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OVEN KASHRUS: For Shabbos Use
Rabbi Avrohom Mushell, Star-K Kashrus Administrator

Cookin’ just ain’t what it used to be. Technological advances have taken the old stovetop and oven and upgraded them to be safer, more efficient, and smart for today’s lifestyle. They are also far more complicated. With these transformations, the observant Jew is faced with challenges that did not confront him in the past. To understand how these changes affect the halachic use of the range on Shabbos and Yom Tov, it is worthwhile to review some laws and concepts as they relate to cooking on Shabbos and Yom Tov.

Definition of Melacha
Cooking on Shabbos is a Torah prohibition derived from the constructive acts done in erecting the mishkan. This forbidden act is known as a melacha. There are 39 categories of acts that are prohibited.

Melacha of Cooking
The prohibition of cooking on Shabbos is defined as the act of using heat to make a substance edible or to change its state. In order for food to be considered hot, the food must reach a temperature of yad soledes bo (120°F), hot enough to cause one to withdraw his hand due to the heat. If the food will not reach a temperature of yad soledes bo there is no concern of cooking. Lighting a flame on Shabbos is also prohibited as it is written, "Do not burn fires in your homes on the Shabbos day."1 The Torah prohibition of creating a fire on Shabbos also includes adding to an existing flame. This is referred to as mosif havarah. Furthermore, one may not carry out an action that will “cause” the flame to igniten if it is the end result of his action. The term for this is gram havarah.

Aino Mechaven
There is a general rule regarding actions prohibited by the Torah that states that when one performs an action and his intent is not for the prohibited reaction that results, it is permitted. This is called aino mechaven, which literally means that there was no intent to perform the activity. (For example, dragging a bench on the ground on Shabbos to bring it to another location is permitted, even though it may make a groove in the ground [plowing].) However, if this unintended consequence must result in the prohibited activity being done, it is as if one had initially intended to perform the prohibited action, and the action is prohibited (i.e. dragging a heavy bench on soft earth where it will surely make a groove in the ground). This is called a psik reisha. Nevertheless on Shabbos, where the resulting consequence is neither wanted nor intended, it is classified as a psik reisha d’lo nicha leih, which is permitted by Torah law but prohibited by Rabbinic law.2

The halachic interpretation of a melacha is the action that one performs which causes a direct result. For example, when one strikes a match one directly causes a fire to ignite. When the resulting prohibited action is an indirect result of one’s action, it is called a grama. For example, setting a mouse trap is a grama for the melacha of tzod (hunting). Grama of a melacha is permitted by Torah law, but is Rabbinically prohibited.

Where there is a combination of factors that individually may have been restricted by Rabbinic law, there may be room for leniency when combined with one another. Therefore where a grama will cause a melacha to be done that is unintended and unwanted on Shabbos (lo nicha leih), the action may be done. This is the basis for allowing one to open a refrigerator door on Shabbos. In that case, a thermostat will sense the change in temperature and cause the compressor motor to run; This is considered a grama. The running of the motor gives off sparks of fire which are not wanted or intended. Thus the melacha taking place is lo nicha leih. Opening the refrigerator, results in a grama to an unintended and unwanted melacha. In the same vein one may open an oven door on Shabbos when one removes all the food from the oven. The resulting grama (the melacha of havarah) is unwanted and unintended.

Rabbinic Ordinances Regarding Food Preparation
Many Rabbinic laws were initiated to prevent one from transgressing the Torah’s prohibitions. They are intended both to distance us from what is prohibited, and to prevent us from doing actions which can be misconstrued with a prohibited melacha.

  • Shehiyah - Among these Rabbinic laws are shehiyah, literally, one is prohibited to leave the food on or in the place where it will be cooking, even if it was placed there before Shabbos. There is concern that leaving food that is not ready to be eaten on the cooking surface or in an oven may lead one to add to the heat on Shabbos. The Rabbis are concerned that one may adjust the heat to enhance the food.

    In the past, when cooking was done directly over burning logs, there was a concern that someone might stir the embers. This would add oxygen and genrate heat. By stirring the embers, one transgresses two Torah prohibitions: burning a fire on the Shabbos day and (if the food is not yet cooked) cooking. In order to prevent any wrongdoing, the Rabbis decreed that unless the food is edible before Shabbos,3 one may not leave it on or in the oven once Shabbos begins, unless the embers are removed or covered to prevent someone from stirring them.4 In lieu of covering the coals, we have the custom of placing a blech5 over the flames before Shabbos. It should be noted that the main function of the blech is to make sure that one does not adjust the fire. Therefore, with a modern oven or cook top, one should cover the temperature controls in addition to covering the flame with a blech.

  • Chazarah - Another Rabbinic prohibition is chazarah, returning cooked food to the heat source on Shabbos. Even if the food is still hot and fully cooked, one may not return it to an oven or a covered stove unless it was removed with the intention of being replaced, and had not out of his hand from the time it was removed to when it is replaced on the heat. This certainly would prohibit taking a cold pre-cooked food and placing it by a blech on Shabbos. This Rabbinic decree was instituted because placing the food on the heat it appears as if one is beginning to cook. It is important to note that reheating cooked foods that are liquid or contain liquid may be a transgression of the Torah’s prohibition against cooking on Shabbos. Solids that have been fully cooked before Shabbos may be re-heated (i.e. kugel or roast) on Shabbos. However, due to the prohibition chazarah, reheating must be done in a way that cannot be confused with cooking. Therefore one may place a kugel or challah on top of a pot of food that is on the blech, but not on top of the blech itself.

Ovens and Warming Drawers:
Now that we have discussed some of the basic principles, of warming food on shabbos, let us examine what happens in practice when using an oven or warming drawer.

As mentioned, aside from the prohibition against cooking on Shabbos there is a prohibition against initiating a fire or causing increased burning. In the case of thermostatically controlled ovens and warming drawers, opening the oven or warming drawer will cause the mechanism to call for increased burning to make up for the heat lost by opening the door or drawer. The resulting effect is a grama of havarah, which is not permisible on Shabbos. However as discussed earlier, where one does not want or intend for an action to take place, and has no need for its result, the initial action is prohibited only by Rabbinic law. When coupled with the fact that the ensuing melacha is a reaction that was brought about indirectly, but was initiated through a grama, there is room for leniency and the initial action is permitted. Therefore food left in the oven or warming drawer from before Shabbos may be removed on Shabbos, despite the fact that this will eventually cause the oven to burn. This is because with the removal of the food the resulting additional burning is not wanted or intended. However this can be said only where all of the food is removed at one time. If some food remains in the oven to be heated, then the additional burning caused by the door opening is viewed as intentional and therefore prohibited. Most warming drawers and ovens are thermostatically controlled and would fall into the above category.

If a warming drawer is not controlled by a thermostat one must check with the manufacturer to be sure that by opening the drawer he is not turning off the heating element. If there are multiple temperature settings, these controls must be covered as discussed earlier regarding stovetop controls. Even where the warming drawer is not controlled by a thermostat and the opening of the drawer will not affect the flow of power to the heating element, one cannot place food into the warming drawer on Shabbos if its operating temperature is higher than yad soledes, 120 degrees, as this is prohibited under the laws of chazarah.

Induction Cooktops
An induction cooktop heats ferrous metals using strong magnetic fields.  By placing or removing an iron vessel on the induction cooktop, you will initiate or stop the process of heating the metal.  Therefore, they cannot be used on Shabbos or Yom Tov.

Sabbath Mode Ovens
Due to the halachic complications that technological innovations have placed upon the Jewish consumer, the Star-K has been working with some manufacturers to design ovens that are more user friendly to the Jewish consumer (see appliance section for names of appliance manufacturers). Some of the common problems found in new ovens are twelve hour safety cut off, lights, icons and temperature displays that may be turned on by opening the oven door, and time bake features that must be manually turned off to silence the bell. In certified models, many of these features are disabled. (See appliance section for details of individual models.)

In addition, some Sabbath mode features such as temperature adjustment are quite practical and allow for easier use of the ovens on Yom Tov where the restrictions of cooking and burning are lifted when done under prescribed conditions. However, the Sabbath mode features do not in any way circumvent the regular restrictions involved in food preparations on Shabbos Kodesh.The laws of Bishul, Havarah, Shehiyah and Chazarah must still be observed even when using a Sabbath mode oven (see memo regarding oven use on Shabbos).

Please note that these are limited to the oven and do not apply to the use of the stovetop.

Common Questions & Answers
Now that we have reviewed the basic rules, let us look at some frequently asked questions about oven and stovetop use on Shabbos and the responses given by Rabbi Moshe Heinemann, Shlita, Star-K’s Rabbinic Administrator.

I have a smoothtop electric stove. The manufacturer says that this should not be covered or it will crack. Can I leave my food on the smooth cooktop on Shabbos without a blech?
It is customary to cover the heat source as was done in the past when one cooked directly on the embers. The concern at that time was to prevent stirring the embers to add heat. As noted in our introduction, today the primary concern is that one should not try to raise the heat so that the food will cook faster. When one cannot place a blech on the stove top, it is sufficient to cover the controls and leave the cooked food on the stovetop.

May I adjust the temperature of an oven that has a Sabbath mode feature on Shabbos?
No! The temperature adjustment feature in the Sabbath mode oven is for Yom Tov use only. (This issue is addressed in the Kashrus Kurrents article titled, “Oven Kashrus: For Yom Tov Use.” ) On Shabbos, one may not adjust the temperature, as that causes the fire to burn or be extinguished. Nor does the Sabbath mode allow you to put food up to cook or reheat on Shabbos.

May I leave cooked food in an oven that is on if it was placed in the oven before Shabbos?
Yes. However, because of shehiyah, the controls for the oven should be covered or taped. It is customary to cook all food before Shabbos to the point that it is edible for the average individual.

May I open my oven to take food out on Shabbos?
First, one must be sure that opening the oven door does not automatically cause a light, icon or electrical switch or flame to go on. In the case of convection ovens, the door opening may cause the circulating fan to go off. Even though one does not intend to do these actions, it is prohibited, as if there were intent, since this is an automatic consequence. If opening the oven door does not automatically set off an electrical reaction, then one may do so in order to remove food on Shabbos, provided that all the food is removed at that time. Note: Often the door will have a plunger switch which turns on lights or icons as a door is opened. If this plunger switch is disabled it may prevent any prohibited reactions from taking place. Some Star-K Sabbath mode ovens have a feature to disable icons, lights or signals so that the oven door may be opened on Shabbos and Yom Tov.

May I take out some food from the oven and leave the rest to remove later?
No. When one opens the oven door, one is letting cool air into the cabinet. The thermostat will sense the loss of heat and make up for it by additional burning. When one opens the oven door, one indirectly causes additional burning. This is gram havarah which, in its own right, is Rabbinically prohibited. However, normally one does not want the burner to go back on if the oven is empty. Even though opening the oven door will cause the fire to burn longer, one does not want this to happen. On the contrary, it is a needless waste of gas or electricity. This is considered a psik reisha d’lo nicha leih. Although we do not allow a psik reisha d’lo nicha leih on a Torah prohibition, this action occurs indirectly as a grama and is only a Rabbinic prohibition.6 Therefore, here where there is a combination of factors (a grama on a psik reisha d’lo nicha leih), it is permitted. If one leaves food in the oven after the door has been opened, he obviously wants the oven to go back on. This is prohibited as a psik reisha d’nicha leih, as if one intended to cause the fire to burn longer. If one accidentally opens the oven door, he must remove all the food. Therefore, the oven door cannot be opened to check on the food. If the door was accidentally opened and closed and no food was removed, the food is still permitted to be eaten provided that it was completely cooked before Shabbos.

May I use a warming drawer on Shabbos?
As discussed earlier, one may not put food into a warming drawer on Shabbos. Most warming drawers are regulated by a thermostat. When you open the drawer to put the food in, you are going to cause the burner to go on and compensate for the heat loss that you created. By keeping food in the drawer, you are showing that you want this extra heat to be generated. This is prohibited on Shabbos.7

If the food was placed in the drawer before Shabbos, a warming drawer must be emptied the first time it is opened. A warming drawer that has adjustable temperature settings that include temperatures over yad soledes (120°F) is like an oven, and must have its controls covered. If the warming drawer’s settings are all below yad soledes, there is no gezeirah, Rabbinic prohibition, regarding raising the setting. Therefore, the controls do not have to be covered. However, one may not change the setting on Shabbos.

My oven and warming drawer have a delayed start timer feature. May I set it to go on Shabbos morning and place the food to be heated there on Shabbos before the pre-determined time?
No. The food should not be placed there to be heated on Shabbos.

For information on ovens and cookware and further parameters
under which they may be used, see the
appliance section of our website.

1. Shemos 35:3.

2. Psik resha d'lo nicha leh asur l'rov harishonim.

3. See Biur Halacha 253:1 Venohagu.

4. Garuf v'katum.

5. Yiddish for metal sheets.

6. Also, it is a melacha she'aino tzricha legufo.

7. Psik reisha on the burning.

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