Reheating Cooked Food on Shabbos
ANSWER: There is a well-known Talmudic dictum that “ain bishul achar bishul” (there is no cooking after cooking, and cooked food may be reheated). The Shulchan Aruch (OC 318:4) limits this precept to dry foods which are changed by the cooking process. When solid food cools, it is still cooked, and reheating it is not considered an act of bishul. As such, on a Biblical level it is permissible to reheat dry cooked food on Shabbos because “ain bishul achar bishul”. On the other hand, a liquid that is cooked does not undergo a structural change and is only considered cooked while it is hot, but not when it cools down. A cooked liquid that has cooled may not be reheated on Shabbos because “yesh bishul achar bishul bidavar lach”, there is cooking after cooking for a liquid.
Although reheating dry food is permissible on a Biblical level, Chazal prohibited placing cooked food on a stove or in an oven on Shabbos because it might appear to the onlooker that one is cooking raw food on Shabbos (michzi ki’mevashel), and also because one might adjust the fire (shema yechateh). One permissible method for warming fully cooked dry foods on Shabbos is to place the food into a bowl of hot water. Since the bowl is not on the fire, it does not give the impression that the food is raw, and there is no fire that can be adjusted.
In halacha, there are different levels of cooking and heating food: on a stove or in an oven, in a kli rishon (a pot that was removed from the fire), in a kli sheini (a secondary vessel which was filled with liquid from a kli rishon) and in a kli shlishi (a third vessel, which was filled from a kli sheini). In future Halacha Yomis' we will discuss the status of cooking and reheating food in each of these different manners.
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The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt"l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.