Summer 2024

Slow cookers and hot plates are the workhorses of many kosher kitchens as they enable the Sabbath-observant hostess to serve piping hot dishes to her family and guests to enhance the Shabbos seuda. In recognition of their importance in a Jewish home, it behooves us to review the halachos involving these appliances about which many users might not be aware.

This article will try to clarify the potential issues and how to address them in a practical way.

Slow Cookers

There are two basic types of electric slow cookers: an insert type (often referred to as a Crockpot®), in which a stoneware vessel sits inside a heated base; and a flatbed type, in which a metal pot sits atop a griddle base. Halachic issues involving their use include hatmana, shehiya and chazara. These will be explained below. (There are some more expensive models equipped with variable thermostats which make their usage on Shabbos more complicated; these are not addressed in this article.)

► Hatmana – Insulating Food on a Fire on Shabbos

Chazal forbade the wrapping of hot food on Shabbos to preserve its heat. They also forbade placing wrapped food on a heat source even before Shabbos – even if the wrapping was also done before Shabbos – or if the wrapping itself adds heat to the food. This halacha is called hatmana b’davar hamosif hevel.[1]

Rav Shlomo Zalman Auerbach zt”l is famous for his opinion that an insert-type slow cooker is by definition a situation of hatmana b’davar hamosif hevel, since the pot is completely inserted in a base which houses the heating coils.[2]

Other opinions disagree, based on a Rama who states that hatmana (wrapping) only occurs when the food is covered on all sides and the top.[3] When the lid of the slow cooker isn’t covered, according to most opinions it is not considered hatmana, and an insert-type slow cooker may be used on Shabbos.[4]

One who wishes to be stringent and follow the opinion of Rav Shlomo Zalman should place something (e.g., balled up sheets of aluminum foil) under the pot to slightly lift the sides so that it is no longer completely submerged within the base. Using a slow cooker in this way will not be considered hatmana according to most opinions.[5]

► Shehiya – Leaving an Uncooked Food on a Fire on Shabbos

The Mishna in Shabbos teaches us that one is forbidden to leave an uncooked item on the fire on Shabbos lest he might come to stoke the fire and hasten the cooking process.[6] This concept applies to any food being cooked on any heat source, which includes a slow cooker.

The way to permit the above situation is to cover the heat source that is under the pot, thereby creating a heker, a distinctive difference which would stop a person from stoking the fire. If the heat source is covered with a blech, food may be left on a flame.[7]

Some contemporary opinions hold that covering a fire only works when the covering diminishes the heat at least slightly, but if there is no minimization of the heat through the blech, that will not satisfy the rabbinic necessity for it.[8] In the case of a slow cooker, placing a blech (e.g., a sheet of aluminum foil) in the small space between the crock and the base not only does not diminish the heat, but may in fact increase it by insulating the pot, and thereby trapping the heat. Thus, according to this opinion, the use of a blech inside an insert slow cooker will not resolve the issue of shehiya.

Other opinions hold that the main function of a blech is to make a heker, and that doing so allows one to leave a pot on a fire even if it does not diminish the heat.[9] According to this view, one could create a blech simply by placing foil between the pot and the base.

Another option to satisfy the need for a blech and to avoid the above dispute is by covering the knob on the front of the slow cooker. This eitzah is a matter of dispute by poskim: whether the takana (rabbinic law) to place a blech must be over the actual fire or over the spot where one would actually “stoke the coals” – which, in modern times, is the knob. This view – that it is sufficient to cover the knobs – is that of the Rosh Yeshiva, Rav Aharon Kotler zt”l.

According to his talmid, STAR‑K Rabbinical Administrator Rav Moshe Heinemann shlit”a, one may follow Rav Aharon’s opinion, especially in the case of an insert-type slow cooker in which it is questionable if a regular blech works as explained above. Still, it is preferable, whenever feasible, to cover both the fire and the controls.

► Chazara: Returning a Cooked Food to a Fire on Shabbos

Chazal forbade one who removes a pot from the fire to place it back on the fire (constituting an act of chazara), unless certain requirements are met. One of these is the necessity of a blech.

Even if one relies on the above ruling of Rav Aharon to satisfy the need for a blech, we must discuss if he intended to be lenient with covering only the knob/control with regard to shehiya (as discussed above) or even to allow chazara (returning a pot to the fire on Shabbos).

A very brief explanation of this question is as follows. There are two reasons mentioned for the rabbinical prohibition of chazara:[10]

• shema yechateh (one may come to stoke) – upon returning the food, one may be enticed to stoke the fire to maintain a hot pot.

• michzi k’mevashel (one appears to be cooking) – the action of placing a pot on a normal fire appears like one is cooking on Shabbos. When the fire is covered, the fire is clearly different and placing food on a covered fire does not look like regular cooking.

Does covering the knob correct the second issue of chazara, which is that it appears to be cooking? Maybe it’s only corrected when the fire is altered slightly? Or is a fire whose controls are altered by being covered also not appear as cooking?

It is brought down that the Chazon Ish held that covering the knob only helps for leaving a pot (shehiya) but does not help for returning it (chazara).[11] In the sefer Kovetz HaMishor, however, it states clearly that Rav Aharon held that covering the knobs works for chazara as well, and this is the understanding of Rav Heinemann – that Rav Aharon intended to be lenient even for chazara.[12]

To conclude, one can rely on the ruling of Rav Aharon if necessary on this point as well – to allow chazara with just the knobs of the slow cooker covered – provided one adheres to all the other halachos of chazara: i.e., the food is fully cooked, the food is still warm, there was an intention to return, and one never let go of the vessel.[13]

Hot Plates or Warming Trays

As with slow cookers, there are different types of electric hot plates and warming trays: a simple plug-in type with a single setting that cannot be adjusted versus others that offer variable temperature settings with adjustable temperature controls.

Although simpler than an insert-type slow cooker, a hot plate – popularly referred to as a “plata” – still raises halachic questions regarding shehiya and chazara on Shabbos.

► Shehiya: Is a Blech Required to Leave Uncooked Food on a Hot Plate Over Shabbos

A warming tray that has adjustable temperature controls unquestionably needs a blech for the same reason cited above by an insert-type slow cooker: Chazal were worried that one might want to “stoke the flame” – that is, to adjust the temperature. For a one-setting hot plate, a blech would not be necessary for shehiya.

► Chazara: Can Cooked Food be Returned to a Hot Plate on Shabbos

Rav Moshe Feinstein zt”l has a teshuva in which he writes that one may do chazara on a single-setting hot plate (or any heat surface) that is made specifically to keep food warm or to re-heat food without placing a blech. He also permits one to take a fully cooked, dry item directly from the fridge on Shabbos and place it on such a surface (i.e., without the need for a blech).[14]

The rationale for this view is based on what was explained earlier regarding chazara, which has two reasons for its prohibition: shema yechateh and michzi k’mevashel; on such a surface there is no concern about “stoking the fire” because there is no control at all, and there is no concern about the appearance of cooking because, in general, people do not cook on a hot plate.

Contemporary poskim point out, however, that Rav Moshe’s teshuva – which allows one to do chazara without a blech and even to put a cold item directly on a hot plate – only applies in the case of an appliance on which it is not possible to cook at all.[15]

Once cooking (i.e., heating to 120°) on this surface is a possibility – regardless of how long it may take – we don’t differentiate between this appliance and any others that enable one to cook. Whether a hot plate can or cannot be used for cooking will vary according to different appliance models, but the rule stays the same: if it is possible to cook on the surface (even if it would take a while), one can only return food to it if it has a blech, keeping in mind all the other rules of chazara cited above. If cooking is not possible on this surface, then both opinions agree that Rav Moshe would allow chazara without a blech, and even to place a cold, dry and fully cooked item on it for the reasoning explained above.

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[1] שו”ע או”ח סי’ רנ”ז סעי’ א.

[2] ספר ארחות שבת עמ’ תקמ”ד.

[3] שו”ע שם סי’ רנג סו”ס א ומ”ב שם ס”ק מח.

[4] עי’ שו”ת שבט הלוי ח”ט סי’ נ”ב ושו”ת עמק התשובה ח”ד סי’ י”א אות ב’, וכן בספר אוצרות השבת עמ’ תקי”ט.

[5] קובץ תשובות למרן ר’ אלישיב זצ”ל ח”ג סי’ מ”ג וספר אוצרות השבת עמ’ תקי”ז.

[6] משנה שבת דף לו ע”ב.

[7] שם ובשו”ע שם סי’ רנ”ג ס”א.

[8] לשון המחבר שם סי’ רנ”ג ס”א למעט חומם.

[9] שמעתי מאבי מורי שליט”א.

[10] עי’ מ”ב סי’ רנ”ג ס”ק ל”ז ובשער הציון אות ל”ז שם.

[11] ספר מעשה איש ח”ז עמ’ קמ”ב.

[12] קובץ תורני המישור (על עניני שבת) עמ’ כ”ד (לייקווד תשס”ח).

[13] שו”ע סי’ רנ”ג סעי’ ב.

[14] שו”ת אגרות משה או”ח ח”ד סי’ ע”ד הל’ בישול אות ל”ה.

[15] כן שמעתי מאבי מורי שליט”א והרב יעקב אפרים פארכהיימר שליט”א.