In a coffee grinder or with a mortar and pestle, grind salt, thyme and coriander together. Set aside.
Using a mandoline or sharp knife, slice beets very thinly.
Fill fryer to appropriate level and set temperature to 325ºF.
Once oil temperature is within range, add a few beet slices at a time without crowding the fryer. Fry approximately 2–3 minutes. Remove beets after they begin to turn from burgundy to orange, but before the edges start to turn brown. Thicker slices may need more time, so remove beets a few at a time as you see them turning the desired color. They will not be crisp like potato chips, but will firm up slightly as they air-dry.
Drain chips on a paper towel. While chips are still warm, sprinkle with the coriander-thyme salt. Store any leftover beet chips in a covered container or paper bag to prolong crispness. If they wilt, they can be crisped up again