Sugar Production: From Cane Cultivation to Crystallization
**Sugar: From Field to Table**
Sugar, also known as sucrose (C12H22O11), is a disaccharide composed of glucose and fructose. It is commonly referred to as table sugar. Sucrose is primarily obtained from sugar cane or beets. In industrial settings, the term “sugar” or “sugars” may refer to various monosaccharides and disaccharides, which generally have a sweet taste. However, by extension, it refers to all carbohydrates.
Sugar can caramelize when heated above its decomposition point, resulting in a browning reaction. If heated above 145°C in the presence of amino compounds, such as proteins, the Maillard reaction occurs. This complex process generates desirable colors, smells, and tastes, along with small amounts of undesirable compounds.
Sugar is a significant source of calories in the modern diet. However, it is often associated with “empty calories” due to its lack of vitamins and minerals.
**History of the Sugar Industry in Colombia**
Sugar cane was introduced to Cali by Sebastián de Belalcázar, who cultivated it during his stay in Yumbo. From there, the crop spread throughout the Cauca River basin. During colonial times, the production of sugar cane, sugar, and molasses was a traditional activity. This continued until the early 20th century when the modern Manuelita mill was established. By 1930, there were only three mills in the Cauca Valley: Manuelita, Providencia, and Ríopaila. From that point on, the sugar industry began to expand in the region, eventually growing to 22 mills.
**Sugar Cane Cultivation**
One of the most meticulously planned agricultural operations in Colombia is undoubtedly the cultivation of sugar cane (Saccharum officinarum). The sugar industry in this region of the country operates step-by-step, with specific tasks designed to achieve the best possible yield from the cane, from which sucrose is extracted.
The “template” work begins with preparing the land where the sugar cane will take root. This involves specialized machinery and personnel dedicated to soil preparation.
Specialized design personnel determine the direction in which the cane will be planted, the location of water reservoirs for irrigation, and the layout of lanes for harvesters and transport vehicles. The team consists of agronomists, civil engineers, surveyors, draftsmen, and field assistants. Certain tasks may be outsourced to private companies if the existing staff is insufficient.
**Pre-Cultivation Work**
Deep plowing involves using a disk plow that can penetrate the soil to a depth of 50 to 60 cm. This allows the cane roots to penetrate the soil more easily. If the soil is compacted, it is very difficult for the root system to establish itself and absorb the nutrients necessary for stem growth and size. This process can take about 9 to 12 hours per area.
**Cross Plowing**
After deep plowing, the field is fragmented. Due to the nature of the plow used, the land may have irregular clumps. To achieve greater uniformity, a new plowing process is performed using smaller, shallower disks. This is known as “cross plowing.” This phase takes approximately one to two hours.
**Polishing**
A third plowing phase, called “polishing,” is carried out using even smaller disks and shallower depths. Similar to the previous phases, this aims to further break down soil particles. It is performed in various directions, similar to cross plowing, and also takes about two hours.
Once the soil is compacted, it is leveled. In Colombia, this practice is primarily implemented for sugar cane due to the high costs associated with its development.
Leveling begins with mapping to identify the terrain’s contours and determine areas with excess or deficient soil. The surface is then smoothed by removing or adding material until it is considered a plain ready for planting.
Leveling facilitates weed control, pest management, cutting, and cane transport. Regular terrain allows for more efficient mobility for both humans and machinery.
Currently, the “Cauca” mill has a single device capable of performing the entire process. Known as a “leash,” it works with the help of lasers. It consists of a tractor with a cab from which commands are given to two trailers that pull, dig, and collect or deposit soil according to the terrain’s irregularities.
**Subsoiling**
Before planting sugar cane, holes are dug in rows, reaching depths of 50 cm to 1 m. The distance between holes can range from 5 mm to 15 m. These holes collect excess water that runs down the furrows, acting as drains.
**Seeding**
Seeds are placed in the prepared field. They have been selected and prepared under specific temperature and humidity conditions to ensure the healthiest possible crop. The seed resembles a piece of sugar cane stem, about 30 cm to 45 cm long, with rootlets on the sides that will be consumed as the plant grows. Planting is done manually.
All seeds are transported to the field in a closed vehicle, in a tank, which is then sealed inside the future plants. A tank car carrying the seed is called a “gondola” and is moved using a tractor.
The process is as follows: The tractor pulls the wagon carrying seeds, where four workers are stationed. Every 10 meters, they throw a package containing 30 seeds. Behind them, “ushers” deposit the seeds in the furrow, lying down but not buried. There are 7 workers in the gap between each package of seeds. Another seven workers are responsible for covering the seeds with a shovel.
Depending on the soil’s moisture content, newly laid seeds may or may not be irrigated. This is called germination.
**Cultural Practices for Cane Crops**
In agronomic terms, cultural practices refer to all tasks designed to care for and improve a crop’s growth and maximize its yield.
The cultural practices for sugar cane include irrigation, weed control, pest and disease management, hoeing, and fertilization.
Seeds are also disinfected before planting by trained personnel.
The main causes of diseases are certain types of fungi and bacteria, such as smut, a fungus that turns the plant into a brittle stick. During the plant’s growth, tasks such as weeding or hoeing are performed. Hoeing involves loosening compacted soil with a hoe.
At this point, the cane has concentrated the highest level of sucrose, and the second stage of the field phase, the harvest, begins.
**Cutting and Transport**
**Cutting**
Two types of sugar cane are planted, which determine the type of cut to be made:
- Canal Point (CP): These are of Australian origin. Their stems grow erect, which is advantageous for cutting. However, they are very susceptible to crop diseases. They are cut after 15 months.
- POJ 2878: This variety has high resistance to sugar cane diseases. The stems grow intertwined, and it is cut after 18 months. It has a high purity of juice and is largely resistant to drought. Its most important feature is that it can be grown on land of medium fertility.
Before cutting, a controlled burn is necessary. This involves setting fire to certain points of the crop in a controlled manner to facilitate the cutter’s work. Burning reduces the amount of leaves per stem and prevents the cane lint from making it difficult for the cutter to breathe.
The burning time is controlled because the plants begin to lose their sucrose concentration as the burning time increases. It is said that initially, this burning was used to force cutters to work since, in the early 1970s, there was a lot of immigration to Venezuela, and they demanded higher pay. Thus, landowners used burning to maintain their opposition to higher pay, as the cane had to be harvested.
After burning, the cutter uses a machete to cut the sugar cane stalk from the base and remove any leaves that were not burned. The cutter piles this material in a designated area called a “nest.” Each cutter has a certain number of furrows, and their pay is based on the number of tons of cane cut.
There is also a lifter that lifts the piled cane and places it in a railway car. Mechanical lifters or loaders are also used, which lift the cane using pressing hooks.
**Transport**
The crop is transported directly to the industry via a train, which carries the material in cars. Generally, the distance between the crops and the industry does not exceed 30 km. When distances are greater, the cane is moved to trailers that can carry between 3.5 and 5 tons to the industry.
When the cane arrives at the industry, it is placed on a conveyor belt that leads directly to a grinder, which crushes the cane completely.
**Factory Stage**
In this stage, tasks are performed to extract the cane juice, which, through certain industrial practices, is transformed into sugar and molasses.
The first step is to shred the cane. The resulting fiber is then macerated by a set of mills, producing bagasse (macerated fiber) and juice (from which the sugar will be extracted). Bagasse is used as fuel in boilers connected to turbines that power the mills and heat the juice at different stages of the production chain.
The juice is initially heated, filtered, and clarified before the dissolved sugar is converted into crystals. Once a certain point is reached, the crystals are spun and completely separated from the cane syrup (liquid), which is also stored for the market. The type of crystallization performed determines the level of refinement. Finally, the cycle concludes with packaging and storage.
**The Cane Arrives at the Mill**
The plant material enters the factory through the “cane yard.” Its first stop is the scale, where the transport vehicle is weighed, recording the amount of cane and the individuals responsible for cutting and lifting. Once this data is collected, the vehicle moves toward the unloading cranes. These cranes have the capacity to dump the entire contents of a trailer or a car in a maximum of three minutes. The operation is as follows: the vehicle is positioned parallel to the crane, and cables are used to hook the stems and deposit them in the yard. In the case of trailers, they are designed to tip their contents, like a swing, to one side.
The cane that has been unloaded in the yard must then be taken to the “shredders.” For this, another set of cranes (the “thread” or “portal”) is used. These consist of a large structure on which cranes equipped with pulleys move. With the help of cables, they lift and tilt the “bundles” of cane stems onto the tables.
The “cane table” is a metal sheet bent over one of its sides, which borders the “conveyor belt.” The stems, when placed there, slide down a slope onto the “belt” that introduces them to the mill.
The “Manuelita” mill, used as an example, has two unloading cranes (in the “yard”): one with a capacity of 7 tons and another with a capacity of 8 tons. It also has two “thread” cranes to place the cane on the “table,” each with a capacity of 30 tons. Currently, operating all the cranes requires 5 workers and a supervisor.
**Shredders**
The first station the cane passes through is the shredder. The belt enters a tunnel, inside which a screw holds the knife-like machetes. As the plant material passes through, the stems are transformed into something resembling wood shavings, but with white, long particles. The mill used as an example has a first shredding section with 32 knives rotating at 600 rpm, followed by a second section with 64 machetes at the same speed but positioned closer together than in the first section. The motors that power the shredders are electric and are controlled from the mill’s control panel.
The fiber travels on the conveyor belt to a train of mills for maceration.
**Mills**
Each set of mills consists of three masses. Each mass is a sort of cast-iron barrel. To build a horizontal mill (used by refineries), two masses are placed on the same horizontal plane, and a third is placed at their junction. A large industry’s train (or battery) consists of six mills, preceded by two masses placed vertically, one above the other, known as the “shredder.”
The entire industry is powered by large steam-powered turbines (six mills, three turbines) with a processing capacity of 4,800 tons/day. The fiber first passes between the shredder’s masses and then continues through the masses of the mill train.
The personnel assigned to operate the machinery include: an engineer and an operator who monitor the control panel, a “greaser” responsible for lubricating the gears that transmit motion from the turbines to the mills, another “greaser” who ensures the proper rotation of the mills on their axes, and a “tree-man” who prevents blockages in the channel where the fiber travels through the mill train.
At this point, bagasse and cane juice are obtained. The description will follow the process for each of these substances.
**Bagasse (Boilers)**
The mills’ conveyor belt takes the bagasse directly to the boilers, where it is dried and stored for later use as fuel. The material is also sold to the paper industry, where it is a potential raw material.
Large industries have six boiler units. The water inlet and the pressure generated by them are monitored automatically from an electronic bulletin board. There are 10 “firemen” and an equal number of “fire feeders” to control the entry of fuel and water.
The energy produced is converted using turbines of 1,200 kW, 2,000 kW, and 3,500 kW. High-temperature steam is also used to heat the juice in later stages.
**The Juice**
Below the mill train, the cane juice that trickles down between the grooves of the masses is collected. The liquid is pumped into tanks (two) where it is weighed. The weight of the juice is recorded in tons per hour for a shift. Large mills have a capacity of 7 tons per tank and are filled 50 times per hour, controlled automatically.
The juice at this point is full of impurities collected in the field during transport and in the cane yard. It is dark gray and has a density similar to water. The process of heating and clarification then begins to achieve the best possible sugar.
**Crystallization**
Crystallization takes place in single-effect vacuum pans, where the syrup is evaporated until it becomes saturated with sugar. At this point, seeds are added to serve as a medium for sugar crystals, and more syrup is added as water evaporates. Crystal growth continues until the pan is full.
The “tuning” (the contents of the pan) is then discharged through a foot valve to a mixer or crystallizer.
**Centrifugation or Purging; Reboiling of Molasses**
The cooked dough from the mixer or crystallizer is transferred to rotating centrifuge machines.
The cylindrical drum, suspended from a shaft, has perforated side walls lined with fabric on the inside. Between the fabric and the walls are metal plates containing 400 to 600 holes per square inch. The drum rotates at speeds between 1,000 and 1,800 rpm. The perforated lining retains the sugar crystals, which can be washed with water if desired. The mother liquor, or molasses, passes through the lining due to the centrifugal force (500 to 1,800 times the force of gravity). The purged sugar is then cut, leaving the centrifuge ready to receive another load of cooked mass. Modern machines are exclusively high-speed (or high-gravity) and equipped with automatic controls for the entire cycle. Sugars of a certain grade can be purged using continuous centrifuges.
**Machinery and Equipment**
The first types of cane mills employed vertical wooden rollers powered by animals, water, or wind. Sematon is credited with being the first to use three horizontal rollers in the current triangular shape, and some renowned authors claim that he devised the first steam-powered mill of this type in Jamaica.
**Equipment Capacity**
Due to the many factors that influence the selection of appropriate equipment in the sugar industry, average figures can be misleading. Local conditions, characteristics and richness of the cane’s content, the type of process, the desired quality of production, and many other considerations affect the size and capacity of machines and equipment in the different seasons of the factory.