Oven Kashrus: For Shabbos Use

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 stovetop on Shabbos and Yom Tov, it is worthwhile to review some laws and concepts as they relate to cooking on Shabbos and Yom Tov.


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


The prohibition of cooking on Shabbos is defined as the act of using heat to make a substance edible, or to change its current 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 havara. Furthermore, one may not carry out an action that will cause the flame to ignite if it is the end result of his action. The term for this is gram havarah.


There is a general rule regarding actions prohibited by the Torah which 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 when 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 he 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). A 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 performed that is unintended and unwanted on Shabbos (lo nicha leih), the action may be performed. This is the basis for allowing one to open a refrigerator door on Shabbos. In such a 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 havara) is unwanted and unintended.


Many rabbinic laws were initiated to prevent one from transgressing the Torah’s prohibitions. They are intended to distance us from what is prohibited, as well as to prevent us from performing actions which can be misconstrued with a prohibited melacha.
Shehiya– Among these rabbinic laws is Shehiyah. 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 were 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 which would add oxygen and generate heat. By stirring the embers, one transgresses two Torah prohibitions: burning a fire on the Shabbos day, and cooking (if the food is not yet cooked).
In order to prevent any wrongdoing, the rabbis decreed that unless the food is edible before Shabbos3 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 cooktop, one should cover the temperature controls in addition to covering the flame with a blech.
Chazara– Another rabbinic prohibition is Chazara, 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; it may not leave his hand from the time it was removed to the time it was replaced on the heat. This certainly would prohibit taking a cold pre-cooked food and placing it on a blech on Shabbos. This rabbinic decree was instituted because by placing 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. Solid foods that have been fully cooked before Shabbos may be reheated (i.e., kugel or roast) on Shabbos. However, due to the prohibition of Chazara, 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.


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 previously noted, aside from the prohibition of 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 a mechanism to call for increased burning in order to compensate for the heat lost by opening the door or drawer. The resulting effect is a grama of havara, which is not permissible 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 by rabbinic law only. When coupled with the fact that the ensuing melacha is a reaction that was brought about indirectly, 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 action will eventually cause the oven to burn. This is because removing the food results in additional burning that is not wanted or intended. However, this can be said only when all of the food is removed at one time. If some food remains in the oven to be heated, the additional burning caused by opening the door is viewed as intentional and is, 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 opening the drawer will not turn off the heating element. As previously discussed regarding stovetop controls, if there are multiple temperature settings these controls must be covered. Even when the warming drawer is not controlled by a thermostat, and opening 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, 120oF. This is prohibited under the laws of Chazara.


An induction cooktop heats ferrous metals using strong magnetic fields. By placing or removing an iron vessel on the induction cooktop, one will initiate or stop the process of heating the metal. Therefore, induction cooktops should not be used on Shabbos or Yom Tov.


Due to the halachic complications placed upon the Jewish consumer by technological innovations, STAR-K has been working with some manufacturers to design ovens that are more user friendly. Some of the common problems found in new ovens are 12-hour safety cut offs lights, icons and temperature displays that may be turned on or off by opening the oven door; and timed bake features that must be manually turned off in order to silence the buzzer. In certified models, many of these features are disabled.
Additionally, some Sabbath mode features such as temperature adjustment are quite practical and allow for easier use of the ovens on Yom Tov where restrictions of cooking and burning are lifted 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, Havara, Shehiyah, and Chazara must still be observed, even when using a Sabbath mode oven. Please note that the Sabbath mode programming is limited to ovens and does not apply to the use of the stovetops.

Now that we have reviewed the basic rules, let us look at some frequently asked questions about oven and stovetop use on Shabbos. The responses have been provided by Rabbi Moshe Heinemann, shlita, STAR-K Rabbinic Administrator.
Q. 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?
A. 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 earlier in the 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.
Q. On Shabbos, may I adjust the temperature of an oven that has a Sabbath mode feature?
A. 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 entitled, “Oven Kashrus: For Yom Tov Use.” ) On Shabbos, one may not adjust the temperature as this would cause the fire to burn or be extinguished. The Sabbath mode does not allow one to put food in to cook or reheat on Shabbos.
Q. May I leave cooked food in an oven that is on if it was placed in the oven before Shabbos?
A. Yes. However, due to Shehiya 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.
Q. May I take out some food from the oven and leave the rest to remove later?
A. No. When one opens the oven door, he is letting cool air into the cabinet. The thermostat will sense the loss of heat and compensate for it through additional burning; when one opens the oven door, he indirectly causes additional burning. This is a gram havara 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, when there are 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, all of the food must be removed and the oven door cannot be opened again during Shabbos. (If the oven door was accidentally opened and closed, and no food was removed, it is still permitted to eat the food provided that it was completely cooked before Shabbos.)
Q. 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?
A. No. The food should not be placed in the oven to be heated on Shabbos.
Q. May I open my oven to take food out on Shabbos?
A. 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 or off. In the case of convection ovens, opening the door may cause the circulating fan to go off. Even though these actions are not intended, they are prohibited as if there was 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 that 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.
Q. May I use a warming drawer on Shabbos?
A. 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 inside, 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 with adjustable temperature settings that include temperatures over yad soledes (120°F) is like an oven, and its controls must be covered. If the warming drawer’s settings are all below yad soledes there is no gezeira, rabbinic prohibition, regarding raising the setting and the controls do not need to be covered. However, one may not change the setting on Shabbos.

1. Shemos 35:3
2. Psik resha d’lo nicha leh asur l’rov harishonim
3. See Biur Halachah 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