“Leaving,” Insulating, and Returning”
In the previous Halachot we have discussed when it is permissible to place a pot of food on a stovetop or electric hotplate before the onset of Shabbat. These laws are nicknamed the laws of “leaving,” i.e. leaving the food on the fire before Shabbat. We then discussed the laws of “insulating” the pot of food with clothing and the like before Shabbat or on Shabbat itself.
We shall now discuss situations when it is permissible to warm up a food which was fully-cooked before Shabbat on Shabbat itself. These laws are referred to as the laws of “returning,” i.e. returning a fully-cooked food onto the fire on Shabbat.
Placing a Fully-Cooked Food on an Open Flame
Before we discuss the permissible methods of warming up foods on Shabbat, let us introduce this topic with a law that is certainly always forbidden. It is forbidden by means of a rabbinic injunction to place a fully-cooked food on an open flame on Shabbat, for this appears as if one is cooking on Shabbat.
Placing a Fully-Cooked Food on an Electric Hotplate
However, regarding placing a fully-cooked food on an electric Shabbat hotplate, which people do not usually cook on, or on top of a gas stovetop covered by a metal sheet (“Blech”), there is room for leniency in several situations as we shall soon discuss since it does not appear that one is cooking.
“Cooking after Cooking Regarding Dry Foods”
As we have already mentioned, it is absolutely forbidden to cook on an electric hotplate on Shabbat. It is therefore forbidden to place a clump of dough or a pot of milk on a hotplate on Shabbat, for this constitutes a complete Torah prohibition. However, it is sometimes permissible to place a food which has already been cooked or baked on a hotplate on Shabbat based on the Talmudic edict of “there is no cooking after cooking.” Indeed, it is permissible to warm bourekas, rice, Schnitzel, or bread on an electric hotplate on Shabbat.
“Cooking After Cooking Regarding Liquids”
Nevertheless, there are certain foods which can halachically be recooked on Shabbat in spite of the fact that they were fully-cooked before Shabbat. The general rule is that reheating any food that is liquidy in nature, such as a sauce, soup, milk, and the like, on Shabbat incurs a Torah prohibition of cooking after cooking. However, reheating dry foods, such as meat, fish, Kugels, and the like does not constitute the prohibition of cooking on Shabbat. This is because there is no cooking after cooking regarding dry foods and there is cooking after cooking regarding liquid foods.
It is therefore forbidden place a soup on an electric hotplate on Shabbat, even though it was fully-cooked before the onset of Shabbat, since reheating a liquid food on Shabbat constitutes the prohibition of cooking on Shabbat.
In the following Halachot, we shall explain this further.