As we learned in the previous section, if food was placed on a plata before Shabbat, even those who are stringent permit removing this food from the plata and replacing it. Therefore, if food was placed on the periphery of the plata before Shabbat, one may move it to the center to allow it to heat more effectively on Shabbat, since it was already on the plata and this is not considered a new placement. Of course, this only applies to food that is fully cooked. If the food is not fully cooked, any action that raises the temperature of the food will cook it, and is thus prohibited by Torah law.
Similarly, one who uses two platas may move a pot from one to the other on Shabbat, as long as the food in the pot is fully cooked and still hot. If one placed a pot of fully cooked food on a blekh before Shabbat, and the fire underneath it goes out on Shabbat, he may move the pot to a second blekh or plata. As long as the food is still hot, it is clear that it was on the plata before Shabbat, and moving it to a different plata is thus considered haĥzara and not initial placement.
When one wishes to heat numerous foods for Shabbat, one may place two layers of pots on the plata. Friday night’s food may be placed in the lower level of pots and removed when needed for the meal. The pots that were on top of them may then be placed on the plata, as long as the food in them is fully cooked. This is not considered a new placement as long as they are yad soledet bo and the person’s intention was always to place them directly on the plata once there was room to do so.
If one wishes to warm up fully cooked food, and there is an open fire, one may cover the fire with a blekh, set a plate on it (following the position of most poskim, quoted above in section 18), and place the food upon the plate. Even if this covering changes the shape of the flame, it is not prohibited since the strength of the fire remains unaffected (SSK ch. 1 n. 66).
. Some are stringent, however, maintaining that since the fire underneath it went out, it is as if the pot is resting on the ground. Thus, if one wishes to move it to a different plata, it is considered a new placement, and is prohibited unless he places an overturned plate underneath the pot. This is the opinion of SSK 1:27. However, n. 79 there cites R. Shlomo Zalman Auerbach’s rationale for leniency. Igrot Moshe takes the latter approach as well in OĤ 4:74, Bishul §38, and this is also the opinion of R. Shmuel Wosner and R. Yosef Shalom Elyashiv as cited in Otzrot Shabbat 70:89-90. This whole discussion is only relevant for the stringent approach, which does not allow placing cold food on the plata, as explained in section 18 and n. 19. But for those who are lenient and maintain that one may put fully cooked cold food on a plata (Yeĥaveh Da’at and Igrot Moshe), one may certainly be lenient in this case.. However, some are stringent and maintain that since the pots on the top level were not resting on the plata, moving them directly to the plata would be considered a new placement, which is forbidden according to the stringent opinion described in section 18. This is the approach of SSK 1:44, Ĥazon Ish 37:11, and Shevet Ha-Levi 1:91. (Ĥazon Ish also maintains that one may not place these pots on top of an empty pot, as explained in Az Nidberu 3:14.) In SSK n. 125 is mentioned the rationale of R. Shlomo Zalman Auerbach to be lenient and rely on the position of Ran. Since we saw in section 18 that some maintain that le-khatĥila one may place fully cooked cold food on the plata, in this case even those who are usually stringent may be lenient le-khatĥila.
There is another case where the poskim disagree about haĥzara: If there is a large pot on a plata or blekh whose heat source is covered, may one pour its contents into a smaller pot, and then place the smaller pot on the plata? According to MA 253:20 this is forbidden, while according to SHT 253:47 this is permitted. Therefore SSK ch. 1 n. 49 and Brit Olam, dinei hashhaya ve-hatmana §17, state that le-khatĥila one should be stringent, but if necessary one may be lenient. It seems reasonable to be lenient in this case even le-khatĥila, since we can also invoke the opinion allowing one to place things on the plata le-khatĥila (see section 18 above). Regarding liquids, as explained in n. 12, some maintain that according to SA 253:4 it is forbidden because of the possible prohibition of cooking. But Rema and other poskim maintain that even according to SA, in times of necessity it is permitted.