Shiur #20: Ovens
LAWS OF SHABBAT: COOKING
By Rav Yosef Zvi Rimon
Dedicated in memory of Joseph Y. Nadler zl, Yosef ben Yechezkel Tzvi
Shiur #20 - Ovens
How is one allowed to leave food in an oven on Friday in order to eat for the Shabbat meals?
Is it permissible to return the food to the hot oven after the meal?
Shehiya in an Oven
Until this point, we have dealt with heating on the fire. We have seen that one may leave foods before Shabbat on a covered fire. If these foods are cooked to the level of maakhal ben Derusai, in the view of the Ashkenazim and some Sefardim, one may leave foods even on an open fire. Similarly, by the letter of the law, one may leave, on an open fire, a totally uncooked food as well.
What about shehiya in an oven? Can one put foods in an oven before Shabbat and take them out afterwards for the Shabbat meal?
Oven vs. Stove
The mishna (38b) explains that the law of the oven is more severe than of a stove:
If an oven stove is heated with stubble or twigs, one may not put a dish therein or thereon.
In other words, even though there is no problem with a stove fueled in that way (as there are no coals to stoke, as explained in a previous shiur), one is not allowed to leave food in an oven fueled with stubble or twigs. The Rambam (3:5) explains:
The above applies to a stove, which produces minimal heat. With regards to an oven, in contrast, even if one removes the coals, covers them with ash or uses straw or stubble as fuel, we are not allowed to leave food in it or on it
This applies to food that has not been cooked to completion or to food that has been completely cooked, but will benefit from continued cooking. Since an oven is very hot, a person will not divert his attention from it. Hence, we are concerned that one will stir the small fire that remains, even if it is fueled by straw or stubble, even if it is covered.
This indicates that the Sages treat the oven more stringently in another aspect: shehiya is allowed upon a stove that has been swept or sprinkled, but not an oven (see Rashi 37b, s.v. Ha).
Rashi (s.v. Tannur) explains that the Sages ovens were hotter than their stoves, since the ovens were narrow at the apex and wide at the base, allowing the oven to maintain its heat. A number of Rishonim (Rabbeinu Chananel, 38b; Meiri, ad loc.; Ran, 17b, Rif, s.v. Matnitin) write that their ovens have the status of a stove, since they are not that warm, and this is how the Rema (253:1) rules. On the other hand, the Maharshal (cited by Tiferet Shemuel on the Rosh 3:5) argues that their ovens are also like the Sages ovens. The Mishna Berura (28; Shaar Ha-tziyun, 30) writes that in a bakers oven, which gets very hot, one must be stringent.
What about our electric ovens?
In Iggerot Moshe (6), Rav Feinstein writes that modern ovens have the status of a stove, because they do not become very hot (since they have a thermostat). According to this, (according to the Ashkenazim and some Sefardim) one may leave food that has reached the level of maakhal ben Derusai in an oven, and if the oven is defined as swept or sprinkled, one may leave on it a food that has not reached the level of maakhal ben Derusai.
How may we render our ovens swept or sprinkled? Rav Feinstein (op. cit. 27) writes that one may put an aluminum pan in an oven and put food in it. The Az Nidberu (Vol. VIII, ch. 16) writes that one may be lenient about an empty pan that is put on the bottom of the oven.
However, there is a simpler solution. In a previous shiur we saw that if the oven is daubed with clay in such a way that there is no possibility of stoking, it is considered swept and sprinkled, at least according to the Ashkenazim. Therefore, in an oven as well, if we seal the knobs in a way that there is a need to remove the glue in order to turn them, this makes it an oven daubed with clay, and it would be permissible to leave in an oven such as this even a food that has not reached maakhal ben Derusai. All the more so, removing the knobs should be sufficient, because in such a case, one cannot alter the temperature.
As we have said, if the food reaches the level of maakhal ben Derusai, so that for Ashkenazim and some Sefardim, it is permissible to leave anything in an oven, even if the knobs are not sealed. In any case, it is always preferable to seal the knobs.
Opening the Oven
However, there is an additional problem. In ovens, there is usually a thermostat; opening the oven accelerates its activation. Some ovens have a Shabbat setting, which uses a timer instead of a thermostat, and this setting circumvents this problem (one should ascertain that the Shabbat button actually disconnects the thermostat). In ovens with a Shabbat setting, one may set the oven so that the timer will turn the oven off before the time of taking out the food, and the food may be then be removed when the oven is off.
If one finds himself in a situation in which the oven does not have a Shabbat setting and has not been set to shut off at mealtime, one may be lenient and remove the food at the time that the oven is hot and the thermostat light is on; in this situation the person only prolongs an existing situation, but one does not cause the oven to go on.
If this is also not feasible, one may open the door with an alteration even at the time that the oven is not heating (in other words, the thermostat light is off), because it is not necessarily the case that opening the door will cause the oven to go on, and even if it would bring this about (and this is considered a pesik reisha), we are talking about causation (and there are those who allow a pesik reisha by causation). If one does this with an alteration (e.g., with ones elbow), then there a number of rabbinical doubts coinciding, and one may be lenient, particularly for a need such as that of the Shabbat meal.
To summarize, it is permissible to leave a food in an oven on Friday if it has been cooked to the level of maakhal ben Derusai (at least for the Ashkenazim and some Sefardim), and it is permissible to leave it even it has not reached the level of maakhal ben Derusai, if the knobs have been sealed or detached. One should strive to use an oven with a Shabbat setting that disconnects the thermostat, or alternatively to ensure that the oven will be off at the time that the food is removed. (In a case of need, when one has not done so, one may remove the food at the time that the oven is heating up. In a case of pressing need, one may take it out even at a time that the oven is not heating up, but in this case it is better to open the oven with an alteration.)
After one has taken food out of an oven, may one replace it? Apparently, if the oven is swept or sprinkled and one is stringent about the conditions of hachazara (intention to replace and holding the pot or at least not putting it on the ground, but only on the countertop), one may put it back in the oven.
However, one must examine whether one can turn the oven into a swept and sprinkled stove. As regards the prohibition of shehiya, we have seen that it is enough that one seal or detach the knobs. However, as we explained in previous shiurim, it may be that these solutions are effective only when dealing with the issue of shehiya, not hachazara. Shehiya is based on the suspicion of stoking the coals, and therefore when one performs operations that prevent a person from turning up the fire, there is no reason to forbid the act. On the other hand, according to many Rishonim, hachazara is based on mechzi ke-mevashel (the appearance of bishul), and for this purpose, it may not help that a person cannot turn up the fire; one must take actions to turn down the heat and express his diversion from cooking. Therefore, one must put an empty pan on the bottom of the oven (in the view of Rav Feinstein, there is a need for a metal box with four walls, as we have mentioned above).
Moreover, it may be that even if the oven is defined as swept and sprinkled, it is still forbidden to put food back in it. This is based on a statement in the Gemara (37a):
Rabbi Chelbo says, quoting Rav Chamma bar Gurya, in the name of Rav: This is only true thereon, but therein is forbidden.
In other words, one may replace food on top of a stove on Shabbat, but not inside a stove (as their stoves were deep). This limitation does not spring from the prohibition of hatmana, which does not apply when the cover is not touching the pot (we will discuss this more next week in our shiur on hatmana); rather, it is forbidden because it looks like bishul. This is also the Shulchan Arukhs ruling (253:2): one cannot put food back into a stove on Shabbat. According to this, it is apparently forbidden to put the food back into the oven, and this is the ruling of the Minchat Yitzchak (Vol. III, ch. 28), as well as the one found in Shemirat Shabbat Ke-hilkhata (1:17) and other authoritative works.
However, one who is lenient has upon whom to rely. The Arukh Ha-shulchan (253:17) writes that the prohibition of putting food inside the stove relates only to the situation Talmudic times, in which there were two possibilities to heat with a range: inside it or on top of it. Therefore, if one would have chosen to put a dish inside the stove instead of on top of it, it would have appeared more like bishul. However, in our times, there are not two different ways to place the dish in the oven, so it is permissible to put foods inside it, because this does not testify to ones desire to cook them:
Our ovens are like a stove, as will be explained, and concerning them there is no thereon, and one must always put it therein. Therefore, there is no distinction about this, and therein is like thereon.
This is what the Shevet Ha-Levi (Vol. III, ch. 48) writes as well.
In conclusion, if one wants to put food back on the fire on Shabbat itself, ab initio it is best to put it on a Shabbat hot plate; however, if this is not possible, one may be lenient and put it back into an oven with the following conditions: the dish is fully cooked, one holds it and intends to replace it, an empty pan is put on the bottom of the oven (or a separation between a heating element and the food), and the oven is on the Shabbat setting. (If one has forgotten to put the oven on the Shabbat setting, see above about the laws of shehiya in an oven).
In any case, one may not take food out of the refrigerator to put it in the oven on Shabbat, even if the oven is on the Shabbat setting and the food is fully cooked, even if one puts it in the oven on top of a full pot. This solution only works in a stove, which is heated from below, so that putting food on top of a full pot distances it from the heat, and the act does not look like bishul. In an oven, on the other hand, the heat spreads throughout the entire space, so that there is no significance to the question of whether the pot is on the bottom of the oven or another pot inside it in any case, this looks like bishul, and one may not do so on Shabbat. This is also what the Chazon Ish (37:9) writes:
Inside the oven, it is certainly forbidden to do so, because this is all about placing food on top; however, within the airspace of the oven, all of the air is warm, so the separation between the floor and the pot does not allow anything.
Therefore, it is better that one have a plata at home, because on it one can both replace the food and place food ab initio on Shabbat itself, according to the conditions mentioned in previous chapters.
 However, see Minchat Yitzchak, Vol. III, ch. 28; this is not the place to elaborate.
 This serves two potential aims: to prevent mistakes and to respond to the view that there is a prohibition of shehiya even for foods cooked above the level of maakhal ben Derusai.
 A similar problem exists also with a refrigerator, but there the aim is accomplished by sealing a circuit, which is forbidden according to the view of most authorities rabbinically, while the oven involves heating filaments, which is forbidden biblically according to everyone.
 See below, note 152.
 In Yalkut Yosef (253, n. 5), we find a lenient view: one may open an oven that has a thermostat because this constitutes a pesik reisha of causation (amid other reasons). Rav Feinstein (28) is lenient about this, but his justification is that opening the door will not definitely cause the oven to be activated. This would mean that in a reality in which we know that opening the door will cause the oven to be activated, one may not be lenient according to his view. In any case, even though ab initio it is good to be stringent about this, as we have written, it appears that the authorities do provide a basis on which to rely to be lenient if one has not arranged for the oven to be off when one removes the food, particularly if one opens the door of the oven with an alteration.
 This is also written by the Minchat Yitzchak (Vol. III, ch. 28). However, see the Mishna Berura (253:81). This view requires some explanation, but this is not the place to elaborate.
In a case of pressing need, one may be lenient to put food in an oven on Shabbat itself under a number of conditions:
A. One should put an empty pan on the bottom of the oven (making it swept).
B. One should put the (cooked) foods before Shabbat in an oven for a number of minutes, so that at the beginning of Shabbat they will be inside the oven (one may then put them in the refrigerator). Thus, one may enlist the view of the Ran based on the Yerushalmi (see above, note 117): once the food has been on Shabbat itself in the oven, the laws of hachazara are nullified, and one may put them now directly on a swept and sprinkled fire. Indeed, the Rema (253:2) cites the view of the Ran, and he writes that it is fit to be stringent about this. Therefore one may not be lenient following this view alone, but only in conjunction with the following condition.
C. One must put the food in the oven on Shabbat before it is ignited. In this way, there are those who believe that it is ab initio permitted to put cooked food in the oven, for in their view, this does not look like bishul (see Rav L. I. Halperns Kashrut Ve-Shabbat Ba-mitbach Ha-moderni, p. 231).