Koschitzky Virtual Beit Midrash
The Laws of Shabbat
Yeshivat Har Etzion
Generating Heat in a Cold Food – Defining the Prohibition
By HaRav Baruch
Translated by David
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]."
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.
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.
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.
will begin with the first approach, that reads the sugya
as dealing with the Torah prohibition of bishul.
Tosefot (s.v. mai shena) work off the clear assumption that
the sugya refers to the prohibition of bishul. They write:
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
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.)
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:
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
proves that the issue here is one of hatmana, and it is this Berayta
that Rabbi Zeira invoked to challenge Rabba's ruling.
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):
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 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).
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):
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
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.
(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:
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.
As mentioned earlier, neither of
these approaches yields any significant chiddush in the laws of bishul
or the in laws of hatmana, 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.
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
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", 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. Nevertheless, he forbids placing a utensil
containing a cold food on top of a hot utensil, because it generates heat
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.
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.
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.
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.
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):
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. 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. Rather, since heat reaches it, it is
considered like hatmana with hot food, 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.
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?
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.
Tur writes (258):
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
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.
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.
practice, however, all the poskim ignored this halakha that seems
to very clearly emerge from the comments of the Rambam and the Tur.
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". 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
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
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
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.
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
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
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
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
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
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
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.