Question: If kosher wine is served at a kosher restaurant and poured by a non-Jewish waiter, is the wine forbidden for consumption?
Answer: In olden times, idolatrous non-Jews would customarily pour wine as a libation offering to their various idols and deities. This was quite a common practice. Such wine is forbidden for consumption or to derive benefit from (such as by selling it to another non-Jew) by Torah law, for anything that is an accessory to idol-worship is forbidden to benefit from.
Our Sages further decreed that even the “random wine” of non-Jews should likewise be forbidden to benefit from. This means that although one is unsure whether or not a non-Jew’s wine was offered as a libation to an idol, our Sages nevertheless decreed that one may not derive benefit from it. The reason why our Sages distanced us so much from their wine is because drinking wine brings people together in a closer way and as a result of Jews sitting together with non-Jews and drinking wine, this may bring them together to such an extent that a Jew may end up marrying a non-Jew’s daughter. It is for this reason that our Sages banned deriving any benefit from non-Jewish wine. Thus, even in our times, even “random” wine of a non-Jew is forbidden to derive benefit from and is certainly forbidden for consumption.
We must ask ourselves: Why is it that our Sages ruled so stringently and forbade even deriving benefit from non-Jewish wine, something we do not find regarding other prohibitions meant to distance us from non-Jews? The answer is that since wine that was actually poured as a libation offering is forbidden to derive benefit from as it shares the same law as an accessory to idolatry, our Sages enacted that we must treat all wine of a non-Jew as if it was certainly poured as a libation to an idol although we are uncertain of this fact. Nevertheless, as we have stated above, the primary reason for this edict was because of the concern of intermarriage.
We must therefore discuss the status of non-Jewish wine nowadays: Shall we consider it forbidden to derive benefit from as well or is it merely forbidden for consumption but permissible to derive benefit from?
Maran Rabbeinu Ovadia Yosef zt”l deals with this matter at length and rules that regarding this law, there is a distinction between the various non-Jewish religions. Regarding religions which worship a foreign deity, their wine is forbidden even to benefit from. Nevertheless, regarding religions which believe in the ultimate oneness of Hashem, although they may deny several teachings of the Tanach and believe in other prophets, they are not considered idolatrous and their wine is only forbidden for consumption (due to the rabbinic concern for intermarriage) but one may still derive benefit from it by selling it to a non-Jew and the like.
Not only is a non-Jew’s wine forbidden for us, rather, even if a non-Jew touches our wine, the entire bottle or barrel becomes forbidden by virtue of the above rabbinic enactment. Similarly, wine poured by a non-Jew is likewise forbidden.