May grape juice be used for Kiddush and Havdalah?
Pure “homemade” natural grape juice: The juice of grapes is valid for Kiddush even though it has not fermented and does not contain any alcohol content. Thus, it is permitted to squeeze grapes [before Shabbos/Yom Tov] and make Kiddush on it. It is likewise permitted to use grape juice that is made through soaking juicy raisins in water. In the wording of Chazal, this grape juice is known as Yayin Megito or Tirosh. The above is only from the letter of the law, however, it is a Mitzvah Min Hamuvchar to make Kiddush on aged wine [that contains an alcohol content] as it is of better quality. Thus, if one has wine available, he should not make Kiddush on grape juice [unless he made a vow against drinking wine or he is unable to drink wine due to health reasons]. If one is unable to make Kiddush on wine for whatever reason, one is to make Kiddush on grape juice rather than Chamer Medina. [The above only refers to pure natural “homemade” style grape juice that does not contain additives. However, processed grape juice sold by stores, which contains additives such as sulfur, is debated amongst the Poskim as to its validity, as explained next.]
Processed store bought grape juice: Processed grape juice sold by wineries [i.e. Kedem] goes through pasteurization and commonly contain additives and preservatives such as sulfur, sodium benzoate or potassium sorbate. Some Poskim rule that such grape juice is not considered grape juice at all [and rather falls to the category of Chamer Medina [tea/coffee/beer] and all its regulations and limitations]. However, other Poskim rule it is valid just like 100% pure grape juice. Practically, the widespread custom is to be lenient even initially to permit using processed grape juice for Kiddush, and the four cups. Certainly, Bedieved, it is valid for Kiddush even according to the former approach, just like any other Chamer Medina.
Chabad custom & suggested practice: The Chabad custom is initially not to make Kiddush on any grape juice, as stated above that it is a Mitzvah Min Hamuvchar to use actual wine. Nonetheless, if wine is not available, or one is unable to drink wine due to its alcohol content, one may use grape juice. If available, one should use 100% natural grape juice without preservatives. If not available, one may use even regular grape juice, as is the widespread custom. Those who have wine available and simply avoid wine due to its alcohol content [i.e. health reasons, women, children], preferably should mix wine with grape juice for Kiddush. Initially it is best to have a ratio of 2/3 wine, but one may go down up until 17% wine in the mixture. One can also purchase what is called “Light wine” which contains a very minimal alcohol content. If one cannot have any alcohol at all, then as stated above, natural, and store bought grape juice may be used.
It is a Mitzvah Min Hamuvchar to use actual wine for Kiddush, Havdalah and the four cups and so is the initial Chabad custom. Nonetheless, from the letter of the law, grape juice is also valid. Thus, in a time of need, such as if wine is not available, or one does not want to drink wine due to its alcohol content [i.e. women, children, health reasons], one may drink grape juice. Nonetheless, the following order of preference is suggested to be followed:
1. Mix wine with any grape juice. Best to use a ratio of 2/3 wine, although one may decrease until 17% wine.
2. If one does not want to mix wine, use 100% natural grape juice without additives.
3. If 100% natural grape juice is not available. use any store bought grape juice.
If one is unable to get wine under a Rabbinical supervision of his satisfaction, is it better to use homemade grape juice?
It is recorded that in years that the Rebbe Rayatz and Rebbe were unable to get wine that was made according to their Kashrus standards they squeezed grapes at home and used it for the four cups.
 See Bava Basra 97a; Admur 272:2 and 7; 472:27; 600:6; Piskeiy Teshuvos 272:6
 Admur 272:2; Michaber 272:2; Bava Basra 97a
 This is the definition of Yayin Megito, brought in Admur, Michaber and Gemara ibid
The reason: Some suggest that since grape juice is able to eventually become wine, therefore, it is even initially valid prior to becoming wine. Others, however, negate this reason. [See Meiri on Bava Basra ibid; Rashbam in Bava Basra ibid; Shevet Halevi 9:58; ]
 Kneses Hagedola 1; Orchos Chaim p. 64; Kaf Hachaim 272:16
 Admur 272:7; 472:27 regarding four cups; Michaber 272:6; Bava Basra 97b; Shiyurei Kneses Hagedola 472 regarding four cups; Olas Shabbos 472:8 regarding four cups; Chok Yaakov 472:22
How it is made: Raisin grape juice is only valid for Kiddush, and only receive the blessing of Hagafen, if one uses raisins that still contains ome juice to the point that they excrete juice when pressed on, and not just through soaking in water. [Admur 272:7; 472:27; Chok Yaakov ibid; Rif Bava Basra 22b; Rosh Bava Basra 6:10; Rivash 9] If they are so dry that they do not excrete any juice upon being pressed on, then they are invalid for Kiddush or Hagafen. [Admur 272:7] One takes these raisins, crushes them, and soaks them in water for three days. [Admur 272:7]
 Admur 272:2 “Yayin Megioto”; 600:6 “Tirosh”
 Admur 272:2; 600:6; M”A 272:3; 600:1; See Elya Raba 272:4; Birkeiy Yosef 272:2
Regarding grape juice made from raisins: Admur 472:27-28 concludes it should only be used
 Admur 472:27 regarding raisin wine
 Admur 600:6; M”A 600:1; Darkei Moishe 600:1; Tashbatz 120; Hagahos Maimanis 29:23-7; Minhagim Tirana p. 101
 See Admur 472:28
 Dvar Yehoshua 1:11; 5:5; Beir Moshe 6:53; Shvus Yitzchak Pesach in name of Rav Elyashiv; Rav Yaakov Yosef Za”l
 The reason: As the preservatives kill the juices ability to ferment, hence preventing it from ever becoming wine, thus negating its entire reason of validation [according to the understanding of these Poskim]. [Poskim ibid]
 Har Tzevi 1:158; Minchas Shlomo 1:4; Minchas Yitzchak 8:14; Shevet Halevi 9:58; Yechaveh Daas 2:35; Yeshuos Moshe 1:30; Mishneh Halachos 13:38 [Says its better to sue grape juice than today’s wines] Piskeiy Teshuvos 202; 272:6
 The reason: As since the grape juice was fit for fermentation and wine production prior to adding the preservatives, it therefore retains its valid state even afterwards. [Minchas Shlomo ibid] Furthermore, many grape juices today do not contain preservatives that prevent it from becoming wine, and it is still possible to ferment grape juice made today. [Piskeiy Teshuvos ibid]
 Piskeiy Teshuvos 272:6 that so is custom of many Gedolei Yisrael in this generation, including the Chazon Ish, Brisker Rav, Tchebiner Rav
 See Admur 472:28 that for the four cups, Chamer Medina is valid to be used if wine is not available.
 See article of Rav Raskin printed in Hiskashrus 691 that so was the custom in Lubavitch, and so would rule Rav Z.S. Dworkin; It is told that on the night of Shemini Atzeres 5738 when the Rebbe had his heart attack, he was offered to make Kiddush on grape juice and replied “Kiddush is made on wine” [Kfar Chabad vol. 497]
 See Igros Kodesh 19:213 that the Rebbe advised an ill person to squeeze cooked grapes and use its juice for Kiddush
 See Otzer Minhagei Chabad Nissan p. 139 that the Rebbe Rayatz and Rebbe used 100% natural grape juice [i.e. squeezed grapes] for the four cups when they were unable to get wine that was made according to their Kashrus standards.
 Piskeiy Teshuvos 272:6
 See Admur 204:9; Tzemach Tzedek O.C. 28; Piskeiy Teshuvos 272:6