It depends on the grain!

Barley and wheat can both be made into flour and thus bread, though wheat requires additional preparation like cracking or milling before it's really edible. Barley still needs to be ground to make flour, but it can be easily cooked and eaten like rice. The lower gluten content means barley bread is denser and generally less appetizing, so wheat was considered more prestigious. They could both also be made into a simple gruel, which took less effort.

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Rice, much like today, would generally be boiled to cook it.