Continuous distillation


Continuous distillation introduction

Distillation column
Rhum, eaux de vie de canne D Kervegant - 1946

From the second half of the 19th century, new distillation devices are introduced in Martinique. Those devices are adapted from the apparels used in the production of alcohol from sugar beet and are producing alcohol through continuous distillation.
This way of distilling is said to be continuous as the liquid to be distilled does not need to be injected several times in the device. The distilled liquid, stays in the column as long as it is necessary for alcohol extraction.
These devices offer better yield in means of energy consumption and can handle large batches in short times. This fast process is essential as sugarcane tends to be extremely perishable and the vésou being easily spoiled under the West Indies climate.
Sugar beet designed apparels had to be heavily adapted to the rhum specificities. Rhum produced in the first imported columns were of extremely low quality. Separation of the heart from the heads were poor and the low exposition time of fermented vésou to heat did not help in producing the esters so specific to agricole rhum.
Columns had to be adapted to the agricole rhum specificities. Trays had to be enlarged to increase the vésou exposition time. Esters are essential to the rhum agricole's bouquet. These complex esters being stripped away in the original devices, the number of enrichment trays has also been reduced to avoid their excessive elimination.
The Creole distillation column, devoted to rhum agricole, was born.

Continuous distillation operation

Distillation columns are made of several trays. Each tray is a level of the column where descending liquid meets the ascending vapours. The vapours get richer in alcohol and aromas aqs the liquid gets poorer.
There is two separate areas in the column:

  • The stripping section of a column is situated below the feed point. The trays of this section make ascending vapour bath in pools of descending liquid.
  • The enrichment section of a column is situated above the feed point. The trays of this section do not handle the liquid fed into the column but rather make the vapour coming from below richer in alcohol.

 

colonne a distiller

A: Vapour injection
B: Vinasses extraction
C: Feed point, where the fermented vésou is fed into the column;
D: Reflux injection.
E: Vapour extraction
F: Heat exchange device which cools extracted vapours [E] and heats then incoming fermented vésou[C] and reflux[D].
Stripping area is situated between B and C,
Enrichment area is situated between C and E.

 

 

 

The stripping section receives in its lower part the vaporized water supply and hte fermented vésou to be distilled in its upper part. The vapours go up through the trays and dabble in the liquid vésou which is going down. While dabbling, the vapours strip alcohol and aromas from the liquid. At the bottom, the stripped liquid gets out of the column. This remaining liquid is called vinasse and is usually from 2 to 3 % abv (4-6 US proof).

The vapours coming from the stripping section travel across the enrichment zone. These vapours have been enriched with alcohol and aromas taken from the fermented vésou and come out of the column on the top of it. They are cooled and turned into liquid.
A part of that liquid, called reflux is injected back to the column on the upper part of the enrichment section. This reflux is made of the heaviest compounds (mainly aromatic compounds) of the distilled liquid. The reinjection of the aromatic compounds helps getting rid of some of the bad tasting ones. The reflux reinjection also allows to reach higher concentration of alcohol by reducing the percentage of non alcohol compounds.

Some facilities only reinject a small part of the reflux. The rhums hence produced tend to be more aromatic since fewer heavy compounds are removed. This way of producing rhum calls for more carefully monitored fermentation to avoid the production of compounds with bad tastes.
It is interesting to note that those heavy compounds were responsible of the average low quality of the French rhums in the 17th century.

AOC specifications regarding continuous distillation

The AOC "rhum Martinique" specifications regarding continuous distillation are:

  • The column must only be heated through vapour injection
  • The plates in the stripping section must have a diameter between 0,7 and 2 metres (20 to 78 inches)
  • The enrichment area must be made of 5 to 9 copper plates
  • The stripping section must have at least 15 copper or stainless steel plates.
  • The reflux has to be made through the use of one or several wine-heater or copper condensers.
Distillation column
Distillation column
Trois Rivières facility, Martinique.
Distillation column
Distillation column
Neisson facility, Martinique.

Rectification is also forbidden and on exiting the column, the distilled liquid must have an alcohol concentration between 65 and 75% abv (130 to 150 US proof).

These specifications have been edicted to fit all the existing columns in Martinique. They are not hence discriminating to any column but rather guarantee that the current specificity of agricole rhum will be present in the rhum produced in the columns to come.