Types Of Materials
We discussed above that, in determining how to kasher a utensil, one must consider how the utensil was used when it absorbed the non-kosher or chametz flavor. Yet another determining factor is: Which material is the utensil made of? Not all materials can be purged of their absorptions, and some can only be purged in specific ways. We will first discuss the various methods of kashering for different materials, and then discuss the type of kashering relevant to common household utensils.
It should be noted that, nowadays, utensils are often made of one material and coated with another. For example, the interior of a metal frying is often coated with Teflon. These utensils can only be kashered if both the interior and exterior are made of substances which can be kashered.
The following is a list of various materials, and the laws of kashering that pertain to each one:
Earthenware
The Gemara (Pesachim 30b) states that an earthenware utensil cannot be fully purged of the forbidden absorptions imbued within it when cooking.91 This is understood from the Torah’s instruction (Vayikra 6:21) that earthenware utensils used for the meats of korbanos must be broken; there is no other recourse other than the utensil being returned to a kiln and “recreated.”92
Enamel
Enameled pots are metal pots covered with a layer of enamel, which is a material that, halachically, may be considered as cheres (earthenware). According to common practice, these utensils are not kashered.93
Glassware
Shulchan Aruch and Rema94 disagree whether or not glass is a material that is considered permeable and absorbs flavor. The minhag of Sephardim is to act leniently, in line with Shulchan Aruch’s ruling — that glassware requires no kashering beyond scrubbing and rinsing non-kosher residue from its surface.95 Rema, however, rules stringently; since glass is made by heating sand (which is a type of earth) glassware is essentially the same as earthenware, which absorbs and cannot be kashered. The general Ashkenazi custom is to refrain from using glassware on Pesach even if, throughout the year, it was primarily used only for cold drinks.96
Mishnah Berurah97 notes that, according to everyone, glassware may be kashered with milui ve’irui. However, the custom is not to do so for Pesach if new glassware may be easily obtained.98
The same general ruling applies to Pyrex®, Duralex®,99 crystal, and Corelle®.100
Metal
Depending on how the non-kosher taste was absorbed, a metal101 utensil or surface may be kashered with libbun 102 or hagalah.103
Question: When is libbun necessary? When is hagalah necessary?
Discussion: Libbun is necessary for metal utensils — such as barbeque grills, stovetops, and oven racks — which absorb chametz via direct contact with fire (or other dry heat).
Hagalah is necessary for metal utensils, such as pots, which absorb chametz via a medium of hot liquid. Hagalah may also be used to kasher knives, even if they were used for a hot dry solid — provided they were not used over a direct heat source.
Plastic
The Poskim of recent generations have discussed whether hard plastics and other stiff synthetic materials may be kashered. On one hand, Chazal did not specify that these materials cannot be kashered, as they did when discussing earthenware.104 But on the other hand, we cannot be certain that kashering is effective in fully removing all absorptions, for we have no tradition from Chazal that this is the case. 105
Question: Teflon is a form of plastic as well. May it be kashered?
Discussion: The Poskim disagree whether Teflon, which includes pans that have a Teflon coating, may be kashered. R’ Moshe Feinstein106 rules that a Teflon-coated metal utensil can be kashered, as long as it has been twenty-four hours since the utensil was last used. Although it is uncertain whether or not Teflon can be kashered, the requirement to kasher a utensil that is eino ben yomo is an obligation that is not Torah-mandated but rather rabbinic, allowing room for leniency in situations of uncertainty such as this one. Other Poskim107 rule more stringently, stating that, due to the added stringency of Pesach, a utensil with a Teflon coating should not be kashered for Pesach, unless it was only used as a kli sheini.108
Porcelain and China
Porcelain and china are types of dishware made from claylike materials that have been baked at high temperatures. Most Poskim109 rule that they have the status of earthenware, which cannot be kashered.110
Stone, Marble, Granite, and Composite Marble
Stone utensils have the same status as metal utensils above.111
Since stone surfaces can be kashered (as mentioned above), a marble or granite countertop made of a single slab of stone can in theory be kashered.112 However, granite may sometimes have other substances added to fill cracks, or to make it shiny — and, it is possible that these substances cannot be kashered. There are divergent opinions among the Poskim whether composite marble that consists of reconstituted marble (such as even keisar) may be kashered.113
Question: How about stoneware? Can it be kashered?
Discussion: “Stoneware,” a material used to make fine dishes and other items, is actually not stone, but earthenware; it is dense pottery fired at high temperatures of 2,200°F / 1,200°C to make it non-porous and resistant to liquids. It cannot be kashered.
Wood
Libbun will destroy wood, obviously. Wood utensils or surfaces may potentially be kashered with hagalah,114 depending on how the non-kosher substance was absorbed.
91 If earthenware utensils absorbed flavor from cold foods, such as through the process of kavush, then they can sometimes be kashered via milui ve’irui, discussed above.
92 See Shulchan Aruch 451:1
93 See The Kosher Kitchen, Rabbi Binyomin Forst, p. 346; Sefer Hagalas Keilim 13:7 fn. 6.
94 451:26.
95 Yechaveh Daat I:6. Ohr Letziyon III:10:12 notes that some Sephardic authorities are stringent to require milui ve’irui before using glassware.
96 Mishnah Berurah 451:154.
96 The Acharonim discuss whether the opinion cited in Rema — that glassware cannot be kashered — is intended only for Pesach, based on the added chumrah of chametz, or whether it applies throughout the entire year in regard to all non-kosher foods, as well as for milk and meat. Practically speaking, some refrain year-round from using glass for hot meat and dairy, whereas many are lenient to use the same drinking glasses for meat and dairy meals. Some Poskim prefer designating drinking glasses for each type of meal if possible. This topic is discussed in Pri Megadim, Mishbetzos Zahav end of Chapter 451; glosses of R’ Akiva Eiger to Magen Avraham 451:49; Igros Moshe, Orach Chaim V, 32:1; Halichos Shlomo, Hilchos Pesach Chapter 3 fn. 76; Emes L’Yaakov Al Daled Chelkei Shulchan Aruch, Orach Chaim 451, fn. 443; and Sefer Hagalas Kelim, Chapter 13, fn. 38, pp. 312-314.
97 451:155.
98 Ibid. 56.
99 See Sefer Hagalas Keilim 13:375.
100 See Orchos Habayis Chapter 10, fn. 25.
101 Igros Moshe, Orach Chaim III:58 notes that this includes aluminum.
102 See Avodah Zarah 75b; Ramban to Bamidbar 31:23; Beiur Hagra to 451:8.
103 On a practical note, many metal pans have a layer of Teflon. Its kashering status would therefore depend on whether Teflon is a material that can be kashered, discussed below.
104 Minchas Yitzchak III:67; Cheshev Ha’ephod I:117; Ohr Letziyon III:10:13.
105 Igros Moshe, Orach Chaim II:92; Chut Shani pp. 127, 129. Yet other Poskim take a middle position, ruling leniently when kashering for issurei derabanan, but stringently for issurei deoraisa; see Be’er Moshe II:53; and R’ Yosef Shalom Elyashiv, cited in Haggadah Shel Pesach of R’ Yosef Shalom Elyashiv, p. 11.
106 Igros Moshe, Even Ha’ezer IV:7.
107 R’ Yosef Shalom Elyashiv and R’ Nissim Karelitz, both cited in Siddur Pesach Kehilchoso I 9:25 fn. 49*.
108 Siddur Pesach Kehilchoso, 8:12 fn 53, further notes that libun kal, which can sometimes substitute for hagalah, is also impractical to be done to Teflon, for it will ruin the utensil. Another issue regarding Teflon is that a Teflon-coated pot may often be used with only a small amount of liquid. This would require libun which, as stated, is unfeasible.
109 Cf. Emes L’Yaakov Al Daled Chelkei Shulchan Aruch, Yoreh Deah 121, fn. 54.
110 A halachic authority should be consulted in the event that one’s porcelain or china absorbs non-kosher food, or a meat dish came in contact with hot milk.
111 Shulchan Aruch 451:8.
112 Specific instructions of how a counter may be kashered for Pesach are provided in Section VII below.
113 This issue is discussed in Halichos Shlomo, 3:4, Devar Halachah 6; Sha’arei Mishor, III:31; Libun Hilchesa pp. 17-24; Pischei Megadim, Biurim 18:2; and in an article in Hilchesa Mibei Dina, Pesach, p. 185.
114 Shulchan Aruch 451:8.