Yayin Nesech-The status of wine that a gentile or non-Frum Jew looked at?
A. Halacha-Letter of the law:
From the letter of the law, wine can only become potentially forbidden due to contact with a Gentile [i.e. Yayin Nesech or Stam Yayin] if the Gentile comes into physical contact with the wine. However, if he simply looks at the wine, then it does not become Yayin Nesech and there is hence no prohibition to drink from this wine and it remains Kosher even initially. This applies, even if the wine is not Mevushal or pasteurized.
B. Kabbalah-Stringency of many:
Despite the above letter of the law allowance, the Poskim record that a Gentile has ability to defile the wine and enter impurity into the wine even through a mere stare. Thus, if a gentile looked at one’s [non-Mevushal] wine one is not to drink from it. Men of stature and Chassidim are stringent like this opinion. This especially applies by a Kos Shel Bracha [i.e. Kiddush etc]. [The Chabad custom is to be very stringent in this. Accordingly, we are very careful to always cover the wine so a Gentile does not look at it, and to not drink it if this occurred. Others, however, are lenient in this matter.] One who is careful in this will merit to drink from the Yayin Hameshumar.
Mevushal wine: The above stringency only applies to non-Mevushal wine, however, Mevushal wine [or wine that is Mevushal through pasteurization] does not get affected by the sight of a Gentile, just as it cannot become Stam Yayin even through touch.
An open glass bottle or glass cup: Some Poskim rule that the above stringency applies even if the Gentile did not see the wine directly, but rather through glass, such as if the wine is being held in a glass wine goblet, or in an open glass bottle. If, however, the glass is opaque through which the wine cannot be seen, then there is no issue so long as the Gentile did not look into the wine from its open top. Furthermore, some Poskim argue on the above and are lenient even if the gentile saw the wine through a transparent glass bottle so long as the Gentile did not look into the wine from its open top. Regarding a close glass bottle see next.
A closed and sealed bottle: Some Poskim rule that the above stringency only applies to an open bottle of wine, however, a closed bottle of wine cannot become Yayin Nesech and hence does not become defiled by a Gentile looking at it. This applies even if the bottle was already opened and then closed with the cap, and certainly applies if the bottle has never yet been opened and is closed with a cap and seal [i.e. two Chosmos]. This applies even if the wine is in a glass bottle through which the wine can clearly be seen, and certainly applies to shaded glass. [Accordingly, there is no issue with having gentiles carry unopened bottles of wine from one area to another, even though they will see the wine through the glass bottle. Practically, the widespread custom is to be lenient like this opinion to not beware from allowing a gentile to see an unopened bottle of wine. However, those who are stringent are blessed.]
Muslims versus Christians and other idolaters: Some Poskim rule that the above stringency against drinking [non-Mevushal] wine that was seen by a gentile, only applies to gentiles who are adherents of Christianity or other idolatry religions. However, gentiles which are adherents of non-idolatry religions, such as Muslims, then their look at wine does not affect it or prohibit it even according to Kabbalah, and thus there is not even an attribute of piety to avoid drinking such wine.
Mumar-Not religious Jew: A Jew who desecrates Shabbos in public [such as a typical Non-Frum Jew] has the status of an idolator regarding many matters, which includes Yayin Nesech. Hence, according to the above stringency, some Poskim rule that one is also not to drink [non-Mevushal] wine which a nonreligious Jew looked at. [The Rebbe’s custom was to be very stringent in this. Accordingly, we are very careful to always cover the wine so a Gentile or nonreligious Jew does not look at it, and to not drink it if it was seen by them.]
 See Minhag Yisrael Torah 272:1; Piskeiy Teshuvos 272:3-4; Chikrei Minhagim [Gurary] 4:105
 Ben Ish Chaiy Balak 16; See Michaber Y.D. 124
 Sefer Taamei Hamitzvos of Rav Menachem Habavli L.S. 360; Midrash Talpiyos Anaf Yayin p. 206; Mamar Yayin Hameshumar p. 18 of Rav Nasan Shapiro; Minchas Sotah p. 415 [custom of Titwan]; Shlah Hakadosh Shaar Haosiyos Kelal 94 Kedushas Hachila 106 p. 77 “I found in the Sefer Taamei Hamitzvos which was written by Rabbi Menachem Habavli under the prohibition against drinking Yayin Nesech as follows: In my younger days I noticed meticulous individuals who were stringent upon themselves that even if a Gentile simply looked at the wine then they would not drink it even though the Gentile did not touch it. Since he looked at it there is no longer a sign of blessing on such wine. This is an old custom. The reason for the custom is because once the Gentile sees the color of the wine or its smell, he begins lusting it in his mind, and the general thoughts of a Gentile is for idolatry. Hence, even though the wine is in the hands of the Jew, the Gentile has already imagined it in his mind. One should not be surprised at this stringency, as whoever is careful in this will merit to drink from the Yayin Hameshumar. I am very surprised to see people being lenient in this in the Gentile lands.”; Yifei Laleiv 5 Y.D. 123:1; Ruach Chaim Falagi 131:2; Zivcheiy Tzedek 3:165; Ben Ish Chaiy Balak 16; Darkei Teshuvah 123:2; Dovev Meisharim 1:124; Kinyan Torah 6:64
 Makor Chaim Kitzur Halachos 183
 Custom of Rebbe Rashab brought in Reshimos Harabash p. 150; The Rebbe was very careful in this, and so were the Chassidim of previous generations. [Chikrei Minhagim 4:105]
 Zecher Asos Mareches Yud 15; Zivcheiy Tzedek ibid that one who is lenient in this should not be protested against; Tiferes Adam Y.D. 33:2, brought in Zichronos Eliyahu [Rav Eliyahu Mani] Y.D. 10:2
 Shalah Hakadosh ibid
 Doveiv Meisharim ibid; Piskeiy Teshuvos 272:3 footnote 20-21; See Teshuvos Vehanhagos 2:401 who leaves this matter in question regarding Kiddush
 Teshuvos Vehanhagos ibid
 See Michaber Y.D. 123:3
 See Piskeiy Teshuvos 272:3
 Yifei Laleiv 5 Y.D. 123:1; See the following Poskim who leave this matter in question: Dovev Meisharim 1:124 [concludes that Chassidim are stringent]; Kinyan Torah 6:64
 Divrei Yechezkal; Suggestion in Doveiv Meisharim ibid based on Avkas Rochel 121 that glass is a valid Mechitza
 See Piskeiy Teshuvos 272:3 footnote 24
 Zivcheiy Tzedek 3:165; Tiferes Adam Y.D. 33:2; Zichronos Eliyahu [Mani] 1:28; Nachalas Pinchas 1:90; Divrei Shalom 4:32; Divrei Yechezkal; Sefer Hakashrus 19 footnote 143; Reply of Rav Groner z”l and Rav Eliyahu Landa Shlita that we are not stringent by a bottle which was never yet opened and has two Chosmos [Rav Groner “Regarding a bottle with 2 seals, we are not Machmir.”; Reply of Rav Simcha Ginzberg that we are only Makpid by wine that can become Yayin nesech through touch
Other opinions: From some Poskim it could be understood that the issue applies even by a closed glass bottle if the glass is see through. [See Yifei Laleiv ibid from which one can understand that even a closed bottle of wine may not be seen by a Gentile, if the glass is see-through; See Dovev Meisharim 1:124 based on Shvus Yaakov 1:126] Indeed, some individuals are stringent even regarding a closed bottle. [Sefer Halichos Chaim p. 74; Piskeiy Teshuvos ibid; Chikrei Minhagim ibid]
 See Michaber Y.D. 125:10
 Rav Landau and Rav Groner ibid and so also related to us Rav Simcha Ginzberg and Rav Asher Lemel Hakohen
Other opinions: Rav Yossi Marlow related to us that in his family they were careful even by unopened bottles that a gentile should not see it, and that he does not understand the difference between if it is closed or open, so longas the gentile can see the wine it is an issue
 See Chikrei Haminhagim ibid
 Ben Ish Chaiy Balak 16
 Admur O.C. 39:1 “He is like a gentile for all matters”; Michaber Yoreh Deah 2:5 “He is like a gentile”; Admur Y.D. 2:10 “He is a like a gentile regarding Shechita and for the entire Torah, except for Kiddushin”; Rashba 7:53; Tiferes Lemoshe 113:9 [brought in Pischeiy Teshuvah 113:1] regarding Bishul Akum [however not Pas Akum]; Erech Hashulchan 112:2; Kaf Hachaim 112:11; Ketzos Hashulchan 101:5 and Kitzur Shulchan Aruch 72: “Anyone who publicly desecrates Shabbos is considered like an idle worshiper and [thus] if he touches wine he forbids it, and the bread which he bakes is like Pas Akum, as well as the food which he cooks is like Bishul Akum.”; See Michaber 119:7 that such a Jew is like a gentile for all matters and is hence Chashud for everything; See also Michaber Y.D. 2:5 and Admur ibid
 See Teshuvos Vehanhagos 2:401 who leaves this matter in question; See Kaf Hachaim 4:81 regarding touching a Mumar; See Chayeh Halevi 2:51 and Piskeiy Teshuvos 272:4 who are lenient
 Reply of Rav Groner z”l “We are very makpid not to drink wine that a non-Jew or non-Shomer Shabbos saw.”