Sugar Manufacturing Process Step by Step

Sugar used for sweetening food items is one of the essential ingredients in a common man’s daily diet. It is regarded as one of the pure and highly refined edible food products available in the marketplace. Sugar manufacturing is a lengthy process that includes crushing, milling, clarification, crystallization, and refining.

In recent years this manufacturing process has evolved with modern technologies and advanced machinery. But still, the essence of the conventional processes of juicing the raw material for syrup, clarifying, and crystallization remains the same.

Sugar Industry

Manufacturing of sugar takes place in almost every region of the globe, thereby making it one of the largest agro-based industries. Sugar industries spread across 120+ countries manufacture around 110 million tonnes of sugar each year. Out of which 80% comes from sugarcane while the rest comes from beetroot.

The beet sugar industries are more prevalent in European countries, the USA, and some colder regions. Whereas the sugarcane sugar industries are widespread throughout the world, including the tropical climate countries like India, Africa, Australia, South America, parts of Asia etc.

Sugar Production in India

You will be surprised to know that due to the extensive sugar production, India is the second largest producer of sugar in the entire world. Sugarcane cultivation is immensely vast in subtropical and tropical areas of India, due to which Indian sugar industries are basically sugarcane sugar industries.

Earlier, the state of Uttar Pradesh was considered to be the Sugar bowl of India with the maximum sugar production. But in recent years, Maharashtra has overtaken UP and has become the top sugar-producing state in India, with 138 lakh tons of sugar production for the year 2021-22.

Such a large production capacity allows India to export a reasonably large quantity of raw sugar to other countries.

About Sugar

Sugar is an umbrella term used for a wide variety of carbohydrates present in plants that may be very sweet or moderately sweet. The primary sugar is glucose, which plants produce during photosynthesis. The one that we consume in our daily life is sucrose with the chemical formula of C₆H₁₂O₁₁.

The main source of commercial sucrose is the two crops- sugarcane and beetroot. But mostly, sugarcane is more prevalent worldwide.

About Sugarcane

Sugarcane is thick, tall and perennial, belonging to the grass family, growing upto the height of 10 to 12 ft. They highly flourish in tropical or subtropical regions. It contains about 9 – 12% of sucrose content. During harvesting, the farmers cut off the stalks close to the ground and remove the top leaves.

The cut stalks are transported to the sugar factory. The juice from the stalks should be extracted within 24 hours; otherwise, the sucrose content of the sugarcane gets inverted into non-crystallizable glucose and fructose. Hence, they pass into molasses without undergoing crystallization. This process of inversion is due to Hydrolysis.

How is Sugar Produced?

The step-by-step sugar manufacturing process involves 5 major steps:

Extraction of Juice
Clarification of Juice
Concentrating of Juice
Crystallization of Sugar
Separation of Sugar Crystals

1. Extraction of Juice

Firstly, sugarcane received from the farms is thoroughly washed with water to remove all the mud and dust present over it. Then it passes through the preparatory devices like huge cutters bearing rapidly moving knives. These knives cut the stalks into fine chips.

Milhouse

Further, they are sent to Milhouse, where they are subjected to crushing in milling tandems. It consists of two rolled crushers and 3-4 three rolled mills; arranged in series.

Each mill has three rollers, with each roller of 6 ft in length and 3 ft in diameter. The three rollers remain arranged in a triangular fashion, i.e., each at three corners.

Milling of Sugarcane

In the mill house, only the top rollers of the crushers rotate while the bottom ones are stationary. Each top roller applies a pressure of 3-6 tons/inch².

Note: To make the extraction of juice more efficient, the cane sugar chips are softened with the help of the compound imbibition method.

The first two mills extract the juice, which directly gets collected into the juice pan. The hot water is sprayed on the third and fourth mill to extract the remnant week juice from the chip. The diluted juice from the third mill goes to the first mill, while the juice of the fourth mill goes to the second mill to get mixed with the concentrated juice.

Around 97% of the juice is collected at the end of milling. The remaining pulp expels out of the mill, which is known as bagasse. The juice is further sent for the clarification process.

2. Clarification or Defecation of Juice

The juice obtained after milling is a greenish opaque colour. This is because of the impurities such as:

Soluble impurities: Glucose, fructose, salts, organic acids, phosphoric acid, gums, proteins etc.

Insoluble impurities: Pith, fibres, and mud.

Therefore, before concentrating on the extracted juice, it needs to get rid of all these impurities. Otherwise, they might affect the purification process and hamper the final yield.

This process of removal of the dissolve and undissolved impurities from the sugarcane juice is known as clarification or defecation.

Purification of Sugarcane Juice

The clarification process begins with screening the juice through large perforated metal sheets. This strains out the bigger floating impurities.

At the time when the juice comes out, it is acidic in nature (pH = 5 – 5.7). This acidity enhances the risk of inversion of sucrose. Thereby, along with clarification, the juice is also normalized by using either Sulphitation or double carbonation or sometimes both.

Sulphitation

It is a quick process that delivers beater precipitation. Also, it helps in the decolourization of the juice, as SO₂ acts as a bleaching agent.

For Sulphitation, the lime is added to the juice till its pH elevates to 8. Later, this limed juice is heated at 325 – 345 K. After this, the alkalinity of the juice increases, and the colloidal impurities get readily coagulated. The non-sugar impurities get precipitated as well.

After that, the SO₂ gas is bubbled into the hot juice till the pH drops to 5.1 to 5.3. During this process, the precipitate of CaCo₃ forms and settles down at the bottom and takes all the impurities with it. At last, the juice is again relimed to pH seven and heated to boiling.

Carbonation

In this process, the juice is heated at 328 K, and then the lime is added to it till the pH becomes 10.8 to 11. This condition is maintained for 5 mins. Due to the high alkalinity, the gums, pectin etc., get precipitated easily. After that, CO₂ gas is passed through hot limed juice till the pH drops to 7.5. Surplus lime gets removed with CaCO₃ precipitate. It settles down at the bottom, taking all the impurities with it. To achieve good results, the carbonation process needs to be performed twice due to, which is called Double carbonation.

Now the clarified juice is filtered to remove precipitates. The filtrate obtained is clear & colourless and is sent to MEE (Multiple effect evaporator) for concentration. The decanted impurities move to the rotatory drum filter, where it removes the unwanted stuff known as a filter cake. Later it is either discarded or reused in the fields in the form of fertilizer.

3. Concentration of Juice

The juice received after the clarification has a transparent and colourless appearance. At this stage, the juice comprises around 85% of water.

Thus, the juice is concentrated in 2 stages:

During the first stage, the juice is concentrated into a syrup with 40% water.
In the second step, the syrup is concentrated into a semisolid mixture of crystalline sugar and molasses known as massecuite. It contains about 9-11% water content.

Multiple effect evaporator

The concentration process is carried out in MEE, where the juice with 85% of water is concentrated in the syrup with 45% water only.

For this, triple or quadruple effect evaporators are used. Each evaporator is a tall vessel of 20 ft in height and 10 ft in diameter. The evaporators remain connected in series.

Multiple effect evaporator Working

Each evaporator has three chambers that are divided by fitting two parallel plates. The top and bottom chambers are for juice and remain connected via narrow tubes and some wider tubes. The middle chamber, known as the calendric, is made of steam used for heating the juice.

The steam inlet pipe at the middle of the Calendrier of the first evaporator. And the outlet of the 1st evaporator is connected to the middle of the Calendrier of the next evaporator. This continues with the third one.

The outlet of the 3^rd evaporator is connected to the vacuum pump. The evaporator is connected at the bottom, where the juice flows from 1^st evaporator to the next evaporator.

During the heating process, the juice present at the bottom goes up via narrow tubes while down via wider tubes. Rapid circulation leads to rapid evaporation. Moreover, the conditions maintained at each evaporator are mentioned below.

4. Crystallization of Sugar

The syrup obtained from MEE needs further water reduction so that the dissolved sugar can come into the form of crystals. For this, the solution passes through heated vacuumed pans, known as single effect vacuum pans, till they reach supersaturation.

The single effect vacuum pan either consists of Calendria or is fitted with a steam coil. It looks much similar to that of MEE but is comparatively larger in size with wider vertical tubes. A mechanical stirrer remains attached to it.

The crystallization process occurs in two stages:

Graining
Growing of crystals

1. Graining

In the pan, the solution is heated by using steam under a vacuum of 28.5 inches. This heating process is continued till the supersaturation solution of sucrose is formed due to constant water evaporation. The supersaturated solution contains about 84-85% of sucrose at 353 K.

The formation of crystals is also known as graining. The process of the graining is induced by adding the seed grain s for breaking the supersaturation of the sucrose. These seed act as the nuclei for the crystal formation, which is known as a seedling.

The graining point is achieved by shock treatment, i.e. by sudden cooling of the solution.

The chilling is done by:

Decreasing the rate of stream flow
Increasing the vacuum
Adding a large amount of cold syrup

2. Growing of crystals

In the second step, as soon as the graining point arrives, the more cold syrup is added to the pan with constant stirring. With this, the sugar in the syrup starts to come out and get deposited onto the seed crystals. This process continues till the desired growth of the crystal is attained.

After this, we get a semisolid mixture containing sugar crystals and molasses (Massecuite). Finally, when the crystallization is complete, the semisolid mass is sent to a centrifugal basket to separate sugar from molasses.

5. Separation of Sugar Crystals

After the crystallization is complete, the separated semisolid massecuite from the crystallizer passes via a centrifugal basket. This basket remains attached to the centrifugal machine. The basket is a perforated cylindrical basket with a vertical shaft. It is made up of finely woven metal mesh (400 to 600 perforations per sq. inch).

The basket is set in motion at the speed of 1800 to 2400 rpm. During the motion, the mixture is drawn towards the outer walls of the basket, and the liquid easily passes out through the perforations leaving the crystals behind.

After completion of the process, the separated crystals are thoroughly washed under the water jet to remove the remnant molasses on the crystals.

However, not all sucrose can be crystalized in a single step because of the high percentage of reduction, such as glucose and fructose. Hence, the final solution has to be worked out further.

The massecuite obtained after the first crystalization is known as Massecuite A and subsequent Massecuite B and C. The molasses C obtained is a black syrup that still comprises about 40 % sucrose, but it is not crystalizable. So, it is discarded as a byproduct of the sugar industry. Sugar C is not marketed and is used for the seedling of massecuite A and B. whereas sugar A and B are transported to the market for sale.

Production of sugar is a lengthy process, and at almost every step, some byproduct is released, such as bagasse, filter cake, mother liquor etc. Thus, in addition to sugar, the sugar industries also make use of the byproducts released from it.