By Mohan Dongare,

Former scientist at National Chemical Laboratory, Pune

India is the second largest producer of sugar in the world, after Brazil. Sugar production in India follows a standard sulphitation process that involves the introduction of sulphur dioxide, SO2, at two stages. Raw sugarcane juice has a low pH value of 4 or 5 which is slightly acidic in nature. At this level, sugar gets converted into other forms, like glucose and fructose which is not desirable. To prevent this, the juice is heated to about 70 degree Celsius and a little bit of lime or calcium oxide, is added to it, which takes the pH value to around 9.5. This mixture of juice and lime is then treated with SO2 to bring the pH value to the neutral level of 7. In the process, the calcium oxide reacts with sulphur dioxide to produce sulphites and sulphates of calcium, which helps in the clarification/purification of the sugarcane juice. The mud thus formed is removed by filtration as ‘press mud’.

Sulphur dioxide is used at a later stage as well, after the juice has been concentrated and is being crystallised. At this point, SO2 works as a bleaching agent and is responsible for ensuring that the end product, sugar, is white in colour.

Once the crystallisation process is over, the soluble sulphur compounds are drained out along with the molasses.

But there are two problems with this process. A little bit of sulphur remains within the final product, that is the sugar that we eat. This sulphur, more than what is required by the body, is known to lead to a variety of respiratory diseases. Additionally, the molasses containing sulphur, when used to produce ethanol and biogas from distillery waste, releases considerable amount of foul-smelling hydrogen sulphide, H2S, that is a poisonous gas and needs to be removed from biogas for its use as fuel, which needs additional treatment plants and chemicals.

This fact is well-known and that is why many countries have banned this process involving sulphur. This is also the reason why Indian sugar cannot be exported to markets in the United States and Europe.

A solution to this has been available for quite some time and has been in use in the United States and Europe. It uses carbon dioxide, CO2, in the place of SO2 and is called carbonation process. However, Indian sugar manufacturers have been sceptical of using CO2 because it does not have bleaching properties. The sugar produced through the carbonation process is not white but brown. This dark-coloured sugar is commonly used in many western countries, but there is a mental block against it in India.

I have been working on this problem for some time and carried out a few laboratory trials along with some researchers from the National Sugar Institute, Kanpur and Deccan Sugar Technologist Association, Pune. Recently, we achieved success in manufacturing white sugar through the carbonation process, without the use of sulphur. What did the trick was the addition of trace amounts of phosphoric acid. This phosphoric acid not just ensures a better neutralisation of pH value, it also helps in a faster and more efficient isolation and removal of floating solids in the juice clarification.

The carbonation process has other advantages as well. Almost all the sugar factories in India have an attached distillery which use the molasses that comes out as the by-product of sugar production. The distilleries release large amounts of CO2 in the atmosphere, which can instead be freely used by the factory. This process therefore is environment-friendly, acting as a carbon sink.

We have tested out the process at the industrial scale as well, at a sugar factory in Solapur, Maharashtra last month.

The sugar produced was comparable in colour to that being produced earlier and was free from sulphur.

The single carbonation process which was used in the above trials, does not involve any change in the present sugar industry’s process or equipments. We just used CO2 from the distilleries instead of the SO2.

For your research to be considered for this column, please write to Senior Editor Amitabh Sinha at amitabh.sinha@expressindia.com