Here we see Demeter of the Mysteries apparently depicting her power
which would be in the Kykeon. We find three elements:
grain, "poppy", and serpents.

It is my experience that psilocybe mushrooms often convey the experience of snakes and serpents.
And opium from poppy would be a useful additive to calm the inebriant when the visions got too scary.
Rather similar to hippy-flipping with X and shrooms.

The LSD theory of Kykeon due to ergot still remains unproven. Can we see something else here?
If looking for a pharmahuasca, then consider that the seed pods of the poppy are an encoded
symbol for the seed pods of Syrian Rue. If that is the case, then we need to supply the source of DMT.
And why not psilocybes? I find Websters argument that the Greeks were not very familiar with them
to disagree with Ruck's work, such as that Mycenae was founded where the "mykes" grew; of that they
appear in carvings of processions for the Antestheria and other Mystery meals.

Also, Webster says they do not keep well. My experience is that they dry easily and keep for years in the
state. They would also be easily transportable from regions where the priests might import them if needed.
Like McKenna, I think psilocybes are the most likely source, and when rue is added, a fine pharmahuasca can be made
in quantity.

The ancient Mediterranean world was awash in poppy extracts and was common. Adding the calming effect of poppy to a
psychedelic brew makes sense to me as it would let a newbie relax into the experience better, and not fight it.
But consider also that the poppy pod looks very much like the Syrian Rue pod. I have always felt an undulating "serpent" effect
from psilocybes and the connection to serpents seems obvious to me. The "poisonous" bite of the entheogenic serpent
is a repeated classical trope.

Barley and mint could still be a component.