Floury Potatoes are the best ones to use for baking and mashing. When cooked, their cells will separate, making for fluffy baked potatoes, good mash and great chips (as in French Fries.) They have high-starch levels (20 to 22%), but are lower in moisture and in sugars than other types of potatoes.They are not good to use, however, when you want to boil or cook potatoes and have them stay together afterward. Used as chunks of potatoes in Potato Salad, they will crumble and fall apart. Used as slices in a baked potato dish, they will also fall apart. Instead, for these uses, you want the other type of potato, which is a “Waxy Potato.”
In North America, it’s very hard to know which kind of potato is which. They are all flogged for the most part as just “potatoes.” Any potatoes being sold as Baking Potatoes are (or at least should be) Floury Potatoes, and so will also be good for making mashed potatoes from.
When harvested early before they have time to develop their full amount of starch, some Floury Potatoes can also be used as you would Waxy Potatoes. Early harvest shortens their storage life potential, however, so they are meant for sale and use straightaway.
In food-writers lingo in America, these are also often referred to as “High-Starch Potatoes”, which is confusing, because while it’s true that they have a higher starch level than waxy potatoes, the truly “High-Starch Potatoes” are referred to just as “Starch Potatoes.” These are potatoes with so much starch in them that they are actually industrially processed just for their starch alone into things such as potato starch, potato flour, alcohol, etc. Consequently, the term “High-Starch Potatoes” is best avoided.
Floury potatoes are the most profitable for farmers to grow because they are in high demand with food processors to make items such as French Fries (aka chips in the UK) and potato chips (aka crisps in the UK) from. Sadly, it seems that in North America few of them make it to the store shelves for consumers, who have them content themselves with potatoes marketed as “all-purpose” which means that sometimes your mashed potato is fine, sometimes it comes out as wall-paper paste.
European potato breeders may refer to Floury Potatoes as “Cooking Type C.”