§ Rav Asi posed a dilemma to Rabbi Yoḥanan: How much time should one wait between eating meat and eating cheese? Rabbi Yoḥanan said to him: No time at all. The Gemara asks: Is that so? But doesn’t Rav Ḥisda say: If one ate meat, it is prohibited for him to eat cheese immediately, but if he ate cheese it is permitted for him to eat meat without delay? Rather, Rav Asi actually asked Rabbi Yoḥanan the following question: How much time should one wait between eating cheese and eating meat? In response to this question, Rabbi Yoḥanan said to him: No time at all.

Mar Ukva said: I am, with regard to this matter, like vinegar, son of wine, with respect to Father, i.e., my practice is inferior to that of my father. As Father, if he were to eat meat at this time, would not eat cheese until tomorrow at this time. But as for me, only at this meal, during which I ate meat, do I not eat cheese; at a different meal on the same day I will eat cheese.

It is forbidden to eat cheese - Because meat exudes fat that stays in the mouth and the taste stays in the mouth.

(28) When a person ate meat first - whether the meat of an animal or the meat of a fowl - he should not partake of milk afterwards unless he waits the time for another meal, approximately six hours. This stringency is required because meat that becomes stuck between teeth and is not removed by cleaning.

Prohibition of Eating Cheese After Eating Meat
After eating meat, even from a wild animal or poultry, one should not eat cheese before an interval of six hours; and even after this interval, one must clean the teeth if there are meat remnants in the gaps. The interval must also be observed when one has chewed the meat to give it to a child.
GLOSS: After cleaning the teeth, one must rinse the mouth before eating the cheese. Some opine that the six-hour interval is not necessary, and one can eat the cheese after removing the dishes, reciting the blessing at the end of the meal, and cleaning and washing the mouth. In our countries, it is customary to wait one hour after the meat meal before eating the cheese; but the mentioned blessing must be recited; because only then are the two meals distinct, otherwise not. It makes no difference if the hour serving as an interval is observed before or after the blessing. Meat remnants found in the gaps must be removed, even after the interval. Some opine that the middle blessing should not be recited expressly to eat cheese afterward; this is generally not taken into account. Some rigorously observe the six-hour interval; it is advisable to do the same.

The mishna cites an additional dispute: One who ate and forgot and did not recite a blessing; Beit Shammai say: He returns to the place where he ate and recites the blessing. Beit Hillel say: That is unnecessary. He recites the blessing at the place where he remembered. Both agree, however, that there is a limit with regard to how long after eating one may recite Grace after Meals. And until when does he recite the blessing? Until the food is digested in his intestines.

The Gemara asks: What is the duration of digestion? Rabbi Yoḥanan said: As long as he is not yet hungry again. And Reish Lakish said: As long as he is thirsty due to his eating.

Until when can one bless? Until the meal is digested in one's stomach. And how much is that measurement? The entirety of the time that one is not hungry on account of that eating. And from the time that one begins being hungry, even though the food hasn't been fully digested, we consider it to be as if it is fully digested. And, similarly, for the matter of eating fruits or drinking wine - if one is neither hungry nor thirsty, and they desire those fruits, they should bless [upon those fruits] if they do not know how much is left for their digesting.