שאני חלב דמפעפע
The Gemara answers: Forbidden fat is different from the sciatic nerve, because its flavor permeates throughout the animal, unlike that of the sciatic nerve.
ובחלב אסור והאמר רבה בר בר חנה עובדא הוה קמיה דר' יוחנן בכנישתא דמעון בגדי שצלאו בחלבו ואתו ושיילוה לרבי יוחנן ואמר קולף ואוכל עד שמגיע לחלבו ההוא כחוש הוה
The Gemara challenges Rav Huna’s statement: And in the case of a kid roasted with its forbidden fat, is the meat forbidden? But didn’t Rabba bar bar Ḥana say: There was an incident that came before Rabbi Yoḥanan in the synagogue of the town of Maon, where a young goat was roasted with its fat, and the people came and asked Rabbi Yoḥanan about the status of the meat, and he said: Peel away the meat and eat it until you reach the forbidden fat? This indicates that the flavor of the fat does not permeate the entire animal in which it is roasted. The Gemara answers: That kid was lean and had so little fat that its flavor did not permeate throughout the animal.
רב הונא בר יהודה אמר כוליא בחלבה הוה ושריא רבין בר רב אדא אמר כילכית באילפס הוה ואתו שיילוה לרבי יוחנן ואמר להו ליטעמיה קפילא ארמאה
Rav Huna bar Yehuda said: That was a case of a kidney of a young goat roasted with its forbidden fat, and Rabbi Yoḥanan permitted it to be eaten because there is a membrane that separates the fat from the kidney and prevents the fat from penetrating the kidney. Ravin bar Rav Adda said: That was a case of a small, non-kosher fish known as kilkhit, which fell into a stewpot [ilpas], and they came to ask Rabbi Yoḥanan about its status. And he said to them: Let a gentile cook [kapeila] taste it in order to determine whether the flavor of the non-kosher fish has permeated the entire mixture.
אמר רבא מריש הוה קא קשיא לי הא דתניא קדרה שבשל בה בשר לא יבשל בה חלב ואם בשל בנותן טעם תרומה לא יבשל בה חולין ואם בשל בנותן טעם
Rava said: Initially that which is taught in the following baraita posed a difficulty for me: With regard to a pot in which one cooked meat, one may not cook milk in it; and if he did cook milk in it, the meat absorbed by the pot renders the milk forbidden if it imparts flavor to the milk. Similarly, if one cooked teruma in a pot, one may not cook non-sacred food in it; and if one did cook non-sacred food in it, the absorbed teruma renders the food in the pot sacred if it imparts flavor to it.
בשלמא תרומה טעים לה כהן אלא בשר בחלב מאן טעים ליה השתא דאמר רבי יוחנן סמכינן אקפילא ארמאה הכא נמי סמכינן אקפילא ארמאה
Rava explains: Granted, in the case of a pot used for teruma, a priest, who is permitted to partake of teruma, can taste the non-sacred food subsequently cooked in the pot in order to determine whether the teruma imparted flavor to the non-sacred food. But in a case where it is not known whether meat imparted flavor into milk, who can taste it? If the meat did impart flavor to the milk, it would be forbidden for any Jew to consume the milk. But now that Rabbi Yoḥanan said: We rely on a gentile cook in the case of the kilkhit, here also we rely on a gentile cook to taste it and say whether the meat has imparted flavor to the milk.
דאמר רבא אמור רבנן בטעמא ואמור רבנן בקפילא
The Gemara summarizes the guidelines that determine when an item cooked with another item affects the status of the mixture. Rava said: The Sages said that there are cases where one relies on a Jew tasting the food, and the Sages said that there are some cases where one relies on a gentile cook to taste the food,