DISTILLATION
HISTORY
• Distilling was used as early as 3500 BC in Mesopotamia where perfume makers had developed it as a technique for isolating the scented oils of flowers and plants, what we know as “attar”.
• Around 1100 AD wine was first distilled to make spirit by Irish monks who traveled around Europe.
• The results of distillation were considered to have magical powers and this led to alcohol being called “water of life” or “usige beatha” in Gaelic, “eau de vie” in French and “aqua vitae” in Latin.
Distillation is the process of separating elements in a liquid by vaporization and condensation. This method has many applications and one of them is the production of spirits. In distillation, the alcohol
present in the fermented liquid (alcoholic wash) is separated from the water. Spirits are examples of distilled
drinks and the plants producing the spirits are known as distilleries.
Brandy, whiskey, gin, rum, vodka, and tequila are examples of spirits, which are prepared from alcoholic
wash as given in the following.
- Brandy – fermented grape juice
- Rum—fermented molasses
- Gin, whiskey/whisky—fermented cereal
- Vodka—fermented potatoes or cereal
- Tequila – fermented sap of agave Tequilana weber
All spirits are distilled from a base of a fermented liquid and have a high percentage of alcohol compared
to fermented drinks. There are many distinct and popular types of spirits, each having its own flavor and
body. There are differences in taste, smell, and color. They may be full-bodied or pale and light-bodied with a strong or mild aroma, colorless or with color, and so on. The differences in characteristics are largely influenced by the following:
- Ingredients used in the fermented liquid – molasses, cereals, juices used in the fermentation process contribute to the character of the final product.
- Proof at which it is distilled – higher the proof, lower the flavor and vice versa
- Amount of congeners allowed to go to the condenser – the congeners influence the flavor, body, and taste of the product (methanol, acetone, acetaldehyde, esters, aldehydes)
- Type of cask used and the period of maturation – the type of wood used in the cask, the type of cask – new, used, toasted – contribute to the flavor and color of the spirit. Longer the maturation period, mellower the product.
- Blending – it is mixing the spirits of a particular kind of varying qualities to ensure consistency.
Types of still
There are two types of still used for distilling spirits
o Pot Still
o Patent or Continous still ( also known as Coffey still and Column still)
Pot Still
The pot still ( or the "Alembic" or "Alambic") method is the oldest method of distillation and most of the finest spirits are made of pot
distillation. The pot still has the shape of a huge onion and has two parts – Still and Condenser with a spiral
tube. Distillation occurs in pairs of copper pot stills with tall swan necks. The first still is called ‘wash still’ which is larger than the second still called ‘spirit still’
The pot stills used in Ireland are much bigger than the pot stills used in Scotland.
The alcoholic wash is directed to wash still where it is heated up. The fermented wash is heated either by
a source of fire from underneath or by steam coils present inside the pot still there mechanical scrapers
present which prevents the solid particles from getting stuck to the base of the still and get burnt. When
the temperature reaches 78’ C. the alcohol vapors rise, pass over the neck of the still, and are led to the
condenser through the spiral pipe which is enclosed in a cold water container. The condensed liquid is
termed as low wine, which has an alcoholic content of around 30%.
Now the low wine is sent to the spirit still for a second distillation. This is carried out to get a drink of higher
alcoholic content. The first part of the distillate, called ‘foreshots/head’ (feints/tête) is kept aside for
further treatment as it is pungent and impure. The central portion is the distillation, termed as ‘heart’ (Coeur) is the best part; it is an alcoholic strength of approximately 75%, is condensed and collected in the
spirit container which is later matured in casks of various kinds. The final part of the distillation called
‘tails/aftershots’ (feints/queue) is weak in alcohol and contains fusel oils and impurities. It is added to the
foreshots and sent back for redistillation. The spirit thus obtained will have a high percentage of alcohol
with some water and minute amount of other substances such as acids, esters, trace minerals, flavorings
oils, etc. that are derived from the base wash and give flavor, body, and aroma to the drink. These
substances are called congeners. Drinks obtained from pot distillation have more congeners than the ones
obtained from a patent still, which contribute to the body and aroma. Cognac, malt whisky, Dutch gin, Irish
Whiskey, Tequila, Liqueurs, and dark rums are pot stilled.
Advantages of Pot Still
o The basic advantage of this pot distillation process is its simplicity.
o It does not require a constant supply of beer, which is often not available in minimum-labor fuel
alcohol processes.
o It also provides a very simple equipment system with cooking, fermentation, and boiling for
distillation carried out in the same vessel.
o This procedure may aid in sterilizing equipment between successive batches, since cooking and
fermenting in the same vessel tends to heat-sterilize.
o Separation of the spent grain and large solids from the beer prior to heating for distillation is not
necessary, an added advantage.
o It produces spirits that are individualistic due to the presence of Congeners
( Note: In the alcoholic beverages industry, congeners are substances, other than the desired type of alcohol, ethanol, produced during fermentation. These substances include small amounts of chemicals such as methanol and other alcohols (known as fusel alcohols), acetone, acetaldehyde, esters, tannins, and aldehydes (e.g. furfural). Congeners are responsible for most of the taste and aroma of distilled alcoholic beverages and contribute to the taste of non-distilled drinks. It has been suggested that these substances contribute to the symptoms of a hangover. Brandy, rum, and red wine have the highest amount of congeners, while vodka and beer have the least).
Dis-Advantages of Pot Still
o The disadvantage of the pot distillation process and its system simplicity is lower distillation
efficiency, because of the diminishing alcohol concentration in the beer under continuous boiling.
o Less stored heat may be used at the end of cooking when the slurry is rapidly cooled for
fermentation; and heat losses during cooking and distillation heating cannot be minimized as
readily as with the constant-feed process.
o Insulation applied to the pot to conserve heat during cooking and distillation heating may hinder
cooling necessary to fermentation in the summer.
o Thus, the amount of energy required per gallon of alcohol for the pot distillation process is high
( Video displaying the difference in Pot Still and Patent Still distillation)
Patent Still/Continuous Still / Coffey Still/Column Still
Patent Still ( See video above this pic for understanding the working )
It was not until the late 1820s that a new form of still was invented by Robert Stien, which produced spirit
in a continuous stream as long as wine, beer, or some such mildly alcoholic wash was fed into it. First
going into commercial production in Cameron-bridge distillery in Fife, Scotland. A Dublin Excise officer, Aeneas Coffey, attended a demonstration of the new still, took the idea and developed it further, and it
was Coffey's version of the continuous still that eventually caught on worldwide.
This new still was called the 'Continuous Still' (also 'Column', or 'Patent', or 'Coffey Still'). In simple terms, it consists of two columns, one of which has steam rising and wash descending through successive storey
inside (referred to as the 'Rectifier'). The steam stripped out the alcohol from the wash and carried over
to the second column (referred to as the 'Analyzer') where it circulates until it can condense at the
required strength.
The benefits of the continuous still is a cheaper and purer spirit [the alcohol produced is high in strength - 90%].
It has two main parts, a 'Rectifier' and an 'Analyzer', which both resemble tall, wide tubes. They are both
filled with steam. The liquid being distilled enters a pipe traveling down the rectifier and is heated
almost to the boiling point. The alcohol from the primary liquid vaporizes and is channeled along with the
steam back to the base of the Rectifier. Here it mixes with more steam around the pipes, brings with it
more liquid to be distilled, hence a 'Continuous Still'. Roughly two-thirds up the Analyser, the vapor hits
a cold plate condensing it into a liquid. This is channeled out as a distilled product.
It does involve the task of emptying, cleaning, and refilling. It consumes less fuel to operate. Today, alternatives open to distillers are to use the labor-intensive pot still which carries the fragrances and
flavors of the raw material, or the faster, cheaper continuous still with its potential for high strength, pure
but a tasteless spirit.
The Process in detail:
This still has 2 main columns namely Analyzer and Rectifier. The role of the analyzer is to separate the
parts in the “wash”. The role of the Rectifier is to enhance the character of the spirit and also to condense the
alcoholic vapors. Inside each of these columns, there are chambers. These chambers are divided by
copper perforated plates. There is a drip pipe that runs through these chambers. The fermented liquid or
the wash enters at the top of the rectifier. The rectifier is heated with steam. As the cold wash passes
through the drip pipe, its temperature increases. By the time it reaches the bottom of the rectifier, it is at the boiling point. When the wash reaches the bottom, it is pumped into the other column called Analyzer. The analyzer too, has chambers that are divided by perforated plates. The hot wash enters the analyzer
from the top and passes through different chambers. While the hot wash is being channeled
downwards, a gush of steam is injected into the analyzer from the bottom. The steam boils the wash and
produces alcoholic vapors. The vapors rise upward and the “spent wash” goes to the bottom of the column. The spent wash is removed from the still at this stage. The alcoholic vapors rise pass through the
different chambers and reach the top of the analyzer. From here, it is channeled into another pipe to the
bottom of the rectifier. These hot vapors pass through the perforated plates. As the fumes go up, it is met
by a drip pipe that is carrying the cold wash. Due to the sudden change in temperature, partial
condensation of the hot vapor takes place. The vapors keep getting cooler and the wash keeps getting
hotter on its way to the analyzer. When the vapor has reached 2⁄3 of its way up, it reaches the cold spiral
plate and condenses fully. The first part of the liquid (heads) that is collected in the spirit receiver sent
back for distillation. This is because it is pungent and it is unpalatable.
The pure spirit, which follows subsequently, is collected. This pure spirit is reduced in strength by deionized water. Deionized water is used since it does not alter the taste of the end product. After it has been
treated with water, it is sent for maturing.
Some of the spirits that use patent still distillation are Vodka, Gin, Rum, etc.
A rectified spirit or rectified alcohol highly concentrated ethanol (drinking alcohol) which has been
purified by means of rectification (repeated distillation). It is used in mixed drinks and in the production
of liqueurs.
FACTORS AFFECTING DISTILLATION COLUMN OPERATION
The performance of a distillation column is determined by many factors, for example:
Feed conditions
Weather conditions
Some of these will be discussed below to give an idea of the complexity of the distillation process.
Feed Conditions
The state of the feed mixture and feed composition affects the operating lines and hence the number of
stages required for separation. It also affects the location of the feed tray. During operation, if the deviations
from design specifications are excessive, then the column may no longer be able to handle the separation
task. To overcome the problems associated with the feed, some columns are designed to have multiple feed
points when the feed is expected to containing varying amounts of components.
Vapour Flow Conditions
Adverse vapor flow conditions can cause
1.Foaming
2.Entrainment
3.Weeping/dumping
4.Flooding
1.Foaming
Foaming refers to the expansion of liquid due to the passage of vapor or gas. Although it provides high
interfacial liquid-vapor contact, excessive foaming often leads to liquid buildup on trays. In some cases, foaming may be so bad that the foam mixes with liquid on the tray above. Whether foaming will occur
depends primarily on the physical properties of the liquid mixtures, but is sometimes due to tray designs and
conditions. Whatever the cause, separation efficiency is always reduced.
2. Entrainment
Entrainment refers to the liquid carried by vapor up to the tray above and is again caused by high vapor
flow rates. It is detrimental because tray efficiency is reduced: lower volatile material is carried to a plate
holding liquid of higher volatility. It could also contaminate high purity distillate. Excessive entrainment
can lead to flooding.
3. Weeping/Dumping
This phenomenon is caused by low vapor flow. The pressure exerted by the vapor is insufficient to hold
up the liquid on the tray. Therefore, the liquid starts to leak through perforations. Excessive weeping will lead
to dumping. That is the liquid on all trays will crash (dump) through to the base of the column (via a domino effect) and the column will have to be re-started. Weeping is indicated by a sharp pressure drop
in the column and reduced separation efficiency.
4. Weather Conditions
Most distillation columns are open to the atmosphere. Although many of the columns are insulated, changing weather conditions can still affect column operation. Thus the re-boiler must be appropriately
sized to ensure that enough vapor can be generated during cold and windy spells and that it can be
turned down sufficiently during hot seasons. The same applies to condensers. These are some of the
more important factors that can cause poor distillation column performance. Other factors include
changing operating conditions and throughputs, brought about by changes in upstream conditions and
changes in the demand for the products.
ALCOHOL CONTENT / PROOF
Different alcoholic beverages have different alcoholic strengths that are indicated by the word ‘proof’ on the bottles. In the early days the distiller used to check the strength by adding gunpowder and setting it alight. If it burst with a bang it was too strong and hence “overproof” and if it fizzed out then it was weak and “under proof”. If it burned with a steady blue flame it was “proved” to be around 50% alcohol and just right to drink. Hence the proof system was developed.
SCALES for measuring alcohol strength
There are three scales of measuring proof namely:
Gay Lussac or GL system: In this system, the proof is equal to the percentage of alcohol in
the spirit. So if Vodka has 43% alcohol it is 43⁰ proof GL.
British or Canadian Proof: Bartholomew Sykes devised a hydrometer which calculated that
57.1⁰ % of alcohol is equivalent to 100⁰ BP. So 100% of alcohol is equal to 175 ⁰ BP.
American or US Proof: In this system, 50% alcohol is equal to 100⁰ US proof. Therefore 100 %
alcohol is equal to 200⁰ US.
Therefore we can say that : 100⁰ GL = 175⁰ BP = 200⁰ US
{ Note: The proofing system led to a lot of confusion and gave producers some labeling problems. Under European Community regulations, since 1st January 1983, alcoholic strength in Britain and Europe is expressed in percent of Alcohol by Volume (ABV) as on the Gay-Lussac scale. Therefore the above-underlined statement stands justified}
Conversion of alcoholic strength from one scale to another:
1) To convert US proof to GL----- US proof ÷ 2
2) To convert US proof to Sikes-- 175 X US proof ÷ 200
3) To convert GL to US proof----- GL X 2
4) To convert GL to Sikes--------- 175 XGL ÷ 100
5) To convert Sikes to US proof---200 X Sikes ÷ 175
6) To convert Sikes to GL--------- 100 X Sikes ÷ 175
- Organization International Metrologique Legale (OIML)
It is now mandatory for all manufacturers to indicate in % the amount of alcohol on the
bottle. OIML is the same as GL, which is the most logical of the systems.
References:
https://www.ihmnotes.in/assets/Docs/Sem-3&4/F&B%20Service/2.%20Distillation%20&%20Proof%20System.pdf
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