How do you refine sugar

how-to-refine-sugarConcentrated juice is then boiled to a supersaturated (highly concentrated) solution in vacuum pans. Crystallization is induced by seeding with a magnum of sugar and syrup to form a mixture of sugar crystals and liquor, known collectively as massecuite. The massecuite is discharged from the vacuum pans at 160° F (71° C) into water-cooled crystallizers where further sugar crystals are formed by reducing the temperature to about 100° F (37.8° C) over a 48-hour period. The raw sugar crystals are separated by reheating the massecuite to 122° F (50° C) to reduce the viscosity, followed by treatment in basket centrifuges operating at 1500 rpm. The residual syrup purged from the massecuite – a dark viscous liquid known as black-strap molasses – is used in the manufacture of rum, industrial alcohol and citric acid.

The first stage of raw sugar refining is called affination and consists of removing the molasses film coating the crystals by mingling the raw sugar in a U-shaped trough with a 73 per cent sugar syrup. The syrup is removed by centrifuging and the affined sugar is melted in pure water at 190° F (88° C) to give a strength of 68 per cent by weight. Up to 50 per cent of the color can be removed by treating the refinery melt with phosphoric acid (H3PO4) to an equivalent dosage of 0.02 per cent P205 and adjusting the pH to 7.3 with lime. After heating to 195° F (90° C), flocculation of the impurities occurs and they can be removed by flotation, often followed by FILTRATION. Final color removal is achieved by adsorption in beds of granular carbon or bone char (carbonized bone particles), followed by filtration to remove the last traces of suspended matter. Today refineries use ion-exchange resins for decolorization.

The pale yellow sugar liquor is concentrated to 75 per cent in a double-effect evaporator and crystallization is initiated in the vacuum pan by further evaporation and seeding with fondant sugar. The Cube sugar is produced by pouring a mixture of dry sugar and one per cent sugar syrup into the molds of a cylinder which rotates against a stationary pressure bar to compress the cubes. The cubes are discharged onto a conveyer and dried in an oven at 140° F (60° C). Soft sugars vary in color from light to dark brown. They have an invert sugar content of up to 6 per cent and a moisture content of 4 per cent.

Liquid sugar can be a pure sucrose syrup of 67.5 per cent concentration or a mixture of sucrose and invert sugar. Some liquid sugars are blended with corn syrup. Powdered sugars, such as icing sugar, are prepared by grinding granulated sugar, and their tendency to cake is often overcome by incorporating 3 per cent cornstarch.