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From Rishikesh to Delhi

Sugar mills first appeared in the medieval Islamic world. They were first driven by watermills, and then windmills from the 9th and 10th centuries in what are today Afghanistan, Pakistan and Iran.

In the Indian subcontinent, sugar mills came into extended use in the 13th and 14th centuries, which greatly increased sugar production. The draw bar was applied to sugar-milling, with evidence of its use at Delhi in 1540, but possibly dating back several centuries earlier, and was mainly used in the northern Indian subcontinent. Sugar rolling mills also first appeared in the Indian subcontinent, using the principle of rollers as well as worm gearing, by the 17th century.

Approaching a sugar mill on the side of the road.
There are a number of steps in producing raw sugar from cane.


Harvest and transport to the sugar factory.
The first step is the harvest and transport to the sugar factory.

  • The overall quality of raw sugar that goes into the factory is dependent on agricultural practices and the cultivar used. Harvesting can be done by machines or by hand. If done by hand, it is normally preceded by burning the field. However, stalks from a burnt field more quickly loose sugar content while waiting to be processed.
  • Cane is transported by truck, narrow-gauge railway, container or cart. On arrival the cane is sold based on weight or sugar content. There are several ways to unload the harvest. Overall, limiting the time between cutting and milling is essential for achieving a high sugar yield and quality.

Juice extraction (cane preparation followed by milling).
Before the actual extraction of cane juice starts, the cane has to be prepared. This can be done by rotating knives or shredders.

  • Juice extraction by milling is the process of squeezing the juice from the cane under a set of mills using high pressure between heavy iron rollers. Those mills can have from 3 up to 6 rolls; every set of mills is called a tandem mill or mill train.

Purification of the juice, evaporation of water, crystallization and centrifugation.
During purification, calcium hydroxide, also known as milk of lime or limewater, is added to the cane juice to adjust its pH to about 7 or 8. This can be done while the juice is still cold (cold liming) or after it has been heated to about 104°C (hot liming).

  • The evaporation process serves to concentrate the clarified juice. The temperature, velocity and retention time in the evaporator are regulated to prevent sucrose inversion, or decomposition of sucrose in glucose and fructose. Another concern is scale formation on the heating surface of the evaporator.
  • Crystallization is done with a single-effect vacuum boiling pan and a crystallizer. In the vacuum pan, the syrup is evaporated until it gets supersaturated with sugar. At this point seed grain is added to serve as nuclei for sugar crystals, and more syrup is added as the water evaporates. The growth of crystals continues till the vacuum pan is full. The crystals and the mother liquor (molasses) now form a dense mass known as massecuite.
  • The sugar centrifuge serves to separate the massecuite into sugar crystals and mother liquor / molasses.

Storage of sugar and molasses.
The sugar from the centrifuges is dried and cooled and then stored. During bulk storage the quality of the raw sugar decreases because of a chemical reaction between amino acids and degraded invert sugars, known as the maillard reaction.

  • The raw sugar can also be directly packed into bags for shipment.

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