Question: How is kashering done?
Discussion: Kashering a utensil may involve one or more of the following methods:
Libbun (Incinerating)
Libbun Kal (Less Intense Burning)
Hagalah (Immersion in Boiling Water)
Irui (Pouring Boiling Water)
Milui Ve’irui (Filling and Pouring Out)
Neitzah Bekarka (Inserting a Knife in the Ground)
Shifshuf (Scrubbing) and Hadachah (Rinsing)
We will now discuss each kashering method in greater detail.
לִיבּוּן / Libbun 43 (Incinerating)
Libbun applies powerful heat to the utensil until a thin outer layer becomes burned off44 or until sparks begin to fly from the hot metal45 — that is, that it becomes red-hot.46 This may be achieved by scorching the utensil with a blowtorch,47 other form of open fire, or by heating it in a very hot oven whose interior reaches this red-hot temperature.48 [An oven set on a self-clean setting (752° F / 400° C) reaches this temperature.] Any absorbed non-kosher flavor or substance will thus be incinerated and destroyed.49 Libbun is the only way to kasher a utensil that was used with intense heat, such as a rotisserie spit, grill grate, or oven pan that absorbed non-kosher food.50 Since it is the most powerful form of kashering, libbun is also effective for kashering any utensils that absorbed non-kosher food at lesser levels of heat and, therefore, would require a less intensive method of kashering, discussed below. However, depending on the material from which a utensil is made, libbun can be impractical — especially for something requiring lesser levels of kashering — since it can destroy the utensil.
Today’s utensils are made out of a much denser metal than was used throughout the ages. Therefore, it is very unlikely that an outer layer will peel off, even when the utensil is heated intensely. Accordingly, as an indication of when libbun has been accomplished, it is sufficient for the metal to become red-hot, or for the metal to be heated to the temperature of a self-cleaning oven.
לִיבּוּן קַל / Libbun Kal (Lesser Intense Burning)
Libbun kal heats a utensil to a high enough temperature that heat penetrates throughout the entire utensil.51 This intensity of heat is strong enough to purge absorptions that were imbued in a utensil in a way that the utensil did not directly touch the fire. The indication to know if a utensil has been sufficiently heated to effect libbun kal is by touching a piece of straw or tissue paper52 to the utensil’s outer surface (that is, the opposite side of where the heat is being applied) and seeing if it scorches or ignites.53
Since libbun kal heats a utensil to a lower temperature than does libbun chamur, it is not effective to kasher an item used directly with solid foods in an open fire or through intense heat.
However, libbun kal is effective to kasher:
A utensil that requires hagalah.54
A utensil that has folds or cracks that may contain chametz, for which hagalah is ineffective until all food residue is burned up.55
In a scenario where it is questionable if libbun chamur is required.56
הַגְעָלָה / Hagalah (Immersion in Boiling Water)
Hagalah, immersing a non-kosher utensil into boiling water, purges any absorptions imbued within the utensil. Hagalah differs from libbun, because hagalah is not hot enough to destroy the non-kosher absorptions in the utensil. Instead, it removes them from within, drawing them out of the utensil into the kashering water.57 Hagalah is effective for kashering utensils that became non-kosher through the medium of hot liquid, including steam. It is commonly done to pots, bowls, and ladles.
Hagalah is perhaps the most common way of kashering utensils for Pesach. Furthermore, it is a process that includes many details. Step-by-step instructions for the hagalah process are provided below.
עֵרוּי / Irui (Pouring Boiling Water)
Irui, which also purges absorptions using boiling water, is a weaker type of hagalah. If non-kosher liquid was poured upon a kosher utensil (or surface), it imbues the utensil with non-kosher absorptions, although to a weaker degree than if the utensil (or surface) had touched the non-kosher food by way of direct heat (for which libbun is necessary), or with a direct liquid medium (for which hagalah is required). Therefore, according to the principle of kebolo kach polto, a weaker method of kashering may be done. The utensil does not have to be immersed in boiling water; rather, the utensil (or surface) may be kashered via irui [also termed irui b’roschin (עֵרוּי בְּרוֹתְחִין), pouring boiling liquid], which is done by pouring hot water from a kli rishon upon it. Note that irui may be insufficient for a surface (or utensil) if hot, solid foods, came into contact with them.58
Similarly, according to kebolo kach polto, the intensity of heat for irui to kasher a utensil must be equal to (or greater than) the intensity of heat through which the non-kosher food became absorbed. Thus, if non-kosher or chametz liquid was poured onto a utensil or surface from a kli rishon,59 then it must be kashered with the same degree of heat — with irui poured from a kli rishon. Likewise, if the non-kosher or chametz liquid was poured onto a utensil from a kli sheini (which is a hot container cooler than a kli rishon), the utensil may be kashered with irui poured from a kli sheini.
In situations where irui may not be considered hot enough to satisfy the kashering requirement, but where hagalah cannot be performed (e.g., when kashering a table), then irui will sometimes be performed in conjunction with an אבן מלובנת — “a heated stone.”60 By pouring the water over the heated stone, the added heat of the stone brings the water to the heat of a true kli rishon (rather than irui kli rishon), and thus, is generally considered to be as effective as hagalah.
43 Libun is also sometimes referred to as libun chamur or libun gamur, to distinguish it from libun kal (lesser burning), which will be discussed below.
44 See Avodah Zarah 76a.
45 Shulchan Aruch Chapter 451, Passage 4. It appears that these standards are referring to the same degree of heat (Sefer Hagalas Keilim Chapter 5, footnote 3.
46 Halachos of Pesach, Rabbi Shimon D. Eider, p. 181.
47 Libun is achieved by applying the blowtorch for seven minutes on each eight-square-inch area of the utensil (Rav Moshe Feinstein, cited in Ohalei Yeshurun vol. 1, Rabbi Aaron Felder, p. 77. See also Halachos of Pesach, Rabbi Shimon D. Eider, p. 180 footnote 139).
48 Teshuvos Vehanhagos, Pesach, p. 21
49 In contrast to other forms of kashering, where heat draws out the absorptions from within a utensil (upon which the principle of kebolo kach polto “it purges in the manner that it absorbed” is based), libun’s intense heat simply destroys any absorptions within the utensil. (See Re’ah in Bedek Habayis 4:4; Shach, Yoreh Deah 21:147; and Igros Moshe, Yoreh Deah I:60.) Based on this distinction, Shulchan Aruch Harav 451:19 rules that one may kasher with libun on Chol Hamoed Pesach, for there is no concern of the chametz absorptions reentering the utensils — which is a concern regarding hagalah (see Section VI below).Other authorities, however, disagree with this leniency; see Sefer Hagalas Keilim, pp. 29-32.
50 Utensils that absorbed flavor in circumstances of heitera bala, discussed above, are an exception to this principle; they may be kashered using hagalah.
51 See Halachos of Pesach, Rabbi Shimon D. Eider, p. 158.
52 Igros Moshe, Yoreh Deah III:25; Emes L’Yaakov Al Daled Chelkei Shulchan Aruch, Yoreh Deah 121, fn. 54.
53 Rema 451:4.
54 Rema ibid. and Mishnah Berurah note 30. Discussion of libun kal’s functioning and effect, and may be found in Sefer Shaarei Shlomo, Chapter 3.
55 Rema 451:4-5.
56 Pri Megadim, Mishbetzos Zahav, at the end of Chapter 452.
57 Sefer Hagalas Keilim, pp. 28-29, provides an alternate explanation of how the hagalah process works, stating that it, too, destroys the imbued non-kosher chametz flavor.
58 Mishnah Berurah 451:114.
59 A kli rishon (first container) is something cooked directly on the fire and still retains a yad soledes bo (literally, the hand recoils from it) temperature. The temperature of yad soledes bo in contemporary measurements ranges from 109° F (43° C) to 174° F (79° C). See footnote k to 318:4.
60 Rema 451:6.