The Torah source for requiring the koshering of pots and utensils that were used by non-Jews (for non-kosher foods) is found in Parshas Mattos (Bamidbar 31: 21-23). Following the war with Midian, the Jewish People were instructed to kasher the spoils of war that were used for preparing food: “This is the law that Hashem commanded Moshe: As far as the gold, silver, copper, iron, tin and lead are concerned, whatever was used over fire must be made to go through fire and purged.”
The Torah mentions six types of metals that can be kashered, from which Chazal deduce that there are types of vessels that cannot be kashered. We find in the Torah itself (Vayikra 6:21) that earthenware vessels in which a chatas offering was boiled must be broken, as opposed to metal vessels which can be kashered.
Thus, ceramic or earthenware vessels are excluded from the koshering process. As the Gemara explains (Pesachim 30b; Avodah Zarah 34a), these vessels absorb taste from foods cooked in them, and kashering processes, predominantly referring to hag’alah (immersion in boiling water, parallel to the cooking method of most pots), cannot fully remove the absorbed taste. This is ruled by the Shulchan Aruch (Orach Chaim 451: 22; note that if the utensil was only used for cold foods, the Shulchan Aruch rules that it often can be kashered for Pesach by means of hag’alah).
The question that is left unanswered by these principles is that of other materials—those that are not metals, but also not earthenware. What is their status concerning kashering? Specifically, of great interest for modern society is the question of glass vessels: Can glass be kashered or not? What is the means of kashering? And does it depend on different types of glass?
We will discuss these questions, among others, in the present article.
Wood, Stone, Bone
The Gemara (Pesachim 30b, citing Rav Huna brei d’Rav Yehoshua) notes that wood, though not mentioned among the materials in the Pasuk, can be kashered. The Gemara elsewhere (Chullin 25b, citing Rav Nachman), concerning vessels that are mekabel tumah, mentions that vessels made of bone have the same halachic status as metal.
These examples are cited by Rishonim—see, for example, the Rif (Pesachim 8b in his pages), Rosh (Pesachim 2:7), Mordechai (Pesachim 553), and Shulchan Aruch (Orach Chaim 451:8)—and others expand the list to other materials whose properties are similar to those of metal. For example, the Rambam (Hilchos Chometz U’Matzah 5:25) rules that stone is halachically equivalent to metal for purposes of kashering. The Tur (Orach Chaim 451:8), notes that Rav Hai Gaon however, compares stone to earthenware vessels that cannot be kashered.
The Shulchan Aruch (451:8), based on these opinions, rules that vessels made of wood, stone and metal can be kashered, and the Rema adds that the same applies to bone. Note that the Darchei Teshuvah (Yoreh De’ah 121: 25) writes that this leniency applies only to utensils made out of whole stones, and not to those made of crushed or ground up stone, which are comparable to earthenware. However, other authorities do not mention this distinction.
The status of glass is a major debate among Rishonim. The disagreement is based on how to view glass as a material: Is it a type of earthenware, since it is made from sand heated to extreme temperatures, or should we look at the final product, which is smooth and non-absorbent, so that it may not need to be kashered at all, as some Rishonim suggest concerning stone vessels (see Ravya, Pesachim 464; Ran, Pesachim 8b in the Rif’s pages).
For example, Rabbeinu Yechiel of Paris (cited by Haghos Maimoniyos, Hilchos Chametz U’Matzah 5:25; Mordechai, Pesachim 574) says that since glass is formed from sand it has the status of an earthenware vessel and cannot be kashered. This is also the opinion of several Rishonim, including the Terumas Hadeshen (1:132; 2:152) and Issur Vehetter (58:50). However, many Rishonim write that glass is smooth (shi’a) and therefore needs no kashering at all. These include Rabbeinu Tam (Tosafos, Avodah Zara 33b) the Ran (Pesachim 9a in the Rif’s pages); the Rashba (1:233); the Rosh (Pesachim 2:8) and others.
A third, minority opinion is that glass is similar to metal: that is, it does absorb taste and, like metal, it can be kashered. This is the view of the Rambam in his commentary to the Mishnah (Avodah Zarah 5:12) and the Ra’ah (cited by the Ritva, Pesachim 30b). The Ra’ah and Ritva write that one may not rely on this for kashering purposes, since due to its delicate nature we are concerned that glassware will not be properly kashered. This concern appears in the Shulchan Aruch (451:7) concerning ivory (keren).
Halachic Rulings: Glass for Pesach
The Shulchan Aruch (Orach Chaim 451:26) rules that glass is smooth and non-absorbent, so that it does not require any kashering. This is true for general kashrus during the year, and even for Pesach.
Based on the Shulchan Aruch, this is the ruling of the majority of Sephardi authorities (see Pri Chadash 26; Shut Yabia Omer Vol. 4, Orach Chaim 41; Shut Ohr L’Tziyon Vol. 3, 10:12), and is broadly the custom of Sephardi communities today. However, there are several Sephardi authorities who dissent, most notably the Ben Ish Chai (Year 1, Parshas Tzav 14; Shut Rav Pe’alim Vol. 3, Orach Chaim 29) and his followers.
Following the Ashkenazi Rishonim mentioned above concerning the status of glass, the Rema argues with the ruling of the Shulchan Aruch, and states that glass is considered earthenware concerning Pesach use, and cannot be kashered. He adds that this is the custom of Ashkenazic communities: to consider glass non-kasherable, just as ceramic vessels.
Glass for Year-Round Use
The fact that the Rema only notes his stringency on kashering glass vessels concerning Pesach (it is mentioned only in Orach Chaim concerning Pesach, and not in Yoreh De’ah for general kashrus matters) has led several authorities to state that for year-round purposes it is permitted, even for Ashkenazi communities, to kasher glass. These authorities include the Knesses Hagedolah (Yoreh De’ah 121, Hagahos on the Tur 25. His opinion is recorded by the Pri Megadim (Orach Chaim 451, Mishbetzos Zahav 31; Yoreh Deah 105 Mishbetzos Zahav 1), the Ya’avetz (Mor U’Ketziah end 451), and others.
Shut Minchas Yitzchok (1:86) writes that for year-round purposes, hag’alah will certainly work for glass for these matters. Rav Shlomo Zalman Auerbach (Halichos Shlomo, Moadim vol. 2, Pesach Ch. 3, footnote 75) is altogether lenient in this matter.
However, the Vilna Gaon (annotations to Yoreh De’ah 135: 28) seems to equate Pesach and year-round matters, implying that the halacha is the same for both. This stringent approach was adopted by Rav Yaakov Kamenetsky (Emes L’Yaakov on, Orach Chaim 451, footnote 443). He states that those who were lenient all-year round were discussing a situation which doesn’t exist today. In the old days glass vessels could not be used to cook non-kosher foods. However, nowadays when they can, Pesach is the same as the rest of the year.
Lechatchila or Bedieved
We have thus learned that at least concerning Pesach, and perhaps even for year-round purposes, the Ashkenazi custom is not to kasher glass utensils. But what is the halacha if a glass utensil was properly kashered? Does this help?
Several authorities, including the Rema himself (Darchei Moshe 451:19), state that the ruling is only on a lechatchila level: bedieved, if the kashering process is done, it is permitted to use the glass utensils, even on Pesach.
The Taz (451:30) and Elyah Rabbah (451:54) explain that in a bedieved situation, such as where food has already been cooked in a glass utensil, we can rely on the Shulchan Aruch’s opinion, that kashering is not required at all.
However, the Magen Avraham (451:49) and others (see Chok Yaakov 68; Pri Megadim, Mishbetzos Zahav 30; Mishnah Berurah 451: 155) maintain that only if the glass utensil was actually kashered is it permitted, bedieved, for use on Pesach.
Other authorities, notably the Vilna Gaon (451:26; see also Kitzur Shulchan Aruch 116:13 and Aruch Hashulchan 451:50), rule that according to the Rema kashering is ineffective for glass utensils even on a bedieved level.
The Mishnah Berurah (451, 55) concludes that on Pesach one who put hot food in a glass vessel which was used for chametz may be lenient if no kashering was done only in cases of significant loss, and only if the glass utensil had not been used for twenty-four hours. Under these circumstances, he rules that one may rely on the Shulchan Aruch’s opinion that there is no requirement of kashering for glass utensils.
Poskim generally classify china, even glazed china which is coated with a layer of glass, as earthenware vessels that cannot be kashered.
However, there are possible leniencies concerning such china, porcelain, Corelle and other tableware, which can be relied on in extenuating circumstances.
We will please G-d dedicate a future article to discussion of these materials, and the further complications of compound materials.