Twisted,
To make pure (no wheat) oat bread, I have used baking soda/powder with a batter. It comes out like bread (some call this a quick bread).
I googled “barley bread recipe”. According to what I found, you can’t make a regular loaf of bread from barley either. Every barley bread recipe that I saw, at least pure barley bread – w/o other flours, also calls for baking soda/powder.
So then, would you now consider barley not one of the 5 grains?