פירוש על עבודה זרה 58:1

A Jew may not benefit from the wine of non-Jews since it may have been used in making a libation to an idol. [This prohibition is still observed by many religious Jews today, even though we can be quite sure that the wine was not used for idol worship. We will learn a lot more material about non-Jewish wine at the end of this tractate.] Similarly, vinegar that was once intended to be wine and then went sour may not be used by a Jew, since it may have been used in idol worship when it was wine. However, if the non-Jew bought the vinegar from a Jew and then gave it back to a Jew the Jew may use it since vinegar itself is not used in idol worship.
According to the Talmud Hadrianic earthenware absorbs wine and when subsequently wetted, will release the wine. If a Jew were to use such earthenware he would be using non-Jewish wine, which is prohibited.
According to the mishnah, idolaters would make incisions in animals to remove animal hearts and use them in idol worship. If one sees a cut in an animal skin at the place of the heart, it is a sign that the animal was used for idol worship and it is forbidden. Rabban Shimon ben Gamaliel claims that only if the cut is circular is the skin forbidden. Since non-Jews do not make oblong cuts as part of their idol worship, the skin is permitted.