Kisel/Kissel consists of a sweetened juice or milk, thickened with arrowroot, cornstarch, potato flour* rye, wheaten or oatmeal flour
Historical Information plus recipes: Moscow Restaurant Guide - Kissel
Kissel / TOP 10 Restoran.ru
* Potato Flour is cooked potato that is dried and then powdered. The equivalent is dehydrated mashed potatoes, to which you add water. It is not in the recipe to act like or replace traditional flour. It smells/tastes like potato, because it is potato. An easy equivalent is packet mashed potato mix that you buy in the supermarkets.
Problems occur when Potato Starch is called Potato Starch Flour, or just "potato flour". Because Potato Starch Flour is a mixture of both names, it can be confusing as to which product the recipe means. They work very differently in a recipe, and cannot be substituted for each other.
Potato Starch is the carbohydrate from the plant cell that is dissolved in hot water, dried and powdered. An equivalent is cornstarch. This is a non-gluten flour that can be in a recipe to act like, or replace, wheat flour. It is odourless and tasteless.
In Allergy-free cooking the distinction between the two is very important.