Distillation

Pot Still Distillation 

Types of spirits using Pot still distillation

Cognac - double distilled in the Charentais copper pot still, must be heated directly and have worm tub condenser

Brandy de Jerez - Holandes distillate by law, also the aguardentes and destilados can be 

Pisco - Peruvian and Chile 

Grappa - premium 

Calvados 

other fruit spirits 

Scotch - malt whiskey 

Irish - triple distilled 

Bourbon and Tennessee - 1st takes place in a column then a type of pot still (doubler or thumper) is used

Japan - malt whisky 

Rum - heavier marks - retort system, placed in between the pot still and condenser 

Jamaican Rum - known for their punchy pot still rums 

Tequila - 100% agave 

Mezcal

Gin - redistilled in pot still 

Cachaca 

Batch Distillation > 2 or more separate distillations in order to produce a final spirit. The still constantly needs to be filled, used, emptied and cleaned. It is very labour intensive. Can take place in a column still, most commonly associated with pot stills. 

Five common elements of a pot still

  1. Heat source 

  2. Pot, into which the liquid is placed

  3. a head, where the alcohol vapours gather and reflux takes place 

  4. a linking tube to the condenser (lynne arm, swans neck)

  5. a condenser 

Heat Source > 3 main options 

More heat causes a fierce boil > resulting in a less temperature difference in the still head and less reflux. 

Direct heating 

  • open flame

  • bottom of the still can become very hot, any solids in the liquid can become stuck and scorched giving unpleasant aromas. 

  • gas burners are used 

  • used to be the only option

  • Calvados by law must use this

Steam 

  • 2 way can be used

  • 1st - circulated through a coil, similar to the element in an electric kettle

  • better control than direct heating

  • still a risk of scorching 

  • 2nd - circulated through a jacket that surrounds the outside of the still, better control and minimises the risk of scorching 

Water bath (Bain maire or Bagno maria) 

  • similar to a steam jacket, it is filled with water and heated 

  • used to make Grappa and Marc, high solids content

  • minimises the risk of scroching

Reflux 

  • helps to increase the amount of separation between fractions

  • useful in producing high-quality spirits

  • ensure less desirable components (fusel oils) return to the still 

  • happens when vapours and liquids come into contact with each other 

  • heat is needed to turn liquid into vapours that rise up the still

  • when heat is lost, some vapours condense and fall back as liquid through the rising vapours

  • liquid and vapour mix in a still

  • heat is shared between liquid/vapour - more volatile fractions become liquid

  • temperature, height/head of the still, angle of linking tube, head condensers all impact the amount of reflux

  • taller stills - more reflux due to a larger temperature gradient

 

Temperature in the still 

Temperature gradient - heat is lost through the still. Taller stills lose more heat, therefore have greater temperature gradient so more reflux takes place 

  • Gentle boil - increase temperature gradient and facilitate more reflux, limiting the passage of less volatile congeners 

  • Boils vigorously - more heat is added to the still, temperature gradient will be small reducing the amount of reflux and resulting in less volatile congeners in the final spirit.

Height and Shape of the head 

  • height contributes to reflux, greater the height, greater the temperature gradient,

  • more reflux 

  • various head shapes can be used 

Angle of linking tube 

  • angled up - reflux can continue 

  • angled down - can not 

Rectifying plates and head condensers 

Rectification > progressive increase in the level of ethanol that is the result of reflux

More reflux = more rectification = more alcoholic product 

Spirit that is very high in alcohol, HRS

Rectification Plates 

  • used in all column stills

  • can be included in modern pot stills NOT Cognac and Scotland

  • this adpation allows the distiller to produce a more HRS

  • suited to distillers who produce various styles of same category spirit who want to make up different brands, also for distillers who produce a wide range of spirits from different categories. > they can bypass the head condenser to suit the style

  • maximise the interaction between vapour and liquid improving rectification

  • few as 3, as many as 42

  • Armagnac limited to 17

  • Vodka - around 42

  • All plates are able to hold a layer of liquid

  • vapours from below are forced through this liquid - as a result of this reflux more highly rectified vapours pass up to the next level

  • mixing between vapours occurs - plate can only reach a certain level before it overflows to the plate below

  • temperature gradient in the still helps to ensure only the more volatile fractions can reach its upper section 

  • the liquid on any plate is more rectified than the liquid below but less than the one above

Head condensers 

  • all stills EXCEPT continuous column stills 

Condenser has 2 parts 

  1. a tube(s) where the spirit enters as a vapour and exits as a liquid

  2. coolant, usually water

A heat exchange between the vapour and water causes the spirit to condense. This heats the water up, therefore needs to be constantly refreshed otherwise it would boil and vapour would not condense. 

2 types of condensers 

Worm Tub 

  • container for cold water and a single coiled tube ( through which vapours pass)

  • the tube is referred to as a worm or serpentine

  • oldest type of condenser

  • still widely used 

  • used in Cognac by law 

Shell and tube 

  • vapour passes through numerous narrow vertical tubes

  • tubes are surrounded by water

  • tubes have a large surface area and the heat exchange can happen more effciently

  • takes up less space 

  • if made out of copper, can increase the reduction of sulphur compounds producing a lighter spirit

Pot Still in Operation

  • pot is filled, heat is applied and vapour is produced which is condensed and collected

  • some residue is left in the bottom of the top 

  • usually double distillation sometimes triple 

1st Distillation

  • separate all of the volatile fractions from some of the water and all of the non-volatile parts of the alcoholic liquid

  • not used for rectification or refining flavours

  • distillation must continue until all the volatile fractions have been separated from the alcoholic liquid 

  • a water non-alcoholic waste product is left in the pot once the 1st distillation is complete

Second Distillation

  • continues the process of concentration

  • determines the style and flavour by collecting 3 parts 

Heads 

  • 1st liquid to flow off the still

  • not included in the final spirit 

  • contain high concentration of volatile fractions with lower boiling points than ethanol in particular methanol ( high concentrations can be toxic)

  • undesirable impact of the flavour

  • flow is monitored, when it is free of all undesirable components the distiller redirects the flow to a separate container and starts to collect the heart

Heart

  • portion used to make the final spirit

  • high concentrations of ethanol and all of the other congeners that give a spirit its flavour and character

Tails 

  • as the heart progresses an increasing number of the less volatile fusel oils start to distill over

  • at low level these can give a spirit a richer, weightier character

  • high concentration of fusel oils with make any spirit unpalatable

  • lighter spirit > cut will come earlier

  • heavier spirit > later cute eg. peat whisky

  • once the cut to tails has been made the temperature in the pot is increased to speed up the process of collection

Heads and tails contain ethanol, many decide to recover the alcohol to maximise the amount of final spirit. This is done by re-distilling with the next batch of the first product.

Column Stills 

Spirits that use column stills 

 

Armagnac

Calvados 

Cheap Grappa 

Vodka

Grain Whisky

Rum - lighter marks

Tequila - mixtos 

Batch distillation can be done using a column still, very rare. Small batch premium vodka who operate on a small scale sometimes use this.

Heat source 

  • heated from the base

  • direct injection of steam OR steam powered heat exchanger known as a re-boiler

Promoting reflux

  • head condensers

  • alcoholic liquid is preheated as it is passed in a tube between the rectification plates

  • pour some of the spirit they have taken back into the still to promote down flow

Continous Distillation

  • only in column stills

  • constant flow of liquid 

  • very efficient process 

  • only for large volume producers, volume of alcohol needed to support the constant flow is massive

Double Column Distillation

  • many different versions eg Coffey, patented by Aeneas Coffey in 1830

  • Alcohol liquid is preheated in a tube that passes through the rectifier, added benefit of promoting reflux

  • hot liquid then enters at the top of the analyser and passes down through the still.

  • hot liquid meets the vapours and steam that are rising in the opposite direction

  • volatile fractions pass as vapour into the rectifier

  • liquid waste is taken off the bottom of the still

  • In the rectifier continuous action of reflux and rectification means that the composition of the liquid on each plate remains constant

  • the distiller will always know where the fusel oils will collect (bottom) and where the methanol collects

  • this balanced system can be maintained as long as the temperature gradient in the still remains constant and the volume of liquid that is constantly taken of the still match the volume of the feed that is constantly entering the still 

  • distiller is able to take off heads,heart,tails at the same time

  • HEADS > drawn off as as liquid or vented off the top of the still as vapour, which can be condensed and collected

  • HEART > can be drawn off rom any number of plates, depending on the alcohol level required for the style of spirit being produced

  • HEADS and TAILS > under further processing to remove any remaining ethanol

Multiple column distillation

  • HRS at 96% still contain small quantities of fusel oils, methanol and other congeners

  • further reduce the flavour of a spirit 2 common techniques 

  • sometimes legally necessary

Hydroselection - remove fusel oils

  • hydroselector column

  • HRS enter near the middle of the column

  • it is then diluted with hot water from above, heated with steam from below

  • fusel oils become volatile and rise to the top of the still

  • diluted spirit is collected at the bottom

De-methylising - reduces methanol 

  • methanol is most volatile when ethanol is at a concentration of 96%

  • de-methylsing column

  • the spirit is gently heated in a reboiler (steam would dilute the spirit)

  • methanol is able to separate out over many plates

  • collected at the top of the still 

  • leaving purifed high strength ethanol spirit in the base of the column

  • usually a necessity of vodka production in the EU, legal minimum is very low.

5 column still operation might include

  • analyser/stripper

  • rectifier

  • hydroselector

  • second rectifier - bring the low strength product of hydroselection back up to 96%

  • de-methyliser 

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