Raw Sugar

Crystallisation is a purification. As sucrose comes out of a boiling syrup it forms an orderly crystal that excludes most of the impurities around it, so the crystal is far purer than the liquid it grew in. Centrifuging then removes the bulk of that liquid. But the film clinging to each crystal is not removed, and it is that residue — not the crystal — that makes raw sugar brown.

This matters for a common misunderstanding. The colour of raw sugar is a coating of impurities, not a property of the sucrose inside it; the sucrose in raw sugar, refined white sugar, and beet sugar is the same molecule. Mills producing for export often aim for a higher-purity crystal, known in the trade as very high polarisation sugar, precisely because a cleaner raw sugar travels and refines better.

Sucrose rotates the plane of polarised light by a fixed and characteristic amount, and that behaviour became the basis for measuring it long before modern analytical chemistry existed. Polarisation — pol, in the trade — is the measurement of sucrose content by that optical rotation, and it remains the central term of the raw sugar trade.

Raw sugar contracts are written on a polarisation basis, with the delivered sugar’s polarisation compared against the contract basis and the price adjusted accordingly: a consignment testing above basis earns a premium, one below it a deduction. Moisture, ash, colour, and the presence of dextran — the gum generated by microbial action on stale cane — are also assessed, since each affects what a refinery can do with the cargo. The specific bases, tolerances, and adjustment scales belong to the contracts and are not reproduced here.

Raw sugar is one of the few food commodities carried as a loose bulk cargo in a ship’s hold, poured in at a bulk terminal and grabbed out at the other end. That is only possible because the crystal is robust and the cargo is destined for a refinery that will dissolve it anyway — white sugar, by contrast, is bagged, because its cleanliness is the product.

Sugar is hygroscopic, and a bulk pile of it is unforgiving of moisture. Damp raw sugar cakes into a mass that must be broken out rather than discharged, and it deteriorates: micro-organisms in the syrup film become active as moisture rises, and the pile can heat and lose sugar. Terminals therefore control the moisture and temperature of sugar going into store and monitor the pile, and cargoes are assessed on moisture as a matter of course.

At the refinery, the syrup film is washed off the crystal, and the sugar is then dissolved, clarified, decolourised, and recrystallised into white sugar. The separation of milling from refining is the structural fact of the world sugar trade: cane mills sit in the cane, refineries sit near consumers or ports, and raw sugar is the form in which the product travels between them.

Raw sugar is never made alone. The same crystallisation that produces it leaves molasses — the liquor from which no more sugar can economically be recovered — and the same crushing that released the juice leaves bagasse. How much sugar the mill drives into crystal rather than leaving in the molasses is an operating decision, which is why these streams are related and not independent.