If you want to have a go at winowing and grinding your own, try animal feed (wheat oat ect) that way you know it is clean. Some ergots that grow grasses aren't as obvious as the a purpera one that you get on wheat and rye. I have seen various fungi on most types of wild grass. This year isn't the ergot year as the previous 3 have been, but I don't bother with wild grass seed it is too high a risk, and too much work. However seeds like plantain and nettle are healthy and nutrious. Stuff like millet and quinoa can be grown easyly. The process is basically the same no matter what seed.
Threshing ; removes stalk, I find lying the sheafs on a sheet on the floor and treading removes seed from stalk.
dehulling ; depends on seeds, plantian needs a light pounding some need rubbing.
winnowing ; put seed in bowl and throw and blow to remove light chaf. I have a plastic bowl that when rubbed with nylon gets static and the chaff sticks to the edge. nettle can be make your lips feel funny at this stage.
grinding ; depends on seed I pound with a rolling pin. a proper grinder makes for a lot less work.
the green bits of grass can be juiced and are supposed to be very nutrious, the roots are said to be edible as well.