Interestingly, these two ingredients are often mistaken for each other, particularly by the gluten-free baking novice. But there are some key differences that make these two flours almost as different as day and night.
Potato flour is heavy and dense to the palate because it’s made from the whole cooked potato; potato starch is lighter in weight, as it’s made only from the starch. Potato starch is similar to corn starch and is often used interchangeably.
Both potato flour and potato starch are rarely used alone in baking, they are generally added to complement the flour blend of a particular recipe. While potato flour can impart a chewy and moist quality to a baked good, potato starch will help bring a lightness to the product.
Potato flour maintains many of its nutrients, including protein and dietary fiber. Potato flour is made by cooking whole potatoes, drying them, and turning them into a finely ground flour. But potato starch has no protein or dietary fiber to speak of. Potato starch is processed from just the starch of the potato and this portion of the potato is not nutrient rich. Consequently, potato flour has nearly three times as many calories per serving. Potato flour is a “food” flour, whereas potato starch is more of an “agent” used to achieve a particular effect, like airiness in baking or thickening for sauces. You don’t run to potato starch for its nutritional value. However, both potato flour and potato starch can be used in lieu of wheat flour for thickening sauces, soups, and gravies.