Just as sugar beets are grown solely as raw material to make sugar from, starch potatoes are grown solely as a raw source of starch for other uses.
On average, a potato is about 20 percent solid matter (the rest being water), and of that 20% solid matter, about 85% is starch.
Starch processors look for potatoes that overall have 17 to 20% of their total weight as starch.
The potatoes are delivered straight from the grower to the factory, and sampled there right away for starch content. The potatoes are washed, then grated, then pressed through sieves to create pulp and juice (sometimes referred to as “starch milk.”) The juice is washed repeatedly in separators, to get solid material out of them and to yield a pure starch. The water is drawn off through a vacuum filter, then the starch is flash dried.
A by-product of starch production is the leftover potato fibre and pulp. This can be used as animal feed, particularly for cattle, by farmers. The juice water can be spread on land as nutrients, or run off as waste water.
In the food industry, potato starch can be used to give texture, as a binder or stabilizer, to help substances gel, etc. Unmodified potato starch is also referred to as “native potato starch.”
Compared to cereal starches (such as those from corn or wheat), potato starch tends to add more flavour (which may or may not be desirable, depending on what the product is), is more viscous, and yields a gel that is more transparent after cooking. Unmodified potato starch, though, isn’t as good for commercial food uses that involve quite high temperatures, or long cooking times.
Potato starch can also be used in making paper.
European potato breeders may refer to starch potatoes as “Cooking Type D.”