As we established in section 3, 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. We must still clarify, though, whether one may change a 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? On the one hand, the meat is no longer raw, as it has already been roasted; on the other hand, adding it to the pot will change its status from roasted to cooked.
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, and this is not prohibited. This is the halakha according to some Sephardic poskim (Yeĥaveh Da’at 2:44; Menuĥat Ahava 2:10:26).
However, according to R. 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 (Yere’im §274). 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 kli sheni, one must take into account the possibility that bread is included in kalei ha-bishul and can become cooked even in a kli sheni. Thus the Ashkenazic custom is to be stringent (Rema 318:5). Some Sephardic poskim as well maintain that le-khatĥila one should be stringent (Ben Ish Ĥai, Year 2, Bo 6; Menuĥat Ahava 2:30:6).
However, even those whose practice is to be stringent agree that if be-di’avad one cooked something that had been baked, or baked something that had been cooked, one may still eat the food, since be-di’avad one may rely on the lenient opinion (MB 318:46).
Following the custom of most Jewish communities who are stringent in this regard, one who wishes to dip a cookie in tea or coffee must make certain that the teacup or coffee cup is a kli shlishi, since a kli shlishi definitely does not cook. One who wishes to dip bread in a bowl of soup may do so, as the ladle used to serve the soup can be considered a kli sheni and the bowl can be considered a kli shlishi (MB 318:45).
. Those who do not allow dipping bread into hot soup in a kli sheni follow two stringencies: a) They prohibit cooking after baking; b) they defer to the opinion that many foods are considered kalei ha-bishul and thus can become cooked in a kli sheni. Nevertheless, when serving soup using a ladle, according to Maharil, Pri Ĥadash, and others, the ladle is considered a kli sheni. Accordingly, the soup bowl is a kli shlishi, and in a kli shlishi there is definitely no prohibition. While Taz and Shakh maintain that the ladle is a kli rishon and MB 318:87 follows this approach, nevertheless this is a case of a twofold doubt, and thus one may be lenient (MB 318:45) as long as the ladle does not remain in the kli rishon long enough to reach the same heat as the vessel itself. Soup nuts may be added to a kli sheni even le-khatĥila, since they are deep fried and are considered cooked rather than baked (SSK 1:70). Furthermore, this further cooking is not desired, as people do not want the soup nuts to get soggy.According to those who maintain that ein bishul aĥar afiya (there is no prohibition of cooking something that has already been baked), one may definitely toast challah. Additionally, MA 318:17, Maĥatzit Ha-shekel, and Ĥayei Adam (Zikhru Torat Moshe 24:7) would permit this even for those who are stringent about bishul aĥar afiya, since they maintain that baking and roasting are the same. In contrast, some are stringent because they maintain that roasting is different from baking (Pri Megadim, Mishbetzot Zahav 318:7; SSK 1:71; Kaf Ha-ĥayim 318:78; Or Le-Tziyon 2:30:6; Menuĥat Ahava vol. 2 ch. 10 n. 154). There is even one opinion that expresses concern that this is considered Makeh Be-fatish (applying the finishing touch) (Rav Pe’alim, OĤ 2:52). In practice, the lenient position (that roasting and baking are the same) seems the more reasonable one, since if one continues to bake food it dries out, and essentially becomes toasted. Nevertheless, one who chooses to be stringent is commendable. This is the case when it comes to completely toasting the bread, but even those who are stringent would allow warming up bread – even to the point that the surface crisps – because doing so does not make a significant change to the baked state. Rav Pe’alim indeed states this in OĤ 2:52, and Nishmat Shabbat 318:26 states similarly.