In the quote from Numbers I mentioned earlier, the rabbis derived from "that which has passed through fire, you shall pass through fire..." the principle is "as it absorbs, so it releases". That means that in the same way a utensil has become non kosher, it can lose that status. If an oven spit became non kosher, it can be kashered by passing it through a fire. The Talmud states to make it white hot (libbun), after which it is again kosher. Some question if "white hot" is actually necessary, or is simply an exaggeration for"very hot". If something became non kosher through boiling, it is to be kashered either by placed into a larger pot that is boiling over a fire, or be filled with water, boiling in it until the water washes over the top. (Some place a hot rock into the pot to make it overflow). If something became non kosher by having a non Kosher liquid poured over or into it, it is sufficient to simply pour boiling water over it. In either case, the pot (or other utensil) should then be rinsed with cold water. According to some, a utensil which has only had hot liquid in it, but was not actually on the fire, needs no kashering at all. In the case of libun, the utensil may be kashered immediately, as all forbidden substances will be burned. . In the case of purging in boiling water (hag'alah), it is required to wait at least twenty four hours. Technically, it could be done immediately as well, but since we are here dealing with nullifying the non kosher substances rather than burning them, great care must be taken that there be sufficient water for nullification to occur. The rinsing afterwards is to wash off the water that has absorbed the non kosher substances. As we have seen, no utensil remains Biblically unkosher for more than twenty four hours. Therefore, the kashering is only a formality at that point, and the amounts of water are not a concern. Likewise, the rinsing afterwards in this case is only a custom, and may be dispensed with when there is fear of damaging the utensil. Now, how hot is "hot"? The Talmud uses the term "yad soledet" (the hand recoils), but quickly redefines that as the temperature at which a baby's belly would become scalded. Many authorities play it safe, and suggest that 104 degrees F (40C) is already "hot". However, scientifically, a burn (rather than just reddening of the skin) occurs at 130 F (54.4 C) with prolonged exposure, and at 140 F (60C) instantaneously. Therefore, "hot" is somewhere between 130 and 140 F. (This debate has huge implications also in the laws of Shabbat, but this is not our topic now). Generally, Ashkenazim go by the lower temperature (or close to it), while Sepharadim go by the higher (or close to it). However there is an alternative (controversial) approach to this topic. Similar to a point I mentioned in my last post. Most rabbis will not change a halachah found in Talmud in favor of an observable scientific fact, while others do. Rabbi Y. Abadi suggests the following: If we were to place a small piece of food in an oven at top heat for a half an hour, it will turn to ash. Why should we not assume that the same thing happens with the minuscule amounts of food absorbed in the utensil?Therefore, he allows kashering by placing in an oven at top heat for half an hour! Other than earthenware, (which I shall discuss next time), this can be done for any material that can withstand this amount of heat. The same would be true of kashering for Passover, with the exception that Sepharadim do not require a one day waiting period for Passover, as before Passover, the hametz is permissible, not forbidden, and requires a far less stringent kashering process..As to hag'alah, he says to put a small amount of water into the pot, cover it, and leave on the fire on until the utensil fills with steam. I do rely on Rabbi Abadi's kashering rules. Most rabbis do not. In my next post, I will discuss the fascinating issue of "tziruf de'ot" (the combining of several minority leniencies to make a "permitted" verdict). Most authorities accept this, but many reject this. It especially plays out in the issue of kashering china.