Halakhah zu Wajikra 19:5

Rav Ovadia Yosef (Teshuvot Yechaveh Daat 2:63) bolsters the position of Rav Soloveitchik and Rav Kotler. He notes that the Rama (Orach Chaim 451:4) cites some Rishonim who believe that libun is accomplished (regarding Pesach, see Mishnah Berura 451:30) when the oven reaches the temperature at which straw burns (kash nisraf). Rav Hershel Schachter told me that it seems to him that common practice in America is to consider the temperature for libun kal to be 550 degrees Fahrenheit. Hence, this lighter form of libun (libun kal) can be accomplished even in most conventional ovens. Although the Rama himself requires libun until sparks fly (libun gamur) for utensils that truly need libun, he permits the more lenient libun kal for items that merely require hag’alah.¹⁶One might, for example, wish to perform libun kal on an item that merely requires hag’alah if it cannot come in contact with boiling water for practical reasons. While hag’alah does not normally suffice for kashering items that cook food without a liquid medium, the Gemara (Avodah Zarah 76a) permits kashering such items through mere hag’alah if they absorbed only kosher food (heteira bala), even though the food subsequently became non-kosher (see Rashi, Avodah Zarah 76a s.v. L'olam).¹⁷For example, when the meat of a korban (sacrificial offering) is cooked in a dish, the flavor of this meat remains in the dish past the time that the korban may be eaten. When this time expires, the meat becomes forbidden (notar; see Vayikra 19:5-8), so the dish now contains flavor that was absorbed from kosher food but is no longer kosher.