Melting a frozen, or partially frozen, bottle of water or juice on Shabbos:
While there is no intrinsic biblical prohibition involved in melting ice on Shabbos, so long as one does not heat it to the point of Yad Soledes and transgress the cooking prohibition, nonetheless, the sages restricted one from doing so due to the Rabbinical Molid/Nolad prohibition, which is a restriction against turning a solid substance to a liquid substance on Shabbos even without using heat.
The reason for the Molid/Nolad restriction: There is several reasons recorded behind the above restriction: 1) Because doing so is similar to a [forbidden] action [as it appears like] he is creating these waters. Through doing so one is creating a new substance on Shabbos which is similar to a Biblically forbidden action being that he is creating this water. This prohibition is formally known as Molid. 2) Others however learn that the prohibition is due to the prohibition of Nolad, which is Muktzah. 3) Others however rule the reason behind this prohibition is due to a decree that one may come to squeeze fruits which are designated to be juiced, being that snow and ice are designated [also] for their liquids.
The cases of restriction: The following are the cases in which the sages restricted melting ice on Shabbos:
- Crushing ice in order to melt it and turn it into water: According to all opinions, it is forbidden to break ice into small pieces in order so it melt.
- Crushing ice into another liquid: It is disputed amongst the Poskim as to whether it is forbidden to break ice that is found within a liquid into small pieces in order so it melt within the liquid, and practically we rule stringently to prohibit it.
- Breaking ice in order to reach the liquid under it: It is permitted to break through the ice which is covering over the water in a vessel, in order to draw water from underneath it, as the ice does not melt by one doing so.
- Placing ice near a source of heat: It is disputed amongst the Poskim as to whether it is permitted to place ice near a source of heat [fire, or sun] in order for it to melt [even if the cooking prohibition will not be transgressed, as explained in B], and practically the custom of Ashkenazim is to be stringent, unless it is a time of need. [It is disputed amongst Poskim if this dispute applies only when placing the ice near a source of heat, such as near a flame or opposite the sun, while placing it by room temperature to melt would be permitted according to all, or if the dispute applies in all cases even by room temperature. Practically, based on the rulings of Admur one should be stringent.] According to all opinions, however, this only applies if the melted substance will be recognizable, however, if it will not be recognizable on its own, then according to all it is permitted to place it near a source of heat so long as the cooking prohibition is not transgressed.
- Placing ice in a cup of liquid: One may place ice into a glass of wine or water in order to cool down the drink even though the ice will melt there on its own, into the drink. [According to Admur, it seems that even if there is only a small amount of water in the cup, allowance applies.]
B. The law:
Smashing the bottle in order to make liquid: If one froze a bottle of water or juice, it is forbidden to smash the bottle in order to break the ice and turn the ice into liquid. This prohibition applies even if the bottle is only partially frozen, and hence it is forbidden to shake a partially frozen bottle in order to melt the ice or turn it into slush. Nonetheless, in the event that it is only partially frozen, one may break through the ice in order to get to the water underneath it and not for the sake of melting the ice.
Placing the bottle near a source of heat: In all cases, due to the cooking prohibition, it is forbidden to place the bottle near a source of heat [other than the sun] if it is possible for it to become heated to the point of Yad Soledes if it were to remain there indefinitely, even if one intends to remove it before it reaches this point. Thus, it goes without saying that it is forbidden to place it on top of a pot that is on the fire or electric plate even if one plans to remove it after it is melted and while it is still very cold. Furthermore, for Ashkenazim, it is even forbidden to place it in an area in which it will never reach Yad Soledes, or even opposite the sun, unless the bottle is not completely frozen, or it is a time of great need. If the bottle is not completely frozen and contains some liquid, then it is even initially permitted to place it opposite the sun so it further melt, or place it near a source of heat at a distance that it can never reach Yad Soledes. In a time of great need, such as if there is nothing is available to drink, then one may be lenient even initially to place even a completely frozen bottle opposite the sun for it to melt or place it near a source of heat at a distance that it can never reach Yad Soledes.
Removing the bottle from your freezer to defrost in room temperature: Bottles of liquids which are completely frozen, are under debate amongst the Poskim if they may be removed from the freezer on Shabbos and defrosted in room temperature, and practically, one should be stringent unless in a case of need.
Liquids of significance, such as wine and milk: Some Poskim allow defrosting liquids of significance [such as milk and wine] even near the sun. Practically however, one is not to rely on this opinion, and is to follow the same ruling as all frozen liquids.
 Admur 320:16; Michaber 320:9; Shabbos 51b
 Admur ibid and 318:25 “He is Molid”; Taz 320:7; Rashi Gemara ibid “The reason is because he is Molid Beshabbos”; Sefer Hateruma 234-235 “Because of Nolad” as understood by Rosh 4:13; brought in M”B 320:33
The ruling of the Sefer Hateruma: Some Rishonim learn the Sefer Hateruma to be agreeing with the reason of Rashi, and that the reason is because of Molid, and the word Nolad in the Sefer Hateruma means Molid. [Rosh 4:13] Others however understand the Sefer Hateruma to be giving an alternative reason behind the prohibition, and that Nolad and Molid are two different concepts, and that Nolad refers to the Muktzah prohibition. [Ramban 51b; Rashba 51b; brought in Shaar Hatziyon 320:35; M”B 318:105] It is implied from Admur 318:25 like the Rosh, that he holds the Sefer Haterumos term Nolad refers to Molid Davar Chadash.
 Admur 318:25
 Rashi ibid; Admur 318:25
 Sefer Hateruma ibid as understood by Ramban 51b and Rashba 51b; brought in M”B 320:33 and 318:105; See Rama 326:10
Opinion of Admur in Sefer Hateruma: Admur does not mention the term Nolad anywhere in the Halachos dealing with this prohibition. Furthermore, when explaining the opinion of the Sefer Hateruma in 318:25 regarding the prohibition to place fat near the sun he writes the reason is due to Molid. Hence, we clearly see that Admur interprets Nolad as Molid and not as Muktzah.
 Opinion in Admur 320:19 [brought in Halacha 1B], as well as 326:10 [brought in Halacha 4]; M”A 320:13; Ramban 51b; Rashba 51b; Implication of Rambam Shabbos 21:12 brought in Maggid Mishneh; brought in M”B 320:33; Vetzaruch Iyun as to why this reason was omitted here, in 320:16, which is the Halacha dealing with the reason behind the prohibition. Perhaps this is because in truth Admur holds that the main reason behind the prohibition is “Nolad” and as he himself rules in both Halachas mentioned above that one is to be stringent like the opinion which holds of the “Nolad” reason. Regarding why Admur in 318:25 mentions this reason to explain why the melted substance is forbidden, see below Halacha 4 in the footnotes.
 Admur 320:16; Michaber 320:9; Shabbos 51b
 Admur 320:19
 Some Poskim rule that this is forbidden to be done, and was included in the restriction of the sages against melting ice due to the Molid prohibition. [1st and Stam opinion in Admur ibid; Michaber 320:11; Rosh and Tosafus 51b] Other Poskim rule that this is permitted to be done, and was not included in the restriction of the sages against melting ice due to the Molid prohibition. [2nd opinion in Admur ibid; M”A 320:13 and 16; M”B 320:34; Tosefta; Ramban ibid; Rashba ibid; Ran; Maggid Mishneh 21:13]
 Admur ibid; Michaber 320:12; Biur Halacha 320:11 “Yizaher”; Shaar Hatziyon 318:146 “It is proper to initially be stringent”; So is evident also from Michaber 320:13-14 and the fact the Poskim don’t argue on the ruling on the basis that it melts into liquid. [Shaar Hatziyon ibid; See Ketzos Hashulchan 126 footnote 2 and 14]; Rav Poalim 3:14
 Admur 320:18; Michaber 320:10; Tur in name of Avi Haezri
 Admur ibid; Taz 320:8
 Admur 320:16; 318:25-27 [regarding fat]
 Some Poskim rule that this is permitted to be done. [1st opinion in Admur 320:16; 2nd opinion in 318:27; Michaber 318:16; 320:9; Ramban Shabbos 51b; Implication of Rambam Shabbos 21:12 brought in Maggid Mishneh; Smag; Smak; Rabbeinu Yerucham] Other Poskim rule that this is forbidden to be done. [2nd opinion in Admur 320:16; 1st opinion in 318:25; M”A 320:14; M”B 320:35; Rama 318:16 regarding fat; Sefer Haterumah 235; Ran in name of Sefer Haterumah; Rosh chapter 4 in name of Sefer Hateruma]
 Admur 318:27; 320:16; Rama 318:16
 Some Poskim rule it permitted to cause items to melt by removing it from the freezer so long as one does not place it near the sun or fire. [Sheivet Halevy 7:40; Az Nidbaru 6:3 and 34; 10:10; Tzitz Eliezer 6:34-30; Divrei Yatziv 159; Shabbos Kehalacha 3 17:3 and 27] Other Poskim rule it is initially forbidden to do so, just as one may not place it near the sun or fire. [SSH”K 10:3; 1:74, as is the simple Halacha ruled by Admur that one may not cause frozen water to melt. [320:16] Rav SZ”A as brought in Mioreiy Hashabbos]
 As according to the opinion which holds that the melting prohibition is due to that it is similar to the flow of juice, based on this there should be no differentiation whether it is defrosted near a flame or on its own. Vetzaruch Iyun, as if so then why did Admur permit placing it near the unlit oven and then having the gentile turn it on. [As asks the P”M 318 A”A 42 and Iglei Tal Dash 36:12] Perhaps one can answer [according to Admur] that the prohibition of Bedieved only applies when one transgressed the Lechatchila, such as one did an action to cause it to melt, however if one did not transgress the Lechatchila, such as the gentile turned on the flame, then even the Sefer Hateruma agrees it is permitted Bedieved. However according to those that hold of the reason of Nolad-Muktzah, seemingly this would not help. Vetzaruch Iyun.
 Admur 318:26; M”A 318:40; Sefer Haterumah ibid; M”B 318:105
 Admur 320:16; Michaber 320:9; Shabbos 51b
 The reason: Some say the reason is because one has not done any actions with his hands [Opinion in Admur 318:27; 320:16; M”B 320:34; Michaber 318:16; Ramban Shabbos 51b; Implication of Rambam Shabbos 21:12 brought in Maggid Mishneh; Smag; Smak; Rabbeinu Yerucham] Others say the reason is because the liquid is entering directly into the water and is hence not recognizable on its own. [Admur 318:26; 320:16 and 19; M”B 320:34] Admur rules mainly like the first reason although states the custom is to be stringent like the second reason. The practical ramification is regarding whether one may place an ice cube in the sun for it to melt, as explained in Halacha 3.
 Implication of Admur and all Poskim which do not mention that Bittul is required [However, see Admur 305:32 and 320:4]; Betzeil Hachochmah 2:26; Shivilei David 20:1; Shabbos Kehalacha 17 Biurim 25 [p. 89] and 16 Biurim 8 [p. 19-24] that every melted drop is individually nullified in 60x [explained next]
Other opinions: Some Poskim rule that one is required to have 60xv original liquid versus the melted ice. [Rosh Yosef of Peri Megadim Shabbos 51a; Implication of Admur 320:4, P”M 320 M”Z 3, M”B 320:14 regarding grapes in a wine vat that 60x is required; Peri Hagan]
 In the event that the bottle was completely frozen, then this prohibition applies according to all, as explained above in case 1.
 In the event that the bottle is only partially frozen, then this prohibition is subject to debate, although practically rule stringently, as explained above in case 2.
 See case 3 above
 See case 4-5 above
 Admur 318:24; Michaber 318:14
Other opinions: Some Rishonim rule that the decree was only made in a case that one desires to warm the food. If however one simply desires to thaw it down then it is permitted. Practically one may be lenient like these opinions in a case of need, and one who does so fulfill the Mitzvah of Oneg Shabbos. [Tzemach Tzedek Orach Chaim 37; Ketzos Hashulchan 124 footnote 36; Tehila Ledavid 318:29; Chayeh Adam 20:13; Shabbos Kehalacha 4:23 p. 211]
 See case 4 above in the brackets.
 SSH”K 10:5 in name of Rav SZ”A; Maor Hashabbos 13:44 in name of RSZ”A allows to defrost even juices near the sun
 Milk and other foods which are not eaten in their frozen state are not considered Nolad as since they are not eaten in their frozen state they are considered by people as liquids as opposed to solids even when they are frozen, and it is thus not considered a new change. Only water which is not a Chashuv item is not considered a liquid when frozen. [Rav SZ”A ibid footnote 15]
 Shabbos Kehalacha 3 17:51; Nishmas Shabbos Sechita 237; Emek Hateshuvah 47
The reason: As the Poskim explicitly rule that wine may not be defrosted. [Elya Raba 318:36; M”B 318:105] Furthermore, the above reason to differentiate only follows those that hold the prohibition is due to Sechitas Peiros while those that hold the prohibition is Nolad Davar Chadash, seemingly it should be forbidden, as it still appears like a new item.