Pot Still Designs

There don't seem to be many instructions around for how to build pot stills. I guess this could be because there are just so many ways, and it really depends on what you have available to you. One factor to consider is the angle of the lyne arm. Even with a pot still you get a little bit of vapour condensing on the head & arm, and running back down into the pot as a bit of reflux. Depending on how much internal reflux is going on, the flavour will vary. An upward sloping arm will cause much to run back into the pot, thus cleaning & lightening the vapour more, whereas a downward sloping arm will send all the vapour towards the jar, and you'll collect a heavier flavour. See my Photos of Distilleries and Photos of Stills sold commercially pages to see what variations in this are around in commercial distilleries, and Portugese Copper Alambics and Alquitars. Some also have a bulge in the head. This constriction then expansion causes some of the vapour to drop out, and again increases the reflux, and lightens the spirit.


Jack writes ...
For a potstill, I've found that the lyne arm (as it comes off the still body) should go up at a 45degree angle for 2 feet, then it should drop into the condensor. The diameter of the tubing depends on the heat - for most stovetop models (typically built out of a pressure cooker) 1/4 to 1/2inch tubing is used for the lyne arm and the condensor. The narrower the tubing is, the lower the heat setting you need to use. The condensor running off of your potstill can be whatever diameter you have (provided it's no smaller than 1/4"). Also, remember that you don't have to have a coiled-tube condensor- you can use a jacketed model just as easily. With stovetop potstills there is a lot of room to adjust the materials dimensions, because the heat source is so easily adjusted.


Wal elaborates ...
The shape and height has an effect on flavor.
  1. Traditional Alambic. This is descended from stills used by alchemists. It consists of a domed cylindrical boiler with a bulbous still head. It sits in a brick furnace. From the still header chamber, the lyne arm usually slopes downwards or is U-shaped ('Swan's Neck'). The condenser is a coil in a tank of water. Raki stills, moonshine stills and the 'Alambic Charentais' for making cognac are examples.
  2. Varied Boiler shapes.
    • Conical, classic whisky pot still ('Springbank' whisky)
    • Onion shape, slightly fatter than the classic shape ('Glenlivet' whisky)
    • Pear shape ('Vintage Islay' whisky)
  3. Varied Neck (Column) shapes and heights.
    • Conical column from boiler. The smallest whisky stills are at 'Edradour'and the tallest at 'Jura', 'Bruichladdin', 'Glenfardas'. The stills at 'Glenmorangie' whisky distillery are ex gin stills and are the tallest at 5.3m
    • Boil ball and conical column ('Strathmill' whisky)
    • Boil ball and cylindrical neck ('Lomond Still')
    • Additional reflux feature in column. Column length and the Milton Ball header chamber create reflux, but some necks are cooled with running water to increase reflux ('Fettercairn' whisky). The traditional Australian brandy pot still has a 'Brandy Ball' water jacket at the top of the column. All are open columns. The 'Lomond Still' has 3 adjustable plates and is used as a wash still at 'Scapa' whisky distillery.
    • Carterhead Still. The column contains a basket holding the gin botanicals ('Bombay Sapphire' gin')
  4. Varied Lyne Arms.
    • Horizontal
    • 30 degree downward slope
    • 30 degree upward slope ('Deanston' whisky)
    • U-shaped or'Swan's Neck'.'Alambic Charentais' for cognac, 'Plymouth' gin', 'Talisker' whisky, 'Lagavulin' whisky.
Ian Wisniewski's article "Still Very Important" in Whisky Magazine describes in more detail how the shape of the still can affect the flavour... Big thanks to Whisky Magazine for permission to reprint the following

Knowing that stills of a certain size and shape yield spirit with a particular flavour profile is all very well, but applying this knowledge the other way around is far more challenging. In fact, designing stills in order to produce a spirit with specific characteristics is merely a starting point, as this is only one factor in a complex (and not always fully understood) equation, which also includes the spirit cut, heating method, rate of distillation and type of condenser.

Even the relationship between the wash and spirit stills is difficult to quantify beyond stating that new make spirit is shaped by wash stills and refined by spirit stills. But if the low wines aren’t right, the spirit stills can’t correct them (and if fermentation is mismanaged, distillation can’t fix that either).

(snip)

As the degree of reflux (condensation) is a key factor in establishing the profile of the spirit, the length of the neck is an important consideration. The taller the still, the greater the degree of reflux. This is because heavier, denser, oilier flavour compounds have a higher boiling point than lighter flavour compounds and as they rise up the still the temperature becomes relatively cooler, which means they condense and return to the boil pot (base).

(snip)

As a shorter neck means less temperature variation, there is consequently less reflux. This promotes the progress of heavier flavour compounds into the condenser, yielding fuller-bodied spirit, with a creamier, earthier, oilier texture.

But size doesn’t always matter, as reflux can also be enhanced by customising stills with various matching accessories, including a boil bowl, pinched waist or flat top, while cooling the neck of the still is another option.

A traditional (cynical) explanation for a flat topped still has been the low ceiling it had to squeeze under. However, the technical influence of a flat top, as at Cragganmore, results in a slightly higher degree of reflux because the progress of vapours is not as gradual or progressive as it is with a swan neck.

A pinched waist (as though a corset had been tightened around the still), can be seen in The Glenlivet’s wash and spirit stills. By reducing the surface area available to the vapours (by about two-thirds at The Glenlivet), a pinched waist initially accelerates the progress of vapours into the neck. The subsequent, sudden widening of the neck, and relatively cooler temperature, consequently increases reflux.

A boil bowl (bulbous section between the boil pot and neck) can vary from being mildly to acutely convex (the more convex, the more reflux). When vapours carrying heavier flavour compounds expand into this larger, relatively cooler area, they condense and return to the boil pot.

Dalmore Distillery effectively doubles up by having a cooling jacket (also known as a water jacket) between the boil bowl and neck of the spirit still through which cold water circulates (using the same water source as for the condenser). This practise dates from 1839, with the oldest jacket still in active service dating from 1874.

At Fettercairn a different approach yields a similar result. From a circular pipe located at the top of the spirit still, cold water runs along the neck and collects in a trough fitted around the still (from which it also drains). This has the effect of “giving the vapours inside a little fright” according to Distillery Manager Willie Tait. His more technical explanation is that cooling a fairly short neck gives it the effect of being much taller.

While purifiers are rarely seen, this is a feature of Glen Grant’s wash and spirit stills. As vapours leave the still and enter a copper pipe in a tank cooled by water, lighter elements within the vapour continue onto the condenser while heavier elements return to the still via another pipe. Without this proceedure Glen Grant’s new make spirit would be oilier and heavier, says Chivas Brothers’ Brand Ambassador Jim Cryle. Similarly, in the opinion of Site Manager John Reid, a purifier in the spirit still increases the buttery, creamy notes of Edradour’s new make spirit.

But just as important as design features that make a still unique, is the manner in which the still is employed. Pungent, fruity esters are more evident in spirit collected between 68 and 72% abv, while a spirit cut extending to around 58% abv includes heavier, oilier, fatty acids. Consequently, altering or separating the spirit cut into batches collected at different strengths would enable varying styles of whisky to be produced from the same still.

(snip)

How [heating] is utilised also affects the degree of reflux. Heating the still more rapidly increases the rate of distillation, driving off vapours more readily. As this reduces the degree of reflux, it promotes a higher proportion of heavier flavour compounds. Driving vapours more rapidly also entails the risk of carrying over some undistilled liquid, showing as a sour note in new make spirit. Correspondingly, a lower temperature means a slower rate of distillation, more reflux and a lighter (some say finer) spirit. At the leisurely end of the scale this means collecting around nine litres of spirit per minute, compared to around 20 litres per minute in the fast lane. Additional reflux can also be prompted en route to the condenser, using a lye pipe (or lyne arm) extending at an incline, which drives heavier flavour compounds back into the still.

By providing a greater surface area than a typical worm, a modern ‘shell and tube’ condenser increases the degree of contact between the spirit and copper, helping to strip out meaty, sulphurous compounds. However, worms (a coiled copper pipe of decreasing diameter, set in a worm tub with cold water) do not neccessarily result in a higher level of sulphurous, meaty flavours and the challenge lies in controlling the level of these characteristics to achieve a complex whisky.

(snip)

So, knowing these principles, is it possible to quantify the importance of the stills within the production cycle? Well not easily, that’s for sure. Beyond the usual 60% of the malt’s eventual flavour being attributed to maturation, I’ll leave dissecting the balance to an expert. “Less than 10% is accounted for by the barrel’s previous incumbent, then maybe 5% is influenced by the barley variety, and 5% by the strain of yeast,” says David Robertson, The Macallan’s Master Distiller. Then the crucial bit. “10% could be the wash still and 10% the spirit still, with the influence of the spirit still being divided into 5% each for the size and shape of the still and 5% for the spirit cut.” Sounds good to me.



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