Barley. Domesticated shortly after zeia, barley became a key ingredient in the ancient Greek diet, arriving from the Middle East sometime around the 4th millennium BC. The Minoans and Mycenaeans fed their palace workers with it, and because it is easier to grow than wheat it's reckoned that up to 90% of the grain grown in ancient Greece was barley.
The grain was a key feature in ancient Greek religion, when the humblest offering one could make to a god was a barley cake. Homer mentioned Greek barley water, kykeon, sometimes flavoured with mint or thyme, or according to Homer himself, with 'ground goat cheese'. Ancients later added honey and wine to the mix.
The agricultural goddess Demeter was closely associated with barley, and the kykeon that was ritually drunk at her Mysteries in Eleusis was very likely purposely laced with hallucinogens from ergotamine (similar to LSD), which was derived from the ergot fungus on the crops (only locally-grown barley was ever used in Eleusis, supplied by two families who knew how to make it). After partaking, the initiate descended into the underground Telesterion, to witness the mysteries in a receptive frame of mind– a life changing experience that offered the promise of life after death.
Today barley is the most popular grain grown in Greece after wheat, and used in breads, (especially paximadi) and beer.
Image by Photo Icarus