Granmirupa is correct. Going to add a little more info. According to the St. Anthony Messenger:
"According to Francis X. Weiser in the Handbook of Christian Feasts and Customs (Harcourt Brace), as late as 1952 Catholics in Central Europe brought wine and cider to church for blessing on the feast of St. John. They then took it home and some of them poured a bit of the blessed wine or cider into every barrel in the cellar."
The book can be found here: (pdf)
The painting below is of "St. John the Evangelist" holding the chalice, by Alonso Cano, from Granada, Spain. It was painted between 1635-1637. It's in The Louvre Museum in Paris, France. The author explaining this painting is Francois De Vergnette. He gives this explanation:
"Saint John the Evangelist is blessing the poisoned chalice given him by a pagan priest of Ephesus to test him, but the poison escapes from the chalice in the form of a small two-headed dragon, as Jacobus de Voragine recounts in his Golden Legend (1228-1298)... Saint John the Evangelist is depicted holding a chalice, an allusion to his being put to the test by the high priest of the Temple of Diana at Ephesus. The high priest said to him: "If you want me to believe in your god, I will give you some poison to drink and, if it does not harm you, it means that your god is the true God." Thus the picure shows Saint John making the gesture of blessing which was to neutralize the poison escaping from the chalice in the form of a small two-headed dragon. He was then able to drink the potion, according to the legend."
De Vergnette further explains that even though this was a legend from Jacobus de Voragine, it was inspired by St. Matthew when Christ says to John and his brother: "You shall indeed share my cup" (Matthew 20:23).
From: Mark 16:18, NIV
"These signs will accompany those who have believed: in My name they will cast out demons, they will speak with new tongues; they will pick up serpents, and if they drink any deadly poison, it will not hurt them; they will lay hands on the sick, and they will recover."