Shiur #13: Cooking with Derivatives of Solar Heat and Using a Solar-Heated Boiler ֠Part 2*

  • Harav Baruch Gigi
The Israel Koschitzky Virtual Beit Midrash

The Laws of Shabbat
Yeshivat Har Etzion

Shiur #13: Cooking with Derivatives of Solar Heat and Using a Solar-Heated Boiler – Part 2*


By HaRav Baruch Gigi

Translated by David Silverberg




The Prohibition of Toledot Ha-chama


            In our last shiur we discussed the sugya in Masekhet Shabbat (39a) where the Chakhamim and Rabbi Yossi argue as to whether cooking with toledot ha-chama – derivatives of solar heat – is forbidden on Shabbat.  The Yerushalmi held that one may cook with toledot ha-chama on Shabbat, and it writes:


There [in Babylonia] they say that [cooking in] the sun is permissible, [but cooking with] derivatives of the sun is forbidden.  The Rabbis here [in Eretz Yisrael] say that both [cooking with] the sun and [cooking with] derivatives of the sun are permissible.


All views agree that cooking with toledot ha-chama does not constitute a Torah prohibition; the debate surrounds the question of whether this is forbidden by force of rabbinic enactment.  We can more readily understand this principle according to the approach (see last week's shiur) that Torah law does not forbid cooking in the sun because this method of cooking did not occur in the Mishkan, or because the term bishul refers only to cooking with fire.  According to these approaches, we can explain that toledot ha-chama is likewise excluded from the Torah prohibition because Chazal determined that this form of heat does not constitute "fire" and this mode of cooking was not used in the Mishkan.  If, however, one explains that bishul does not include cooking in the sun because of shinui (deviation from the standard method of cooking), it is difficult to understand why toledot ha-chama would not constitute a Torah violation, whereas toledot ha-or – derivatives of fire – would violate bishul.  Cooking a food with a garment that was heated in the sun seems to entail no more of a deviation from normal procedure than cooking with a garment that was heated by exposure to fire.


            On the basis of this argument, Rav Shlomo Zalman Auerbach zt"l (Minchat Shelomo, 1:12) dismissed this understanding, and contended that the reason why bishul excludes cooking in the sun has nothing to do with the factor of shinui:


Although Rashi wrote in Shabbat (39a) – regarding the fact that according to all views cooking in the sun is permissible – that this is because "this is not the standard method of cooking," it nevertheless would seem that even in a manner which is commonly used for cooking with the sun, such as a dud shemesh [solar-heated boiler] and the like, one would likewise be exempt [from punishment], as we see from the hot springs of Tiberias, that if we say that [the waters are heated by] passing by the entrance to Gehinnom, it would constitute a derivative of fire and [one] would be liable [for cooking with it]; otherwise, it would be a derivative of the sun, and [one] would be exempt [from punishment if he cooks with it].  Additionally, this distinction between fire and the sun is mentioned also with regard to the paschal offering, matza and challa, etc. and there it makes no difference whether it is customary or not.  Necessarily, then, Rashi meant in his remarks that this is not called bishul.[1]


The explanation we mentioned that cooking in the sun is "natural" – rather than "human" –  cooking is the most difficult to sustain in light of the exclusion of toledot ha-chama.  This theory can stand so long as we deal with cooking in the sun itself.  But when one cooks with a garment that was heated by the sun, this cooking is clearly not a natural process; to the contrary, the individual harnesses the solar heat for his needs, precisely as in the case of a garment heated by exposure to fire.


            I would therefore suggest that we explain this issue in the following manner.  The prohibition of bishul requires a heat source, and this includes only the actual source of the heat.  Toledot (derivatives) earn significance only insofar as they store within them the heat of the original source.  Hence, the moment Halakha established that fire is the sole heat source with which one violates the prohibition of bishul, all its derivatives likewise become included, as they contain the heat of fire.  But since the sun is not deemed a heat source with respect to the bishul prohibition – for the various reasons mentioned in our last shiur – its derivatives similarly do not qualify for bishul, since they received all their heat from the sun, and we cannot afford them a higher status than their source – the sun itself.


            The Yerushalmi, as stated, permits cooking with toledot ha-chama.  In the Bavli, however, the majority view – of the Chakhamim – forbids cooking with a derivative of solar heat because it might be confused with a derivative of fire.  We may suggest two approaches in understanding this gezeira (rabbinic enactment):


1)   Observers might mistakenly think that the cooking is done with a fire derivative and thus suspect the individual of violating Shabbat (mistaken identity of the item currently being used);

2)   People might mistakenly conclude that cooking is permissible with fire derivatives, as well (a mistaken halakhic conclusion).


The practical difference between these two explanations will arise in a case of a derivative of solar heat that cannot be erroneously misidentified as a derivative of fire, such as cooking on a hot rooftop, which quite obviously received its heat from the sun, and not from fire.  According to the first approach, we would allow cooking on a hot rooftop, since nobody would suspect the individual of cooking with fire; according to the second understanding, however, we would forbid this form of cooking, as people may mistakenly allow cooking with derivatives of fire, as well.


            Rashi, commenting on this sugya, writes, "An observer will think that it is a derivative of fire," clearly following the first explanation mentioned above, and we should thus, according to Rashi, permit cooking on a hot rooftop.  One might, however, respond that the Sages drew no distinctions between the various forms of toledot ha-chama and forbade using it for cooking in all instances, even where the reason for the basic prohibition does not obtain ("lo pelug rabbanan").


            The Rambam explicitly applies this prohibition to all instances of toledot ha-chama, without distinguishing between its various forms (Hilkhot Shabbat 9:3):


If one breaks an egg in a hot garment, or in sand or dust from the roads, which had become hot from the sun, even if it is roasted, he is exempt [from punishment] because derivatives of solar heat differ from derivatives of fire, but [the Sages nevertheless] forbade them out of concern for derivatives of fire.


The Rambam forbids cooking even with sand or dust that was heated by the sun, which obviously cannot be confused with a derivative of fire.  This indicates that he either subscribed to the second approach mentioned above[2], or felt that Chazal drew no distinctions and extended the prohibition even to situations where the reason does not apply.


            The Gemara records a Berayta in which Rabban Shimon Ben Gamliel allowed roasting an egg on a hot rooftop.  The question arises, did Rabban Shimon Ben Gamliel follow the view of Rabbi Yossi, who permitted cooking with toledot ha-chama, or did he follow the majority view, forbidding toledot ha-chama, and nevertheless allowed cooking on a rooftop?  Most Sephardic Rishonim explain in our sugya that Rabban Shimon Ben Gamliel followed Rabbi Yossi's position, but Halakha accepts the Chakhamim's position, and thus all toledot ha-chama – including rooftops – are forbidden.  The Ramban writes:


And that which the Berayta states, "Rabban Shimon Ben Gamliel says, one may roast an egg on a hot rooftop…" – Halakha does not follow this view, for he follows Rabbi Yossi.  But the Rabbis, who forbid [cooking an egg] with [heated] garments, would likewise forbid [cooking] on a hot rooftop, since both constitute derivatives of the sun.


The Yerushalmi similarly indicates that roasting an egg on a rooftop would not be permitted according to the view of "the Rabbis there" (in Babylonia), who forbid cooking with toledot ha-chama:


The Berayta disagrees with the Rabbis there, for the Berayta states: "Rabban Shimon Ben Gamliel says, one may roast an egg on a roof of boiling hot plaster, but one may not roast an egg on hot earth."  What would the Rabbis there do with this?  They would answer that they disagree with Rabban Shimon Ben Gamliel."


The Yerushalmi thus explicitly asserts that Rabban Shimon Ben Gamliel disagrees with the Chakhamim.  The Meiri, however, appears to maintain that Rabban Shimon Gamliel stated his halakha even in accordance with the Chakhamim, as he writes, "But [an egg] may be roasted on a hot rooftop, that was heated by the sun."[3]


            The Maharshal (Teshuvot, 61) elaborates on this topic and concludes that we should forbid only those forms of toledot ha-chama that could be mistaken for derivatives of fire.  He maintains that Rabban Shimon Ben Gamliel stated his view in accordance with the Chakhamim, and they, too, would agree that one may cook on a rooftop.


            However, as far as the final halakha is concerned, since, as we have seen, most Rishonim understood the Chakhamim as forbidding all types of toledot ha-chama, we should follow this stringent position.  Indeed, the Acharonim forbid cooking with any toledot ha-chama; see Shulchan Arukh (318:3) and Mishna Berura (318:20).  In situations of dire need however, we may take into account the Maharshal's view; we will return to this point later, in our discussion of solar-heated boilers.


Cooking an Item that Had Been Cooked by the Sun or Derivatives of Solar Heat


            The Peri Megadim (Mishbetzot Zahav, 318:6) raises the question concerning a food that had been cooked before Shabbat by the sun or a derivative of solar heat – which does not constitute bishul on Shabbat – whether one violates Shabbat if he cooks this food on Shabbat over fire or with a fire derivative.  He concludes, "It would seem that he is exempt, because it has already been impacted [= prepared for consumption]; it might possibly be altogether permissible."  The Peri Megadim's ambivalence touches upon the question of whether cooking in the sun or a derivative of solar heat is deemed "cooking" but nevertheless does not render one liable on Shabbat, or is not classified as "cooking" at all.  According to the second possibility, we should perhaps equate an item that had been cooked by solar heat with foods that can be eaten raw, to which the prohibition of bishul applies.


            We might also explain that the Peri Megadim here inquires as to the meaning of the principle of ein bishul achar bishul (bishul does not apply to previously cooked foods).  Is this a practical rule, that once a food has been prepared for consumption an additional act of cooking does not qualify as food preparation?  If so, then we would apply ein bishul achar bishul even to foods that had been cooked through solar heat, even if this type of cooking does not qualify as "bishul" at all.  Alternatively, one might explain the principle of ein bishul achar bishul as relating to an item's formal status as "mevushal" ("cooked")[5], in which case an item cooked in the sun – if we assume that it does not obtain the status of mevushal – would not be subject to bishul.  The Peri Megadim concludes that the food has the status of cooked food, and we therefore apply the principle of ein bishul achar bishul.[6]


            The Iglei Tal (Ofeh, 44) held that cooking in the sun does not qualify as "cooking" at all, even for purposes of cooking the korban pesach,.  He contended that if one boiled a korban pesach in toledot ha-chama and then proceeded to roast it, it is considered roasted and hence permitted for consumption.  (Recall that a korban pesach must be eaten roasted, and not boiled.)  Since Halakha does not classify cooking with solar heat as bishul, the meat is considered only roasted.[7]  He writes (Ofeh, 15:9), "Since cooking with the hot water springs of Tiberias is not considered bishul with respect to the prohibition against [eating the korban pesach] boiled, by the same token, if it is boiled [with this water] and then roasted, it is permissible."


            He linked this discussion to the issue of bishul on Shabbat on the basis of the Yerushalmi (Shabbat 7:2), which records a debate if one may cook on Shabbat with the hot water springs of Tiberias, and then applied this debate to the situation of a korban pesach that was boiled in this water and then roasted.  The Iglei Tal thus clearly felt that the status of cooking with solar heat on Shabbat, and its status regarding the korban pesach, are dependent upon one another.  In his view, then, if one would cook over fire on Shabbat an item that had previously been cooked with solar heat, he would violate bishul.  The rule of ein bishul achar bishul would not apply in such a case, because this food had not previously undergone formal bishul.


            The Iglei Tal's proofs are not compelling and may be refuted.  Practically speaking, it would appear that one may rely on the Peri Megadim's position, that one may cook over fire food that had been cooked with solar heat.  I found that the Minchat Chinukh (mitzva 7) likewise addressed this question:


Would we say that it was, after all, cooked, only a gezeirat ha-Katuv [ordinance of the Torah] dictates that one is not liable for [cooking with] toledot ha-chama, but nevertheless in this respect it is considered "cooked" in that a subsequent cooking would not be considered anything, and one would be exempt?  Or, since it does not constitute cooking for purposes of Shabbat, it is thus not bishul, and one would be liable [for cooking] afterwards.


He ultimately leans towards relying on the aforementioned ruling of the Peri Megadim, both with respect to Shabbat and regarding korban pesach.


Using a Dud Shemesh on Shabbat


            As we approach the issue of using hot water from a dud shemesh (solar-heated boiler) on Shabbat, we must first clarify the technical facts and then address two questions: Does the problem with a dud shemesh involve cooking in the sun, or cooking with a derivative of solar heat, and do we consider the entry of cold water into the dud shemesh the individual's direct act, or merely gerama – an indirect result of his actions?


            The dud shemesh consists of a boiler into which cold water enters from the household faucet (the entrance is located on the bottom side of the boiler), from which it passes into black, glass-covered pipes called koltim.  The hot water then enters the household's faucets from the upper part of the boiler, where the water is hotter.  Generally, the departure of hot water from the boiler causes other, cold water to enter in its place, which is heated in its initial encounter with the water already in the dud, or when it is passed into the koltim.


Halakhic questions concerning a dud shemesh:


1)   If the cold water entering the boiler is heated inside the boiler from the heat of the hot water already there, then this clearly constitutes cooking with toledot ha-chama, which is forbidden mi-de-rabbanan.

2)   If the water is heated only when it passes into the pipes, it would seem that this, too, involves cooking with toledot ha-chama.  We cannot consider this process as cooking with the heat of the sun directly, which is permissible, because the primary heating results from the heat of the pipes, which became hot already before this water entered.  Even if the sun would be concealed, the pipes themselves would heat the water.

3)   We discussed in an earlier shiur that pipes through which hot water passes from a keli rishon have the status of a keli rishon.  This would likewise apply in the case of a dud shemesh.  Even though the heating process occurs in the pipes, the entire system, including the pipes and the boiler, constitutes a keli rishon and thus has the capacity to effectuate bishul.  Recall, however, that we deal with toledot ha-chama, so the bishul here is forbidden only mi-de-rabbanan.

4)   We must also take into account the consideration that when one turns on a faucet he does not intend for cold water to enter the boiler and be heated; his objective is strictly to release hot water from the faucet.


In my opinion, none of these claims suffices to definitively allow using hot water from a dud shemesh on Shabbat.  As far as the cold water entering the system is concerned, it would seem that at least the initial flow of water would qualify as a direct act of the individual, since by removing the obstruction one allows water to enter the system.  This situation would resemble a case discussed in Masekhet Sanhedrin 77b:


Rav Papa said: One who bound his fellow and directed the freshet towards him – this is his "arrows," and he is liable [for murder].  This applies only in [situations of] ko'ach rishon [a direct result of his action]; in [situations of] ko'ach sheni [a result of a result of his actions], this is merely gerama.


Rashi explains, "He turned the flow of water upon him; these are his arrows, and he is considered as if he had shot an arrow at him."  The same principle would seemingly apply in our context.  The initial rush of water into the boiler would constitute ko'ach rishon, the direct result of the opening of the faucet, and the individual would thus be considered as having actually placed water into the system.


            In truth, however, this conclusion is far from simple.  Many Acharonim held that since opening the faucet merely removes an obstruction, this cannot be deemed a direct action, and rather constitutes gerama.  In the case in Sanhedrin, the killer actively channeled the flow of water towards the bound victim, whereas here, one merely removes the valve which allows the water to flow.  This might entail ko'ach sheni, rather than ko'ach rishon.


            And although Rav Ovadya Yosef (Yabi'a Omer, 4:34) writes that one must be stringent in this matter with regard to Torah prohibitions, in this case, perhaps, where we deal with the rabbinic prohibition of cooking with toledot ha-chama, we might allow relying on the lenient positions, which consider this a situation of gerama.  This issue requires further clarification.


            As far as the person's intent is concerned, the fact that he does not intend to heat the new water is of no consequence; since the water will invariably enter the system and be heated – a case known as pesik reisha the act would be forbidden regardless of his indifference towards the heating of the water.


            Nevertheless, Rav Ovadya Yosef (ibid.) discusses this issue at length and permits using hot water from a dud shemesh, based primarily on two contentions:


A. We deal with toledot ha-chama, with which cooking is forbidden mi-de-rabbanan; therefore, those who follow the rulings of the Shulchan Arukh may rely on his ruling that in instances of a rabbinic prohibition, one may perform a pesik reisha – an act that will incidentally but invariably result in a melakha.  The Shulchan Arukh issues this ruling concerning a case of a knife that was thrust into a barrel before Shabbat, where he permits removing and returning the knife, even though this results in the expansion of the hole, thereby creating an opening to the barrel (314:1).  The Rama, however, disagrees, and writes, "[This applies] only if he also removed it once before Shabbat; but if he had not removed it before Shabbat, it is forbidden because it is a pesik reisha, as he creates a hole and opening for the barrel."  The Acharonim understood this debate as revolving around the issue of whether we permit a pesik reisha where the violation that results from the given action is only of rabbinic origin.  The Mishna Berura writes:


It [the knife] is thrust tightly, such that as a result of its removal and placement it is certain that the hole will expand.  Nevertheless, since the actual prohibition is only of rabbinic origin, he [the Shulchan Arukh] holds that it is permissible, since [the individual] does not intend for this [to occur].  The Rama here intends to disagree with him, [claiming] that [this is allowed] only if he had removed it once before Shabbat, such that it thereby expanded somewhat [already before Shabbat], and it is therefore not certain [that it will expand when he removes the knife on Shabbat].  Otherwise, this is forbidden, because it will certainly occur; for although this is an opening that is not made for removing and bringing in [items through it], which is forbidden only mi-de-rabbanan, as mentioned above, he [the Rama] maintains that a pesik reisha is forbidden even with regard to a rabbinic prohibition.


B. Even if we wish to abide by the view that forbids pesik reisha in cases of a rabbinic prohibition, here we have more reason to rule leniently because this is a situation of lo nicha lei – the individual has no interest in the resultant melakha.  In such situations, many authorities rule leniently when dealing with a rabbinic prohibition.  (See, for example, Tosefot, Shabbat 103a.[8])  However, some Acharonim rule stringently even in such cases, and permitted a pesik reisha de-lo nicha lei only when what is at stake is two rabbinic prohibitions; this is the position of the Mishna Berura (337).


            The reason why the case of a dud shemesh involves a situation of pesik reisha de-lo nicha lei is, seemingly, because the boiler is generally large enough to provide enough hot water for one's essential needs on Shabbat: washing one's hands and face, washing infants and washing dishes.  (Bathing one's entire body in hot water is forbidden on Shabbat for other reasons.)  Therefore, one has no need for additional water to come into the boiler on Shabbat.  On the other hand, one might contend that a person has interest in additional water entering the system so he has hot water ready immediately after Shabbat.  This question would thus touch upon the more fundamental issue regarding the definition of nicha lei, namely, the status of an action in which a person has interest, but not interest that concerns a Shabbat prohibition.  This issue clearly requires more thorough elaboration in a separate context.[9]


            Furthermore, one might argue that if the water is heated not immediately upon entering the boiler (because the water on the bottom is not hot enough to heat the incoming water), but only when it reaches the pipes, the heating of the water occurs not through ko'ach rishon – the direct result of the individual's action – but rather through ko'ach sheni – an indirect result.  We would then classify this case as gerama, and when dealing with a situation of a pesik reisha resulting in a rabbinic violation through gerama, it stands to reason that this should be allowed.


            We might add yet another consideration for allowing use of a dud shemesh, namely, the aforementioned position of the Maharshal, who held that one may cook on Shabbat with a type of toledot ha-chama that cannot be confused with fire or a derivative thereof.[10]  Of course, it is far from clear that use of a dud shemesh cannot be mistaken for use of fire-generated heat, since at times – especially during the winter – a person adds electric backing to the heating process of the dud shemesh.


            In summary, it would appear that the matter remains subject to dispute, and we therefore conclude upon the following practical guidelines:


1)   One should preferably refrain from using hot water on Shabbat from a dud shemesh.

2)   Those who do use hot water from a dud shemesh on Shabbat have authorities upon whom to rely, particularly given that we deal with a rabbinic prohibition.

3)   Water from a dud shemesh may be used on Shabbat for the purpose of bathing infants or for washing hands or dishes if a person's hands are particularly sensitive to cold.

4)   This entire discussion applies only if there is no electric backing to the boiler.  If electricity is involved, then we deal with a possible Torah violation, even if the electricity is currently turned off.

5)   Notwithstanding what we just mentioned, if the boiler works only on electricity which is currently turned off, and it is not attached to a central heating system, and one can be certain that the water in the boiler is not hot enough to heat the new water that comes in, one may turn on the hot water.  As mentioned, use of an electric boiler entails a possible Torah violation, so one may employ this leniency only when he can ascertain beyond reasonable doubt that the new water will not be heated.

6)   Some recent water heating systems are equipped with a mechanism that prevents new water from entering the system.  Most systems do not feature such a mechanism, but one who knows for certain that he has such a system may use the hot water without any concern, since no new water will enter the system and be heated.




* This shiur is a continuation from last week's shiur, and should be studied in conjunction with it.


1)         It is not altogether clear from the Minchat Shelomo why cooking in the sun is not considered "cooking."  He perhaps held like the view we cited from the Rambam and others that the Torah prohibition of bishul pertains only to fire and its derivatives.


2)         The Maharshal (siman 61) adopted this understanding of the Rambam's position:


But one who sees that toledot chama are permissible will then say that a derivative of fire is likewise permissible, for with respect to derivatives the onlooker will think that no distinction is drawn between them, because in the end they are both heated through another item and it constitutes a subcategory of bishul.


3)         One might contend that the Meiri considered cooking on a hot rooftop equivalent to cooking in the sun directly, rather than toledot ha-chama, but this does not seem reasonable at all.  The Rif in this sugya brings several views among the Amora'im in interpreting Rabban Shimon Ben Gamliel; now if Rabban Shimon Ben Gamliel was following the view of Rabbi Yossi, which Halakha does not accept, the Rif would have no reason to record in his work the Talmud's discussions concerning Rabban Shimon's position.  The Ramban explained, "…even though he [the Rif] wrote the reasons [given by] Rabba and Rav Yosef for Rabbi Yossi in order to explain our Mishna, with which Rabbi Yossi agrees."  His answer is difficult to understand.  See also below, in our discussion of the Maharshal's view.


4)         We discussed this subject in an earlier shiur which dealt with the issue of cooking raw fruits.  According to the Peri Megadim's conclusion, we would explain that here one merely increases the food's temperature, whereas the taste of a fruit undergoes a significant change through the process of boiling.


5)         Compare this rationale with the formulation of the Tosefta (Shabbat, end of chapter 15), "One may bake that which was already baked, and cook that which was already cooked."


6)         In his closing remarks, the Peri Megadim refers us to the next se'if, where he addresses the topic of boiling an item that had been previously baked.  His intention, perhaps, is to compare cooking with fire an item that had been cooked in the sun to the case of boiling an item that had been previously baked.  Clearly, however, there is no comparison between the two cases: when one boils a previously baked item, the food's taste changes as a result of the second mode of cooking from the taste of a baked item to that of a boiled item.


7)         Whereas we generally maintain that one violates a Torah prohibition if he eats meat from a korban pesach that was boiled and then roasted, the Iglei Tal contends that if one boiled it with the hot springs of Tiberias and then roasted it, it may be eaten, since bishul does not occur with derivatives of solar heat.


8)         The Yabi'a Omer there discusses this issue at length.


9)         See Yabi'a Omer, ibid.


10)       Although most Acharonim, as mentioned earlier, rule against the Maharshal's view, we may nevertheless include his position as one of several factors to allow using a dud shemesh.