Barley - The Secondary Grain
Although barley plays a secondary role to wheat and was traditionally used more for sustaining animals rather than humans, there were special functions in religious life in which it featured.
Along with its subspecies, rye and oats, barley qualified for use in baking the matzos for Pesach as did wheat. There were two flour offerings in the Beit Hamikdash for which only barley could be used.
One of these was the Omer flour offering which was brought to the altar along with an animal sacrifice on the second day of Pesach (16th of Nissan). Once this offering was made it was permitted to enjoy the new grain.
The second use of barley was in the flour offering brought to the Beit Hamikdash by a sotah, a married woman suspected of adultery. The reason why barley, usually animal food, was designated for this offering is given by Rabbi Gamliel (Sotah 14a):
“Her behavior (becoming involved with another man) was like that of an animal, so must her sacrifice be one of animal food.”