The magic cognac pot still! How does it work?
Distillation takes place in traditionally shaped copper stills, also known as “Alembic Charentais”. Also known as alambic, it depends on the language.
The design and dimensions of the pot stills are legally controlled. Two distillations must be carried out; the resulting eau-de-vie is a colourless spirit of about 70% alcohol (the aging process afterwards makes the alcohol level drop to around about 40%).
How does Cognac distilling work?
The wine that is supposed to be used for the pot still is called Vin de Chaudière. Basically, it’s not the best wine in the world – it’s actually quite a lousy wine to drink. But there is a reason for this of course: The wine should be low in alcohol, only around 9%.
At the same time the wine should not be too intense in terms of aromas and taste. This is necessary for producing good eau-de-vie.
Is it true that you need bad wines to produce good Cognac?
Also, the wine needs to be acid so the chemical reactions work better. The lower the alcohol degree, the better the concentration of aromas. The wines dedicated to Cognac production are basically quite natural, because the wine makers do not add anything superficial to the process.
Nothing to make them sweeter, more balanced or to protect them from bacteria. This totally restricted in Cognac-making, it’s simply not allowed. The grapes must be totally clean and pure, no additives whatsoever. It would create an aroma one would notice in the eau-de-vie afterwards – as it becomes so concentrated.
Regarding the grapes: There are some varieties one can use for producing wine that is used for distilling. There is only one single variety, which is used by almost everyone in Cognac: Ugni Blanc. Okay, this could seem a bit boring. One single variety only?
The basic procedure of distilling is quite simple: You heat a liquid and it starts evaporating. If the vapours then get in contact with a cold surface, they condensate.
Creating the eau-de-vie
Alcohol evaporates quite easily. So if you heat wine, the vapours are quite concentrated with alcohol. The vapours that make their way through the pot still are more concentrated with alcohol than the liquid that remains in the boiler.
The wines are injected to alembics, where the boiling of wine produces vapours. The vapours go into tubes, which pass through cold water – the tubes are cooled and the vapours inside as well. They then condensate into eau-de-vie: Far less in quantity and much more concentrated than the original wine.
So in theory all this seems to be easy. But it isn’t. There are so many different distilling techniques, rum, gin or whisky distillation works very differently. Every brandy from Obstler to Armagnac to Spanish brandies. The Alembic Charentais (the pot still from Charente) is very different to others, such as the Armagnac pot stills. Spirits are all produced in slightly different way.
The Alambic Charentais is not something one can just build like that. Exact rules are set and it is exactly described how the alembic is supposed to look – and how it’s supposed to work. And this has been a tradition since decades.
First, an Alembic Charentais is made of copper, because heat spreads well in the metal. The “chapiteau” and the “chauffe-vin” look like huge balloons. The bricks it is built on guarantee a stable ground for the huge tool and a good isolation.
Cognac gets distilled twice
The wine in the “cucurbite” is heated and the vapours rise, pass through the swan’s neck and then condensate into the serpentine. The liquid, which comes out of the alembic is quite low in alcohol, about 30%. This one is called “Brouillis”.
The distiller will do this procedure twice. The Brouillis is distilled one more time, called “seconde chauffe” or “bonne chauffe”. And during this step, the final eau-de-vie is produced.
The next part is called “coupe” or cutting. The distiller seperates the “hearts” from the other parts of the liquid. The “hearts” holds the delicate fragrances of flowers and fruits, it’s quite a complex process: Liquid comes out of a tab, the heart somewhere in the middle of the flow, at the end the “tails”.
The eau-de-vie at this stage is totally transparent, also called “Blanches” -it looks just like water. It only gains its golden colour by being stocked in oak barrels for at least two years.