Batch distillation Flashcards
Where did the pot still originate?
Dating back to early Egyptian times, pot stills were brought to western Europe through early trading channels, reaching Ireland first and then Scotland.
What material are pot stills in Scotland made from and why?
Copper
This easy to shape common metal is an effective conductor of heat. Copper is a good catalyst which means that it speeds up chemical reactions.
Copper also reacts with various compounds in the gaseous phase. Most notable, copper removes some of the sulphur containing compounds from the wash.
Describe the features of the pot still.
At the bottom, sits the body - or pot - which is where the liquid is boiled.
Moving upwards, you’ll find a column and neck where the vapour rises.
At the top, is the lyne arm or lye pipe which is where vapour leaves the still and is directed to the condenser.
Each pot still will also have a safety valve to ensure it does not collapse due to the creation of a vacuum.
What features of the pot still can differ from one design to the next?
The size, dimensions, shape and configuration of each still is different.
The body, column and neck can all be shaped (and sized) by design, as can the angle at which the lyne arm (or lye pipe) is positioned.
The condensing system that a still connects to can also vary.
Name the different still shapes.
- Onion
- Plain
- Straight
- Ball
- Lantern
What other features may be incorporated into the pot still?
A ball, boil pot or ‘ogee’ (an onion style bulge located at the foot of the still column). This can act as a purifier to trap the heavier impurities and return them for further boiling and refinement through evaporation.
Why is the size and shape of the still important?
It can directly impact the flavour of the final product. Each individual design decision affects how the spirit is processed in some way, however minute the differences may seem.
Many of the design differences are important simply because they determine the extent of ‘reflux’ within the still.
What occurs during the distillation process?
As liquid boils various compounds are vaporised and turn into a gas. These gases start to rise up the still, and if they reach the condenser they turn back into a liquid and are collected as distillate.
During batch distillation, the alcohol and flavour congeners are separated from the waters in the wash.
What is reflux?
When a compound will cool down (or lose energy) as it rises in the still and condenses back into a liquid while in the still, in which it drops back down into the pot to be boiled again.
This process amounts to a progressive refining, purifying action which develops sophistocation of the resultant distillate, eliminating impurities and other baser, oilier elements.
How does the level of reflux activity influence a new make spirit?
More reflux leads to a lighter and more refined new make spirit.
Less reflux leads to a heavier, oilier and denser new make spirit.
What is the relationship of still size to the level of reflux that occurs during distillation?
The still size determines the volume of liquid that constitutes a fill or “charge”.
A smaller fill increases the distance - and energy - required for vapours to reach the condenser, creating the opportunity for more reflux to occur inside the still.
A larger fill, reduces the opportunity for reflux to occur as there is simply less space and energy required to push gaseous compounds over into the condenser.
What is the relationship between the shape/size of the still neck to reflux during distillation?
A tall neck creates more reflux. This, along with the increased copper contact, contributes to a light and floral spirit character.
A short neck creates less reflux. This, along with the decreased copper contact, contributes to a heavy and oily spirit character.
A neck with an ogee (boil pot) creates more reflux, making for a light and floral spirit character.
How does the slope of the lyne arm impact on reflux?
A lyne arm that slopes upwards from the still to the top of the condensers, vapour will likely condense into liquid in the pipe and fall back into the still, enhancing reflux. This typically makes for a light, refined and floral spirit character.
If the lyne arm slopes downwards, the liquid generated will flow down into the condenser, resulting in less reflux. This makes for a heavier, oilier spirit.
A straight lyne arm will not impact the character of the spirit with regards to reflux.
What are the 2 different types of still used in to make Scotch?
- Wash stills: carries out first distillation.
- Spirit stills: carries out second distillation.
How are stills heated in Scotland?
Originally heated by direct peat or coal firing, nowadays it tends to be by internal steam coils or more recently by external heating.
Describe a wash still.
Wash stills are usually larger than spirit stills and have a sight glass fitted so that frothing levels can be monitored.
Explain the process of liquid flow within a wash still.
The still is charged with wash from the wash charger, which had been previously filled from a washback that had fermentation completed. As the charge is heated, ethanol and other compounds are vapourised. As the vapours rise from the still, they are turned back into liquid (distillate) in the condenser and are collected as low wines (about 25% ABV) in the low wines receiver.
After the distillation is complete, the residue (waste) in the wash still, known as spent wash (pot ale) is discharged prior to treatment. Spent wash can be used to produce cattle feed.
Diagram the process of distillation from the washback to the Intermediate Spirit Receiever (ISR).
