Potato Starch

A starch factory buys dry matter, not appearance. It cares nothing for skin finish, shape, or size — the qualities the table market pays for — and everything for how much starch a tonne of tubers delivers. Two supply routes follow from that. Dedicated starch varieties, bred for high dry matter and grown on contract for the purpose, are a commercial category of their own; and ware potatoes that fall outside table specification for cosmetic reasons find a home here, since a misshapen tuber makes exactly the same starch as a handsome one.

Extraction is a wet, mechanical process and runs quickly, because a rasped potato oxidises and spoils in short order. Tubers are washed, then rasped to rupture the cells and release the granules into a slurry. The starch is washed out of the fibrous pulp, separated from the soluble fraction, refined through successive washing stages, dewatered, and dried. Starch granules are dense and insoluble in cold water, which is what makes them separable this way at all.

Two other streams leave the factory with the starch. The fibrous residue — the ruptured cell walls — goes to feed. The soluble fraction, known in the industry as potato fruit juice, carries the tuber’s proteins and is recovered as a protein product where the plant is equipped for it. Both are real outputs; neither is described further here.

Potato starch granules are the largest of the commercial starches, and the granule carries phosphate groups covalently attached to the starch. The phosphate makes the granule swell readily and strongly when heated in water, so potato starch pastes at a comparatively low temperature, reaches a high peak viscosity, and produces a notably clear, bland, long-textured paste. It also holds a great deal of water. These are the reasons users choose it.

• Food — thickening, binding, and texturising, where clarity and neutral flavour matter
• Industrial — paper and board manufacture as a surface and wet-end additive
• Industrial — adhesives and textile sizing
• Feedstock — the base for modified and derivatised starches

The same properties are also its limits: the high peak viscosity falls away under prolonged heating and shear, and the paste is not stable to the conditions many processed foods impose. Much potato starch is therefore chemically or physically modified before use, and native starch and modified starch occupy distinct places in the market.

The traded product is a dry, fine, free-flowing powder shipped in bags, big bags, and bulk. It takes up moisture from humid air and cakes, so it is kept dry and sealed; damp starch is both a quality and a microbiological problem. Like any fine organic powder handled in bulk, it presents a dust explosion hazard, and pneumatic conveying and silo systems are designed and operated with that in view.