Reference for Avodah Zarah 109:11

<big><strong>מתני׳</strong></big> לוקחין גת בעוטה מן העובד כוכבים אף על פי שהוא נוטל בידו ונותן לתפוח ואינו עושה יין נסך עד שירד לבור ירד לבור מה שבבור אסור והשאר מותר

A winepress [containing] trodden [grapes] may be purchased from a non-Jew even though it was he that lifted [the trodden grapes] with his hand and put them among the heap. And [the juice] does not become yen nesek (wine assumed to have been used as a libation) until it descends into the vat. When it has descended into the vat, what is in the vat is prohibited; But the remainder is permitted.

Jastrow