Using a Warming Tray on Shabbos

Kashrus Kurrents Winter 2009

Q:       I would like to buy a warming tray that has been manufactured for the Shomer Shabbos community. It is a glass covered warming tray and has a variable temperature dial with a removable knob. It can be set at a minimum temperature of 110 0F and a maximum temperature of 230 0F. It has a sticker on it stating that it is intended solely for the reheating of cooked foods and is not intended to be used for cooking. How may this tray be used on Shabbos?

A:  In order to answer this question, one must have an understanding of the Rabbinic prohibitions of shehiyah and chazarah.  The parameters of these two prohibitions differ for Ashkenazim and Sefardim.  This response will explain the halachah as it applies to Ashkenazim.

Shehiyah:  Shehiyah is the act of placing food on an open flame before the onset of Shabbos so as to allow it to remain there when Shabbos begins.1  The Torah permits one to do this, even though the food will cook on Shabbos, because the person has placed the food on the flame before Shabbos and  no action is being performed by him during Shabbos itself.2  However, the Rabbonon forbade this unless a number of conditions are met.  In certain circumstances, Chazal necessitate covering an open flame.  Due to the complexity of hilchos shehiyah, and the difficulty of assessing whether or not this ruling applies, it is customary to always cover an open flame.3  Regarding our stovetops, where the flame is controlled by knobs, Rav Ahron Kotler, zt”l, paskened that covering the knobs is equivalent to the classical covering of the flame, although he advised covering the flame as well.4  However, Rav Moshe Feinstein, zt”l, took the opposite position.  He paskened that the flame itself must be covered, and he encouraged covering the knobs.5

For this reason, it is customary to place a blech on the stovetop which serves as a covering for the flame.  The food to be heated is then placed on the blech before Shabbos.  If the food is not fully cooked, any action taken on Shabbos which speeds up the cooking process would be considered bishul.6  For example, one would not be allowed to remove and then replace the lid of a pot, since replacing the lid causes the food to cook faster.7 In order to avoid this issue, it is customary to fully cook all food before the onset of Shabbos.8

Therefore, it is ideal that all food placed on a warming tray be fully cooked at the onset of Shabbos, and that the knob be covered or removed.  It is not advisable to cover the flame of a glass covered warming tray, as such a covering traps the heat and may cause the glass to crack.  Consequently, the custom to cover the flame would not be applied, and the fully cooked food  may be placed directly on the warming tray before Shabbos.

Chazarah:  Chazarah is the act of replacing fully cooked food onto a flame during Shabbos.9 The Torah permits the reheating of fully cooked solid food, as the melacha of bishul is limited to cooking raw food.10  The Rishonim debate whether or not the Torah permits the reheating of fully cooked liquids.11  However, the Rabbonon forbade the reheating of fully cooked food unless all of the following conditions are met: (i) the food had already been on a flame during Shabbos and was temporarily removed, with the intention of returning it to the flame; (ii) the pot containing the food was in one’s hand the entire time that the food was off the flame; (iii) the food did not cool down completely; (iv) the food is not being returned into an oven; and (v) the flame to which the food is being returned is covered.12

Therefore, it would be halachically acceptable to reheat food on a warming tray on Shabbos if the food had been temporarily removed from the tray, and the flame had been covered.  However, as previously mentioned, it would not be advisable to cover the glass tray, as this may trap the heat and cause the glass to crack.  Although the heating element in the warming tray is not visible (as it is covered by the metal of the tray), this is not considered a sufficient covering for Shabbos, as the metal is part of the unit and the flame has not been covered specifically for Shabbos.13  It would, therefore, seem that food cannot be reheated on this warming tray during Shabbos.

However, some Poskim do allow the reheating of food on a warming tray during Shabbos.  This is due to the fact that there is a situation where chazarah is permitted.  One is allowed to place a fully cooked solid on a heat source which is not normally used for cooking.  For example, one may reheat fully cooked solid food by placing it on top of other food which is on a flame, as food is not normally cooked in this manner.14  Similarly, one may reheat fully cooked solid food by placing it on a radiator, which is not normally used for cooking.15  It could be argued that the same principle would apply to a warming tray, as it is intended to be used for reheating food and not for cooking it.  If so, chazarah would be permitted on a warming tray, and the prohibition of shehiyah would also not apply.  Contemporary Poskim debate this issue.

Rav Shlomo Zalman Auerbach, zt”l, was of the opinion that a stovetop and a warming tray may be considered as two halachically distinct items, and he therefore allowed the use of warming trays for both shehiyah and chazarah on Shabbos.16  He limits this to returning food which had originally been on the tray from the onset of Shabbos and was merely temporarily removed.  He  does not allow the reheating of food which had not been on the tray during Shabbos, and would not allow one to take a fully cooked food out of the refrigerator and place it on a warming tray during Shabbos.17

However Rav Elyashiv, shlit”a, paskens that the same halachos would apply to both a stovetop and a warming tray.18  Even though a warming tray is designed for reheating, it reaches a high temperature which could be used for cooking; it should not be considered different than any other cooking surface.  Therefore, chazarah would be permitted only if all of the previously mentioned conditions set by the Rabbonon are met.  The warming tray would need to be covered with heavy duty foil before Shabbos so that the flame would be considered covered.19

Rav Moshe Feinstein, zt”l, paskens that chazarah would be permitted on a warming tray that cannot be used for cooking.20  The implication is that the rules of chazarah would apply to a warming tray which is hot enough to be used for cooking.21  The glass topped warming tray in question reaches a temperature of 230 0F, which is hot enough to cook food.  However, it has been claimed that since the heat emanating from the warming tray is not confined to an enclosed area, the ambient heat of the food would not be high enough to fully cook it.  Rav Heinemann, shlit”a, does not accept this claim and paskens that the rules of chazarah would apply to this type of warming tray.  He adds that the sticker on the warming tray stating that it is not intended to be used for cooking does not change the fact that it could be used for cooking.  Therefore, Rav Heinemann paskens that the rules of chazarah would apply.22

There is another exception stated by Chazal.  One may place uncooked food in an oven before Shabbos  if the oven is then sealed shut.  The prohibition of shehiyah would not apply, due to the fact that the oven  has been sealed before Shabbos.23  It could be argued that removing the knob of the warming tray is equivalent to sealing the oven.24  Rav Shlomo Zalman Auerbach, zt”l, states that it is not clear as to whether shehiyah is permitted after the knob has been removed.  Furthermore, he adds that chazarah would certainly not be permitted.25  Rav Elyashiv, shlit”a, has been quoted as saying that one should not rely on removing the knob in order to permit shehiyah.26

Therefore, a person who would like to use this warming tray in a manner that all Poskim would accept should ensure that all food placed on the warming tray be fully cooked before the onset of Shabbos and cover or remove the knob.27


Halachic queries regarding all topics may be presented to The Institute of Halacha at the Star-K by calling 410-484-4110 ext. 238.

1.עי’ הקדמת המ”ב לסי’ רנג

2.שו”ע או”ח סי’ רנב ומ”ב שם ס”ק א

3.עי’ שו”ע ורמ”א סי’ רנג סעי’ א וביה”ל שם ד”ה ונהגו, ועי’ ברמ”א שם סעי’ ב ובמ”ב שם ס”ק עב וס”ק עד ובשש”כ פ”א סי’ סג 

4.שמעתי ממו”ר ר’ היינעמאן שליט”א

5.שו”ת אג”מ או”ח ח”א סי’ צג, וכן דעת הגרש”ז אויערבאך זצ”ל בשלחן שלמה סי’ רנג אות ה קטע ג שצריך לכסות האש דוקא, וכ”כ בס’ שבות יצחק ח”ב עמ’ כא בשם הגרי”ש אלישיב שליט”א

6.שו”ע סי’ שיח סעי’ ד ומ”ב שם ס”ק כו

7.שו”ע סי’ רנז סעי’ ד וביה”ל שם ד”ה גורם

8.שש”כ פ”א סי’ סג, ושמעתי ממו”ר ר’ היינעמאן שליט”א שכן נוהגים

9.שו”ת אג”מ יו”ד ח”ב סי’ נב, וסיים שם שמדת החום לענין להתחשב יין מבושל הוא יד סולדת בו ואף שכתב הש”ך סי’ קכג ס”ק ז דבעינן שיתמעט ממדתו ע”י רתיחה מ”מ גם ביד סולדת כבר נתמעט משהו, וממו”ר ר’ היינעמאן שליט”א שמעתי שבזמנינו שעושים יין מפוסטר בכלים סגורים יתכן שהיין לא נתמעט ממדתו ולכן במקום שעושים יין מפוסטר תחת השגחת הStar-K מקפידין שיהיה פתח להכלי כדי שהיין יתמעט ממדתו

10.שו”ע סי’ שיח סעי’ ד וסעי’ טו

11.עי’ רמ”א שם סעי’ טו

12.עי’ שו”ע ורמ”א סי’ רנג סעי’ ב, ובמ”ב שם ס”ק נו כתב שבעת הצורך יש להקל אם עודן בידו אפילו אין דעתו להחזיר וכן אם דעתו להחזיר אף שבינתים הסירן מידו

13.עי’ בר”ן שבת דף טו ע”ב בדפי הרי”ף ד”ה עד שכתב שצריך לעשות מעשה להכירא

14.שמעתי ממו”ר ר’ היינעמאן שליט”א

15.שו”ת אג”מ או”ח ח”ד סי’ עד אות לד (ומש”כ שם שהמאכל חם קצת נראה דמיירי בדבר לח)

16.עי’ שש”כ פ”א הערה עא בשם הגרש”ז אויערבאך זצ”ל, ואף הוא לא כתב להתיר אלא בפלטה שא”א להגדיל את מידת החום שלה

17.עי’ שש”כ ח”ג בתיקונים ומלואים שם

18.שבות יצחק ח”ב עמ’ צו בשם הגרי”ש אלישיב שליט”א, וכ”כ בעל השבות יצחק תשובה מפי ר’ אלישיב שליט”א בספר אוצרות השבת עמ’ תד, וכ”כ בס’ הל’ שבת בשבת ח”א עמ’ רד בשם הגרי”ש אלישיב שליט”א, וע”ע בס’ ארחות רבינו עמ’ קב אות יא שהביא כן בשם החזו”א

19.שבות יצחק שם בשם הגרי”ש אלישיב שליט”א, ועי’ בשלחן שלמה סי’ רנג אות ה קטע ב

20.שו”ת אג”מ ח”ד סי’ עד אות לה

21.אוצרות השבת פ”ב הערה קל

22.שמעתי ממו”ר ר’ היינעמאן שליט”א

23.עי’ שו”ע ורמ”א סי’ רנד סעי’ א ומ”ב שם ס”ק יד

24.ספר ארחות שבת פ”ב סעי’ יח

25.שו”ת מנחת שלמה מהדורא תנינא (דפוס ראשון) סי’ לד אות כא ושלחן שלמה סי’ רנג אות יא

26.מאור השבת ח”ב עמ’ רפו בשם הגרי”ש אלישיב שליט”א

27.כן שמעתי ממו”ר ר’ היינעמאן שליט”א שיש להשתמש בפלטה חשמלית רק באופן זה