How sugar is made

White sugar is pure sucrose, squeezed out of cane or beets, clarified with lime and spun in centrifuges.

stations: 8
things upstream: 5
raw sources: 4
steps from the ground: 2

The short version

Sugar mills crush sugarcane, or wash and slice sugar beets, to get a sugary juice. Lime clarifies the juice, evaporators thicken it into syrup, and seed crystals trigger sugar to crystallize out. Centrifuges spin off the molasses, and a refinery then washes, filters and decolorizes the raw crystals until they are white.

Press out the juice

Cane is chopped and either milled with water or run through a diffuser to extract the juice. Beets are first washed and sliced into thin strips, and the sugar is soaked out of the strips in the same kind of diffuser. The leftover cane fiber, called bagasse, is burned to power the factory.

Goes in
Sugarcane Sugar beet Water
Clarify with lime

Lime is added to the raw juice. It neutralizes acids and makes impurities clump together so they can be settled or filtered out. For cane the juice is also heated to destroy enzymes that would break the sugar down.

Goes in
Quicklime
Boil down to syrup

A chain of evaporators drives off water until the thin juice is a thick syrup. Beet factories boil under a vacuum so the sugar does not scorch at high temperature.
Seed the crystals

Syrup is boiled further until it is supersaturated, then seeded with tiny sugar crystals. Sucrose comes out of solution onto the seeds and the crystals grow in a pan until the mixture is a thick mass of crystals in syrup.
Spin off the molasses

The crystal mass drops into centrifuges that fling the liquid through a fine screen. Beet factories get white sugar from this step. Cane factories get raw sugar with a sticky brown coating, and the liquid that spins off is molasses.
Wash and filter the raw crystals

In a refinery, raw crystals are soaked in concentrated syrup that softens the brown coat without dissolving the sugar. They are spun again, dissolved in water, and treated so a fine solid precipitates in the liquid. Filtering that solid out takes many impurities with it.
Strip out the color

Beds of granular activated carbon or ion-exchange resin hold on to the color compounds that are left as the syrup is pumped through.
Crystallize and dry

The clear syrup is boiled and seeded once more. Spinning off the white crystals, drying them in hot air and packing them follows. What is left over becomes refiners' molasses.