"Make a fence for the Torah," the Sages say.1 That is, enact laws that guard against the possibility of violating halacha. In this lesson, we will study a number of laws which the Sages set out to prevent one from inadvertently engaging in Bishul on Shabbat.

Recall from what we've learned that it's acceptable to start something cooking before Shabbat and leave it to cook overnight (as is done with the common cholent). It is also acceptable to reheat foods on Shabbat, given certain specific conditions. The requirements we're about to learn place limitations on these activities.

She'hiyah – Leaving Food on a Flame

Cooking, of course, is an everyday activity. The Sages were therefore concerned about us momentarily forgetting that it is Shabbat, or forgetting that cooking isn't allowed on Shabbat, and just going about our usual business.

Thus, the Sages prohibited leaving an uncooked food on an open flame during Shabbat. This is known as she'hiyah.2 According to the Torah, there's nothing wrong with this, since the cooking is happening by itself. But there is concern that we might adjust the flame if it is open and easily accessible.

To avoid this problem, and also to generally differentiate between Shabbat and other days, the Sages stated that you could leave uncooked food only on a covered flame.3 This is the source for that indispensable tool of the Shabbat kitchen, the blech.4

We've referred to the blech before – it is a flat metal sheet (with one side bent over) that we put on the range top, so that it covers the actual flame but allows heat to penetrate through. (Additionally, knobs on the stove-top should also be covered, so there is no opportunity to alter the flame.)5

An electric hotplate accomplishes the same halachic purpose, since it maintains a constant heat and does not have any knobs.6

We place cooked food on the blech before we light candles on Friday evening, so that the food remains warm until our meal. It is highly recommended to put the food on the blech after it is fully cooked. Technically you are allowed to put uncooked food on the blech, but in such a case you would be restricted from moving the pot in any way whatsoever, since this will accelerate the cooking. In practice, then, we make sure our food is fully cooked before Shabbat. (An exception would be a case of great need, such as if unexpected guests showed up.7)

(When it comes to putting the food onto the blech for Shabbat lunch, we get into a different issue, known as chazarah ('returning'), which we'll address a little later.)

Beyond the stove-top, how do we deal with she'hiyah regarding other cooking surfaces?

  • Ovens – Cooked food may be put in an oven on Friday and left there on Shabbat. Uncooked food cannot, since the 'flame' – that is, the walls of the oven – are exposed to the food, it is the regular mode of cooking, and thus 'uncovered'.8 However, even with cooked food, there are restrictions on use of an oven, since opening the oven to remove the food often activates the thermostat, which is of course prohibited on Shabbat. In practice, you can take food out of an oven that has been shut off before Shabbat. (Or, if the oven has a timer, that could be set to shut off the oven shortly before the food is needed.)9

  • Slow cookers10 – Some slow cookers have only one temperature setting: when you plug them in, they turn on. These can be used on Shabbat, so long as the food is put in there (and preferably fully cooked) before Shabbat starts.11 Because there is no way to adjust the temperature, the central concern behind the concept of she'hiyah does not apply.

More sophisticated models have several settings. In such a case, one must cover the knobs, as a clear sign that they can't be manipulated on Shabbat.

The rules of she'hiyah do not require a blech-type cover for slow cookers, since the 'flame' (i.e., the electric element) is already covered. However, as we'll see later, a cover may be needed to deal with other issues.

Chazarah12 – Returning Food to a Heat Source

Here is a central challenge of Shabbat: We want to have warm food for Shabbat lunch,13 yet we can't cook. So what do we do?

There are two options:

  1. leave something cooking overnight so that it is still hot when lunchtime arrives
  2. find a halachically acceptable way to reheat your food

Recall that in our previous lesson (#21), we discussed the basics of reheating. We learned that solid foods can be reheated on Shabbat, while liquids cannot. We also learned that foods can be reheated only using the same cooking method by which they were initially prepared.

The Sages added another layer to these halachot. In order to avoid even the appearance of cooking, we cannot place foods directly onto a blech on Shabbat, even if the food is solid, and was fully cooked already, and was originally prepared using dry heat.14

It is permitted, however, to return food to the blech, under the following conditions:

  1. When you remove the food from the blech, you intend to put it back15
  2. You continue to hold the pot by its handle while it is off the blech, and may rest on the counter16
  3. The food does not cool off completely before you return it17

By acting in this way, we maintain a continuous connection between the food and the original source of heat, the blech.18

In case of necessity, the food could be returned to the blech even if conditions (1) and (2) were not fulfilled, provided that the pot was not put on the ground. Condition (3) must always be fulfilled.19

Let's consider the following case:

Before heading off to bed on Friday night, Rachel notices that her electric stovetop has turned off, leaving no source of heat for the cholent that sits on her blech. Rachel feels the pot and it is still warm. But of course, by the next morning it will be spoiled. Is there any way for Rachel to save her cholent?

There is a very good solution. Rachel can take her pot of cholent to a neighbor and have it continue to sit overnight on her neighbor's blech. The reason this is permitted is because although technically speaking Rachel's pot has been "removed" from the blech (without fulfilling the conditions of her holding it and intending to put it back), this constitutes a case of great need, and Rachel can still "return" the pot to any blech.20

A Map of the Blech

Normally, when we put a blech on the stove, we keep only one of the stove's flames on. This generates a sufficient amount of heat to spread throughout the blech's surface. At the same time, not all parts of the blech will heat evenly: the closer you are to the actual flame, the hotter it will be.

For this discussion, it is helpful to classify the blech into three sections:

Point A – the area of the blech directly above the flame (or electric heat element)

Point B – the area of the blech not directly above the flame, yet hot enough to cause the food to reach the temperature of yad soledet bo – which, as we learned, is the threshold for determining halachic cooking.21

Point C – the area of the blech not directly above the flame, and just warm, but cannot cause the food to reach the temperature of yad soledet bo. If you place food on this area, it cannot become cooked.22

Here's one application:

The halacha prohibits removing food from a pot while it is on point A. But if you slide the pot to point B (or point C), it is permitted to remove food from the pot without having to go to the trouble of taking the pot off the blech and supporting it the entire time, etc. (as per the three conditions above). But we need to put the cover back onto the pot before sliding it back to point A.23

Food from the Fridge

Okay, you say. This works if you are scooping some food out of a pot, and you need to momentarily remove it. But this still assumes that the food has been on the blech through the whole Shabbat. What if you have food that you are not going to leave on the stove overnight? For example, is there any way to heat up kugel or challah for Shabbat lunch?

The short answer is yes. The common solution is to reheat the food by placing it on top of another pot which is on a heat source. For example, you take a clean, empty pot24 and put it on your stove, which is already covered with a blech. Then you place the food you want to reheat on that pot (perhaps by inverting the lid and putting the food in the hollow space). Unusual? Yes. But here the problem of giving an "appearance of cooking" is solved, since no one would ever think you are cooking by such a convoluted method.25

Another solution is to place the food on an area near the stove, so that the heat radiating from the blech will warm it. This will work if you have a surface in your kitchen that gets heated nicely from the stove's heat. And of course, this is permitted because there is no appearance of cooking so long as the food is not on the blech (i.e., the stove).26

What about warming up uncooked food?

Since cooking does not occur at less than yad soledet bo, you can put uncooked food in any place where the food will not reach that temperature. As a result, you can usually safely heat up uncooked food on top of a radiator.27 Similarly, it is permitted to place cold food onto point C of the blech (but you would not be allowed to move it to any hotter area of the blech).28

This raises the question: If I want to warm a piece of uncooked food, can I put it in a place that is hotter than yad soledet bo, as long as I remove the food before the food itself reaches yad soledet bo? The answer is 'no,' because you may forget and leave it there.29

The litmus test is: Will this food reach yad soledet bo before the end of Shabbat?

In our next lesson, we will explore other rabbinic laws regarding Bishul.


  1. Talmud – Avot 1:1.
  2. Pronounced sheh-hee-YAH (or, in Ashkenazic style, sheh-HEE-yeh).
  3. If one mistakenly left uncooked food on an open flame, it must be removed immediately. Orach Chaim 253:1; 39 Melochos, p. 608.
  4. The etymology of the word blech is “tin” in Yiddish. It is a harsh-sounding term for something so central to our Shabbat observance, but that’s what we usually call it. In Israel, many use an electric warmer, called a platta.
  5. Shu”t Igros Moshe (Orach Chaim 1:93). See also 39 Melochos, p. 610-11; Halachos of Shabbos, XIV:E.12 (p. 339). It does not matter if the range uses gas or electricity. A blech is needed in either case.
  6. If the hotplate does have different settings, those knobs should be covered before Shabbat.
  7. Biur Halacha 253 s.v. V’Nohagu.” For further study on this issue, see 39 Melochos, p. 611. In an emergency where food would need to be left on an open flame, it must either be totally raw, or minimally one-third cooked.
  8. There is something known as an oven insert, which serves the same purpose as a blech. With such an insert, the oven’s ‘flame’ is ‘covered’, and as a result uncooked food can be put in it. Shu”t Igros Moshe (Orach Chaim 4:74 Bishul 27); 39 Melochos, p. 612.
  9. 39 Melochos, p. 613.
  10. These are often referred to by the trademarked term ‘Crock Pots’.
  11. According to some opinions, the food may even be uncooked.
  12. Pronounced cha-zah-RAH or cha-ZAH-ruh.
  13. Chollent was invented to fulfill the special mitzvah of having warm food on Shabbat day (Baal HaMe’or – Shabbat 45).
  14. Orach Chaim 253:2, with Mishnah Berurah 37, 56; 39 Melochos, p. 618.
  15. In Hebrew, da’ato l’hachzira
  16. In Hebrew, odo b’yado. Orach Chaim 253:2; Shu”t Igros Moshe (Orach Chaim 4:74 Bishul 33).
  17. In Hebrew, odo ro’tachat. Rema – Orach Chaim 253:2, with Mishnah Berurah 54; Halachos of Shabbos, XIV:F.1 (p. 350); 39 Melochos, p. 619.
  18. Orach Chaim 253:2, with Mishnah Berurah 55.
  19. Orach Chaim 253:2, with Mishnah Berurah 56, Sha’ar Hatziyun 50.
  20. Shu”t Igros Moshe (Orach Chaim 4:74 Bishul 38).
  21. See lesson #19.
  22. Shemirat Shabbat K’Hilchato 1:22; 39 Melochos, p. 645.
  23. Shu”t Igros Moshe (Orach Chaim 4:61).
  24. Of course, if you have a pot containing food that is already on the stove, you may use that as well. Most authorities allow you to place any item – for example, an upside-down tinfoil pan – that has height and is thus recognizable as an addition to the blech.
  25. Mishnah Berurah 318:55. This approach is explained in Orach Chaim 253:5; 39 Melochos, p. 621. See Principles of Hilchos Shabbos, ‘Bishul’, section D. The food may not be fully wrapped in tin foil, as we will discuss in the next lesson.
  26. Orach Chaim 318:15, with Mishnah Berurah 92, 94; 39 Melochos, p. 621.
  27. Since this is such an unusual place to “cook,” any knobs need not be covered.
  28. Shu”t Igros Moshe (Orach Chaim 4:61); Shemirat Shabbat K’Hilchato 1:13; 39 Melochos, p. 644- 45.
  29. Orach Chaim 318:14, with Mishnah Berurah 90.