In the ancient Greek and Roman world, it was customary to offer libations to the gods by pouring a few drops of wine onto the ground during a symposium
, among other things. The Greek writer Lucian (120-180 B.C.) noted that the souls of the dead were fed by the drinkers. On ships, this is still a widespread custom today, at the beginning of a voyage or after successful manoeuvres, to give a few drops of mostly liquor
to the sea god Poseidon (Neptune). However, the quantity must be well dosed, because a "too little" can annoy him and a "too much" can lead to a storm.
Under Customs in viticulture
you will find a comprehensive list of relevant keywords related to rituals, festivals and customs "around wine".