The Laws of Shabbat
Yeshivat Har Etzion

Shiur #26: Generating Heat in a Cold Food – Defining the Prohibition

By HaRav Baruch Gigi

Translated by David Silverberg

            The Gemara (Shabbat 48a) tells that Rabba reprimanded a servant who placed a container of water over a kettle on Shabbat.  Rabbi Zeira observed this incident and questioned Rabba's response in light of a Berayta later in the chapter, which explicitly permits placing a pot of water on top of another pot of water.  Rabba replied, "There, it merely maintains [the water's heat], whereas here, it generates [heat]."

            Rashi explains that the servant placed a utensil containing cold water over a kettle of hot water.  The Berayta, which permits placing a pot of water on top of another, refers to two pots of hot water, and the individual wishes to sustain the heat of the pot placed on top.  Here, however, where the servant places a container of cold water over a kettle of hot water, the intent is to generate heat in the container, which is forbidden.

            We derive from this sugya that it is forbidden on Shabbat to generate heat within a cold food, but the precise definition of this halakha remains unclear.  We will try to explore the nature of this prohibition by studying the various views mentioned in the Rishonim.

            Generally speaking, we may point to two main approaches taken in explaining this sugya.  The first sees it as dealing with a potential Torah violation of bishul, in which case its relevance to this chapter, which deals with the Rabbinic prohibition of hatmana, seems unclear.  According to the second approach, this sugya refers to a problem involving hatmana, which seems more logical, in light of the context in which it appears.

            We will begin with the first approach, that reads the sugya as dealing with the Torah prohibition of bishul.

Tosefot

            Tosefot (s.v. mai shena) work off the clear assumption that the sugya refers to the prohibition of bishul.  They write:

It is difficult – to what [case] does this refer?  If [the water will reach the point of] yad soledet bo, then how did he [Rabbi Zeira] want to permit this, even though it is cooking?  Did he not know that a derivative of fire is the same as fire [with respect to the prohibition of bishul], as the Mishna states, 'One may not place an egg alongside a pot,' and that it says that if it boiled, one is liable [for a Shabbat violation… And if [the servant's intention was merely] to warm [the cold water], how does it conclude that this is forbidden?  The Berayta states in the chapter Kira, "A person may place a jug of water opposite a flame, not so that it will be heated, but to remove its chill" – and this refers to warming [the water], as evidenced by the sugya there… It seems to the Rashba [of Shantz] that when we allow placing a jug of water opposite a fire, this is only at a distance from the fire, where it can never reach the point of bishul.  But near [the fire] it is forbidden [to place a jug of water], even for the purpose of warming it [as opposed to heating it], lest he forget and leave it there until it cooks.  It therefore concludes here that it is forbidden [to place cold water on top of hot water].  And when the Mishna there states, "not so that it will be heated," it refers to a place where it can be heated, though the formulation is a bit forced.

Tosefot thus conclude that the prohibition stems from the concern that one may forgot to take away the water before it reaches the point of yad soledet.  It is permissible, however, to place cold water in a place where it can never reach the point of bishul.  According to this view, the expression, "it generates [heat]" refers to actual bishul, and Rabba and Rabbi Zeira debate the point of whether we allow placing the container on the pot to remove its chill, or if we forbid doing so out of concern that it may result in bishul.  (This is also the view of the Rosh, 4:3.)

Rabbenu Yona

            After proving – both from context and from the Tosefta at the end of the fourth chapter of Masekhet Shabbat – that this sugya deals with hatmana, the Rashba presents the approach taken by his rabbi, Rabbenu Yona:

He z"l explained that here the case involved placing a container on the opening of a kettle in order to conceal both with something [else] that does not increase heat, and this occurred on Shabbat, such as he covered the kettle while still daytime [before the onset of Shabbat], in which case it is permissible to expose it and then cover it [again] on Shabbat… And he wanted to conceal the container in the opening of the kettle, for we hold that it is permissible to conceal cold [food], even for the purpose of removing its chill, as we will see later.  Therefore, Rabbi Zeira initially thought that it is permissible even on a pot of water.  But Rabba forbade [this], because they allowed concealing cold [food] only with something that does not increase heat; on a pot it is [therefore] forbidden because the additional heat of the pot is discernible in it, and it is thus akin to concealing on something that increases heat, which they did not allow when [they allowed] placing a pot on another pot.  Only when the heat of the bottom pot is not discernible in the upper pot, when it merely maintains its heat, [is this permissible].  He drew proof from the Tosefta (3:14), which states explicitly, "One may conceal a kettle on top of a kettle and a pot on top of a pot."

In order to explain our sugya as referring to hatmana, Rabbenu Yona was compelled to claim that the servant placed the container of water inside the hatmana in which the kettle had been placed before Shabbat.  He had thought this was allowed by virtue of the halakha permitting hatmana with cold food, but Rabba forbade doing so because the heat in the container is increased, and thus this resembles a case of davar ha-mosif hevel, which is forbidden, even when dealing with cold food.  Rabbenu Yona supported his approach from the Tosefta, which, according to his version of the text, reads, "One may conceal a kettle on top of a kettle."[1]  This proves that the issue here is one of hatmana, and it is this Berayta that Rabbi Zeira invoked to challenge Rabba's ruling.

            We should note, however, that this case differs from the standard case of hatmana with a davar ha-mosif hevel, in that the heat of the kettle progressively decreases; nevertheless, this is forbidden on Shabbat due to the increase in the cold water's heat, which renders this forbidden even when dealing with cold food or water.  Before Shabbat, however, this would be permissible, since in truth the bottom pot is a davar she-eino mosif hevel.  We treat it as a davar ha-mosif only with respect to the halakha concerning hatmana of cold food on Shabbat itself.  Since its heat is discernible, the bottom pot is treated as a davar ha-mosif with which hatmana is forbidden even for cold food and water.  The Bei'ur Halakha writes (257):

Nevertheless, you must know that it is not actually like [something which] increases heat, for if so, then it would be forbidden even while still daytime [before the onset of Shabbat], so how did the Shulchan Arukh rule later, in 258, that while still daytime this is permissible?  The Vilna Gaon there also writes explicitly that it is forbidden only on Shabbat itself, and it appears there that this is not considered mosif hevel; rather, it means that since it generates heat in a cold item, the Rabbis likened it in this respect to [something that] increases heat, that it should be forbidden at least on Shabbat.

According to this explanation[2] of Rabbenu Yona's position, this sugya teaches that hatmana of cold food is permissible only in something that does not increase its heat at all.  Hatmana of cold food is forbidden on Shabbat in something that increases heat even if it cannot be formally classified as a davar ha-mosif hevel (because its heat continuously escapes and thus it gets progressively cooler[3]).

            The two approaches mentioned thus far, though different from one another in terms of their understanding of the Gemara, do not necessarily yield conflicting halakhic conclusions.  Indeed, the Shulchan Arukh and its commentaries mention both cases.  The Shulchan Arukh rules (318:17)[4]:

It is forbidden to place cold [food or water] (on a kettle), even just to warm it, so long as the kettle is hot enough that it could reach the point of bishul – meaning, that one's hand would immediately recoil [on contact] – if it is left there for an extended period, for the law regarding placing [food or water] on top of a kettle is the same as the law regarding placing opposite a fire.  But if it is not this hot, then it is permissible.

This follows Tosefot's reading of the sugya, whereby it forbids placing a utensil with cold water on a kettle in a place where it could potentially reach the point of yad soledet bo, given the concern that he may forget and leave it there until it reaches this point.

            Later (258), the Shulchan Arukh rules, "It is permissible while still daytime to place a utensil containing a cold item over a hot pot, for this is not similar to concealing [food] in something that increases heat."  The Vilna Gaon, in his commentary to the Shulchan Arukh, explained this ruling on the basis of Rabbenu Yona's approach to our sugya.  The Mishna Berura likewise cites this understanding of the Shulchan Arukh:

Meaning, even if he then covered the utensil and pot with garments, such that the heat of the cold item was certainly increased as a result of the pot, this is nevertheless permissible, for the pot is not considered like peat and the like, which increase heat, for in those cases [the given material] increases heat intrinsically, whereas the pot does not contain intrinsic heat.; to the contrary, its heat continuously diminishes at every moment.  Therefore, it is permissible.  [This applies] specifically to placing the cold item [there] while it is still daytime; it is forbidden, however, to place it on Shabbat under the covering of garments on the pot for it to become hot, even if there is not enough heat for it to reach the point of yad soledet bo, because they allowed hatmana for cold food on Shabbat only for the purpose of removing its chill.  In this case, where heat is generated through hatmana, it is forbidden.  And if the pot is not covered with garments, there is no prohibition against placing the cold item on it unless it can reach the point of yad soledet bo, as we see later, 318:6.[5]

As mentioned earlier, neither of these approaches yields any significant chiddush in the laws of bishul or the in laws of hatmana[6], and we may therefore embrace both as practical Halakha.  Later, however, we will address several points of contention that arise in the poskim in these contexts.  In the meantime, however, let us turn our attention to yet another approach to this sugya, which yields a very significant chiddush in the definition of hatmana – the approach taken by the Rambam.

            The Rambam writes in Hilkhot Shabbat (4:6):

One may place a kettle on top of a kettle on Shabbat, or a pot on top of a pot, or a pot on top of a kettle, or a kettle on top of a pot, and seal their opening with dough, not so that they will become hot, but rather so that they will retain their heat, for they forbade on Shabbat only concealing [food within something to retain its heat].  But placing a hot utensil on top of a hot utensil so that they will retain their heat, is permissible.  However, one may not place a utensil containing a cold item on top of a hot utensil on Shabbat, since it generates heat within it on Shabbat.  But if he placed it already the night before this is permissible, as it does not resemble hatmana with something that increases [heat].

The Rambam's version of the text of the Tosefta reads, "One may place a kettle on top of a kettle and a pot on top of a pot"[7], and in his view, this passage teaches that this arrangement does not constitute hatmana since we deal with simply placing one utensil on top of another, rather than a covering.[8]  Nevertheless, he forbids placing a utensil containing a cold food on top of a hot utensil, because it generates heat within it.

            We thus have here an entirely new halakha that the Rambam introduces in a chapter that deals entirely with hatmana.  Even though the upper utensil is not "concealed" within the lower utensil, nevertheless, if the lower utensil generates heat in the food in the upper utensil, the prohibition of hatmana applies.  The Rambam restricts this prohibition to Shabbat itself, as he allows placing the utensil of cold food on the hot utensil before Shabbat, even though it will increase the food's temperature, since this is not actual hatmana.  According to our understanding of the Rambam's ruling, we should call this halakha "the prohibition against generating heat in a cold food," and perceive it as an extension of the hatmana prohibition to situations where the food is not actually "concealed," and therefore this prohibition applies only on Shabbat, and not before Shabbat.

            We explained the Rambam's view in accordance with our understanding of this passage.  The Maggid Mishneh, however, understood this passage as referring entirely to the prohibition of bishul (as opposed to hatmana).  He writes that one may not place a utensil containing a cold item on top of a hot kettle in situations where the cold item can reach the point of yad soledet bo; even if one intends merely to warm the cold food, this is nevertheless forbidden due to the concern that he may forget to remove the utensil.  But the Maggid Mishneh's reading of the Rambam becomes very difficult in light of the Maggid Mishneh's own comments later in Hilkhot Shabbat (22:4).  There, he understands the Rambam as allowing placing a jug of water opposite a fire even at a short distance where it could potentially reach the point of yad soledet bo.  Thus, according to the Maggid Mishneh's understanding, the Rambam does not forbid warming water out of the concern that one may forget and come to violate bishul – seemingly in direct contradiction to the Maggid Mishneh's reading of the Rambam's comments in our context.  One might suggest that the Maggid Mishneh sought to establish precisely this very distinction, between a case of placing water opposite a fire, where no prohibition was enacted, and our case, which involves direct contact between the cold water and a source of heat, and there is thus more reason for concern.[9]

            According to our understanding of the Rambam, however, that the prohibition here stems not from the concern that one may forget to remove the utensil, and the potential violation of bishul, but rather as an extension of hatmana, there is no contradiction between the two contexts whatsoever.

            I believe the Rambam would allow placing before Shabbat a utensil containing a cold item on a kettle situated over the fire, even though in this case the heat of the kettle does not continuously diminish (since it sits over the fire), because this is not actual hatmana.  As we explained earlier, this extension of the hatmana prohibition applies only on Shabbat itself.  Rabbenu Yona explained the sugya as dealing with actual hatmana, a case where cloths are used to cover the pots, and we were therefore compelled to say that he allows this arrangement before Shabbat only if the lower pot's heat continuously diminishes.

            But all this presumes the Vilna Gaon's reading of Rabbenu Yona, as discussed earlier.  We may, however, explain Rabbenu Yona's comments differently.  According to the standard principles of hatmana, we would allow placing the container of cold water on the hot kettle because this constitutes hatmana with a davar she-eino mosif hevel, given that the kettle's heat continuously diminishes.  However, this sugya introduces a new provision, forbidding hatmana on Shabbat for cold food items in a davar she-eino mosif hevel if the lower utensil adds heat to the upper utensil.  As the upper utensil is warmed, heat is generated within it, and this thus becomes a situation of hatmana of a hot food item, rather than a cold food item, which is forbidden on Shabbat with a davar she-eino mosif hevel.  This would be permitted before Shabbat, since the lower pot, as mentioned, constitutes a davar she-eino mosif hevel.  This explanation of the Gemara emerges from the following comments of the Chazon Ish (37:17):

Earlier we wrote that placing a container of water over a kettle of hot water and covering it is forbidden, as this is considered concealing cold food in a davar ha-mosif hevel, given that the upper [utensil] generates heat in the entire covering, and this is not permitted for cold foods[10].  But this is imprecise, for the issue at hand is not hatmana in a davar ha-mosif hevel; were this to be the case, then it would be forbidden even while still daytime[11].  Rather, since heat reaches it, it is considered like hatmana with hot food[12], and not like hatmana with cold food.

According to the Chazon Ish, we have here a new halakha, that a cold food item in which heat has been generated assumes the status of a hot food item, and it thus becomes subject to the standard laws of hatmana.

            This gives rise to the question of what level of heat must be generated for this halakha to take effect.  According to the Rambam, this halakha forbids generating heat within a cold food item; according to Rabbenu Yona as understood by the Chazon Ish, it lends a cold food item the status of a hot food item with respect to hatmana; and according to the Vilna Gaon's reading of Rabbenu Yona, it requires that we consider the bottom utensil a davar ha-mosif hevel.  What level of heat is required for this to occur, according to each of these three views?[13]

            The Mishna Berura (258:2) writes that the food need not reach the point of yad soledet bo for this halakha to take effect, and the prohibition applies once heat is generated through hatmana.  He himself, however, in Sha'ar Ha-tziyun (258:4), raises the possibility that the prohibition perhaps takes effect only at the level of yad soledet bo, since we do not acknowledge the generation of "heat" below this level.  Furthermore, according to the Chazon Ish, who explained this halakha to mean that the food now attains the status of hot food, we would certainly require that the food reaches the level of yad soledet bo for it to attain this status.

            The Tur writes (258):

It is permissible to place a utensil containing a hot item on a pot concealed [in some material to retain its heat] so that it retains its heat and will not cool… But one may not place a utensil containing a cold item on top of a hot pot on Shabbat, because it generates heat within it on Shabbat.  If one placed it on Erev Shabbat – this is permissible, for this is not akin to concealing [food] with something that increases heat.

The Tur appears to have adopted the Rambam's position, and it is very surprising that he makes no mention of the approach taken by his father – the Rosh – in explaining this sugya.  It indeed seems that the Tur refers here to a new halakha relevant to the laws of hatmana, for were he referring here to a potential violation of bishul, this is already discussed later (318).  And if he follows the understanding of Rabbenu Yona, that this resembles hatmana of cold food, the basic principle of this halakha is mentioned already in siman 257.  He should have at least added relevant details there in siman 257, as do the Vilna Gaon and Bei'ur Halakha in their respective commentaries to siman 257.

            That the Tur designated a special siman for this halakha testifies to the fact that he refers here to a provision that is included neither in siman 318 nor in siman 257; thus, he likely followed the Rambam's view, as we explained.

            In practice, however, all the poskim ignored this halakha that seems to very clearly emerge from the comments of the Rambam and the Tur.

            The Beit Yosef seems to have indeed understood the Tur as referring to a new halakha of generating heat in a cold food item.  However, he writes that this halakha applies only to generating heat at the level of yad soledet bo – "for he had the impression that it is considered generating [heat] only if it reaches a boil"[14].  Accordingly, this halakha is of no practical relevance, since the Tur and Shulchan Arukh maintain that the bishul prohibition applies to previously-cooked liquids.  Hence, it is forbidden to bring the upper utensil the point of yad soledet in any event due to the Torah prohibition of bishul.[15]

            The Shulchan Arukh (258) makes no mention of this discussion concerning placing a kettle or utensil containing a cold item on a hot utensil on Shabbat, because he discusses these issues later (318:6-8).  Here, in siman 258, he mentions only the halakha allowing doing this before Shabbat: "It is permissible to place while still daytime a utensil containing something cold on top of a hot pot, for this is not akin to concealing [food] in something that increases heat."  The Acharonim argue in explaining the Shulchan Arukh's intent:

1)   The Taz explained that the Shulchan Arukh here deals not with hatmana, but rather with the prohibition of bishul.  This is allowed before Shabbat because the prohibition of bishul does not apply until the onset of Shabbat, whereas on Shabbat it is forbidden out of concern that it may result in bishul.  If the food is already fully cooked, or if the arrangement would not allow for it to reach the point of yad soledet bo, the prohibition does not apply.  And when the Shulchan Arukh concludes, "for this is not akin to concealing [food] in something that increases heat," he means simply that the prohibition of hatmana does not apply in this case at all.

2)   The Mishna Berura, based on the Vilna Gaon, explained the Shulchan Arukh as referring to a case where both pots are covered, in accordance with Rabbenu Yona's understanding of our sugya, despite the fact that the plain reading of the Shulchan Arukh does not appear to lend itself to this interpretation.

According to both readings, it appears that the Shulchan Arukh had no need to designate siman 258 as a separate siman, since this halakha is, in his view, subsumed under his discussion in siman 318 regarding bishul, and his discussion in siman 257 regarding hatmana.  But since the Tur allocated a siman for this halakha, the Shulchan Arukh was compelled to do so, as well, and kept his comments in this siman to a minimum.[16]

Notes:

1.         According to Rabbenu Yona's reading, the question arises as to why it is allowed to insert the upper kettle into the hatmana.  Even if the material used for hatmana does not increase its heat, this is allowed only before the onset of Shabbat, and not on Shabbat itself.  We might suggest that since this does not constitute a new hatmana, and, as we will explain in the next shiur, one may return the hatmana to the bottom pot, it is likewise permissible to insert the upper pot into the hatmana.  See Mishna Berura 318:51, and compare with his comments to 253:88; this requires further explanation.

2.         Later, we will mention a different understanding of Rabbenu Yona's approach.

3.         The Taz (258:1) writes that this applies only if the hatmana is done for an extended period of time.  If the hatmana is done for a brief period, in which the pot will not have a chance to cool, then we consider this a situation of davar ha-mosif, and the hatmana is forbidden even before Shabbat.  Most poskim, however, disagreed, and drew no distinction between the duration of time for which the hatmana is done; in all cases, if the pot continuously cools we cannot consider it a davar ha-mosif hevel in the true sense of the term.

4.         This basic principle appears elsewhere in siman 318, as well; see se'ifim 6 & 14.

5.         See also Bei'ur Halakha, where it is clear that this reading is based on the Gaon's comments, in accordance with Rabbenu Yona's understanding of our sugya.

6.         Rabbenu Yona's reading does, however, yield a very specific chiddush with respect to the law of hatmana of cold food, in that he forbids hatmana in this case with something that resembles a davar ha-mosif hevel.  But this does not entail a novel theory, but rather an extension of the prohibition of hatmana of cold food with a davar ha-mosif hevel.

7.         This is as opposed to Rabbenu Yona's version, which reads, "One may conceal a kettle on top of a kettle and a pot on top of a pot."

8.         Although the Rambam held that even a partial hatmana constitutes hatmana, nevertheless, in this case the upper utensil does not come in direct contact with the coals, and touches only the lower utensil, which is not the source of the increased heat, and it therefore does not constitute hatmana.  Furthermore, we contended in an earlier shiur that even if partial hatmana constitutes hatmana, we require that the utensil is placed on the davar ha-mosif in such a manner that it can be viewed as to some extent embedded or concealed within it.  According to this contention, placing one utensil on top of another would not comprise hatmana at all.

9.         The Even Ha-azel commentary to the Rambam (Hilkhot Shabbat 22:4) elaborates at length to explain the Maggid Mishneh.

10.       This is in accordance with the Vilna Gaon's understanding of Rabbenu Yona.

11.       We refuted this proof earlier, explaining that this is not a case of mosif hevel in the true sense of the term; we consider the bottom pot a davar ha-mosif only with respect to the laws of hatmana for cold food.

12.       Meaning, this is a case of hatmana of cold food with a davar she-eino mosif hevel, which is forbidden on Shabbat itself and permissible before Shabbat.

13.       At first glance, we might claim that heat beneath the level of yad soledet bo does not qualify as heat, for as we saw in the previous shiur, once a food's temperature drops below yad soledet, it has the status of "cold food" and hatmana is permissible.  On the other hand, we might argue that there the keli rishon is in the process of cooling, and for this reason, perhaps, we consider its food "cold" with respect to hatmana.  Here, the cold food is being warmed, and so perhaps at even a lower temperature we would recognize the presence of "heat" with regard to this halakha.

14.       See our earlier discussion concerning the comments of the Mishna Berura and Sha'ar Ha-tziyun.

15.       One might have claimed that this halakha still bears relevance with respect to generating heat in a cold, solid food that had previously been fully cooked, to which the prohibition of bishul does not apply.  However, it seems from the Beit Yosef that the prohibition against generating heat applies only to liquids; in any event, the Beit Yosef's comments are not abundantly clear and require further elucidation.

16.       I would like to apologize for the fact that we dealt in this shiur with a complicated sugya, the interpretation of which remains obscure even after our discussion.  According to my understanding, from the comments of the Tur and the Rambam a new halakha of hatmana emerges, one which the poskim ignored, as they preferred following other views among the Rishonim.