Rabbi Mendel Agranovich
A Metal Sheet (“Blech”) - A Detailed Rationale for Its Use
We continue our discussion of “leaving food on the heat,” and in this article we will discuss the following question: why is it permissible to use a metal sheet (called a “blech” in Yiddish—the term used by all observant people familiar with this concept)?
Let us recall that in Talmudic times, stoves were fueled with coals, and the fire could be covered with ash or all the coals raked out, after which a pot of food could be left on the stove for Shabbat. Where, then, did the blech come from? What is its Talmudic source? Why is it considered the equivalent of the permitted methods of use described in the Talmud and the Shulchan Aruch?
Our story, then, begins with a question posed by the author of the hagahot (annotations) to the book “Mordechai” (written by Rabbi Mordechai ben Hillel, who was killed during the Crusades). The question is this: what should a person do if he gets up in the morning and smells something indicating that his roast is starting to burn? He may not lower the flame, so what should he do? How can he reduce the amount of energy reaching the pot without removing it from the heat or lowering the flame?
A solution was found. If the food is fully cooked, the pot may be removed from the heat and, without being put on the ground, returned to a fire covered by another pot (empty and upside down), placed there to separate the fire from the food. All the conditions for returning food to the heat will be explained later, so we will not go into their details here. One point matters: food may be returned only to a fire “covered with ash”; there is no permissible way to return it unless the fire has been covered with ash or all the coals have been raked out. It follows that a pot placed over the fire to reduce its intensity is the equivalent, at the very least, of covering it with ash. In fact, whenever we put food on an ash-covered fire before Shabbat, we are using a weaker flame. This is why the Sages permitted leaving food on a fire “covered with ash”: the homemaker inwardly accepts that she cannot increase the heat under her culinary masterpiece and resigns herself to it.
We might suppose that this action (covering with ash) works only if we cover the coals themselves with ash. In other words, we perform an action that is the opposite of stoking and kindling them... But our example shows that for a fire to be considered “covered with ash,” it does not have to be sprinkled with ash; it can simply be covered. Although nothing has happened to the heat source itself, we are leaving our food in a state in which it does not receive the maximum possible amount of energy, so this is sufficient and permitted.
But a reasonable question arises here: a pot has height, whereas our “blech” is flat. How can the two be compared? Furthermore, the Tur (Rabbi Yaakov ben Asher, son of the Rosh, who belonged to the last generation of the Tosafists) states that in Talmudic times people commonly cooked on a burner covered with a lid. How does our “blech” differ from a lid that allows a pot to be placed over the fire when its diameter is smaller than the burner's opening? These questions were raised by none other than our teacher, the Chazon Ish, in his book (Orach Chaim, section 37, subsection 11). On the other hand, the Chazon Ish himself attests in the same passage that in the Land of Israel it was customary to leave food on a “blech.” He writes, however, that this method is not comparable to the example in “Hagahot Mordechai,” and therefore food may be left on a “blech” just as it may be left over an uncovered flame. This is because, according to the Chazon Ish, one may rely from the outset on Chananya's opinion—if the food is one-third or halfway cooked (ma'achal ben Derusai), as we wrote above. But this flame is not considered to have been covered with ashes. How, then, can we explain our people's custom?
The authors of “Orchot Shabbat” (chapter 2, section 8, footnote 12) cite the opinions of many leaders of their generations (great halachic authorities), rishonim and acharonim, who maintained that even if a pot was placed on the bottom without touching the coals, and a pot containing food was placed inside it on its bottom, this too is permitted. Since “Hagahot Mordechai” does not specify that one of the two possible methods is permitted and the other forbidden, we can conclude that both are permitted. This is the basis of our custom. Its logical explanation is as follows: since we see that coals may be covered with ashes, and there are no restrictions on the covering except regarding the area covered (the thickness of the layer does not matter), a covering over the flame must likewise cover the entire surface of the burners and reduce the heat at least a little. Nevertheless, it is not customary to place food on a sheet of foil spread over the burners.
But what about the example described in the Tur of a burner's opening covered with a lid? Surely one may not place a pot on it? We can answer as follows: the example described in the Tur is a standard method of cooking, so leaving food over an opening covered with a lid does not count as leaving it over a covered flame. It is simply a way of cooking on a stove, like cooking in a pot of a smaller diameter or over a smaller flame. A comparable example for us would be a heat diffuser—a disk placed over a single burner to provide a larger surface. Our “blech,” however, covers all the burners, and its sole purpose is to reduce the flame.
Practical Conclusions
It is customary to leave food at any stage of doneness on a copper or aluminum sheet—a “blech.” Remember that it is preferable for everything to be ready before Shabbat (“Orchot Shabbat,” ibid.).
According to the Chazon Ish, the “blech” must have some height.
It is NOT necessary to cover the gas control knobs, since the food is placed over a covered flame, but it is preferable to cover them as well (ibid., footnote 14)
It is preferable not to turn up the flame after placing the “blech,” since this contradicts its entire purpose (although there is no change in the flame, the very act of leaving food over a covered flame already shows our acceptance that we cannot turn it up on Shabbat) (ibid., footnote 15).
One may not place it on a gas burner turned up to its maximum setting, since no action has been taken to show our acceptance that the flame cannot be increased. Although it cannot be increased, this inability is unrelated to the blech—“covering with ashes”—and is due only to the burner already being turned up as far as it will go.
One may cover the flame with a “blech” even on Shabbat and return food to the flame in accordance with all the rules, provided the metal does not become hot enough to begin glowing red.
One may not use a sheet of foil as a “blech.”
Shabbat shalom!