Rabbi Mendel Agranovich
Definition and General Concepts
We are beginning the final topic related to cooking—the prohibition against insulating food.
Let us define insulation: wrapping a pot containing food, or the food itself, to preserve or add heat.
The Talmud (Shabbat, 34b) distinguishes two separate aspects of this prohibition, each with its own reason and explanation.
1) The prohibition against insulating food in such a way that heat is added during Shabbat. Specifically, a pot may not be wrapped in any material that gives off heat, whatever kind of heat it may be. For example, red-hot sand, carbonate, or rotting olive pomace—all are prohibited. This prohibition applies both on Friday and on Shabbat. The reason is that this form of insulation may lead someone to assume that, just as food may be buried in hot sand, it may also be buried in sand or earth mixed with smoldering coals. After all, what difference does it make? And one might then stir the coals, which is already prohibited by the Torah. Our Sages therefore ruled out this entire form of heating and retaining warmth (by adding even small amounts of heat). And since there is no distinction, and heat is added even on Shabbat itself, such a setup may not be arranged before Shabbat and left in place for Shabbat. Its resemblance to the “sand with coals” system remains, and the reason for the decree still applies.
2) The prohibition against insulating food even if the heat is only retained. In other words, even wrapping a pot in blankets or towels is prohibited. But this method is prohibited only on Shabbat itself. Before Shabbat, a pot may be surrounded with blankets or pillows and left there—without any additional heat being supplied. Interestingly, the Talmud distinguishes between dry sand, a material that does not add heat, and wet sand, which does, and the same is true of wool. Some types of dry wool merely insulate, while other types release additional heat because of moisture and decomposition. This is why sand is sometimes classified in the Talmud under different categories of materials. Sometimes it is among those prohibited for insulation only on Shabbat itself, and sometimes it is prohibited even before Shabbat.
The reasons given in the Talmud for the second prohibition are as follows. To create an insulating system, the food must be heated as much as possible, brought to a boil, so that it takes as long as possible to cool. A person might therefore heat the food on Shabbat before insulating it and violate either the prohibition against kindling a fire (by stirring the coals) or the prohibition against cooking (by placing cooled food on the fire) [this is a dispute between Rashi and Rashba; see our introductory article on all the prohibitions instituted by the Sages, as well as the article on cooking previously cooked liquids, where these passages from the Talmud were analyzed in detail]. Since the main concern behind this prohibition is connected with the actual moment of insulating the food, it is permitted if we placed the food in blankets before Shabbat.
By the way, those who do not want to leave a hot plate or blech on during hot summer Shabbats, but also do not want to eat cold food in the morning, can wrap mashed potatoes or something else before Shabbat, thus solving the problem of an extra source of heat in the home. Just put the food in the blankets while it is piping hot, and do not skimp on layers, so that the food does not spoil or go sour by morning.
Try a few experiments before Shabbat so that you do not find yourself without food on Shabbat. The first time, you can also leave food both on the blech and in blankets and see how it turns out.
It is important to understand what it means to “wrap a pot.” Does it mean wrapping it on all sides and over the top, or is even partial wrapping forbidden? And what about the usual method: placing it over the flame and putting a towel over the lid to retain heat? Is that also wrapping, or not?
There is a dispute among the Rishonim on this subject: Tosafot (Rabbeinu Tam and others), as well as the Ramban, held that partial wrapping is not forbidden, while the Rashba and Rabbeinu Yonah held that this, too, falls under the Sages’ prohibition. This dispute is reflected in halachah. Rabbi Yosef Karo held that the halachah follows the Rashba, while the Rema leaned toward ruling on the basis of the opinion of Tosafot and others. It would therefore seem that the halachah in this matter should depend on one’s background: Sephardi Jews may not wrap a pot partially, while Ashkenazi Jews may. However, the Chazon Ish agreed with Rav Karo on this matter, so there is also room for stringency among Ashkenazi Jews.
Another point: does placing a pot in an oven constitute wrapping? Heat clearly reaches it from all sides, but there is no covering at all. Our readers may object: we have already written about ways of using an oven on Shabbat that are permitted by halachah. So what is our uncertainty? Our answer is that we simply want to draw a clear distinction between the prohibition against wrapping and other situations. The Shulchan Aruch clearly distinguishes between “wrapping” and “leaving” a pot on the flame (257, 8). Rav Karo’s definition of wrapping is as follows: whenever the sides of the pot touch coals, blankets, or other wrapping materials, this constitutes wrapping. If nothing touches the sides of the pot, it is simply being left on the flame. The “Mishnah Berurah” (ibid., section 45) notes that the Shulchan Aruch considers partial contact with coals to be wrapping in keeping with his consistent position, discussed above: partial wrapping is forbidden. According to the Rema, only completely wrapping the sides falls under the Sages’ prohibition against wrapping. It should also be noted that if the pot is standing on coals, and all the more so if coals have been piled around its sides, a new problem arises. The coals move when the pot is removed from them. What should be done? The Rema and the “Mishnah Berurah” (253, 51) advise using the help of a non-Jew in this case, but in our circumstances this is practically not an option; we mention it only as an illustration.
The Sages did not prohibit wrapping cold food in materials that do not add heat.
Practical conclusions:
A pot of hot food may not be wrapped in any way on Shabbat. Cold food may be wrapped only in materials that insulate it, rather than generate heat.
Food may not be wrapped in any materials that generate heat, even before Shabbat.
You may place a pot on a blech or hot plate and cover it partially with a towel, leaving part of the pot uncovered. According to the Chazon Ish, this is forbidden. The custom in Ashkenazi communities is to be lenient in this matter, following the Rema and the “Mishnah Berurah” (“Orchot Shabbat” 2, 78, 135-137).
“Partially” means that a substantial part of the pot is not covered by anything. This allows heat to dissipate.
It does not matter whether the uncovered area is at the top or the bottom.
Even if the covering on the outside of the pot extends over the full height of the food inside, this is permitted, since it is considered partial wrapping.
Covering only the pot’s lid with a towel is permitted; even according to the Chazon Ish, this is not considered wrapping.
Placing a pot in the oven before Shabbat is not wrapping, since the Sages prohibited only covering the surface of the pot, not heat reaching it from all sides (“Orchot Shabbat” 2, 78-81, and the notes to these sections).