גריי מאטר ב, פסח, האם אפשר להכשיר תנור אפייה לפסח?Gray Matter II, Pesach, May One Kasher a Conventional Oven for Pesach
א׳
1In many observant homes, people wish to kasher (render as kosher) their conventional ovens for Pesach. No consensus has emerged regarding the proper way to perform this task, so different families and communities follow different practices. This chapter explores the opinions of several major contemporary authorities.
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2An Introduction to Kashering
ג׳
3In Parshat Matot (Bemidbar 31:21-23) the Torah presents the basic rules of kashering: “Every object that has gone through fire, you shall pass through fire and it will become pure.” This verse teaches that every non-kosher utensil that was used directly with fire must be kashered with fire. Rashi (ad loc., based on Pesachim 30b and Avodah Zarah 75b) explains that the phrase “has gone through fire” alludes to one of two methods for kashering utensils, depending on how the utensil cooked the non-kosher food. If the non-kosher food was cooked directly on the utensil (such as on a grill), absent a liquid medium, then one kashers the utensil by heating it in a fire (libun). If, however, the non-kosher food was boiled in a pot containing hot water, then the utensil may be kashered via boiling hot water (hag’alah). The Torah also teaches that if only cold non-kosher food was placed in a utensil, one merely needs to clean the dish before using it with kosher food (Bemidbar 31:23).1Of course, any metal or glass utensil acquired from a non-Jew must also be immersed in a mikvah (see Rashi, Bemidbar 31:23).
ד׳
4Rashi articulates the general principle that emerges from these verses: kederech tashmisho hag'alato - the manner in which a utensil was used for non-kosher food preparation is the manner in which it should be kashered. The Gemara (Pesachim 30b) formulates this rule similarly: kevol'o kach polto - the manner in which the utensil absorbed the flavor of non-kosher food is the same manner in which it will let out that flavor.
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5Preventing the Non-Kosher Food’s Reentry
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6At first glance, the kashering process appears to contain a glaring contradiction. Kashering a utensil extracts the non-kosher flavor that had been absorbed within it from past cooking. However, the process itself essentially cooks the same food particles in the utensil! Why do we not worry that the flavor will thus immediately reenter the utensil?
ז׳
7Tosafot (Avodah Zarah 76a s.v. Mikan) acknowledge this problem and therefore suggest kashering utensils in at least sixty times as much water as their own volume. In this manner, the immense quantity of water nullifies the non-kosher flavor emitted into the hot water, so the flavor does not reenter the utensil.
ח׳
8Tosafot add that if the utensil has not been used within the past twenty-four hours (eino ben yomo), then such a great volume of water is not necessary. Their ruling stems from the principle that after twenty-four hours of sitting in a utensil, the non-kosher food develops a foul taste (notein ta'am lifgam), so the flavor no longer prohibits use of the pot. This reason alone, though, does not suffice to permit use of the pot without kashering, because the Gemara (Avodah Zarah 76a) mentions that the Rabbis prohibited even using a pot containing a foul non-kosher taste, lest one come to use a pot containing a non-kosher taste within twenty-four hours, when the taste has not yet spoiled. The Rosh (Avodah Zarah 5:36) explains that kashering a utensil solves this problem, as the pot releases the flavor into the water and then reabsorbs it. Thus, by the end of the process the foul taste is permitted even on a rabbinic level because it is several steps removed from the non-kosher food that emitted it (nat bar nat).2Moreover, this “non-kosher” flavor is fundamentally permissible because twenty-four hours have passed since it entered the utensil (nat bar nat d’heteira). Also see Encyclopedia Talmudit (8:202-209).
ט׳
9The Rama (Yoreh Deah 121:2) rules that one may kasher a utensil only if it has not been used within the past twenty-four hours. However, the Chazon Ish (Yoreh Deah 23:1) offers a method of kashering utensils that have been used within twenty-four hours, without requiring a huge volume of water. He suggests placing a foul-tasting substance in the kashering water, so the extracted taste from the utensil will instantaneously turn foul upon contact with the water (see Shulchan Aruch, Y.D. 95:4).3However, see Mesorah (12:72-73), where Rav Yosef Efrati cites Rav Yosef Shalom Eliashiv as requiring a 24-hour wait after the last time that machinery processed non-kosher food before using the machinery. Rav Efrati implies that Rav Eliashiv permits the Chazon Ish’s method of kashering only in cases of need. Rav Moshe Feinstein (Teshuvot Igrot Moshe, Y.D. 2:31) also objects to kashering within 24 hours, in the manner described by the Chazon Ish, except in cases of great need. Thus, even if the utensil reabsorbs what it released into the pot, the utensil will remain kosher. I have heard that many reliable kashrut agencies follow this leniency of the Chazon Ish in cases of great need.
י׳
10Deliberately Nullifying a Prohibition
י״א
11Kashering also seems to violate the prohibition against intentionally mixing small quantities of non-kosher food with larger amounts of kosher food for the purpose of nullifying the non-kosher food (ein mevatlin isur lechatchilah). However this prohibition applies only when one intends to benefit from the non-kosher food that is nullified in the kosher food.4See Semag (Negative Commandments 78), Biur Hagra (Yoreh Deah 121:7), Taz (Yoreh Deah 99:7 and 84:18), and Shach (Yoreh Deah 84:38). When kashering, though, one has absolutely no interest in the utensils’ non-kosher taste.
י״ב
12The Distinction Between Hag’alah and Libun
י״ג
13We mentioned that sometimes kashering is effected by placing a vessel in boiling water (hag’alah), while other times a utensil must be placed directly in a fire (libun).5Kashering with a flame is called libun (literally, whitening) because fire often heats the substance to the point where it has a white glow. The two processes function differently; kashering with boiling water extracts (maflit) absorbed taste, whereas kashering with fire chars the absorbed taste until it is utterly destroyed, removing its halachic status as food.6See Taz (Yoreh Deah 121:7) and Shach (Yoreh Deah 121:17).
י״ד
14The Problem with Kashering Conventional Ovens
ט״ו
15Kashering a conventional oven is significantly more difficult than kashering a pot. Hag’alah is not practical, and it seems that libun would anyway be required because the oven’s walls appear to absorb directly from the fire.7See, however, Mesorah (4:83-96, especially pp. 86-87), where Rav Mordechai Willig notes that the oven’s walls only absorb either through steam or through liquids that spray or spill. The Shulchan Aruch (Orach Chaim 451:4) rules that libun is accomplished when sparks fly (nitzotzot nitzin) from the object being kashered.8This ruling is based on a passage from the Yerushalmi at the conclusion of Masechet Avodah Zarah. Rav Hershel Schachter told me that it seems to him that the general practice is to require 950 degrees Fahrenheit for libun, since that is the temperature at which sparks fly from untreated iron.9See, however, Badei Hashulchan (92:8 Bei’urim s.v. Lechatchilah) for a dissenting opinion. Also, see Sefer Hagalat Keilim (13:464 note 432) that states in the name of Rav Moshe Feinstein that libun is accomplished at 700 degrees Fahrenheit. Since conventional ovens that do not self-clean can be heated only to approximately 550 degrees Fahrenheit, it would seem that they cannot accomplish libun. Nevertheless, as we shall see, contemporary authorities have debated this point.
ט״ז
16The Strict View - Rav Moshe Feinstein
י״ז
17Both Rav Shimon Eider (Halachos of Pesach 1:180) and Rav Aharon Felder (Ohalei Yeshurun p. 77)10In note 136, Rav Felder cites many other 20th-century authorities who discuss this issue. record that Rav Moshe Feinstein (Teshuvot Igrot Moshe, Yoreh Deah 1:59) requires libun for an oven, which may be accomplished only by focusing a blowtorch for seven minutes on an area no larger than eight square inches at a time. Since this task is time-consuming and difficult for many people to perform, many families instead thoroughly clean their ovens and then insert a box that covers the walls of the oven. In this way, no chametz can move from the oven walls to the food, as the chametz particles do not penetrate the insert’s walls.11See Rama (Yoreh Deah 92:8) and Teshuvot Igrot Moshe (Yoreh Deah 3:10:1).
י״ח
18The Lenient View - Rav Yosef Dov Soloveitchik and Rav Aharon Kotler
י״ט
19Many families follow the lenient opinion of Rav Yosef Dov Soloveitchik and Rav Aharon Kotler (quoted by Rav Eider, ibid.) that one can kasher a conventional oven by setting it to its maximum temperature for an hour or two.12Rav Soloveitchik’s position is cited by Rav Mordechai Willig (SOY Guide to Kashrut p. 67), and I have also heard it from Rav Aharon Lichtenstein (in a lecture at Yeshivat Har Etzion) and Rav Yosef Adler. They base their view on the aforementioned principle of kevol'o kach polto (flavor is extracted from a utensil in the same manner as it was absorbed). Rav Soloveitchik argues that this principle can determine precisely how to kasher a specific item.13The Aruch Hashulchan (O.C. 451:14-18) appears to share Rav Soloveitchik’s conceptual understanding of kevol’o kach polto. Since an oven never absorbs flavor at a higher temperature than its maximum setting, it can be kashered at that temperature.14See Yesodei Yeshurun (6:157-158), Minchat Chein, Hagadah Shel Pesach (pp. 12-14) and Badei Hashulchan (92:8 Bei’urim s.v. Lechatchilah) regarding the efficacy of libun when the heating source is outside the item that one wishes to kasher and how this issue impacts the kashering of ovens. On the other hand, Rav Moshe Feinstein believes that this rule merely determines which fundamental method of kashering should be used (hag’alah or libun), and that once one has determined that libun is required, rather than hag’alah, the general parameters of libun apply. Thus, sparks must fly from the utensil even if it never absorbed food at such intense heat.15The Mishnah Berurah (451:85) appears to share Rav Moshe’s interpretation of kevol’o kach polto (also see Shaar Hatziyun 451:100). For a thorough discussion of this issue, see Teshuvot Minchat Yitzchak (3:66), Sefer Hag'alat Keilim (introduction to Chapter 4), and Rav Mordechai Willig’s essay in Mesorah (4:83-96).
כ׳
20Libun Kal for Chametz?
כ״א
21Rav 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.
כ״ב
22Many Rishonim equate chametz with food that was absorbed while it was still kosher and only later became non-kosher (since chametz was permitted at the time it was absorbed into the oven, before Pesach). Consequently, hag’alah would suffice to kasher utensils even if they absorbed chametz through fire.18See Shulchan Aruch (Yoreh Deah 121:4) and Bi'ur Hagra (Y.D. 121:9). Based on this logic, Rav Ovadia Yosef argues that many authorities would permit kashering an oven for Pesach through libun kal. Those Rishonim who equate chametz before Pesach with food that only later became non-kosher would permit kashering an oven for Pesach by heating the oven to 550 degrees even if they did not accept Rav Soloveitchik’s interpretation of kevol'o kach polto as applying to individual utensils. Accordingly, Rav Ovadia rules (like Rav Soloveitchik and Rav Kotler) that one may kasher an oven for Pesach by running it on its highest setting.
כ״ג
23Despite Rav Ovadia’s reasoning regarding chametz, Rav Gedalia Felder (Yesodei Yeshurun 6:157-158) writes the exact opposite, that one should be even stricter regarding Pesach than when kashering non-kosher ovens for year-round use. He notes that we routinely treat the prohibition against chametz on Pesach with unusual stringency (chumra d'chametz), so even one who kashers an oven during the year by running it on its highest setting should obey Rav Moshe’s view when kashering for Pesach.
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24Conclusion
כ״ה
25Since there are cogent arguments for both strict and lenient approaches to kashering conventional ovens before Pesach, one should consult a Rav for guidance regarding this issue. This chapter does not address self-cleaning ovens, which appear to be easier to kasher. As Rav Elazar M. Teitz (based on the position of his father, Rav Pinchas Teitz) writes in his community Pesach guides (for Elizabeth, New Jersey), “Self-cleaning ovens are self-kashering.”19Nevertheless, some people blowtorch or cover the door of self-cleaning ovens, as the door reportedly does not reach such intense heats even during the self-cleaning cycle. See Yesodei Yeshurun (6:159-160), where Rav Gedaliah Felder expresses concern regarding the parts of a self-cleaning oven that do not reach a high enough temperature. Indeed, Rav Aharon Felder (Ohalei Yeshurun p.77) cites Rav Moshe Feinstein who requires that the door of a self-cleaning electric oven be kashered with a blow torch. In addition, see Badei Hashulchan (92:8 Bei’urim s.v. Lechatchilah) who rules that self-cleaning ovens cannot be kashered. Indeed, Rav Noach Oelbaum (Minchat Chein, Hagada Shel Pesach p. 23) writes that a regular cleaning cycle suffices to kasher a self-cleaning oven “since experience indicates that its heat exceeds the heat generated by conventional libun.”
כ״ו
26It is worth noting that the rules for kashering between milk and meat during the year might differ from kashering for Pesach.20One might rule more leniently during the year because in general we act more strictly regarding Pesach than regarding separating milk and meat. For example, we do not require a twenty-four hour waiting period before kashering an oven from meat to milk, or vice versa, because the original flavor in the oven passes through many stages before reaching food that will be cooked in the oven (see Tosafot, Avodah Zarah 76a s.v. Bat Yoma and Shach, Yoreh Deah 94:15). Also, libun kal would suffice for kashering between milk and meat, because they are both kosher (heteira bala; see our earlier discussion of whether libun kal suffices for chametz before Pesach). On the other hand, the Chelkat Yaakov (2:136) objects to kashering an oven at all between meat and milk, for there is an Ashkenazic custom (recorded in the Magen Avraham 509:11) not to kasher between them. However, Rav Yaakov Kaminetzsky (cited in Emet L'Yaakov p. 307 note 41) permits kashering ovens between milk and meat, apparently believing that the Ashkenazic practice does not apply to ovens. For an explanation of this position, see my article about cooking milk and meat in the same oven (The Journal of Halacha and Contemporary Society 32:34-35, note 19).