Alcohol is obtained by fermenting the cane juice or a mixture of molasses and cane juice, through a biochemical process. However, before being sent to the fermentation process, this juice has to be submitted to a purification treatment.

Juice cooling generally takes place in two stages.
. Passing the hot juice through a heat exchanger (regenerative) in a contra-flow to the cold mixed juice, where the mixed juice is heated and the juice for the distillery is cooled (=60ºC).
. Final cooling to approximately 30ºC. normally carried out in plate exchangers using contra-flow water as cooling liquid.

Free from impurities (sand, bagacilhos etc.) and duly sterilized, the juice is ready to be taken to the distillery.

Before to be returned to the fermentation process this yeast undergoes strong acid treatment consisting of yeast dilution with water followed by the addition of sulfuric acid, normally to a pH of 2.5 - 2.8 depending of the bacterial level infection.

This diluted and acidified suspension or treated yeast stays under agitation for one to three hours before recycling to the fermentation vat.

The sugars are transformed into alcohol, according to the simplified reaction of Gay Lussac:
C12H22O11 + H2O -> C6H12O6 + C6H12O6
C6H12O6 -> 2CH3CH2OH + 2CO2 + 23,5 kcal

During the reaction there is a strong release of carbon dioxide, the solution gets hot and some secondary products are formed such as: superior alcohols, glycerol, aldehydes, etc.

Fermentation time ranges from 4 to 12 hours. At the end of this period practically all the sugar has been consumed, with a consequent reduction in gas release.

At the end of fermentation the average alcohol content in these vats varies between 7% to 10%, and the mixture is called fermented broth. Due to the large amount of heat released during the process and the need to maintain a low temperature (32ºC), it is necessary to cool the broth, circulating water through internal pipes in the vats, or in heat exchangers through which the broth is pumped continually against a counter flow of water.

This process can be carried out continuously or discontinuously in open or closed vats. In the latter, the liberated gases are sent to a washing tower to recover the evaporated alcohol, by the absorption in water, which is returned to the process reducing alcohol losses.

Centrifuging the wine
After fermentation, the fermented wine is sent to the centrifuges for yeast recovery. The recovered yeast concentrate, called yeast milk, returns to the storage tanks for acid treatment. The light centrifuged phase, or “deyeasted” wine is sent to the centrifuged wine vat for further distillation.

Distillation
The composition of the fermented wine from fermentation is 7º-10º GL (% by volume), containing other liquid, solid and gassy components. Among the liquids, in addition to alcohol there is water ranging from 89% to 93%, glycerin, homologous higher alcohols, furfural, acetic aldehyde, succinic and acetic acids etc., in much lower amounts. While solids include bagacilhos, yeasts and bacteria, un-fermentable sugars, mineral salts, albuminoid materials, and mainly CO2 gases.

The alcohol in this wine is recovered by distillation, which uses the different boiling points of the various volatile substances present to separate them. The operation is performed using seven columns spread through four set:

• Distillation
• Rectification
• Dehydration
• Dehydration Agent Recovery

Distillation
Distillation is a process using three superimposed columns: A, A1 and D. In these columns the ethanol is separated from the fermented wine (initially 7º to 10º GL), and concentrated up to 40º to 50º GL as phlegm vapors. The distillation phase also eliminates impurities (esters and aldehydes)

The fermented wine is fed into the top of column A, descending through the trays, being purified, with the phlegm being removed from the bottom of the tray A16 and sent to column B. Volatiles, principally esters and aldehydes, are concentrated in column D and removed from the top, being condensed in two condensers R and R1, where a proportion of this liquid (90% to 95%) returns to the top of D, and the rest is removed as 2nd grade alcohol with a level of approximately 92ºGL.

The purpose of this column is to recover the largest possible amount of alcohol from the base product, which is called vinasse. The vinasse is removed in a proportion of approximately 13 liters to each liter of alcohol produced, consists mainly of water, organic matter, soluble and suspended mineral salts, and is used in the fields as fertilizer, with its heat being partially recuperated for the broth in the heat exchanger. Alcohol level should not be more than 0.03º GL.
Set column heating is carried out by steam injection (exhausted or bleed vapor) in the bottom of this column, or indirectly through an evaporator-exchanger. The purpose of this trunk is to concentrate the phlegm at a level of approximately 96º GL, and continue its purification with removal of its impurities such as higher superior alcohols, aldehyde, ester, acetal and many others organic compounds. The phlegm is fed into this column where it is concentrated and purified, with the two trays at the top of the column being removed in the form of hydrated alcohol.

Volatiles removed from the top of the second column pass through a sequence of condensers where part of the heat is recuperated by the broth, one portion of the condensed material is recycled and the other portion removed from the 2nd grade alcohol. An aqueous solution called flegmaça, which has been exhausted, is removed from the bottom of the trunk and recycled in the process or discarded. The higher superior alcohols, called fusel oil, as well as low and high oils, are removed from trays in a very well defined extraction points, near the phlegm entry.
Generally both oils return to the centrifuged wine vat or to a special vat where the fusel oil is cooled, washed settled and stored for later marketing. Heating of the column is performed by steam injection as in purification.

Dehydration
The hydrated alcohol, the end product from the purification (distillation) and rectification processes, is a binary alcohol-water mixture reaching a level of 96ºGL. This occurs due to the formation of an azeotropic mixture, which is a physical phenomenon in which the components are not separated by a conventional distillation process.

This hydrated alcohol can be marketed in this form or it can be submitted to one of the three dehydration process as follows.

1 - Azeotropic distillation by cyclohexane
This process utilize a dehydration column been the cyclohexane fed in the top of the column and the alcohol to be dehydrated fed at one third below the top of the column. In this process the cyclohexane has the characteristic to form with the alcohol and water a ternary mixture (azeotrope) with a boiling point of 63ºC.

This lower boiling point for the mixture in relation to the boiling point of the pure alcohol (78ºC) allows the water to be removed at the top of the column.

By condensation this azeotropic mixture will be divided in two phases, been the lower phase, richer in water, sent to a second column to cyclohexane recovery which returns to the dehydration process.

The anhydrous alcohol obtained having an alcohol content around 93% w/w is removed in the lower part of the column from where is condensed and sent for storage.

2 - Extractive distillation by Mono ethylene glycol (MEG)
Similarly to the former process a dehydration column is utilized, where the mono ethylene glycol (MEG) is fed on the top of the column and the alcohol to be dehydrated is fed one third below the top of the column.

Inversely to the cyclohexane process MEG absorbs and entraps the water to the bottom of the column. The anhydrous alcohol vapors leave the top of the column from where they are condensed and sent to the storage tanks.

The mixture of water, MEG and a small quantity of alcohol is sent to a specific column for MEG recovery whic is further recycled to the dehydration process.

Due to the fact the MEG concentrate the impurities contained in the alcohol and become more and more corrosive it is necessary to provide its purification passing the vapors through an ion exchange column where salts are retained and the MEG acidity is reduced.

3 - Adsorption dehydration by molecular sieve
Initially the alcohol to be dehydrated is vaporized and superheated before to be sent to the dehydration columns that contain inside a low porosity material basically constituted by aluminum hydro silicate, known as zeolite and popularly called molecular sieve.

This net of micro-pores material absorbs the water and leaves a free route for the alcohol vapors that a re further condensed as anhydrous alcohol.
Regularly the zeolite is regenerated by feed interruption and vacuum application in the column from where a mixture of water and alcohol vapors which is distilled to recover its alcohol content.

Alcohol storage
The alcohols produced – hydrated and anhydrate – are quantified by drainage measurers or calibrated tanks and sent for storage in high volume tanks in tank parks, where they await marketing and later removal by trucks.