A Practical Substitution
Potato starch is used in the same way as cornstarch. Whisk it first into a little bit of cold water or broth, then pour the resulting slurry into the simmering soup or sauce in a thin, steady stream. Potato starch has an especially strong thickening effect when it's first added, then it slowly relaxes and loosens. If you over-thicken the soup or sauce, stirring it for a few minutes usually fixes the problem.
Although they have similar uses, potato starch and cornstarch may behave slightly differently from one another. Soups and sauces thickened with cornstarch tend to set to a gel-like consistency, while those thickened with potato starch remain pourable.
When frozen and thawed, cornstarch weeps liquid and gains an uneven consistency. Potato starch thins when thawed, but otherwise retains its texture.
Potato starch also thickens at a slightly lower temperature than cornstarch, so it's useful as a last-minute addition if a soup or sauce hasn't been adequately thickened.
- On Food and Cooking: The Science and Lore of the Kitchen; Harold McGee
- The Cook's Thesaurus: Starch Thickeners
Fred Decker is a trained chef, former restaurateur and prolific freelance writer, with a special interest in all things related to food and nutrition. His work has appeared online on major sites including Livestrong.com, WorkingMother.com and the websites of the Houston Chronicle and San Francisco Chronicle; and offline in Canada's Foodservice & Hospitality magazine and his local daily newspaper. He was educated at Memorial University of Newfoundland and the Northern Alberta Institute of Technology.