Angostura - The Rum Process

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From Sugar to Rum - The Technology of Rum Making

Summary of the Rum manufacturer Trinidad Distillers Limited

The Technology of Rum Making

The definition of Rum as outlined in the Caribbean Community Standard for Rum, (Revised March 2003) is as follows:
Rum is a spirit drink –

obtained exclusively by alcoholic fermentation and distillation of sugar cane molasses, sugar cane syrups, sugar cane juices or cane sugar produced during the processing of sugar cane
distilled at an alcohol content of less than 96.0 percent alcohol by volume at 20 degrees Celsius
produced in such a way that the product has the organoleptic characteristics derived from the natural volatile elements contained in the above raw materials or formed during the fermentation or distillation process of the named raw materials.

Steps in Rum Making
The basic principle of rum making is quite simple. The raw materials required are molasses, water and yeast. The juice of the mature sugar cane plant is extracted and refined as sugar, while molasses, the final by product of sugar refining, which is the black treacle-like substance which remains after sugar crystallization, is used as the raw material for the fermentation process. The yeast, which is also an integral part of the fermentation process, also imparts various flavours to the rum. There are four major processes involved in rum making, fermentation, distillation ageing and blending.

Angostura Limited
Angostura Limited has been in the business of rum making through its production company, Trinidad Distillers Limited, since 1947. We ferment, distill, age, blend and bottle alcoholic beverages, mainly rum, in Laventille, Trinidad, West Indies. We started with a French designed still made by Savalle capable of producing 5400 litres of alcohol/day to today’s production capacity of over 65,000 litres of alcohol/day. We have 6 ageing warehouses with a total capacity of 80,000 casks. Our bulk storage facilities feature a Tank Farm on the Distillery compound with a capacity of 5.0 million litres and a dock side facility in Chaguaramas with 3.8million litres of tankage. We bottle over 600, 000 cases of rum/year. Exports are mainly to the US, UK, Europe and the rest of the Caribbean.

Molasses
Molasses is the most widely used raw material for rum production. Its composition varies and depends on the quality of the cane, composition of soil, climatic conditions, methods of harvesting cane, manufacturing process for sugar and handling and storage of molasses. The composition of molasses is referred to as the “quality of the molasses” and is what contributes to quality and intensity of the rum flavour. (Shete, 2000)

Yeast (Saccharomyces cerevisiae) used in fermentation:
Louis Pasteur in the mid 1800s discovered that there was actually a single cell microscopic organism responsible for the conversion of fermentable barley malt into alcohol, carbon dioxide and flavour compounds. This microorganism was named yeast – Saccharomyces cerevisiae (a single cellular fungus). In the biochemistry of fermentation, Gay Lussac suggested the following biochemical pathway:

Sugar + Yeast = Alcohol + Carbon Dioxide

Saccharomyces yeast normally converts 88-90% of fermentable sugars into ethanol and carbon dioxide. The balance of the sugar is mainly utilized in the fermentation process for cell growth (about 3-5%), glycerol formation (3-5%), and by products that are responsible for flavour and aroma.

Fermentation:
Fermentation is a living process. The molasses is diluted with water to reduce the sugar content to approximately 15% and a pure yeast culture is added to the mixture. The yeast cells convert the available sucrose to ethyl alcohol (C2H5OH) and carbon dioxide (CO2) with the release of heat energy. This mixture is called the “live wash”. Fermentation takes approximately 30 hours to be completed during which time the yeast in the mixture uses up the available sugar in the molasses. The liquid left at the end of the fermentation process which is called “dead wash” is used for distillation.

During fermentation, a number of constituents called congeners are also manufactured. These congeners, which are regarded as the rum flavours, are the major constituents of the heavy type rums. They are necessary when blending because they give flavour and character to the rum.
Congeners formed during fermentation:

Aldehydes – by oxidation of alcohol
Acids – by oxidation of aldehydes
Fusel Oil – by conversion of free amino acids in water to higher alcohols
Easters – by esterification of alcohols and acids
Volatile sulphur compounds – by combination of sulphate and sulphur with amino acids.

Distillation:
After fermentation, the fermented wash is fed to the still. Distillation is the process of boiling the “dead wash” and condensing its vapour to produce the alcohol that is collected. The distillation process is done mainly to separate and concentrate the alcohol component of the liquid mixture. During this process, the undesirable congeners are removed and the desirable ones that add significantly to the taste and aroma of the raw rum are retained in the heavy type rum that is distilled from the first distillation column.

The plant uses 5 columns:

Hydroselection column
Rectifying column; (70 trays)
Recovery column (45 trays)
Final polishing column.

The distilled product of the mash column or “wash stripper” is referred to as “heavy rum”. For production of light and neutral spirits, the remaining columns are used.

Ageing:
After distillation, the rum is drawn off into large stainless steel vessels for storage before being barrelled off into forty gallon oak barrels and moved to the warehouse for ageing. Although the ageing process is not fully understood, it is considered to be the most significant aspect of the rum manufacturing process because the rum improves with age.
Immediately after distillation, the rum, which is a raw clear liquid with a hot harsh taste and an acrid odour still contains small amounts of hydrogen sulphide gas formed during the fermentation process. During ageing many changes occur as a result of the oxidation and selective diffusion though the pores of the oak barrel and the chemical interaction between the congeners. Rum ageing was practiced since the sixteen hundreds when seafarers found that as rum was carried on long journeys in wooden barrels it improved even more and it also became darker in colour. Today all the ageing of rum is done in oak wood barrels that were previously used for the ageing of cognac, wine and predominantly, bourbon. After the barrels are used once for the ageing of other liquours, they are employed in the rum industry as “Once used” barrels. Regulations that require producers of bourbon to use barrels only once assure a steady supply of barrels for the rum industry. Oak wood barrels are used because they do not contribute offensive odours or tastes to the rum during the ageing process .

Oak wood is used for storage because it is tight grained wood capable of making leak proof barrels that are ideal for strong liquids. The size of the radial rays of oak wood is what gives the strength to its barrels and also allows it to meet the characteristics required for storage containers such as porosity, strength resilience workability and lightweight.

There are three types of reactions occurring simultaneously in the barrel during the ageing process. They are

An extraction of complex wood constituents from the wood by the liquid.
Oxidation of components originally present in the liquid as well as of the material extracted from the wood.’
Reactions between the various organic substances present in the liquid that lead to the formation of new congeners.

Blending is the secret of fine rum. It allows the master bender to use many different types and styles of rums to create a particular blend or brand. The barrels of rum used for a particular blend are selected with age as the major selection criteria. The skill of blending involves the mixing together of light and heavy type rums of different ages that have been carefully analysed and selected by the blender for the characteristics specified. Through a “marrying process” the different rums are allowed to fuse together to give the blend a smoothing effect. After the rum is blended it is stored in bottling vats and reduced to bottling strength by the addition of deionised water. It is then passed through filters and polishers before being bottled and packaged for sale.

Summary of the Rum Manufacture Trinidad Distillers Limited

The distillery is designed to produce 60,000 litres of a 96% w/w alcohol product from the anaerobic fermentation of the sugar in molasses by yeast. The following is a simple process flow diagram that gives an overview of the operations at the distillery.

1. MOLASSES
To make rum one has to start with sugar from sugarcane. Molasses is a by-product from the sugarcane industry. It is the slurry that remains after most of the recoverable sugars have been extracted from the crushed cane. Generally, it is composed of 70-80% w/w solids and 20-30% w/w water. Of particular interest to the distillery is its fermentable sugar content which typically amounts to 35-55% w/w (sucrose, glucose, fructose); this is what the yeast “feed” on during fermentation.

2. YEAST
This is a uni-cellular organism of the Saccharomyces Cerevisae family. Aerobic conditions promote propagation and growth of the yeast, while anaerobic conditions result in alcohol fermentation – the basis of the rum industry. Yeast, being living organisms, requires a controlled environment with the right amounts of vitamins, minerals and nitrogen. All of these are present in sufficient quantities in the molasses, except for the nitrogen, which must be supplied as Ammonium Sulphate (NH4)2SO4.

The sensitive nature of the yeast means that their performance and productivity are greatly affected by the molasses composition. The distillery has included a molasses clarification unit as a means of ‘cleaning up’ the molasses before being sent to the fermentation process.

3. MOLASSES CLARIFICATION UNIT

Molasses + H2SO4 + Water + Heat → Decanter (Allow to settle for 20 hrs) → Fermentation

At this point, the molasses is heated and diluted to a 45º Brix mixture and then acidified to a pH of 4.5, maximum, using dilute sulphuric acid. The mixture flows to the decanter that provides a residence time of 20 hours (hence the need to start this unit -20 hours before the fermentation process requires the molasses). The conditions in the decanter promote the precipitation of Calcium Sulphate and other suspended particles. The clarified phase continues to the fermentation process after being cooled to approximately 32-33ºC.

N.B: This unit should reduce the downtime due to sludge accumulation in the beer pre-heaters and stripping column.

4. YEAST GERMINATION, PROPAGATION & GROWTH

4.3 Germination (Growth of new yeast cells):
Clarified mash of specific gravity 1.050 – 1.060 is sent to a germinator, along ammonium sulphate. This mixture is sterilised using low-pressure steam before the yeast culture is added. This culture is either obtained as 2-6L lab grown cultures or retained contents of the propagator. Germination proceeds for approximately 12 hours before the contents of the vessel are transferred to the propagator. During this time filtered air is injected into the vessel to maintain circulation and aerated conditions.

4.3 Propagation (Increase in the number of yeast cells):
Contents of the germinator are added to the sterilised contents of the propagator (Yeast feed, mash and ammonium sulphate). Propagation continues for 18 hours, before being transferred to the growing tanks. Aerobic conditions are maintained in the vessel by the addition of filtered air to the propagator. This, as well as the water circulation through the external water jacket, maintains the temperature at 30-32ºC.

4.3 Yeast Growth (Increase in the size of the yeast cells):
Mash + (NH4)2SO4 + Propagated culture → Growing Tanks

The culture is allowed to grow for 24 hours. Injected air and circulation through the wash cooler maintain the growing temperature at 30 + 2°C. Antifoam (food grade) is also added during the growing process, before the contents are transferred to the designated fermenters.

5. YEAST FERMENTATION
Propagated Yeast Culture + Mash (s.g. ~1.096) + Nutrients → ‘Wash’ (8-10% alcohol)

Alcohol is formed according to the following equation:

C6H12O6 + Yeast → 2 C2H5OH + Heat
100 lb → 51.11 lb + 48.89 lb + 17,000 BTU

Fermentation is completed within 36-48 hours and the temperature is maintained by recirculation through a cooler. A pH of 4.2 - 4.5 and a temperature of 32-35°C are considered to be optimum for alcohol production. The above equation also shows that carbon dioxide is produced. This gas is collected and purified in the Carbon Dioxide Recovery Plant.

6. CARBON DIOXIDE RECOVERY PLANT
This plant produces a liquid carbon dioxide product from the CO2 produced during fermentation. The gas is scrubbed with water in three scrubbers to remove entrained material. It is the deodorised with vegetable carbon. Some components of the gas are further oxidised using potassium permanganate solution. After oxidation, the CO2 steam is then compressed, deodorised, cooled, dried and cooled again to yield a liquid product.

7. DISTILLATION
The purpose of distillation is to obtain the alcohol from the fermented wash (8-10% w/w alcohol composition) and ultimately refine it to produce the spirits that will be used to make the rum. The fermented wash contains not only alcohol but also many by-products that as a group are called congeners. These congeners are vital to the taste and aroma of rum.
The first column is the Wash Stripper or Beer Column; it removes water and residual solids from the ‘wash’ stream. The product from this column is heavy rum steam (80-85% ethanol by vol). This is our first product. It contains all the congeners from the fermentation. It is very flavourful and aromatic and it is inevitably aged. To make light, the heavy rum is then sent to the Purifier (Hydroselector) Column. Here the water added changes the vapour/liquid equilibrium so that the light components separate easily from the alcohol. The head goes to the alcohol recovery column, while the bottoms feeds the Rectifier Column; this stream is typically 12% alcohol. The rectifier concentrates the alcohol to be separated; a stream close to the top of the column is sent for final rectification, the bottoms is recycled to the purifier and the other cuts are sent to the Alcohol Recovery Column. This Recovery Column recovers the alcohol from all the by-product streams from the other columns.
The Final Column produces a bottoms product of 96.6% alcohol (light rum) that may be used to make rum.

The light and heavy rums are aged in oak barrels for periods of not less than two years and up to fifteen for the heavy rums. The spirits are eventually blended and sometimes colouring is added. For white rums, the residual colour from the barrel is actually removed.

Whisky
The difference between rum and whisky manufacture begins with the starting point. Whisky starts with barley that must be malted before it is converted from a starch to a sugar that can be fermented. After fermentation, it is also distilled usually using a pot still or single column.

Cognac
The sugar that is fermented to make cognac, come from grapes. As is the French style, only grapes grown in a particular area in France can be used. First the grapes are fermented into wine and this is distilled in special stills to yield cognac.
Brandy is made the same way but because the grapes aren’t grown in the Cognac region, it can not be called cognac. All spirits are aged in a special barrel prior to blending and bottling.