Rabbi Mendel Agranovich
Let us consider the following question: may food be left in an oven (electric or gas)?
Many ovens sold in Israel have a setting on the control called “Shabbat mode” or “matzav Shabbat.” It means that food left on this setting will be kept at a constant low temperature, so that, on the one hand, it will not burn, and on the other, it will remain hot. Is this sufficient from the standpoint of Jewish law? This is the subject of today’s article.
We know that the Talmud (Shabbat 37a) permits leaving food for Shabbat not only on top of a stove but also inside it. In other words, if the fire has been covered with ash, or all the coals have been removed from the stove, and there is no concern that the fire will be increased by stoking the coals, a pot of cholent may be placed inside the stove as well. We pick up a cast-iron pot with a poker and put it into the Russian stove. With the qualification that in the days of the Talmudic Sages there was no Russian stove, which our Sages call a “household winter stove,” but rather a “kirah” — a two-burner stove shaped like a large pot with clay walls. One can cook on it by placing a pot of food on a burner on top, or lower the pot inside without even touching the coals or the bottom, supported, for example, by the pot’s own handles. The Talmud says that food may be left for Shabbat in either position, but may be returned only to the top, not inside. We will discuss returning food later; as for leaving it in place, the matter is clear: all the rules stated earlier apply to this position as well.
Our Sages equated the “Russian stove” with a “kirah.” Food is always placed inside a Russian stove, so it is clear that food may be left in an oven provided that the flame is covered, or the food has reached the stage of “ma’achal ben Derusai,” meaning at least a third or half of its cooking time. But how can we cover the heat source in an oven? One option is to put a metal box inside the oven, in which case food at any stage of doneness may be left there... However, the author has never seen such oven equivalents of a blech for sale. There is therefore another option: leave only food that has reached the stage of “ma’achal ben Derusai”—permitted by the Chazon Ish—or food that is fully cooked and does not improve with further heating—permitted by the Mishnah Berurah (after the fact, the Chafetz Chaim also permits leaving “ma’achal ben Derusai”).
If the food is not cooked, the authors of “Orchot Shabbat” suggest putting a sticker over the temperature control knob so that it cannot be turned without removing the sticker.
What is the source for this option? “Orchot Shabbat” explains that the Talmud (Shabbat 18b) states that if food is placed in a stove, the stove is covered with a lid, and the lid itself is sealed with clay, food may be left inside at any stage of doneness. The prohibition against “breaking” or “destroying” on Shabbat is a separate discussion, but as far as the concern about stoking the coals is concerned, we see that it does not apply. To stoke the coals, one would have to perform a laborious and time-consuming action that cannot be done absentmindedly. A person will therefore always catch himself before stoking the coals. BUT... This explanation follows only the opinions of Rashi and the Rema; the Rambam and the Shulchan Aruch disagree with it...
Remember that we wrote that taping over the controls does not help, and qualified this by saying that perhaps it does not help. The reasoning behind the decree according to the Shulchan Aruch is that an action must be taken with the fire itself. Yet this does not happen in our case, since neither the sticker nor the clay has anything to do with inwardly accepting that the food will be left over low heat. What, then, about the passage in the Talmud? According to the Shulchan Aruch and the Rambam, it concerns a particular case: meat on the coals will spoil if the stove’s lid is opened, and only for this reason is there no concern that it will be opened. It follows that this option is not acceptable according to all opinions...
Let us return to the oven’s “matzav Shabbat” setting. In the author’s opinion, it has no clear halachic significance (although there is value in the temperature remaining constant, with no concern that opening the oven will cause the thermostat to switch it on). Think about it: if the food is cooked, it may be left in the oven at any temperature; if it is not, we have taken no action demonstrating that we have accepted that the heat cannot be increased.
If someone asks: “What about a hotplate? Didn’t we write that the Rashba held that food may be taken off a high flame and moved to smoldering coals, and that this is sufficient?” And this setting does indeed resemble that description. The answer is that Rabbi Shlomo Zalman Auerbach did not present this idea as sufficient on its own, but added that people do not cook on a hotplate during the week and that its heat cannot be increased. Nowhere do we find that our earlier halachic authorities relied on this idea without support from others. We therefore cannot rely on this setting alone. After all, if we put in a metal box, everything is permitted, while taping over the control is sufficient according to the Rema and insufficient according to the Shulchan Aruch. The only possibility is that, when the two measures (“matzav Shabbat” and a sticker) are combined, the Shulchan Aruch would agree with the Rema, but we have no basis for this.
Practical conclusions:
Food may be left in the oven for Shabbat if it is fully cooked and does not become tastier with continued cooking. From a practical standpoint, the “matzav Shabbat” setting is useful because our dish will not burn on it (check the temperature beforehand, and if it is high, the author is not to blame if your shish kebab dries out).
If the food has reached the stage of “ma’achal ben Derusai,” it may also be left in an oven, whether electric or gas. Remember: according to the Mishnah Berurah, one should make an effort to have everything cooked before Shabbat.
If the food has not reached the stage of “ma’achal ben Derusai,” it may be left in the oven if there is a metal box—the equivalent of a blech—covering the flame or heating elements. This option is suitable for both Ashkenazi and Sephardi Jews.
According to the Rema, and only for Ashkenazi Jews, taping over the oven’s temperature control is sufficient. The Chazon Ish also suggested installing a latch on the oven door.
Removing the control knobs is a matter of dispute among the Sages. Opinions differ, so one should avoid relying on this option from the outset unless necessary (“Orchot Shabbat,” chapter 2, section 19). This applies not only to an oven but also to a stovetop.
If the oven has a thermostat, it may be opened when the thermostat has already switched on (and turned the oven on), because otherwise there is a concern that the cold air we let in will cause it to switch on (this is a subject for a separate article: the use of thermostats in refrigerators, ovens, heating systems, and so on).