A SAVU glass guide to the art of distilling
So, how is whisky made when viewed through the eyes of a scientist? Let’s take a look
Distilling whisky, an alcohol, is basically a fairly simple and quick process. It requires three raw materials: water, sugar and yeast. The yeast causes fermentation, in which the sugar turns into ethanol.
Various raw materials containing sugar can be used to produce alcohol, for example grain, fruit, rice. The raw material affects which compounds are distilled and collected.
In addition to ethanol, the mash contains thousands of different compounds. Their chemical and physical properties determine their behavior. Some compounds are abundant and some are few.
In the case of SAVU glass, we are only interested in volatile compounds and specifically compounds that distill close to ethanol.
From malting to distillation
However, spirits have their own production stages that achieve the best end result. The stages of whisky production are:
malting, mashing, fermentation, distillation and barrel maturation.
The formation of alcohol, or fermentation, usually takes a couple of days. After this, the task is to separate the ethanol from the rest of the solution.
Distillation is easy to understand by thinking about boiling water. When water reaches a temperature of 100 C, it starts to boil and evaporate. After a while, the kettle is empty. When ethanol is added to the boiling water, the ethanol starts to evaporate when its boiling point, or 78 C, is reached.
Strictly speaking, different substances have different vapor pressures, which can be used to fractionate or separate the substances.
There are many types of distillation equipment, but the 2 most common are: pot distillation and column distillation.
- Pot distillation is a one-off process and is often distilled 2 or 3 times to achieve the desired result.
- Column distillation can be automated and can operate on a continuous principle.
Ethanol can never be obtained 100% by distillation because it forms a so-called azeotropic mixture with water. In this case, it distills at a 96/4 ratio, meaning that the water molecules are so tightly attached to the ethanol molecules that they cannot be separated. Only chemically different methods can produce 100% ethanol.
Where do aromas come from
A lot of aroma compounds can already be found in the mash and they are recovered by distillation. Many important aroma compounds only come about over the years, such as when stored in whisky barrels.
For example, French Calvados is made from apples. Apple mash already smells good and has aromas all over the bottle. However, water and ethanol make up 99% of the content of the finished product.
It is typical for aroma compounds that they can be sensed even in small concentrations. Some experts say that the properties of the drink depend most on the raw materials, some say that fermentation, some say that distillation and some say that maturation.
What is certain is that all factors have an impact. For now, we will focus only on distillation.
The art of whisky distillation
A master distiller must have the know-how to get a decent end result that is pleasant to enjoy. I already explained the principle of distillation, but you could also say that in the process, a liquid is evaporated, condensed back into a liquid and collected.
Very simple, right? We can say that ethanol is our main goal and the master distiller tries to collect as much as possible the compounds that evaporate more easily and more difficultly than ethanol.
If we were only concerned with separating ethanol from water, the task would be easy and the result would be excellent. But we have a challenging multi-component mixture (fermentation mash).
Many of the compounds in the mash differ greatly from each other and some only slightly. For example, the boiling point of acetaldehyde is 21 C and that of benzaldehyde is 179 C. In distillation, the aim is to separate the volatile compounds, i.e. the compounds that distil before the ethanol, and the more difficultly volatile compounds that distil after the ethanol.
In principle, the distillation temperature decides the matter. It must be remembered that the mash contains a lot of unwanted volatile compounds. For example, methanol, which is toxic and easily blinds – its boiling point is 65 C.
At the beginning of distillation, a lot of ethanol comes in and with it volatile compounds. This fraction is called, “the head”. In the middle fraction, the ethanol content decreases and a lot of desired fruity aroma compounds come in, “the heart”. The last fraction is, “the tail”. This is usually quite clearly delimited from the middle fraction. The water content is high and a lot of polar, larger molecular unwanted compounds are carried along. The master distiller can smell this fraction. However, the “tail” is collected because it contains a relatively high amount of ethanol, which is distilled again and collected.
How does a master know how to properly do “the cut” or fractionation?
There are a couple of different methods for this.
Usually, a master has a good nose that can smell when to stop collecting. Tasting is also an important tool. Smells become familiar based on experience and are stored in the memory. In the fractions being cut, the smell changes from pleasant to dull and pungent.
Another, perhaps a little more scientific way is to monitor the ethanol concentration. The composition of the mash also determines what ethanol concentration to use for recovery or waste.
Thirdly, the master can monitor the temperature and use it to increase or decrease the ingredients being collected. The basis is the boiling point of ethanol, 78 C. For example, the first collections can be before the temperature reaches 75 C. The middle distillate, or main fraction, can be up to 87 C and the second distillate can be collected until the temperature reaches 93 C.
Surely each whisky quality has its own parameters that only the master distiller knows.
Distillation is one of the most important factors that can be influenced by whisky. The distillation method affects the result. If something goes wrong during fractionation, it can no longer be corrected later.
However, it must be noted that it is the maturation of whisky that shows us how complex the chemistry and achieving the right harmony are.
Maturation depends on the distillate, time and the quality of the barrel. The choice of distillation method and fractionation method have a great impact on the type of final product.
You could say that with pot distillation you get more at once and it is possible to produce a “big bouquet”. Column distillation makes it easier to plan what you want and what you don’t want. More about the methods in another article.
Author: Jari Tuominen, chemist, inventor of SAVU glass
