P - like Pot Still
What is meant by the term pot still?
A pot still is a distillation apparatus used in the production of spirits, especially whiskey. The name is derived from the special shape of the apparatus, which is reminiscent of a large, bulbous pot. The pot stills are the heart of single malt whisky production both in Scotland and at St. Kilian Distillers in Rüdenau.
What does pot still derive from?
Today's pot still is derived from the original form of a distillation apparatus, the alambic (also alambic or alembic). This simple apparatus, consisting of a pot (still), a helmet (neck) and a condenser, was already used in ancient times to obtain essential oils and perfume by distillation.
What material is the pot still made of?
The pot still is made of elemental copper. In German, pot stills are therefore also referred to as copper stills. When making a pot still, copper plates of about 4 mm to 6 mm thickness are riveted together and then shaped into the desired form by hammering. This manual work is a very time-consuming and cost-intensive process, but essential for the production of an individual pot still.
How many pot stills does St. Kilian Distillers have?
Two copper stills operate at St. Kilian - a Wash Pot Still and a Spirit Pot Still. Both stills are identical in shape and size and have a capacity of 6,000 liters each. They were manufactured in Speyside, Scotland, by Forsyths, a copper smithy steeped in tradition. For better cleaning and also for cosmetic reasons, our two shiny copper pot stills are coated with a clear varnish on the outside.
What is the shape of the pot stills?
Our two stills are pear-shaped and were designed by the Irish Master Distiller legend and mentor of St. Kilian Distillers, David F. Hynes. The size and geometry of the stills have been adapted to the given building structure of our production and designed in such a way that after double distillation we obtain the fruity New Make Spirit we desire.
How is a pot still constructed?
This still essentially consists of a pot, also called the bottom tray. This contains the wash, i.e. the beer, which is slightly alcoholic at 8% vol. and is heated. Connected to this pot is the neck of the still, the so-called swan neck, which usually tapers towards the top and makes a bend at the upper end. Connected to this is a copper tube, the so-called Lyne arm, which is connected at the other end to a condenser - in the case of St. Kilian, a vertical shell-and-tube condenser. In this condenser, the vapors produced during distillation are liquefied again by cooling with water, i.e. condensed.
What influence does the geometry of the pot still have on the spirit?
The part of the still from the top of the pot to the condenser has a great influence on the character of the distillate obtained. In addition to possible built-in chicanes, such as bulges or constrictions at the bottom of the gooseneck, the inclination of the Lyne arm is of great importance. This is because the Lyne Arm conveys the alcoholic vapors to the condenser for cooling. However, since the ambient temperature around the Lyne Arm is much lower than the temperature in the copper tube, the vapors in the Lyne Arm cool down and partially condense. If the Lyne arm is slightly inclined downward, the vapor, even if it is already condensing in the Lyne arm, reaches the condenser and is liquefied and collected there at the latest. If, on the other hand, the inclination of the Lyne Arm is slightly upward, as is the case at St. Kilian Distillers, then the vapor condensed in the copper tube can flow back into the still due to this slight incline. There, this liquid is evaporated again at the temperature of 80°C to about 100°C prevailing in the pot still. This is referred to as reflux.
What does the reflux mean?
When more distillate flows back into the pot due to external cooling and due to the special geometry of the still and is thus heated and evaporated several times, then ultimately only the lightest vapors reach the condenser, are liquefied therein and collected. This produces a light distillate. Light in the sense of easily volatilized substances and aromas, which are extracted from the wash or, in the case of the second distillation in the Spirit Still, from the low wines. The distillate tastes comparatively mild and fruity without the low-volatile substances that are retained by the reflux.
What does the Reflux Condenser do?
As a major special feature, St. Kilian has an additional cooling coil in the Lyne Arm of the Spirit Pot Still, the so-called Reflux Condenser. Cold water can be passed through this supplementary cooling device at a controlled flow rate. Thus, with the help of the reflux condenser, the reflux can be further intensified to maximized and in this way a multiple distilled spirit is obtained. We refer to this as "multiple distilled". Only the lightest and lowest boiling substances reach the condenser at the end and are liquefied there. The reflux condenser is an essential element for us to influence the spirit character during distillation.
How is the pot still heated?
While in the past the pot stills were fired directly with wood, peat or later with gas, nowadays the heating of the contents of the still is mainly done indirectly by means of steam. At St. Kilian, heating plates are installed inside our two pot stills, which are heated with 140°C hot steam generated by a flash evaporator.
What are the advantages of indirect firing of the pot still?
In contrast to direct heating, indirect firing by means of steam allows the temperature for heating the wash or low wines in the pot still to be controlled more precisely. This means, for example, that the wash is brought to the boil more gently and evenly and that the solid components in the wash (e.g. yeast residues) are not burned on the copper wall of the still, which can lead to undesirable aromas.
How is the pot still cleaned?
Inside each of our two pot stills there are several spray heads which are used to clean the stills with the aid of water after distillation and draining and thus prepare them for the next distillation. We use caustic soda and, rather rarely, acid as additional cleaning media.