Here's a newsgroup post that gets into the processing necessary to make
grains edible:

Newsgroup: sci.med.nutrition
Subject: Grains: (was: Milk: No Longer Recommended or Required)
From: "angela" <[log in to unmask]>
Date: Tue, 13 Apr 1999 18:12:03 -0700

Don Wiss <[log in to unmask]> wrote in message...

> You have to remember that grains are inedible without grinding them. So
> tools were needed, and tools leave evidence behind.

Actually, it's entirely possible to cook whole grains, but many of them
require a LOT of soaking, and a LONG cooking time - which probably made them
too time-intensive and fuel-intensive for nomadic peoples, per calorie of
nutrative value. Also, they need to be husked, which requires some sort of
flail or other abrasion (didn't one people have oxen walk back and forth
over the grain for this?), and winnowed, and you can see how it all becomes
very labor-intensive, particularly if the grain did not grow in thick,
easily gathered patches, and especially if the seed heads were not
generously filled.

As a side note, grains do not need to be ground with a mill.  A simple stone
metate will work - this would leave evidence. But so will a heavy wooden
pole in a section of hollowed-out wooden log, which might *not* leave
evidence.  (In an emergency (I got this out of a nuclear war preparation
book) whole grains can be "ground" in a metal bucket, with 3 equal lengths
of metal plumbing pipe taped together - lift *whump* lift *whump lift
*whump*.  It's not rocket science, and while it won't give you bleached
white bread flour, you *can* bake with it if you must. You can also cook it
like Malt O Meal for a hot porridge, or throw it into stew to thicken and
fortify it.)

--angela