We have learned last week that one may reheat fully cooked food on Shabbat, because the prohibition of bishul applies when one changes the status of food from raw to cooked. However, once a food is cooked one may reheat it, but what about changing food’s status from cooked to roasted, or from baked to cooked, etc. For example, may one take a piece of meat that was roasted before Shabbat and add it to the cholent pot?
According to Raavya, Mordechai, and most Rishonim, this is permitted. Since the heat of the fire has already transformed the raw food to cooked, baked, or roasted, there is no longer a prohibition of bishul. Further changing the status from roasted to cooked or vice versa is not considered bishul, but merely adding flavor (but on Pesach, since we are obligated to feel the taste of a baked matzah, we are not allowed to change the status by cooking it).
However, according to Rabbi Eliezer of Metz, although one may reheat cooked, baked, or roasted food, one may not change a food’s status from roasted to cooked, because that is considered cooking it anew. Therefore, one may not take baked bread and put it in a pot of food because this would effectively change the bread from baked to cooked – even if the hot food is in a k'li sheni.
The Shulchan Aruch (318:5) cites the opinion of Rebbi Eliezer Mi’Metz that it is forbidden, but concludes with the opinion of Raavya that it is permitted. Maran Hrav Ovadya Yosef zt”l in his book Yebia Omer (OC 8:35) says that based on the principles of the Shulchan Aruch Maran follows the lenient approach, and this is the halakha according to many Sephardic poskim.
In contrast, the conclusion of the Rema is to follow the stringent opinion of Rebbi Eliezer Mi’Metz, and this is the position followed by Ashkenazim. Accordingly, one may not place bread into soup, even if the soup is in a k’li sheini (secondary vessel, such as a bowl that was filled from a heated pot). If the bread was already put in the k’li sheni, Mishnah Berurah (318:46) writes that we may rely on the lenient opinion and eat the food. Furthermore, Mishnah Berurah (318:47) writes that it is permissible to place bread into a k’li shlishi, and for these purposes a bowl of soup can be viewed as a k’li shlishi, provided that a ladle was used to serve the soup.