How do I make beet powder?

[carfreemama]

Hi:

I have beets I want to dry in my Excalibur food dehydrator, to sweeten and add nutrition to cookies. The instructions I have are to cook, cool and slice them and dry until they are "leathery." But I want them to be brittle enough to put in the food processor after they dry, so they will be ground to a powder. Have you ever had success with this? Do they ever get that hard?

Thanks.