Sabbath Food Preparation - Reheating Foods

Reheating Foods

While it is prohibited in most instances to initially heat a food item to the temperature of yad soledet bo, foods that have already been fully cooked may sometimes be reheated. In terms of reheating, a distinction is made between dry foods and liquids.

Dry food that has been completely cooked is no longer subject to the prohibition of bishul; this is based on the principle of ain bishul achar bishul (אין בישול אחר בישול, "Cooking does not take effect after cooking"). Thus, a completely cooked, dry food item, such as a piece of chicken or potato kugel, may be reheated once it has been fully cooked.

However, there is a great dispute as to whether this rule applies to liquids: whereas Rashi, the Rosh and Rabbeinu Yonah agree that this rule does not apply and reheating of liquids is forbidden, Maimonidies, the Rashba and the Ran assert that liquids are in fact no different from solid dry foods. In practice, we are stringent and apply the principle of yeish bishul achar bishul (יש בישול אחר בישול, "Cooking does take effect after cooking"). This prohibition of reheating liquids, however, only applies when the liquid has completely cooled. If the liquid has only partially cooled and still retains enough heat to be enjoyed as the warm liquid as it was intended to be, it may be reheated.