Answer by Rabbi Chaim Hillel Raskin – rov in Kfar Chabad Beis, Israel:
Chazal prohibited crushing ice to produce water on Shabbos, and Rishonim offer different reasons why: (1) forming a new entity (borei), (2) the resulting liquid is nolad (a new entity which is muktza).
Taking ice out of the freezer and allowing it to melt on its own is not an active deed of producing water, though the resulting liquid is nolad. The Alter Rebbe advises being stringent except when there is a need.
Placing liquid in the freezer also results in a new entity, ice, coming into existence in a passive manner. Some poskim write that since ice generally becomes water, but water doesn’t become ice at room temperature, ice is considered a new entity according to all opinions.
Others write that it is the same as melting, and one should only freeze when there is a pressing need (i.e. food that will spoil if not frozen).6 A third opinion is that since ice doesn’t last, it isn’t considered a new entity at all, and can be created according to all opinions, (especially when the food item isn’t improved by freezing, e.g. all foods besides ices and ice cream).
Chazal say that creating a mass of cheese on Shabbos is an offshoot of boneh, “building.” Poskim explain that ice is different since (a) there are no particles that need to pressed together, (b) ice has no lasting “structure,” unlike cheese or a building.
In practice, the middle opinion is followed and liquid may be frozen in case of great need, such as food that will deteriorate, ice cubes on a hot Shabbos day, or ices for a children’s program (when one forgot before Shabbos).
Freezing leftover food or soup to preserve their flavor is not considered to be preparing for after Shabbos, since it is standard practice to put away food after use to prevent it from deteriorating.
Placing drinks in the freezer to chill is definitely permissible, and there is no concern that they will be left to freeze, (as the concern exists by warming liquids near a source of heat). The reason is that freezing is certainly not a Torah prohibition, and is even permissible according to some.
One may also place liquid in the freezer even shortly before Shabbos so that it will freeze on Shabbos, since one did not do anything at all on Shabbos.
Published by The Weekly Farbrengen, published by Merkaz Anash. See sources
if you turn it off before shabbos, the ice may be used.
If the icemaker is left on, you cannot use the ice on shabbos, since it detects that the amount of ice is going down and therefore makes more ice.
What about a freezer that has a waterline and automatically makes its own ice? Does that have to be disabled for Shabbos? Can you use the ice it produces on Shabbos?