Years ago, Jared and I tried winnowing the chaff from the tiny seeds by playing "parachute" with a sheet on a slightly breezy day. Chaff and seeds flew about. I asked others about winnowing amaranth (less nicely called "pigweed), and they hadn't had success either.
The finest chaff fell through the screen, and the seeds and large chaff remained. I blew the remaining chaff away…while photographing because it looked so interesting. A small percent of chaff remained, but it's better than previous harvests.