Avodah Zarah, Chapter Four, Mishnah Ten
This mishnah discusses different types of contact that a non-Jew may have with wine that may or may not make the wine into yen nesekh, which is forbidden to Jews.
1) If a non-Jew was found standing by the side of a vat of wine, if he had loaned money to the Jew, then [the wine] is prohibited;
a) but should he not have loaned money to the Jew, then it is permitted.
2) If [a non-Jew] fell into a vat and climbed out, or measured it with a reed, or flicked out a hornet with a reed, or tapped on the top of a frothing cask
a) All of these things actually happened, and [the Rabbis] said that the wine may be sold, but Rabbi Shimon permits it [even to be drunk].
3) If [a non-Jew] took a cask, and in his anger threw it into the vat this actually happened and [the Rabbis] declared it fit [for drinking].
Section one: If a non-Jew is seen standing next to a vat of wine we need to know if the non-Jew touch the wine, for if he did touch the wine he would have made it into yen nesekh. Our mishnah teaches that if the non-Jew had loaned money to the Jew then the wine is prohibited. In such a case, the non-Jew has a lien on the Jews wine and might at some point say to the Jew, give me the wine and I will forgive you the loan. Since he has this financial connection to the Jew, and in some sense he has ownership over the wine as well, he will feel free to take some of the wine for himself. Therefore we must assume that he has come into contact with the wine. If, however, he has not loaned money to the Jew, then we do not assume that he had come into contact with the wine, and it is permitted.
Section two: This section lists all sorts of circumstances in which a non-Jew might come into contact with wine and yet it is highly unlikely that he used it to make a libation. Since in all of these cases we can be almost one hundred per cent sure that he didnt do so, there is room to be lenient. The Sages, in front of whom cases such as these came, said that the wine could be sold to a non-Jew. In other words, it is forbidden to drink the wine but it is not forbidden to derive benefit from it. If it had truly been considered yen nesekh, then it could not even be sold. Rabbi Shimon is even more lenient and allows a person to even drink the wine.
Section three: If a non-Jew throws an empty cask into a vat of wine the wine in the vat is not forbidden at all. Since in this case the non-Jew certainly did not make a libation with the wine, it is permitted and a Jew may even drink the wine.