Wikipedia
Pyanopsia (Πυανόψια) or Pyanepsia (Πυανέψια) was an ancient Greek festival in honor of Apollo, held at Athens on the 7th of the month Pyanepsion (October). Its name literally means "bean-stewing", in reference to the sacred offerings given during this time, and is derived from the Greek words πύανος - pyanos "bean" and ἕψειν - hepsein "to boil" (the root of the verb variates between ὀπ- - op- and ἑπ- - hep-; cf. ὄπτησις - optesis "baking").
A hodge-podge of pulse was prepared into a stew and offered to Apollo (in his capacity as sun god and ripener of fruits) and the Horae, as the first-fruits of the autumn harvest.
Another offering on this occasion was the eiresione - εἰρεσιώνη (also referred to as eiresin). This was a branch of olive or laurel, bound with purple or white wool, round which were hung various fruits of the season, pastries, and small jars of honey, oil and wine. It was intended as a thank-offering for blessings received, and at the same time as a prayer for similar blessings and protection against evil in future; hence, it was called a suppliant branch (ixr~p(a). The name is usually derived from ἔριον "wool" in reference to the woolen bands, but some connect it with εἰρ-/ἐρ- "speak" (cf. εἴρω "I speak"; ἐρῶ "I will say"), the eiresione being regarded as the spokesman of the suppliants. It was carried in procession by a boy whose parents were both alive to the temple of Apollo, where it was suspended on the gate. The doors of private houses were similarly adorned. The branch was allowed to hang for a year, when it was replaced by a new one, since by that time it was supposed to have lost its virtue. During the procession a chant (also called eiresione) was sung, the text of which has been preserved in Plutarch (Theseus, 22): "Eiresin carries figs and rich cakes; Honey and oil in a jar to anoint the limbs; And pure wine, that she may be drunken and go to sleep".
The semi-personification of eiresin will be noticed; and, according to Mannhardt, the branch embodies the tree spirit conceived as the spirit of vegetation in general, whose vivifying and fructifying influence is thus brought to bear upon the corn in particular.
Aetiologists connected both offerings with the Cretan expedition of Theseus, who, when driven ashore at Delos, vowed a thank-offering to Apollo if he slew the Minotaur, which afterwards took the form of the eiresin and Pyanopsia. To explain the origin of the hodge-podge, it was said that his comrades on landing in Attica gathered up the scraps of their provisions that remained and prepared a meal from them.