Duchka D'Sakina - Borrowed

QUESTION: My non-Jewish co-worker borrowed my knife and sliced through a hard chunk of cheese. Does my knife require kashering?

ANSWER: Yes. The Chochmas Adam (Kelal 47:4) writes that if a knife was used to cut through a hard non-kosher food, such as hard cheese, the knife requires ne’itza (abrasive cleaning). Because pressure is needed to cut through hard cheese, residue of the cheese will remain on the blade, even if the knife was only used once and only one cut was made. Since the co-worker is not Jewish, one must assume that the cheese was non-kosher. Similarly, if a fleishig knife was used even one time to cut through hard kosher cheese, the knife would require ne’itza before it can be restored to use as a fleishig knife. Ne’itza (thrusting the blade into hard ground) is ineffective if there are any grooves in the knife, and in practice is rarely done. In a previous Halacha Yomis, we discussed what methods can be employed in place of ne’itza.

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The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt"l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.