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Friday, 2nd October 2009

The story of sugar

Great scholar, Ji Xian-lin

Great scholar, Ji Xian-lin
Courtesy of Radio Television Hong Kong

The little packet beside the coffee reminds me of the history of sugar in China written by Ji Xian-lin, a great Chinese scholar who passed away in July.

By sugar we mean cane sugar. Crystalline sugar was first discovered in India a long time ago, before or during the Gupta dynasty (around 350 A.D.). Compared to sugarcane, a big advantage of crystalline sugar is that it is easy to store and to transport. The method to produce crystalline sugar spread to Persia (now Iran) in around year 600, and later on to Arabia with the advent of Muslim.

How was crystalline sugar produced? Sugarcane was first crushed to give juice. The juice was then boiled, and the scum that rose to the surface was skimmed off. The sediment was allowed to cool, drain and dry, resulting in granulated crystals which was purplish black in colour.

The dark colour of the sugar is associated with impurities. Sugar refining means the removal of impurities. In the history of sugar refining in India, limestone and ash were variously added during the heating process to purify the sugar by precipitation. Milk, coconut juice and flour were also used whereby impurities were removed through coagulation or thickening. The outcome was sugar with a brownish or yellowish tint.

Except for some parts in the south, sugarcane was not common in China. Refined sugar was brought in from India along the same route as Buddhism. China was so impressed that in the 7th century, the second emperor of the Tang dynasty, Li Shimin, sent craftsmen to India to learn the way to refine sugar. For hundreds of years thereafter, China adopted similar techniques described above to refine sugar, but in the meantime the use of eggs, a good coagulator, seemed to bring sugar purity to a higher level.

During the Arab Agricultural Revolution which started in the 8th century, it was discovered that the use of ash from burnt trees was very effective in producing sugar with an even lighter colour, though not exactly white. The technique was brought to China by the time of the Yuan dynasty (13th century), as reported by Marco Polo in his travel log.

A breakthrough in sugar refining in China occurred during the 16th century when it was inadvertently discovered that mudwater was capable of producing pure white sugar --- so much so that by the end of the Ming dynasty (early 17th century) sugar was exported to Europe through the East India Company.

A friend of mine in the chemistry field tells me that the purification effect probably comes from the clay particles in mudwater, which have good adhesion property. However, this has to be confirmed through experiment.

The rest of the story, of course, is "history". With the advent of industrialization in the west which started in the late 18th century, sugar has since been produced in large-scale refineries. Nowadays sugar is refined by the use of limewater and carbon dioxide (or phosphoric acid) which removes impurities by precipitation. As you can see, the chemical process is not much different from the old.

Though not scientific in the modern sense of the word, the history of sugar does tell us quite a lot about the experimentation, empiricism and technology involved in the development of sugar refining.

B.Y. Lee

Last revision date: <17 Jan 2013>