Case study: Bury St Edmunds factory How is sugar made?

1. Case study: Bury St Edmunds factoryHow is sugar made? Bury St Edmunds factory is the United Kingdom’s largest milled sugar plant.

2. 1. Weighing and sampling The factory processes 14,000 tonnes of sugar beet per day during the beet processing campaign. A sample from each delivery of sugar beet entering the factory is weighed and then tested to determine its sugar content. Two million tonnes of sugar beet are produced by some 1,200 UK growers, at an average distance of 31 miles from the factory.

3. 2. Cleaning The first stage of processing involves cleaning the sugar beet with water. Two co-products are collected at this point. 60,000 tonnes of soil is separated, dried, screened and blended before being sold as high quality soil to landscapers and construction projects. 1,600 tonnes of stones are removed and washed from the sugar beet delivered to the factory and are sold as an aggregate.

4. 3. Slicing and diffusion The clean beet is sliced into thin ‘V’ shaped strips called cossettes. These are pumped to three diffusion towers where they are mixed with hot water to extract the sugar. The rawjuice is used to preheat the cossettes before passing to heat recovery systems and onto purification.  Juice  Cossettes

5. 3. Slicing and diffusion The remaining fibre is mechanically pressed before being dried in coal fired rotary driers. The dry fibre is then compressed into pellets which are sold in bulk as animal feed. In total over 100,000 tonnes of dried animal feed is sold each year. In addition, over 10,000 tonnes of wet animal feed is sold annually.

6. 4. Purification The raw juice is progressively heated through complex heat recovery systems which minimise the energy demand of the plant. Milk of lime and carbon dioxide are added to precipitate calcium carbonate, or chalk, which removes the impurities in the raw juice.

7. 5. Evaporation The extracted thinjuice passes to multiple effect evaporators which boil off the water and produce syrup known as thickjuice. The steam and water that has been removed by evaporation is condensed and used for heating in the factory. Up to 50% of the thick juice which is produced can be stored in seven large storage tanks with a combined capacity of 220,000 tonnes. This is returned to the factory outside of the beet processing campaign to allow sugar to be produced throughout the year.

8. 6. Crystallisation Crystallisation of sugar takes place in pans which boil the thick juice under vacuum. This lowers the operating temperature and reduces energy demand. The thick juice is seeded with tiny crystals of sugar to provide the nucleus for the grains of sugar to form and grow.

9. 6. Crystallisation When the crystals are fully formed the mixture of the crystal sugar and syrup, known as massecuite, is spun in centrifuges to separate the sugar from the syrup or motherliquor. After the sugar crystals are washed, dried and cooled, they are conveyed to five concrete sugar silos, with a total bulk storage capacity of 73,000 tonnes.

10. 7. Packaging At Bury St Edmunds factory 210,000 tonnes of granulated sugar and 40,000 tonnes of milled sugar products are produced annually. A machine automatically channels and measures the amount of bags going through and pulls them onto a pallet. Once on pallets, the bags of sugar are shrink wrapped to protect them from moisture.

11. Summary The stages of sugar beet processing include: • Sampling • Cleaning • Slicing and diffusion • Purification • Evaporation • Crystallisation • Packaging