Opinion: Rashi explains that the case is where the Nochri cooked with this pot today. However, if he cooked with it yesterday, the taste that was in the pot has already gone bad by being extant overnight. Rashi implies that leaving it overnight makes it go bad, and therefore twenty four hours are not necessarily required.

Opinion (cont.): This is also the opinion of Rabeinu Tam. It was uncommon in the early days for people to cook at night, as is implied by the Gemara's discussion in Berachos (2b) of the times that they established one should say Kriyas Shema. The Gemara says (various opinions, such as) that this is when people go to sleep, and when Kohanim, the poor, and regular people go to sleep.

Proof #1: One can see a hint to this opinion by the fact that something left out overnight is deemed as changing its form.

Proof #1 (cont.): It would seem that this is a Kal v'Chomer. If food that is extant is considered to change its form at night, certainly something absorbed in a pot overnight is considered to do so (and change for the bad).

Proof #2: The term "Bas Yoma" implies that he cooked with it today. The Gemara did not say that the Torah only forbade a pot with which one cooked within the last twenty four hours.

Opinion: However, this is only if the pot stood unused the entire night without being used for cooking, as it is not clear if the beginning, end, or entirety of the night causes it to have its taste go bad. One does not need to wait twenty four hours. One who is stringent (and waits twenty four hours) should receive a blessing.

Question: One can ask on Rabeinu Tam that he brings proof from the fact that a food left overnight is considered to change its form. This should show that the end of the night, or rather Amud ha'Shachar, is what causes the food to change its form. At this time, Kodshim is called Nosar and must be burned. In Zevachim (19b), regarding Kidush Yadayim, the Gemara implies that Amud ha'Shachar causes something to be considered left overnight. (In other words, the source of this phrase is regarding Nosar which is clearly only transformed into being prohibited at the end of the night, not beforehand.)

Answer: Perhaps this is why Rabeinu Tam says that it is not a real proof, but rather a hint at this concept, in order that one should not say that the Gemara there is a proof to this law.

Question: One should deduce that the end of the night cannot be the only cause, but rather the entire night must be the cause. This is apparent from the fact that the Torah required breaking an earthenware vessel and scalding and rinsing metal vessels in which a Chatas was cooked, even according to the opinion that Nosen Ta'am l'Fgam is permitted. Why should this be necessary? Shouldn't it be permitted Lechatchilah to cook in these vessels after Amud ha'Shachar?

Observation: Rabeinu Baruch wrote in Sefer ha'Terumah that one must ensure that there was not any hot water in the vessel in the last twenty four hours, as hot water is considered the same as the prohibited item itself being that it turns into Neveilah when there is not sixty times more water than Neveilah being emitted by the vessel. We measure this based on the entire surface of the vessel. The water then goes back and is absorbed by the vessel again (and it is now considered that the water is forbidden, causing a massive amount of forbidden absorbtion in the vessel).

Observation (cont.): This specifically is regarding a vessel containing forbidden items. However, in a permitted vessel such as a case where meat is deposited into a milchig vessel or visa versa, even though hot water was in the vessel within the last twenty four hours, there is no reason to worry. This is because the water is permitted, as we only say that the piece (in our case water) becomes like Neveilah itself regarding forbidden items.

Observation (cont.): Additionally, this is a case of Nosen Ta'am bar Nosen Ta'am. Even according to the opinion that the case in Chulin where roasted fish are permitted after being placed in a pot where hot meat was eaten is only if they were placed in the pot, not if they were cooked in this pot, there are three Nosen Ta'am's in this case. The first one was absorbed in the vessel. The second was when the taste was emitted into the water. The third was when the water was absorbed back into the vessel.

Observation: Accordingly, something that was cooked in a pot that was not a Ben Yomo is permitted.

Implied Question: One must give a reason why Chazal saw fit to say that the food is permitted, but the pot is forbidden.

Answer: Being that the pot originally had something totally forbidden in it, Chazal decreed it is forbidden. However, the food itself never absorbed anything forbidden.

Opinion: When one does Hagalah to a pot that is a Ben Yomo, he must only do so with water that is sixty times the amount of the forbidden item that is going to be emitted by the pot, as the forbidden item is still deemed as giving a good taste.

Opinion (cont.): The Gemara earlier (38b) only permits hot water made by Nochrim because of the rule that a pot of a Nochri is presumed to have a status of Aino Ben Yomo (unless we know otherwise).

Opinion (cont.): However, when we do Hagalah to Chametz vessels on Erev Pesach in the first four hours of the day, at a time when Chametz is still permitted, one can even do Hagalah with water that is less than sixty times the amount of Chametz emitted by the vessel. This is because Chametz is a Nosen Ta'am ben Nosen Ta'am of a permitted item.

Opinion (cont.): The Chametz is absorbed in the bowl, it is emitted into the water, and the water goes back into the bowl. This is at a time when everything is still permitted.

Opinion (cont.): Additionally, the taste of Chametz absorbed in a vessel becomes ruined and inedible more than the taste of meat that is emitted into fish that is cooked in the same pot after the meat. This is because the fish are fit to be eaten, and the meat gives the fish a good taste.

Implied Question: It is difficult to understand why the custom is to put a vessel that has had Hagalah done to it in cold water.

Answer: One cannot say that this is because the Mishnah states in Zevachim (97a) that the Chachamim say one should scald the pot with hot water and then rinse it with cold water. (Why isn't this an answer?)

Question: The Gemara in Zevachim (97a) explains that this is only regarding Kodshim, and does not even apply to Terumah!

Answer: Some explain that when the Gemara (ibid.) says that an extra rinsing is not needed for Terumah, it means that a second cold rinse is not needed. Terumah only requires one rinsing. The term "extra" (used by the Gemara there) indeed implies this. This could be the reason why the custom is to always wash vessels in cold water after doing Hagalah to them.

Implied Question: However, Rashi (ibid.) explains that the Gemara there means a single rinse with cold water that does not apply to Terumah at all. According to this explanation of the Gemara there, a reason is still needed for the custom to wash the vessel with cold water after Hagalah.

Opinion #1: One must stick it into the ground ten times.

Opinion #1 (cont.): The Yerushalmi says one must stick it in the ground three times. This indicates (being that we would like to say they are not arguing) that our Gemara does not literally mean ten times.

Opinion #2: However, being that the Gemara later says that he stuck the knife in the ground ten times, it implies that one must specifically do so ten times. One should indeed be stringent to do so.

Opinion #1: However, if one wants to use it to eat boiling hot food, it requires Hagalah.

Proof: This is also implied in Pesachim (30b), as the Gemara says regarding knives of Chametz that are koshered for Pesach that the law is that "both" can be kashered with boiling hot water. "Both" means both the handles and the blades.

Question: However, there is a difficulty, as in Chulin (8b) the Gemara says that a knife of a Nochri requires Libun. This implies knives require Libun. The Tosefta in Avodah Zarah (8:2) also states that knives, spits, and grills require Libun.

Opinion #2: It therefore appears that in order to be able to use an unkosher knife to cut boiling hot things, one must first do Libun.

Opinion #2 (cont.): When the Gemara in Pesachim (30b) says that it only requires Hagalah, it is only because it absorbed something that was permitted (Chametz before Pesach). However, knives of Nochrim that have absorbed a lot of forbidden items require Libun.

Proof: Our Gemara (see Seder Yaakov that this is the correct text) also implies that there is a difference between whether something absorbed a permitted item or a forbidden item (see Rav Ashi's statement on 76a).

Opinion #3: Rabeinu Tam says that when we say that a knife requires Libun if it absorbed forbidden items, it is only if it is a big knife which is normally used during the roasting of meat.

Proof: This is apparent from the fact that the Tosefta (ibid.) lists knives and spits etc., indicating that the knives have a similar usage to the spits and grills.

Opinion #3 (cont.): However, small knives that one does not normally use for roasting can merely have Hagalah done to them, even if they belonged to a Nochri.

Opinion #4: The Riva requires Libun for small knives as well, as they are sometimes used to flip over meat that is roasting over coals.

Question: Rabeinu Tam says that this is not called something that is used with fire, being that something that is not permanently used with fire can be kashered through Hagalah.

Proof: The Yerushalmi also states that this is only regarding a small knife, but regarding a big knife Libun is required.

Question: One can push aside this proof, as the Yerushalmi there is discussing our Mishnah that says (see text correction in Avodah Berurah) that one can stick the knife in the ground and it is kosher etc. This means it is discussing being used for cold items. Regarding cold items, there is indeed no difference regarding whether or not it was used with fire. (Why, then, should Libun be required?)

Explanation: Rabeinu Elchanan explains the Yerushalmi as follows. The Mishnah is referring to a small knife that does not usually have holes (i.e. nicks) in it. There is therefore nothing absorbed in these holes, and it is enough to stick it in the ground to kasher it.

Explanation (cont.): However, a big knife that normally has nicks requires Libun. This is because sticking it in the ground does not help to rub those nicks, and to take away the prohibited absorption that is stuck in these holes. Therefore, even to cut cold items with it requires Libun.

Explanation (cont.): It is not even enough to do Hagalah to enable it to be used with cold, because Hagalah will only help to emit the prohibited matter that has been absorbed in the knife. However, it does not help to take away the prohibited matter that is stuck to the knife. Rubbing it in the ground helps take away the prohibited matter that is stuck to the knife. Being that there are nicks in the knife, there is no way to take away the stuck prohibited matter without Libun.

Question: In any event, the proof of Rabeinu Tam from the Yerushalmi has been pushed aside, as the Yerushalmi is not discussing a knife used with fire.

Answer: Rabeinu Baruch explained the Yerushalmi in a way which defends Rabeinu Tam's proof. The Yerushalmi means that this is only referring to a small knife that is not used with fire. It therefore only requires being stuck in the ground. Afterwards, it can even be used to cut boiling hot items.

Answer (cont.): The explanation for this law is that a regular knife is only used with cold items, and has nothing absorbed in it. There are only things that are stuck on the outside of the knife. However, a large knife is used with boiling hot items, and is also used with fire. Therefore it requires Libun in order to be able to be used to cut boiling hot things. This is how my teacher understands the explanation of Rabeinu Baruch.

Opinion: My teacher explained that when our Gemara says that the knife should be stuck in the ground ten times, it means that it should be stuck in hard ground that takes away the fat and sharpens it. However, it cannot be stuck in soft ground that does not take away the fat. It should also not be stuck in extremely hard ground. This is why the Gemara specifically says the word "Karka" - "land" and not stone, ash, or soft land.

Explanation: Rashi explains that he sent them two maidservants. Rav Yehudah did not accept the maidservant, while Bati did.

Observation: It does not seem that Bati sinned by doing so, as he was still partially an Eved Kenani, as he never accepted a Get Shichrur (document freeing him). This is as the Gemara states in Kidushin (70b) that Bati bar Tuvi did not accept a Get Shichrur due to his haughtiness.