Avodah Zarah 31A

סתם יינם ⁠— אסור בהנאה, ומטמא טומאת משקין ברביעית. המפקיד יינו אצל גוי ⁠— אסור בשתיה, ומותר בהנאה.

It is prohibited to derive benefit from nondescript wine of a non-Jew, and the wine imparts the ritual impurity of liquids when it has the volume of 1/4th of a log. With regard to the wine of one who deposits his wine with a non-Jew, one is prohibited from drinking it, but one is permitted to derive benefit from it.

והתנן: המפקיד פירותיו אצל גוי, הרי הן כפירותיו של גוי לשביעית ולמעשר! כגון שייחד לו קרן זוית.

The Talmud raises a difficulty: But didn’t we learn in a Mishnah (Bekhorot 11b): With regard to one who deposits his produce with a non-Jew, it has the status of the produce of a non-Jew with regard to the halakhot of the Sabbatical Year and with regard to tithe, as the non-Jew might have exchanged the Jew’s produce with untithed produce or produce of the Sabbatical Year. According to this logic, wine deposited with a non-Jew should be entirely prohibited, due to the concern that the non-Jew exchanged it with his own. The Talmud answers: It is permitted for one to derive benefit from the wine in a case where the non-Jew designated a corner for the Jew’s wine, i.e., if the wine was locked away in a specific place to which only a Jew has access.

אי הכי, בשתיה נמי לישתרי! דהא רבי יוחנן אקלע לפרוד, אמר: כלום יש משנת בר קפרא? תנא ליה רבי תנחום דמן פרוד: המפקיד יינו אצל גוי ⁠— מותר בשתיה.

The Talmud questions this: If that is so, drinking from the wine should also be permitted. As R' Yoḥanan once happened to come to Parod, where the deceased tanna bar Kappara had lived. When he arrived, he said: Is there any Mishnah of bar Kappara here? In response, R' Tanḥum of Parod taught him the following baraita, citing bar Kappara: With regard to one who deposits his wine with a non-Jew, drinking from the wine is permitted.