I’ve done some experimenting with beet chips in an attempt to determine what is the best way to turn out reliable results. The most important factor is using a mandoline
(Protect those fingers!) so that the chips’ thickness is uniform and they dry out evenly.
It is possible to bake the chips on a parchment lined baking sheet in an oven set to a very low temperature (150 degrees Fahrenheit or lower) for a few hours. While the oven works well at higher temperatures if your timing is perfect, the chips can burn in an instant and the second they burn even slightly the sweetness of the beet disappears. Using a food dehydrator
is the safest bet since the temperature can be set very low.
Also, beets that are at least three inches wide have less of a tendency to shrivel up during dehydrating.