Distillation technology produced in the production of alcohol

Distillation Theory

Simply put, distillation is the process in which a liquid is evaporated (turned into a vapor), recondensed (turned into a liquid), and collected in a container. Distillation is a very old separation technique that separates a liquid mixture into its individual components by heating. The basis for the separation of components is their different boiling points. A mixture of two or more compounds is separated by heating the mixture of two or more compounds to a certain temperature and condensing the resulting vapor. The vapor above the boiling mixture becomes richer in volatile components. As a result, the boiling mixture becomes richer in less volatile components. This means that the original mix will contain more less volatile substances.

The distillation cut

During distillation ran the ethanol and water are the two main components which are actually carriers of all other volatile compounds. It could be considered that the ethanol vapour will carry over the compounds favouring spirits aroma and flavour and therefore the quality.

At the very beginning, the high volume of ethanol comes out of the still together with high volatile compounds. Through the time volume of alcohol is decreased followed by water, and low volatile compounds increased. According to this, the distillate is cut to three cuts or fractions: the head, the heart and the tail. The heads contain higher concentration of low boiling point components and mainly contain undesirable compounds. These compounds would give the distillates an unpleasant, strong and sharp flavour. In the first cut, there is a higher concentration of some toxic compounds, and therefore it must be eliminated. The best part of the run is the middle part of the distillation, the final spirits. It is a distillate rich in ethanol that is carrying a pleasant and fruity aroma compounds. The heart cut is a very clean taste lacking the sharp bite of the heads. The last cut is the tail fraction, which has to be eliminated from the heart, since it contains unpleasant fatty and oil compounds. In this fraction, the main carrier is the water. The water is carrying longer molecules, which are usually unpleasant and can be identified by the distinctive smell of ‘wet dog’. The tail fractions (with or without head adding) are collected and redistilled, because it contains a relatively high concentration of alcohol and a valuable congeners.

How to make cuts during distillation run

In order to produce an aromatic, harmonised and pleasant fruit distillate, it is necessary to know the right time for distillation cut. During the distillation of ethanol and congeners, it is possible to manipulate the separation of volatile compounds, to clean undesirable and to concentrate desirable aroma compounds. Aroma profile of distillates very often depends on the skill of distiller to cut adequately distillation fractions. The head and tail fractions could be cut on the basis of sensory evaluation of distiller. The presence and absence of volatile congeners that give a sharp, strong and unpleasant smell to the head fraction can be cut points for the switching to the heart fraction. Also, the tail fraction starts with flavour that gives a faded, dull character to the distillates, and it should not be difficult for the sensory evaluation and separation. Experienced distillers do this very well by smell. Taste and smell still remain the most reliable method of determining when to make a cut.

The second indicator of cut points that can be used is the percent alcohol of the spirits that’s flowing out of the still, especially for the separation of the heart from the tail cut. The ethanol strength could be the limiting values for the switching from the heart to the tail. This limiting value varies depending on distillation equipment involved, the fruit variety used, the quality of fermented mash, etc. Finally, the third indicator of the cut points that can be used is the temperature of the vapour before its entering to the condenser. Distiller can make the first cut in the run, when the temperature of vapour in the copper pipe reaches approximately 74–76°C. The heart cut from the tail can be made when the temperature of vapour in the copper pipe reaches around 87–88°C, and tail distills until temperature reaches 92–93°C, when distillation could be over.

Each of above-mentioned manners of distillation cut has a shortcoming, and the best way is to use all of them as guideline for the separation of congeners during distillation.

Alembic pot still vs column still

One of the most relevant steps in elaboration of spirits is distillation process. Distillation process can be used to correct possible mistakes that have occurred during the previous processing of the raw material. In addition, inadequate distillation can cause many defects that are difficult to eliminate by the following technological processes. During the distillation, heat facilitates the fitting of volatile compounds into resulting spirits. For the production of fruit spirits, alembic pot still and batch distillation column are the most suitable because spirits will retain the decent fruit aroma and flavour. For most of the compounds, there were no difference in concentration regarding the distillation equipment used. However, the concentrations of volatile compounds were influenced by processing and storage of raw material more than distillation equipment used.

Alembic stills yield better aroma that comes from fruit, the so-called primary flavour. The alembic pot still produces distillates that retain the character and personality of their source ingredients. This method is slow and requires more labour, but the usage of simple copper still was preferred by several authors. Also, results showed the distillation of pear wine with less in copper alembic leads to a better quality product.

Higher concentration of alcohol and higher separation of other volatile compounds were achieved during distillation in batch column still, giving a decent aroma of distillates. The greater yield is obtained in recovered ethanol, allowing an increased productivity by means of column distillation. This type of distillation is more effective. Nevertheless, the column-distilled spirits contained four times more esters, 20% more higher alcohols, 40% less acetaldehyde and 10% less methanol than alembic spirits. Some results referred that distillates made by using a distillation column had higher sensory acceptance than distillates made in alembic pot. According to these authors a sensory acceptance of cleaner fruit spirits (spirits with lower content of esters, aldehydes, higher alcohols, and methanol) was higher. The art of distillation run is to obtain the best balance between congeners present.

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Also, less aromatic fruit varieties can be used to produce distillates with aromatic characteristics similar to more aromatic variety if a suitable distillation process in distillation column is used.

The traditional distillation with an alembic pot still allows limited intervention during the distillation process (only the heating power in the boiler can be manipulated) to modify the composition of the distillate. A more flexible system is the batch distillation column (in which the reflux rate can be varied in a wide range). In the same time, the other investigation showed that the process with batch distillation column is much less reproducible than alembic distillation.

Someone are observed that distillates produced in the alembic pot still are usually stored in wood for many years (e.g. Cognac and Whisky), whereas the distillates produced in the distillation column are stored in the glass and consumed as clear spirits. I consider that raw material rather determinates whether distillates will be stored in wood or not. The author of this chapter considers the way of ageing that is determinates by raw material used rather than the distillation apparatus. In fruit spirits long ageing would mark the primary flavour of fruit. If distiller produced a distinctive flavour of some fruit, regardless of distillation apparatus used, it should protect the pure fruity note, not to give the distillates a strong and too much complex flavour gained during maturation in wood (quaternary flavour). If aromatic fruit spirits need to be stored in wood, then it should be just for a whilst how they would retain a fruity touch.