Ideally, you need to harvest them before frost and process them pretty quickly. Once they have been chilled or removed from the plant, conversion toward fructose begins. If you wait too long, you end up with a fructose / fos syrup. You also need to reduce to syrup with minimum heat, because heat also causes conversion. Basically, press out the liquids and remove
water over very low <170F heat. It is a lot of work for not much syrup unless you are set up to process large quantities of chokes.
As far as I can tell, the powders are probably produced by freeze drying and grinding.