The refining process
The refining process begins with a process called affination which involves mixing the raw sugar with hot concentrated syrup to soften the outer coating on the crystals. The crystals are then separated from the syrup by spinning in a centrifugal.
The crystals are discharged from the centrifugal and dissolved in hot water to form a sugar liquor. The melted sugar liquor is then purified, utilising either the carbonation or phosphatation process. These processes trap suspended impurities in larger particles which are easier to separate from the sugar liquor.
Carbonation involves adding carbon dioxide and lime to the melted sugar to form a precipitate of calcium carbonate. The carbonatation precipitate is removed by pressure filtering the sugar liquor through cloth in a pressure leaf filter, leaving a straw-coloured, crystal clear liquid.
Phosphatation involves adding phosphoric acid to the melted sugar and removing the precipitate as a layer from the top of a flotation clarifier. The phosphatated liquor is generally also filtered through sand in a deep bed filter to remove any residual precipitate left after clarification.
This liquid passes through decolourising columns which adsorb the colourant molecules. The clear liquid is then concentrated by boiling in a vacuum pan. It is then seeded with fine sugar crystals which are grown to the required size by adding more liquor. When the crystals are large enough, the crystals and syrup are discharged from the pan.
This mixture of crystals and syrup (called a "massecuite") is processed through a set of centrifugals where the crystals are separated from the syrup. The separated syrup is boiled again and more sugar crystals are extracted from it. This process can be repeated a number of times.
The refined sugar crystals are dried by tumbling them through a stream of air. The dried sugar is graded into the required crystal sizes ready for delivery to customers either packaged or in bulk.