OPINIONS: Rav Huna states that the Torah forbids only the non-kosher absorptions in a pot which has the status of a "Bas Yoma" -- "it is from that day"; the pot was used to cook the non-kosher food within the past 24 hours. However, if the pot is not a Ben Yomo (although the Gemara uses the term "Bas Yoma," we will use the more common term, "Ben Yomo"), the absorbed food in the pot is forbidden only mid'Rabanan.

In order not to be considered a "Ben Yomo," is it necessary for the pot to have been left unused for literally 24 hours, or are there other ways in which a pot can become "Eino Ben Yomo," not a "Ben Yomo"?

(a) RASHI (DH Bas Yoma) defines "Ben Yomo" as a utensil in which food was cooked today. Rashi adds that if the Nochri cooked with the pot yesterday, its taste went bad "when it stayed overnight (in the pot)," and then when the taste is transferred into another cooked dish, it does not give a good taste to the mixture. Since it is Nosen Ta'am li'Fegam, it does not make the mixture forbidden. Rashi implies that the status of "Eino Ben Yomo" may be achieved not only by being left unused for 24 hours, but also by being left unused merely overnight. Accordingly, if a person accidentally cooked a non-kosher food in a pot at eight o'clock at night in the summer before sundown, the pot would be considered an "Eino Ben Yomo" by the time dawn arrived the next morning, some ten hours later.

(b) TOSFOS (DH Bas Yoma) writes that this is also the position of RABEINU TAM. Rabeinu Tam proves this from the concept of "Ibur Tzurah." The Gemara teaches that when certain Kodshim have a partial Pesul but do not yet warrant being burned, those Kodshim should be left overnight, which the Gemara refers to as "Ibur Tzurah" -- "changing its form." This implies that the meat actually goes bad as a result of being left overnight. Rabeinu Tam explains that if the Gemara says this about food which has a clear physical presence, then certainly it applies to the absorptions in a pot. Rabeinu Tam says that the pot must have remained unused the entire night, since it is unclear what part of the night makes the taste go bad (or if the entire night is required). He concludes that if one wants to be stringent and rely only on the straightforward definition of Ben Yomo (24 hours), he will be blessed.

(c) Tosfos quotes RABEINU BARUCH who apparently maintains that "Ben Yomo" means 24 hours, and not merely being kept overnight without use. The ROSH agrees with Rabeinu Tam, but quotes the RI who sides with Rabeinu Baruch. (Y. MONTROSE)

OPINIONS: The Gemara teaches that one may make a knife that was owned by a Nochri usable by thrusting it into hard earth ten times (instead of using the process of Hag'alah). The Gemara adds that this method applies only to a knife which has no ridges, and only to a knife which will be used for cutting cold food (and not hot food).

May one use this method for kashering a knife under all circumstances, or only in limited circumstances?

The SHULCHAN ARUCH (YD 121:7) states that this method may be used for any knife which will be used for cutting cold food, even for a Davar Charif (a sharp-tasting object, such as an onion). However, the Shulchan Aruch earlier (YD 89:4) writes that one may not cut cold cheese with a meat knife, and, moreover, one may not cut bread which he wants to eat with cheese with a meat knife. The REMA adds that if one performed the process of thrusting the knife into the ground, then he may use the knife. However, the Rema adds, the custom of all of the Jewish people is to have two knives, and to mark the milk knife so that it will be clearly recognizable. The Rema concludes that one must not change a custom of the Jewish people.

What case is the Rema permitting (if not for the universal custom to have two knives)? Does he mean that one may cut cheese with the meat knife after it has been thrust into the ground, or does he mean only that one may use the knife to cut bread which he wants to eat with cheese?

(a) The TAZ (YD 89:6) asserts that the Rema is referring to cutting cheese with a meat knife. The process of thrusting the knife into the ground enables the knife to be used for cheese. If one wants to cut bread which he will eat with cheese, he may use the meat knife without this process, and it suffices simply to clean the blade of the knife. Moreover, the Taz (89:7) explains that when the Rema says that the custom is to have two knives, he refers to having two separate knives even for cold milk and meat products, where otherwise the process of thrusting the knife into the ground would suffice. The Rema does not prohibit wiping off a meat knife in order to cut bread which will be eaten with cheese.

(b) The NEKUDAS HA'KESEF quotes the TORAS CHATAS who rules that if one wants to use a meat knife to cut bread to eat with cheese, he must perform the process of thrusting the knife into the ground. When the Rema says that the process of thrusting the knife into the ground suffices, he refers to one who wants to use a meat knife to cut bread which he will eat with cheese.

The Nekudas ha'Kesef refutes the explanation of the Taz regarding the custom to have two knives. He understands that when the Rema says that the custom is to have two knives, he means that the custom is to be stringent and not use a meat knife even to cut bread that will be eaten with cheese. This stringency is due to the fact that a cutting knife is used constantly, and thus it always has oily substances on it which cannot be removed with a mere wipe. This is also the opinion of the PRI CHADASH and most Acharonim. (See SHACH YD 89:22, who quotes the MAHARSHAL who is even more stringent than the Rema, as he states that the process of thrusting the meat knife into the ground does not help even for cutting bread that one will eat with cheese.) The BADEI HA'SHULCHAN (YD 89:108) concludes that one should be stringent in accordance with this opinion. (Y. MONTROSE)