate back into the columns instead of mixing with the distilled alcohol in the receiver.
Continuous Versus Pot Distillation
The speed of production offered by continuous distillation, and reduced costs are clear advantages with distillate produced in hours rather than weeks resulting in vast income increases. A serious disadvantage, however, is that the depth, aroma and mouthfeel of the whisky suffer from the faster process and removal of flavour at higher ABV. Likewise as steel is used as the base material for the manufacture of the columns stills the sulfur contained in the liquid cannot be removed by the creation of copper sulfide. As a consequence grain whiskies are generally far less popular and instead used as the basis of blended whiskies.
The Doubler or Thumper in Bourbon Distillation
While American distilleries generally use continuous distillation they also have their own quirks. Most bourbon undergoes a second round of distillation in a second continuous still called a doubler or a thumper. After the alcohol has been extracted from the still, the hot vapors are passed through a copper pot, called a doubler, where a catalytic conversion takes place stripping sulphur from the gas in a similar but far less effective way than a copper still. As the flow of column still is not constant the doubler is sometimes referred to as the thumper, due to the concussive sounds made when the hot vapour enters the chamber.
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