Reheating food on Shabbat (Shulchan Aruch, Siman 318) depends on three factors: a solid food fully cooked and then cooled may be reheated (ein bishul achar bishul), a cooled liquid may not, and the outcome shifts with the heat source (hot plate, fire) and the vessel (kli rishon or kli sheni).
For sauces, mixed solid-liquid dishes, and returning to the hot plate with a lid: ask your Rav.
Cooking (מבשל) is a Torah-level melachah on Shabbat. But a food that is solid, fully cooked and then cooled is not "re-cooked" — this is the principle ein bishul achar bishul. From there, everything depends on three parameters: the food (solid or liquid), the heat source (hot plate, fire, hot water), and the vessel (kli rishon or sheni). For your concrete case — ask your Rav.
Friday night's stew has gone cold. Can you put it back on the hot plate? Pour hot soup over bread? Reheat leftovers with boiling water? These everyday actions touch on one of the most intricate melachot of Shabbat: מבשל (cooking), treated in Siman 318 of the Shulchan Aruch.
Why is cooking so sensitive on Shabbat?
Cooking is one of the 39 melachot forbidden by the Torah (an av melachah). Siman 318 codifies its rules across many seifim. The Mechaber (Rabbi Yosef Karo) even opens with the penalty that applies to food cooked in transgression:
המבשל בשבת… במזיד אסור לו לעולם ולאחרים מותר למוצאי שבת מיד; ובשוגג אסור בו ביום גם לאחרים, ולערב מותר גם לו מיד.
One who cooks on Shabbat intentionally: the food is forbidden to him forever; to others, only after Shabbat ends. Inadvertently: forbidden that day, permitted to him that very evening. This is the principle of ma'aseh Shabbat (מעשה שבת).
In other words, the topic must be handled with care. Let us look at the three notions that govern everything.
The 3 key notions of reheating
1. Yad soledet bo — the cooking threshold
There is "cooking" only from a certain heat: the point at which the hand recoils instinctively (often estimated around 45°C). Below this threshold, many opinions hold that there is no cooking.
2. Ein bishul achar bishul — no cooking after cooking
A food that is already fully cooked is not "re-cooked." Seif 4 makes a decisive distinction: a solid, dry food may be dipped in something hot; but for a liquid dish (with sauce or broth) that has cooled, several opinions hold that there is a renewed cooking ("mitztamek ve-yafeh lo," מצטמק ויפה לו).
3. Kli rishon / kli sheni — the role of the vessel
The kli rishon is the vessel that was heated on the fire: it still cooks while it is hot. The kli sheni is the second vessel into which food is transferred: its walls do not scald, so it cooks far less. Pouring from one or the other therefore does not carry the same status.
Seif 3 adds that even cooking by derived heat (toldot ha-ur, תולדות האור) — for example placing an egg against a scorching pot — is forbidden just like cooking on the fire itself.
Modern application: hot plate, pot, hot water
- The hot plate (Shabbat blech/plata): returning a dish to it raises questions of cooking and of "chazarah" (returning a dish to the heat) — with precise conditions depending on the food and its state.
- A cooled liquid dish: the most sensitive point, since "no cooking after cooking" does not apply to liquids in the same way.
- Pouring hot water: it all depends on whether you pour from a kli rishon or a kli sheni, and onto what kind of food.
- The microwave: this is active cooking — outside the permitted framework of Shabbat reheating.
This article presents what the source says for the purpose of study. Reheating on Shabbat depends on many details (food, state, vessel, minhag). To know what is permitted in your kitchen, ask your Rav.
Frequently asked questions
Can you reheat already-cooked food on Shabbat?
The principle ein bishul achar bishul teaches that a solid food fully cooked and then cooled is not re-cooked — but it depends on the food (solid/liquid), the heat source and the method. For practice, ask your Rav.
What is yad soledet bo?
It is the heat threshold at which cooking occurs in the halachic sense — the temperature at which the hand recoils (often estimated around 45°C).
Kli rishon or kli sheni: what is the difference?
The kli rishon was heated on the fire and still cooks while hot; the kli sheni, into which food was transferred, cooks far less. A central distinction for reheating.
Study Siman 318 in depth
Four levels, from beginner to talmid chacham — Hebrew text, translation, pilpul and the shitah of the Admur HaZaken.