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The distillation process is simple in principle, but quite complicated in practice and in its various applications. This article will therefore deal with the following questions: What is distillation? And how is the distillation of alcohol carried out?
1. Distillation: definition and general mode of operation
2. The history of distillation
3. Distillation of alcohol: How is a good brandy made?
4. The different distillation processes
5. It also works the other way round: distillation for dealcoholisation
Distillation: definition and general mode of operation
Simply expressed, distillation separates two components of a liquid from each other. The separation of several components with the help of fractional distillation is also possible. In this process, the initial mixture or the liquid is first brought to boiling point. Because the different components have different boiling points, the element that is to be extracted can be converted into a gaseous state.
A condenser cools the gas or vapour and converts the distillate back into a liquid. The result still contains several components of the original liquid, but the composition differs from the initial mixture. To improve the purity of the product, the process is usually repeated.
Distillation is mainly used to process crude oil in a refinery (fractional distillation), to distil alcohol or to distil water, with this article focusing on the last two purposes. The advantage of this type of separation of individual elements is that no further additives or chemicals are necessary to achieve the desired result.
The history of distillation
A terracotta distillation apparatus is the earliest known evidence of distillation. It comes from an Indus valley in Pakistan and is dated to around 3000 BC.
The first distillation devices looked very simple: They consisted of a container and a lid. The distilled condensate settled on the lid and was absorbed with sponges or wool and later wrung out. In this way, the distilled liquid did not drip back into the raw material or otherwise get lost.
As early as the Neolithic Age, people distilled pitch and sulphur to seal ships. Adhesives and remedies could also be produced with the help of this process.
It is assumed that distillation was used early on for perfume production and that essential oils were produced using this method during antiquity. According to Aristotle, in the 4th century BC, the Greeks used distillation to make wine and even drinkable water from seawater.
First technical developments in distilling
Among the ancient Egyptians, something like a technical advancement could be detected with the introduction of the distilling helmet. However, alcohol was not produced during this time either, because there were no suitable cooling methods yet. Because the alcohol boiling point is 78.3 degrees Celsius, this component evaporated during the distillation process. Only substances with a higher boiling point than water could be separated.
The Persian chemist Abu Musa Dschābir ibn Hayyān and the Iranian physician and scientist Abu Bakr Mohammed Ibn Zakariya al-Razi further advanced many chemical processes and also distillation in the 9th century AD. The latter even wrote down his techniques and methods, which are still relevant today, in one of the first textbooks on chemistry.
Distilling alcohol in the Middle Ages
In the Middle Ages, scientists - also called alchemists - were able to develop a cooling process for alcohol production using cooled pipes. However, the resulting product, called "fiery water", was still highly diluted.
However, even then it was discovered that a purer alcohol product could be produced from several distillation processes taking place in succession.
From this point on, alcohol fulfilled both medicinal and pleasurable purposes until the 19th century. During the plague period from 1347 to 1350, many people even made their own alcohol. This even led so far that laws had to be passed to stop drunkenness.
Commercial alcohol production in Europe first began in the 15th century. In the south of France in particular, popular wines, fermented apple juices and cognacs or brandies were produced, which consumers still enjoy tasting today. In Amsterdam, Holland, the development of alcohol production did not stand still either. Here, Lucas Bols used the peat-heated still for the first time in 1575.
In the years and centuries that followed, this technique for extracting alcohol was to be refined further and further, from automation processes to the use of artificial intelligence. And even though improved alcohol products with new interesting flavours are always being developed, the basic chemical principle remains the same even today.
Distillation of alcohol: How is a good brandy made?
The key to alcohol as used in the beverage industry is alcoholic fermentation. Alcohol is produced from starch or sugar. A lack of oxygen and bacteria or yeast drive the fermentation process. This is the case, for example, in the production of beer and wine. In the distillation of spirits, another step takes place.
From raw material to spirit
Spirits are distilled from a mash. This is a mixture of fruit pulp, juice, peels and seeds, which also contains sugar or starch. According to the information page of the German customs, the mash can in turn consist of the following raw materials:
• Fruit, berries, beets or roots can be processed into fruit brandies or fruit waters, cherry and plum brandies, Williams pear, gentian, rum or tequila
• Grain, rice or potatoes are turned into grain, vodka, whisky or gin
• Brandy, cognac, armagnac or grappa can be made from beer and wine
The alcohol produced by fermentation within the mash has to be distilled. This means that only the volatile elements such as alcohol, water and aromatic substances change their state of aggregation and turn into steam.
Seeds, pulp and peels are left behind. Glycerol, succinic acid, amino and fruit acids as well as other harmful by-products produced during the fermentation and metabolic process are removed.
In order to obtain the alcohol from it, different distillation processes are used, which provide for equally different results.
The different distillation processes
In general, distillation can be divided into two different methods: continuous and discontinuous distillation. These two methods in turn have different distilling techniques.
Continuous firing or patent firing process
This distillation process is particularly suitable for the mass production of spirits. In this process, mash is added continuously for steady distillation. However, there is only one specific distilling process, which has various names:
• Patent still distilling
• Continuous distilling
• Column still distilling
• Coffey still distilling - Named after the Irishman Aeneas Coffey, who adopted and improved the method from the Scotsman Robert Stein, who invented it in 1826.
Construction and mode of operation of a distillation apparatus for continuous distillation
Distillation is carried out with the aid of a patent or Coffey distillation apparatus, which consists of several copper columns and is therefore also called a column apparatus.
Even though the distillation process is now two centuries old, countless types of this plant design exist today. The reason for its popularity is that such a plant and method can be used to produce spirits quickly and inexpensively. These include vodka and whisky as well as many other popular drinks.
Smaller column stills consist of two, larger ones of several stainless steel columns. There are numerous variations with different sizes. The diameters range from 16 to 96 inches. Here, there is often no bulbous pot design as in other distillation systems (see pot-still process).
To start the distillation process, the producer fills the substance to be distilled into the first column, which is also called a rectification column or rectifier. Here, it passes down through a screw tube and is simultaneously heated by a blast of steam emanating from the bottom.
The liquid produced here flows from the rectifier into the second column, which is called the analyser. Inside, there are several copper plates with holes through which the liquid flows. With the help of gravity, it flows down through these plates. In this column, water vapour also ensures that the ethanol and aroma components volatilise and separate from the mash.
The vapours rise upwards and are channeled back through the bottoms of the column - each plate that now follows is slightly cooler than the one below. Consequently, condensation occurs on each of these plates. Because hot vapours constantly flow through the system, the vapour always turns into liquid and then back into vapour. This therefore leads to an increase in the purity of the spirit.
While the mash residues are drained off at the bottom of the second2. column, the alcoholic vapour is returned to the first column. While the mash residues are drained off at the bottom of the second column, the alcohol-containing vapour is fed back into the first column, where the vapour is cooled down again. Due to different boiling points, liquids are produced during the distillation process that can be divided into pre-run, mid-run and post-run and are distinguished as follows:
• The forerun is formed while the mash is slowly heated. The entire liquid that forms at temperatures below 80 degrees must not be consumed because it may still contain toxic components.
• The middle run is a noble spirit that is produced at temperatures of 81 degrees Celsius and above and has an alcohol content of around 80 percent.
• The cider is produced at about 94 degrees Celsius and has a lower alcohol content of 40 to 50 percent.
Depending on what type of alcohol or spirit is to be produced, fore-run and mid-run can be added back to the mash for distillers to redistil.
Even though the distillation process sounds simple in principle, skilled workers must constantly monitor the process. After all, a small change in the flow rate can already have a big impact on the alcohol level, the cooling and ultimately on the quality of the end product.
Discontinuous firing
As the name suggests, in discontinuous distilling, spirits producers do not constantly add new mash. Instead, they only fill the still with portions to distil alcohol. Discontinuous distilling can be further divided into double distillation, single distillation and pot still method.
Construction of a distillation apparatus for discontinuous distillation
A distillation apparatus usually consists of the following components:
• Distillation bladder
• Firings
• Agitator
• Opening for filling
• Ghost helmet
• Spirit pipe
• Column
• Bell bottoms
• Overflow
• Dephlegmator
• Cooler
• Template
The still is a heatable vessel that is heated directly by a burner or indirectly either by steam or a water bath. Manufacturers usually fill the mash through an opening and empty it again through a flap after the distilling process.
An agitator helps to mix the mash and to heat it evenly and steadily so that the mash cannot burn. This also enables the precise separation of the individual elements during alcohol distillation.
In the spirit helmet above the still, the alcohol gases collect which, in a simple firing, are led via the spirit pipe into the intensifier unit. Water condensation takes place in the rectification column, which in turn leads to a high alcohol content.
The alcohol vapours rise to the dephlegmator. Here, the temperatures are above the boiling point of the alcohol, but still below the boiling point of water. In this way, an even stronger concentration of the alcohol can be distilled.
With stone fruit mashes, a catalyst is usually necessary to filter ethyl carbamate or hydrocyanic acid out of the distillate. However, this can usually be left out of the distillation process if it is not necessary.
The cooling of the steam ultimately takes place in a counterflow cooler. Cooling water in cooling pipes absorbs the heat of the alcohol gas. The steam condenses and the distillate is collected by a long container, also called a receiver.
Double branding
In this process, the producers carry out two or three firing runs. The product of the first distillation - also called raw or rough distillation - still contains alcohol, aromatic substances and fusel oil. A second distillation - the so-called fine spirit - is now necessary to create an edible product that is not harmful to health.
Finally, the careful increase of the temperature during distillation results in three stages again:
1. the preliminary run consisting of methanol, acetone, propanol or ethyl acetate, which is not potable.
2. the middle run with ethanol or potable alcohol and flavourings.
3. the after-run with fusel oil, butanol, hexanol, isoamyl alcohol.
Producers must be extremely careful in this process and only increase the temperature slowly. This is the only way to guarantee that only the undesirable elements and not at the same time the desired flavouring substances are eliminated after the pre-run.
At the beginning of the middle run, the distillate contains 70 to 80 percent alcohol. After the fine spirit, it is 50 to 55 percent for stone fruit and 45 to 50 percent for pome fruit. With 100 litres of rough distillate, 25 to 35 litres of fine distillate can be obtained.
Simple fire
In the case of simple brandy, only mash always serves as the basis. The process is comparable to the fine brandy in the double brandy process. However, the result is a product with a lower alcohol content and a higher aroma content. However, a rectification column can increase the alcohol content again.
Pot-still method
To create Scotch malt whiskey or Irish bourbon whiskey and pot still whiskey, distilleries use the so-called pot still method. This is one of the oldest ways of producing spirits.
In this traditional process, the pot or still is heated from below with the raw material to be distilled. This eponymous pot still looks like a pot on four legs. It is usually made of copper or stainless steel. The shape of the pot is quite bulbous and large at the bottom. Towards the top it gets narrower and narrower and becomes a thin tube, also called a gooseneck or Lyne arm, because it used to look arched - but now it is straight.
This neck leads to the condenser, a spiral-shaped tube located inside a cylindrical container filled with cold water. The vapours thus move from the pot via the gooseneck through the spiral and are cooled by the water. They slowly condense and return to a liquid form as soon as they reach the end of the spiral.
Distillation in the pot still process often requires two passes because the resulting final liquid is often quite low in alcohol. This distillate is called low wine in whiskey production and brouillis in cognac production.
After the first batch, the still is cleaned and the distillate is distilled again. The process is obviously very laborious and is therefore not suitable for mass production. Nevertheless, some forms of alcohol require this special type of distillation in order to maintain a certain integrity.
In the end, it is the combination of the right raw materials and the process technology that determines whether a distillate is good or not. Whether the requirements for a whisky or gin, for example, are met is tested by the German Agricultural Society (DLG). Every year, the DLG awards the Bundesehrenpreis for particularly good products. In this interview, you can read about the trends Thomas Burkhardt, head of the beverages division at the DLG Food Test Centre, has observed among beverage producers in recent years.
Speaking of which, a big trend in the beer business is collaboration brews, or collabs for short. This type of collaboration is not only interesting for classic beer production, because for the perfect taste experience, brewers also like to team up with distillers and create a harmonious composition of beer and gin, for example.
It also works the other way round: distillation for dealcoholisation
Theoretically, distillation can also be used for dealcoholisation. In practice, however, this is more difficult because the temperatures required for this can also affect the taste of the end product. So if someone wants to distil schnapps or distil wine, a simple distillation might not only eliminate the alcohol but also the aromatic substances.
An alternative is reverse osmosis or osmotic distillation. Water and alcohol are passed through a membrane. All other elements, also called retentate, which include the aroma substances, remain in front of the membrane. Distillation separates the alcohol from the water. The latter is mixed with the other elements. This leaves a drink with a reduced alcohol content, but which still has the original flavour qualities.
Vacuum distillation is another option for dealcoholisation. Here, the boiling point of the alcohol is lowered with the help of low air pressure. In this way, the alcohol is separated from the beverage, while the aromatic substances remain relatively untouched.
By the way: dealcoholisation is a big issue, especially in the beer business.
Distilling water: a controversial drink
Water distillation is extremely simple and in principle no different from other types of distillation. Water is heated to separate it from minerals and trace elements. The condensed steam represents distilled water - i.e. pure H2O.
Over the course of time, numerous myths have grown up around water that has been cleansed of minerals: some attributed purifying and invigorating properties to the liquid. Other legends ran in the opposite direction, fuelling fears of harmful and even fatal consequences that could occur after consumption.
The latter is only partly true. Consumers of distilled water do not have to expect health problems immediately. However, the body needs the minerals that are extracted from the water during the distillation process. Those who consume this type of liquid (and nothing else) over a longer period of time must therefore expect corresponding deficiency symptoms.
Distilled water is mainly used for the following purposes:
• In laboratories
• In the industry
• In hospitals
• for the windscreen wiper system and as cooling water for cars and trucks
• for various household purposes such as humidifiers, plant spraying, washing & cleaning
However, it is not suitable as drinking water, even if consumers do not have to fear any immediate health problems when drinking it.