Rashi and Tosefot’s two disagreements TB Avodah Zarah 35-39

Food is a social glue that binds people together. The rabbis were afraid if Jews and pagans regularly ate together, they would socialize together. If they socialize together, they would fall in love and marry. If the Jews married non-Jewish women, the non-Jewish partner would influence the Jew to worship idolatry. Consequently, the Mishna bans certain foods either to prevent intermarriage or to prevent eating foods that include the forbidden yayin nesekh-יין נֶשֶׂךְ, wine dedicated in idolatrous worship. “And these are items that belong to gentiles and are prohibited, but their prohibition is not that of an item from which deriving benefit is prohibited: Milk that was milked by a gentile and a Jew did not see him performing this action, and their bread and oil. The mishna notes that Rabbi Yehuda HaNasi and his court permitted the oil of gentiles entirely. The mishna resumes its list: And boiled and pickled vegetables, whose usual manner of preparation involves adding wine and vinegar to them, and minced tarit fish, and brine that does not have a kilbit fish floating in it, and ḥilak, and a sliver of ḥiltit, and salkondit salt (see 39b); all these are prohibited, but their prohibition is not that of an item from which deriving benefit is prohibited.” (daf Avodah Zarah 35b, Sefaria.org translation)

The rabbis ruled that unsupervised food cooked by non-Jews, bishul akum-בִּישׁוּל עַכּוּם not kosher. Three exceptions were carved out. (1) Food that is unaltered and remains the same like water that is boiled is permissible to eat. An example of this would be roasted grains. “ (2) Rav Shmuel bar Rav Yitzḥak says that Rav says: Any item that is eaten as it is, i.e., raw, is not subject to the prohibition against eating the cooking of gentiles. The Gemara remarks: In the study hall in Sura, they taught it this way. (3) In Pumbedita, they taught it like this: Rav Shmuel bar Rav Yitzḥak says that Rav says: Any item that is not eaten together with bread on the table of kings is not subject to the prohibition against eating the cooking of gentiles. In other words, foods that are not eaten by distinguished individuals are not subject to this prohibition.” (daf Avodah Zarah 38a, Sefaria.org translation) In later halakhic decisions both raw food and food not placed on the king’s table are the requirements for food not to fall under the category of bishul akum.

If the Jew was involved at any time of the cooking like lighting the oven or flipping the meat over on the grill, the food was not considered bishul akum.

The first agreement is found on daf TB Avodah Zarah 38a. Rashi ד"ה מִדְּרַבָּנַן explains the reason why bishul akum is forbidden. He posits the reason that Jews should not regularly eat food and drink with non-Jews for the fear they will eat nonkosher food. Tosefot notes that Rashi contradicts himself. When commenting on the Mishna he posits the reason as the fear of intermarriage. Rebbeinu Avraham ben David holds the reason is the fear of intermarriage because when a non-Jewish chef cooks in a Jewish home, his food may be eaten because there is no fear of intermarriage or treif ingredients. Rebbein Tam still prohibits a non-Jewish chef cooking in a Jewish home for fear that he will not be careful about the ingredients he uses just as he is not careful about them in his own home.

The second disagreement between Rashi and his grandson Rebbeinu Tam is found on daf Avodah Zarah 39a-b. “Rav says: The substances represented by the acronym ḥet, beit, yod, tav are prohibited if they were deposited with a gentile while they were sealed with only one seal. Those represented by the acronym ḥet, beit, peh, gimmel are permitted if they were deposited with a gentile while they were sealed with one seal. The Gemara elaborates: Milk [ḥalav], meat [basar], wine [yayin], and sky-blue dye [tekhelet] are all prohibited when they are found with only one seal; ḥiltit, fish stew [morayes], bread [pat], and cheese [gevina] are all permitted when they are found with one seal.” (Sefaria.org translation)

Rashi ד"ה אֲסוּרִין בְּחוֹתָם אֶחָד explains that the person who would substitute inferior or nonkosher items they’re worried about are the non-Jews. Rebbeinu Tam disagrees with his grandfather and says that the person described is an unscrupulous Jew would make such substitutions. We perhaps can understand Rebbeinu Tam’s commentary based on his social reality. The Jews of his generation were very much involved in a lot of business transactions with Christians. The two seals requirement would make business more difficult and harm the Jewish economically. Consequently, to prevent that from happening he only required one seal.