This chapter discusses whether one may kasher a microwave for Pesach, as well as how to perform the kashering according to those authorities who permit it. While we outline the relevant points of debate, the reader is urged to consult his Rav for guidance concerning this complicated issue.
Objections to Kashering Microwaves
The very possibility of kashering a microwave presents two problems. Some rabbis express reservations about kashering microwave ovens due to the difficulty in thoroughly cleaning their many vent holes and crevices.1The Rama (Orach Chaim 451:18; as explained by Mishnah Berurah 451:100) prohibits kashering certain items for Pesach, such as sieves, due to the difficulty in cleaning them thoroughly from chametz. For this reason, Rav Aharon Lichtenstein told me (in 1987) that one should not kasher a toaster oven, as it is too difficult to clean thoroughly. Additionally, Rav Mordechai Willig told me (in 1992) that he believes one cannot kasher a microwave for Pesach if it is lined with plastic. He notes that Rav Moshe Feinstein (Teshuvot Igrot Moshe, Orach Chaim 2:92) prohibits kashering synthetic materials for Pesach. Indeed, in his discussion of kashering microwaves (Halachos of Pesach pp. 182-183), Rav Shimon Eider quotes Rav Moshe as permitting a microwave to be kashered only if the microwave is not lined with plastic. On the other hand, Rav Eliezer Waldenberg (Teshuvot Tzitz Eliezer 4:6), Rav Yechiel Yaakov Weinberg (Teshuvot Seridei Eish 1:46), and Rav Ovadia Yosef (Chazon Ovadia vol. 2 [Hagaddah Shel Pesach] p. 78) permit kashering plastic for Pesach. Assuming that one fundamentally can kasher a microwave, we will examine the proper ways to implement the kashering.
Kashering Glass
Many microwaves contain revolving glass plates, which should seemingly require kashering for Pesach. However, poskim strongly debate the status of glass.2For a full review of the halachic literature concerning kashering glass, see my essay in the Fall 1993 issue of The Journal of Halacha and Contemporary Society (26:77-87). The Shulchan Aruch (Orach Chaim 451:26) rules that glass need not be kashered, even for Pesach, for it is smooth and thus does not absorb the flavor of non-kosher foods or chametz.3The Shulchan Aruch’s ruling follows the opinion of Tosafot (Avodah Zarah 33b s.v. Kunya), the Ra’avyah (Chapter 464, near end), and the Ran (Pesachim 9a in the Rif’s pages). On the other hand, the Rama, adopting (at least concerning Pesach) the opposite extreme position among Rishonim, equates glass with earthenware, which cannot be kashered at all.4The Rama follows Rabbeinu Yechiel of Paris (cited in the Mordechai, Pesachim 574) and the Semag (cited in Terumat Hadeshen 132). The Rishonim who advocate this position note that glass resembles earthenware in two ways: it originates from sand, and the Rabbis (Shabbat 15b) assigned glass utensils the status of earthenware for tumah (ritual impurity). A third opinion, not codified by the Shulchan Aruch or Rama, is that glass shares the status of metal, so it may be used only after being properly kashered (Or Zarua, Pesachim 256, and Ra’ah, cited by Ritva to Pesachim 30b). Accordingly, it would appear that Sephardic Jews merely need to clean their glass plates, while Ashkenazic Jews undoubtedly must remove or replace them during Pesach.5See (Techumin 8:35-36), where Professor Zev Lev (of the Jerusalem College of Technology) writes that it is best to remove the glass plate from the bottom of the microwave. There might be room for Ashkenazic Jews to kasher a microwave’s plate if it is made of duralex or pyrex; see Teshuvot Yabia Omer (vol. 4, O.C. 41) and Teshuvot Tzitz Eliezer (9:26).
It should be noted that the Rama’s opinion applies only to Pesach, but not to kashering between milk and meat. See The Journal of Halacha and Contemporary Society (26:83-84) for a summary of how Acharonim interpret the Rama’s opinion regarding kashering glass for year-round use.
A Heating Element
Rav Yitzchak Yosef (Yalkut Yosef, Kitzur Shulchan Aruch p. 588) writes that if there is a heating element in the microwave, then it must be kashered in the same manner as an electric oven - by turning the oven to its highest possible temperature for an hour.6Considerable controversy surrounds this procedure; see Halachos of Pesach pp. 180-181 and our earlier chapter regarding the kashering of ovens. Kashering by steam suffices only if the absorption occurs exclusively by steam. However, the heating element constitutes a fire and thus requires similar fire to be kashered (libun).
Rav Moshe Feinstein’s Ruling
Rav Shimon Eider (Halachos of Pesach p. 182 note 166) reports that Rav Moshe requires thoroughly cleaning a microwave, waiting twenty-four hours (since its last use), and then boiling a glass of water in the microwave. The steam will then kasher the entire microwave. This report seems to contradict Rav Moshe’s opinion elsewhere (Teshuvot Igrot Moshe, Yoreh Deah 1:60), that he prohibits using steam for kashering.7Rav Moshe explains that although steam is hotter than boiling water, perhaps steam cannot extract (maflit) non-kosher food particles as hot water can. There has been a great debate over whether steam can be used for kashering; see Hag’alat Keilim 10:4 for a review of the literature regarding this issue. Rav Eider quotes Rav Moshe as explaining that steam works specifically to kasher microwaves, for the steam that rises from the chametz cooking in the microwave is the only means by which its walls absorb chametz. Since we kasher ovens and utensils through the same process that they absorbed chametz, we may kasher a microwave with steam. In fact, the Badei Hashulchan (92:164) cites many Acharonim who permit kashering vessels through steam when that is how they absorb flavor, although he notes (Tziyunim 92:367) that the Chavat Da’at (Bei’urim 92:26) disagrees.
Criticism of Rav Moshe
Rav Yitzchak Yosef (Yalkut Yosef, Otzar Dinim La’ishah V’labat p. 310) and Rav Yisrael Rozen (Techumin 8:35 note 34) question Rav Moshe’s view because we do not find steam as a method of kashering in any traditional codes, which explicitly endorse kashering only via fire or boiling water.8Rav Yitzchak Yosef does not entirely reject kashering via steam, but, after stipulating several conditions that must be met in order to kasher via steam, he writes that it is “more appropriate” not to rely on this method of kashering. In the context of kashering for Pesach (Yalkut Yosef, Kitzur Shulchan Aruch p. 588 in the 5760 edition), he similarly presents the option of kashering via steam but adds that frequently used microwaves should preferably not be used at all on Pesach. Another problem with Rav Moshe’s suggestion is that the steam does not kasher the place underneath the cup of boiling water (since it cannot reach there). The location that had been under that utensil should be kashered separately either by pouring boiling water on it or by kashering the microwave again, with the cup of water in a different place.
Rav Eider himself challenges Rav Moshe’s ruling because the microwave actually absorbs chametz even without steam. Hot foods often spill and splatter, directly imparting their taste into the walls, without a medium such as steam.9Even if the microwave’s walls do not reach yad soledet bo (the heat at which Halachah believes that absorption occurs), the food is hot. In this situation, called cham letoch tzonein (warm into cold), Halachah assumes that a thin layer of the walls does absorb flavor (kedei kelipah). See Shulchan Aruch, Yoreh Deah 91:4. Indeed, during extended use of a microwave, steam can raise the walls’ temperature above yad soledet bo, as noted by Prof. Zev Lev (Techumin 8:35). Rav Binyomin Forst (The Laws of Kashrus p. 234) expresses similar reservations about Rav Moshe’s lenient view. Thus, Rav Eider advises that the places on which chametz may have fallen should be kashered by pouring boiling water directly onto them.10Perhaps Rav Moshe would respond that, during Pesach use, only steam will extract the food particles from the spills and splatters in a microwave. Accordingly, if we accept that the steam can extract chametz particles and thus create a problem on Pesach, then it can also extract chametz to kasher the microwave. One might counter, though, that kashering is a formal procedure, and the prohibition to cook food in a utensil containing non-kosher or chametz particles applies regardless of the fact that they cannot render the food non-kosher (see B’ikvei Hatzon 24:11). However, Rav Eider’s personal suggestion presents its own difficulties. Pouring boiling water into a microwave is not always a simple task. Moreover, during the course of a year, hot chametz splatters throughout the microwave, so hot water would have to be poured over every internal surface of the microwave in order to thoroughly eliminate any traces of chametz.
Support of Rav Moshe’s Ruling
Three lenient considerations exist to buttress Rav Moshe’s ruling. Firstly, a minority opinion permits kashering with steam.11See Darchei Teshuvah (121:16), Teshuvot Achiezer (4:9), and Teshuvot Melamed Lehoil (2:51). Moreover, the Shulchan Aruch (O.C. 451:25) determines the method of kashering by the way the utensil is generally used (rov tashmisho). For example, if one usually uses a utensil to boil food, but occasionally uses it to cook directly over a fire, boiling water alone suffices to kasher it, without employing fire. Accordingly, if we fundamentally permit kashering through steam, the occasional splattering onto a microwave’s walls would not force us to use boiling water for kashering. However, the Rama does not accept this ruling, so Ashkenazic Jews cannot utilize this leniency. Nevertheless, Ashkenazic poskim might take the Shulchan Aruch’s position into account when other lenient considerations exist. Rav Ovadia Yosef rules that Sephardic Jews may rely on the Shulchan Aruch (see Yalkut Yosef, Kitzur Shulchan Aruch p. 588 [in the 5760 edition]).
Finally, some authorities (cited in Darchei Teshuvah 92:165 and Badei Hashulchan 92:166) claim that steam cannot extract that which is already absorbed in the microwave. It may be inferred that the Shulchan Aruch and Rama (Yoreh Deah 92:8) also subscribe to this view (see Mesorah 4:86). A major concern during Pesach is that steam rising from cooking foods will potentially extract previously absorbed chametz from the microwave’s walls. However, no chametz would be extracted according to this lenient view. Rav Yechezkel Landau (Dagul Meirvavah, Yoreh Deah 92:8), though, adopts the strict opinion that steam can extract taste particles, so an unkashered microwave may not be used on Pesach.12For a discussion of this point, see my essay in the Fall 1996 issue of the The Journal of Halacha and Contemporary Society (32:26-37). Nonetheless, perhaps the lenient view (which we do not generally accept) might be used in conjunction with the two considerations mentioned above, as additional reasons (senifim lehakel) to further support Rav Moshe’s ruling.
Contaminating the Water
Rav Yitzchak Yosef (Yalkut Yosef, Kitzur Shulchan Aruch p. 588 in the 5760 edition) and Professor Lev (Techumin 8:35) advise putting a detergent into the water before boiling it to kasher the microwave. The detergent ensures that any chametz particles absorbed into the microwave walls will not impart a positive flavor should they come in contact with food on Pesach.13Interestingly, adding detergent to the water might facilitate kashering non-kosher dishes for year-round use without waiting twenty-four hours for dish’s the non-kosher flavor to spoil (see Shulchan Aruch, Yoreh Deah 95:4, and Chazon Ish, Yoreh Deah 23:1). Instead of waiting for the flavor to naturally turn bad, the absorption of the detergent spoils it immediately. However, see Mesorah (12:72-73), where Rav Yosef Efrati implies that Rav Yosef Shalom Eliashiv permits this method of kashering only in cases of need. Rav Efrati cites Rav Eliashiv as normally requiring one to wait 24 hours after the machinery’s last use with non-kosher food. Rav Moshe Feinstein (Teshuvot Igrot Moshe, Y.D. 2:31) also objects to kashering within 24 hours, in the manner described above, except in cases of great need. Thus, even if we were to assume that steam cannot kasher, the microwave’s chametz particles would not render any food non-kosher on Pesach.14This logic holds true according to the Shulchan Aruch (O.C. 447:10); see, however, Rama (ad loc.), who cites the Ashkenazic custom to prohibit foods that absorbed the flavor of chametz even if the chametz imparted a displeasing flavor.
Conclusion
Several considerations can buttress Rav Moshe’s lenient ruling to permit kashering a microwave for Pesach. Many rabbis, however, feel that it is inappropriate to rely on these opinions for Pesach, since we generally act strictly concerning this holiday’s dietary laws.15See Teshuvot Vehanhagot 2:212 where Rav Moshe Shternbuch expresses serious reservations regarding Rav Moshe’s lenient ruling. Rav Eider even suggests that it is preferable to cover the surfaces of the microwave, as well as the food being cooked in it, during Pesach, even after it has been kashered according to Rav Moshe’s method. One should consult a Rav for guidance in this issue, especially since many of the relevant facts are subject to change in light of technological developments.