WHAT METHOD OF KASHERING IS REQUIRED? [Kashering: method]
97a (Mishnah): A roasting spit or grill is Kashered in hot water.
Avodah Zarah 76a - Contradiction (Rav Amram - Mishnah): A spit or grill (of a Nochri) is Kashered through Libun (heating it until it glows).
Answer #1 (Rav Sheshes): Kodshim Kelim are more lenient because they absorbed permitted taste. Nochri Kelim absorbed forbidden taste.
Objection (and Answer #2 - Rabah): What difference does it make? In both cases, they emit forbidden taste! (After a day or two, Kodshim are Asur due to Nosar.) Rather, the Mishnah requires Hag'alah for Kodshim Kelim, i.e. Shetifah u'Merikah (rinsing and scouring. However, Kashering is only through Libun.)
Objection (Abaye): Shetifah u'Merikah is with cold water. The Mishnah specifies Hag'alah in hot water!
Answer #3 (Rav Papa): Nochrim do not constantly cook in their Kelim, so the absorptions become hard, and Libun is required. Kodshim Kelim are used constantly, so the absorptions never become hard, so Hag'alah (Kashering in boiling water) suffices.
Defense of Answer #1 (Rav Ashi): Kodshim Kelim are more lenient because they absorbed Heter. Even though the absorption becomes forbidden, genuine Isur never touched the Keli.
(Rav Mani): For Libun, one must heat the Keli until the surface peels off.
(Rav Huna): For Hag'alah, one puts a small pot in a bigger pot.
75b (Beraisa): If a Yisrael buys a Keli from a Nochri, if it was used with cold food, such as cups and flasks, he rinses it. If it was used with hot liquids, such as pots and kettles, he does Hag'alah. If it was used to cook over a fire without liquid, such as spits and grills, he does Libun.
Chulin 8b (Rav): If one slaughtered with a Nochri's knife, he must peel off a layer from the areas cut;
(Rabah bar bar Chanah): It suffices to rinse them.
Suggestion: They argue about whether Beis ha'Shechitah (the place of slaughter) is Rose'ach (hot enough to cause absorbed taste in a knife to enter the meat).
Rejection #1: All agree that it is Rose'ach. Rabah says that it suffices to rinse. Since the Simanim are busy exuding blood, they are unable to absorb tastes exuding from the knife.
Rejection #2: No. All agree that it is not Rose'ach. Rav obligates peeling off a layer. The sharpness of the knife causes its absorbed tastes to enter the meat.
Pesachim 30b - Rav Ashi: I make my knives like new for Pesach. I cover the (wooden) handles in mud (so they will not burn during Koshering) and put the blade in fire, then I put the handles (without the mud) in boiling water.
The Halachah is, it suffices to put the blade and handle in boiling water in a Keli Rishon.
(Rav Huna brei d'Rav Yehoshua): A wooden mixing spoon may be Kashered in boiling water in a Keli Rishon.
He holds that k'Bol'o Kach Polto (just like it absorbs, it emits).
(Ameimar): The outer walls of Klei Cheres plated with lead give off moisture. this shows that they absorb, hence they are forbidden.
They cannot be Kashered, for the Torah teaches that absorptions never leave the walls of Klei Cheres ("u'Chli Cheres Asher Tevushal Bo Yishaver").
Rif and Rosh (Pesachim 8b and 2:7): For Pesach, one puts knives with their handles in boiling water in a Keli Rishon.
Rosh (ibid.): Beforehand one must rub and clean them well. If not, the Isur will not be purged. The Sifri expounds that one must remove the rust. Therefore, if a knife has depressions and one cannot clean inside them, Hag'alah does not help, and Libun is required.
Rif and Rosh (ibid.): Metal Kelim used for Chametz in a Keli Rishon require Hag'alah in a Keli Rishon. For Kelim used for Chametz in a Keli Sheni, e.g. bowls, it suffices to pour boiling water on them in a Keli Sheni and wait until the Isur is purged. We learn from pots of Nochrim. Everything is Kashered the way it is used.
Rambam (Hilchos Chametz 5:24): If Kelim of metal, stone or wood were used with Chametz in a Keli Sheni, e.g. cups and bowls, he puts them in a big Keli and pours boiling water over them and leaves them there until they emit (all absorbed taste). Then he rinses them, and he may use them for Matzah.
Rambam (25): Any Klei Cheres used for hot Chametz, whether in a Keli Rishon, e.g. pots, or in a Keli Sheni, e.g. bowls, cannot be used for Matzah.
Rosh (ibid.): If an earthenware Keli is returned to the kiln (in which new earthenware Kelim are made, at tremendous temperatures), this Kashers it. Our ovens do not suffice. Perhaps he will remove it before it gets hot enough. When doing Hag'alah, he must ensure that the water not cease boiling.
Shulchan Aruch (OC 451:1): One cannot Kasher for Pesach any Keli Cheres used for hot Chametz through heating it, even if it was not on the fire, only hot Chametz was poured into it.
Rema: Some forbid even in a Keli Sheni.
Beis Yosef (DH u'Mah she'Chosav Rabeinu): The Tur is stringent even for Kelim not used on the fire, rather, hot food was poured into them. I.e. even if it was used like a Keli Sheni, heating the Keli will not Kasher it. Also the Rambam equates a Keli Sheni to a Keli Rishon regarding Keli Cheres used for Chametz.
Darchei Moshe (1): The Magid Mishneh says that heating a Keli Cheres does not help, even if it was used only like a Keli Sheni. The Beis Yosef says that the Tur agrees. This is wrong. The Tur holds that absorptions occur only in a Keli Rishon or through Iruy, which is like a Keli Rishon.
Magen Avraham (3): The custom is to do Hag'alah on everything. B'Di'eved, if one used a Keli that was never used for a Keli Rishon, this requires investigation. The Rashba is always stringent about a Keli Sheni, and requires Klipah. If so, we should do so on Pesach.
Kaf ha'Chayim (19): This opinion holds that a Keli Sheni absorbs somewhat. This is why they need some Kashering, i.e. in a Keli Sheni (Shulchan Aruch Sa'if 5).
Shulchan Aruch (OC 5): If Kelim were used for Chametz in a Keli Sheni, one Kashers them in a Keli Sheni. If one did Iruy over them from a Keli Rishon, he Kashers them through Iruy Keli Rishon. It is not enough to Kasher them in a Keli Sheni.
Shulchan Aruch (6): The law of Kelim depends on the primary usage. Even if bowls are sometimes used on the fire, since they are used mostly through Iruy, they are Kashered in this way.
Beis Yosef (DH Lachen): Avi ha'Ezri says that one must Kasher all bowls in a Keli Rishon, for sometimes one puts them in a Keli Rishon. He is concerned for the minority usage. The Rif and Rambam follow the majority usage, like the Ran and Rashba.
Gra (13): Even though cups are sometimes used for hot, since they are used mostly for cold, it suffices to rinse them. This shows that we follow the majority usage.
Mishnah Berurah (46): Even if it is used mostly through Iruy or in a Keli Sheni, if it is known that it was used for Chametz in a Keli Rishon in the last 24 hours, all agree that it needs Hag'alah in a Keli Rishon.
Rema: Some are stringent to do Hag'alah in a Keli Rishon. This is the custom. The same applies to anything for which there is concern lest it was used in a Keli Rishon, e.g. spoons.
Taz (11): The stringency is due to ignoramuses who do not know to distinguish between a Keli used mostly in a Keli Rishon and sometimes. The Rema says that we are stringent about anything for which there is concern, e.g. spoons. I say that spoons are more stringent, for they are often put in pots on the fire.
Gra (30): Tosfos is stringent. We exempt from Hag'alah only when we know that the Keli was used only for cold.
Mishnah Berurah (47): B'Di'eved, we rely on the first opinion.
Kesav Sofer (YD 8): According to the opinion that Beis ha'Shechitah is Rose'ach, Libun should be required for knives used to slaughter Kodshim. Why does the Mishnah require this only for spits and grills, but not for knives? The questioner answered that this opinion holds that Hag'alah is Merikah u'Shtifah, and the Torah decreed that this is needed only for what absorbed through fire, but not through the heat of Beis ha'Shechitah. The one who requires Hag'alah in addition to Merikah u'Shtifah holds that Beis ha'Shechitah is cold. This is difficult, for the Gemara rejected the opinion that Hag'alah is Merikah u'Shtifah in cold water. Also, the Rashba says that the knife absorbs even according to the opinion that Beis ha'Shechitah is cold, so Hag'alah should be required! Rather, the knife requires Hag'alah. The Mishnah taught a spit and grill for the Chidush that Libun is not required. There was no Hava Amina to require Libun for a Shechitah knife, which absorbs only through the heat of Beis ha'Shechitah.
Shulchan Aruch (YD 121:4): If one fried in a pan, even though for Pesach Hag'alah suffices, for other Isurim Libun is required.
Shach (8): Hag'alah suffices for Pesach, since it absorbed Heter. This applies even if it was used for meat or milk However, Rama mi'Pi'ano (96) says that a Nochri usually uses it without water, rather, with other liquids such as oil, unlike a pan used for Chametz. If so, also a pan used for meat or milk requires Libun, for it absorbed without any intermediary.
Mishbetzos Zahav (16): Does a Nochri's pan require Libun because the oil is forbidden, so it does not give the leniency of something used with liquid, so that Hag'alah should suffice? No. Rather, it is because the oil burns and dries up, and he fries without liquid.
Rebuttal (R. Akiva Eiger on Shach): The Rama mi'Pi'ano explicitly says that since the forbidden liquid is cooked on the pan and absorbed without any intermediary, this is called cooking through fire without liquid. Also the Shach's conclusion is not necessarily true. Perhaps for Chametz we needed to say that the liquid was permitted because the absorption is called Isur, but regarding meat or milk the absorption was Heter, so Hag'alah suffices. This is why Hag'alah suffices for Klei Kodshim, for the absorption was Heter and only later became Nosar.
Pri Chodosh (93:4): The Ran distinguished between Nosar and Chametz. Chametz is called absorption of Isur. Likewise, meat or milk is called absorption of Isur.
Rebuttal (R. Akiva Eiger, ibid.): The Rashba says that Nat bar Nat (a taste absorbed from an absorbed taste, e.g. water absorbed taste from a solid cooking in it, and a pot absorbed from the water) is not called absorption of Heter, for it is still called Chametz. This does not apply to meat or milk. The Shulchan Aruch (509:5) explicitly says that Hag'alah suffices for a pan used for meat or milk.
Har Tzvi: If a knife absorbed from Beis ha'Shechitah of a Tereifah, according to R. Akiva Eiger this is not called absorption through liquid (blood), for the blood is Isur.