Shiur #02: III) Heat Source

  • Rav Yosef Zvi Rimon







This week’s shiurim are dedicated by Leonard Balanson
in memory of Rose Balanson z”l





III) Heat Source



The Prohibition of Bishul — Action or Result?


Is it the specific action of bishul that is forbidden, or is any action that brings about the result of bishul prohibited?  In other words, is there a possibility to cook on Shabbat in a way that is not forbidden, or perhaps any act that brings the food to a cooked status is forbidden?


Cooking by Indirect Solar Heat


The Mishna (38b) states:


One must not place an egg at the side of a kettle for it to be rolled [cooked],[1] and one must not break it into a cloth [that was heated up by the sun]; but Rabbi Yosi permits it.  Furthermore, one may not put it in sand or road dust for it to be roasted.


This mishna deals with two ways to cook an egg: toledot ha-esh (igneous byproduct) and toledot ha-chamma (solar byproduct).  In each case, the egg is not being fried directly; instead it is an object that has been heated up for another purpose or for no purpose at all that is being utilized to fry the egg: the kettle has been heated over a flame, while the cloth, sand or dirt has been heated by the sun.  This mishna indicates that bishul with an igneous byproduct is forbidden, while using a solar byproduct is the subject of a dispute between Rabbi Yosi and the Chakhamim.[2]


Cooking in the Sun


However, the Gemara (39a) explains that Rabbi Yosi and the Chakhamim disagree about bishul with solar byproducts, but not about cooking in the sun itself. 


R. Nachman said: “In the sun, all agree that it is permitted; in a fire-heated object, all agree that it is forbidden.  Where do they differ?  They differ concerning a sun-heated object: one holds that we forbid a sun-heated object on account of a fire-heated object, while the other holds that we do not forbid it.”


Conclusion — Three Heat Sources


Thus, we must distinguish between three heat sources:


Fire or its byproducts: biblically forbidden (the Gemara notes: “One who rolls is liable to bring a sin-offering”).


Sun: permissible even ab initio.


Solar byproducts (namely, an object heated by the sun): according to Rabbi Yosi, this is permissible; however according to the Chakhamim, this is rabbinically forbidden, as there is a decree lest one come to cook with an igneous byproduct.  This is the halakhic ruling (Rambam, 22:9; Shulchan Arukh OC 318:3).


Reason to Allow Cooking in the Sun


Why is one allowed to cook in the sun ab initio?


Rashi (s.v. De-sharei) explains:


For this is not its way of cooking (derekh bishul).  No one would ever confuse fire with the sun, so there is no reason to decree against the latter because of the former.


In other words, there is no prohibition to cook in the sun, because this is not derekh bishul, and even the Chakhamim do not decree against this as they decree against solar byproducts, since there is no need to be concerned that someone will err and confuse cooking in the sun (permitted) with cooking over a flame (forbidden).


Apparently, Rashi’s words are difficult.  Normally, introducing a shinnui (nuance in the manner of performing an action) means that an act is no longer melekhet machshevet (thoughtful labor), and one is no longer liable on the biblical level.  However, the act remains rabbinically banned.  Why should the fact that solar cooking is not derekh bishul constitute a reason to allow it ab initio?


A)    The results are inferior.


The Eglei Tal (Ofeh 44) responds that the intent is not for a shinnui in the act of bishul, but a shinnui in the quality and result of the act of bishul.  Cooking in the sun is qualitatively different from cooking in the fire; the effect of the flame on the food is different than the effect of the sun.  Writing with one’s left hand is a shinnui, but it only puts the action into the realm of rabbinical prohibition, because the result is identical.  Cooking in the sun, on the other hand, brings about an altered result.  This is a characteristic shinnui that removes the name of the melakha, and therefore he allows this ab initio:


Clearly, it matters whether there is a shinnui in the action or the shinnui is only in the actor…  If one writes with the left hand, the essence of the act remains the letter that is produced, and in this there is no shinnui; the only shinnui is in the person doing it: one performed the action with the left, while it is normally done with the right…


When one cooks with fire, the flame has an effect on the food, and one instead cooked in the sun; it is the sun that has an effect on the food, so that there is a shinnui in the cooking being done…  Thus, there is no further need for the reason of melekhet machshevet, because it is not considered cooking at all…  Therefore, since one who cooks in the sun alters the object itself, it is permissible to do so ab initio.


B)     It is not a generally accepted way of cooking.


In Iggerot Moshe (OC, Vol. III, ch. 52), Rav Moshe Feinstein explains Rashi’s words in a different way.  According to him, Rashi does not intend to say that cooking in the sun is allowed because of shinnui, i.e., that one performs a forbidden labor in an uncommon way, so that one is no longer performing melekhet machshevet.  Rather, he maintains, that cooking in the sun is not included at all in the melakha of bishul, because cooking in the Mishkan was done only via fire.


While it is true that generally even activities that were not found in the Mishkan are forbidden as toladot if they are similar to the melakhot that were done in the Mishkan, this is different.  Bishul in the sun is not considered a melakha similar to bishul in fire, since cooking over a flame is a common and accepted way to cook, while cooking in the sun is not a conventional way to cook at all.  This is the intent of Rashi: since this is not its derekh bishul, this act is not included in the melakha of bishul: 


When it comes to cooking in the sun, there is no Shabbat prohibition, as Rashi notes on Shabbat 39a — the Ran writes something similar — because this is not derekh bishul.  Now, it is clear that even though cooking in the Mishkan used a flame, nevertheless, it would have been appropriate to derive solar cooking from it, as a tolada, because for every av melakha in the Mishkan, we derive that one is liable also for all acts that are similar to the avot.  One is just as liable for these, and they are called toladot.  Therefore, Rashi must explain that we do not derive solar cooking from igneous cooking, which was found in the Mishkan, because this is not derekh bishul. 


The Eglei Tal bases the distinction on the result; according to Rav Feinstein, the distinction is in the act: since solar cooking is an act that is not accepted, it is not defined as bishul at all.


C)    The Torah forbids only cooking over a flame.


The words of a number of Rishonim indicate that the allowance to cook in the sun is based on the fact that the melakha of bishul forbidden by the Torah includes only cooking utilizing fire and its byproducts.  For example, the Me’iri (Pesachim 41a) writes, “one is liable for cooking only for igneous byproducts.”  This is also implied by the words of the Rambam (9:6), concerning bishul of metal: “This is the rule: one is liable for cooking whether one softens a hard mass in the fire or hardens a soft mass.”  The Rambam adds “in the fire,” and it is implied that the liability is only for doing so using a flame.  (However, it may be that the Rambam intends only to exclude using the sun and its byproducts).  This is what the Mabbit writes in Kiryat Sefer (ch. 9): “Bishul only apples to fire and its byproducts, because this is what was used for the dyes of the Mishkan.” 

Rav S.Z. Auerbach (Minchat Shlomo, ch. 12, n. 4) understood this to be Rashi’s view:


Even though Rashi writes on Shabbat 39a that cooking in the sun is permitted by all because this is not its derekh bishul, nevertheless, it appears that even if people do cook in a given way using the sun, such as via a solar heater and the like, one is still not liable for doing so…


Indubitably, Rashi’s intent is that this is not called bishul… they had a tradition that [when it comes to bishul] we require specifically that the act be comparable to what was done in the Mishkan, where bishul was via fire and its byproducts, and nothing else.


According to him, the Sages have a tradition that bishul must be “comparable to what was done in the Mishkan,” where they cooked specifically using fire and its byproducts.  Rashi’s intent, if so, is that there is a biblical rule that using the sun is not the way of cooking; therefore, this type of cooking is categorically excluded from bishul, and this is not dependent on human custom.


Summary: Why is Cooking in the Sun Permitted?


In conclusion, cooking in the sun directly is unquestionably permitted.  There are three approaches as to why:


a.     Eglei Tal: the result of cooking in the sun is not as good as the result of cooking over fire.

b.     Rav Feinstein: the act of cooking in the sun is not forbidden because it is not the way of the world to cook in this way.

c.     Rav Auerbach (as implied by some Rishonim): the act of cooking in the sun is not forbidden because the Torah defines the melakha of bishul solely as cooking using fire.




The electromagnetic spectrum spans, in order of increasing frequency and decreasing wavelength, radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.[3]   Every one of these types of radiation is different, and every type is absorbed by some substances and reflected by others.  For example, visible light is reflected by many substances, but it passes through clear glass.  Infrared radiation, on the other hand, is also absorbed by clear glass and warms it.


Microwave radiation is absorbed by liquids, but not by solids (for the most part).  When a food is heated in a microwave oven, the radiation causes the liquids inside a food to be heated, and those liquids heat the solid part of it.  The result of cooking in a microwave (which does not brown the food) is also different: the original color of the food remains, and its taste is somewhat different from that of a food cooked in the normal way.


By Torah law, it is it permissible to cook in a microwave on Shabbat?  This question depends on the different reasons that we have seen for the allowance to cook using the sun.


Cooking in a Microwave is Biblically Forbidden


Rav Feinstein (Iggerot Moshe, OC, Vol. III, ch. 52) writes that since nowadays (1971) it is ordinary to cook in the microwave (and even if there is a regular oven in the house, people sometimes prefer the microwave), there must be a biblical prohibition:


If so, in the microwave oven, that it is as good as cooking in an actual flame, and those who have it use it more than a flame, and the fact that these are not widespread [in Rav Moshe Feinstein’s time] is because they are not yet common, but when they will be common, everyone will certainly use them, because they are better, so one may certainly derive from bishul over a flame that was in the Mishkan, with the significance of a tolada, that it is for all laws like the av of bishul through flame for a prohibition and for liability for sin-offering or stoning.


Cooking in a Microwave is Biblically Permitted


According to the view of the Eglei Tal, on the other hand, there would not be any Torah prohibition involved in cooking in a microwave, because the result of bishul in it is very different from cooking in an oven.


Similarly, according to Rav Auerbach, there is no biblical prohibition of cooking in a microwave, since this is not a fire, and this is totally different from bishul.  According to his approach, we should prefer cooking in a microwave when we need to prepare food for a dangerously ill person (see Nishmat Avraham, 2nd ed., 318:1, n. 3).[4]


Other Problems with Using a Microwave


We should point out that using a microwave on Shabbat involves additional halakhic problems:


a)  Completing an electrical circuit — according to the Chazon Ish (50:9), this constitutes a violation of building (boneh) and destroying (soter).  However, in Minchat Shlomo (ch. 11) we find a dissenting view, and this is the accepted ruling.

b)  Sparks created by completing the circuit — it is generally accepted that there is no inherent biblical prohibition in this (Chazon Ish loc. cit. s.v. U-le’inyan; Minchat Shlomo 10:7; Yabbia Omer, Vol. V, OC, 27:4).


Summary: Cooking with Alternative Sources of Heat


Practically, we forbid cooking even by using a heat source other than fire, for example, a microwave or chemical means; however, the halakhic authorities argue whether there is a Torah prohibition involved.  According to the Eglei Tal, if the result is comparable to regular bishul, there is a biblical prohibition.  According to Rav Feinstein, if this is an accepted way of bishul, there will be a Torah prohibition in this.  On the other hand, Rav S.Z. Auerbach holds that there is no biblical prohibition unless one cooks using a flame, as it was done in the Mishkan. 





Translated by Rav Yoseif Bloch



[1]      Rashi (s.v. Bishvil) explains that bishul is referred to here with the term “gilgul” (rolling) because a hard-boiled egg usually rolls (see Derisha 318:3). However, the Rambam, in his commentary on the Mishna (3:3), explains that the egg becomes mixed in the process of cooking, and the term gilgul refers to mixing or stirring.

[2]      Rabbi Yosei (Gemara ibid.) in fact concedes that one may not put an egg into sun-heated sand; however, this is only because of ancillary prohibitions such as insulation or moving dirt.

[3]      See also Professor Ze'ev Lev's essay on this, Techumin VIII, pp. 21-36, as well as in his book Maarkhei Lev, ch. 11.

[4]      The halakhic status of salting and pickling on Shabbat is also affected by this argument.  From the words of the Ran (Avoda Zara 38b, Rif), it appears that since we have a principle when it comes to prohibited foods that “salting is like boiling,” salting is considered like cooking, and one who salts a food on Shabbat (with a great quantity of salt) should be liable for bishul. 

Similarly, the Noda Bi-Yehuda writes (2nd ed., YD, end ch. 60) that since we say “pickling is like cooking,” anyone who pickles food and makes it edible is biblically liable for bishul. These views are apparently feasible according to the view of Rav Feinstein that the prohibition of bishul includes every acceptable act that renders a food “cooked,” but according to the view of Rav S.Z. Auerbach, it cannot be that one should forbid salting and pickling on a biblical level because of bishul, as bishul requires the use of fire or its byproducts.  According to the Eglei Tal as well, one should not be liable for this, since the results of salting and pickling are different from the results of bishul.  Indeed, the Ramban (Avoda Zara 74b) writes that one is not liable for salting as a variant of bishul, and this is the view of most Acharonim: one is not liable for salting or pickling as a form of bishul (see, e.g., Chokhmat Adam 58:1).