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Q&A from the Bais HaVaad Halacha Hotline
October 27, 2022
Q I have kitchen utensils in need of kashering, but I need to know whether some of them can be kashered at all. They include metal, glass, china, plastic, and rubber.
A Metal can certainly be kashered, as it says explicitly (Bemidbar 31:22-23), “But the gold, and the silver, and the copper…you shall pass through water.”
Earthenware (klei cheres) is explicitly excluded from kashering, as it says (Vayikra 6:21), “And the earthenware in which it was cooked shall be broken.” The Gemara (Psachim 30b) explains that the taste becomes embedded and cannot be extracted by hag’alah (boiling).
Whether glass can be kashered is a topic of discussion by the early poskim. Some equate glass with earthenware, since it is made from sand, and thus hag’alah doesn’t work. Others go to the opposite extreme and say hag’alah isn’t even needed, because the hard, smooth surface of glass doesn’t absorb any taste. The Mechaber (O.C. 451:26) rules leniently, but the Rama writes that the Ashkenazi minhag is to be strict. Later poskim (Pri Megadim ibid.) point out that this stringency is only regarding Pesach, not other isurim like basar bechalav or beheimah temeiah. But the Minchas Yitzchak says one should nevertheless perform hag’alah in such cases.
Some poskim ruled that china and porcelain, because of their glazing, have the status of glass rather than earthenware. Most poskim don’t adopt this, so, barring dire circumstances, this opinion should not be considered.
Plastic is relatively new, and its halachic status spawned a notable controversy among the poskim of the recent past. All agreed that even hard, smooth plastic doesn’t share the leniency of glass, because it lacks glass’s hardness. The question was whether plastic is equivalent to earthenware. Some argued that the chemical makeup of plastic might share certain qualities with earthenware, and since no lenient precedent exists, hag’alah cannot be accepted. But the consensus of many, if not most, poskim is that nonkosher taste can be extracted from plastic via hag’alah (Minchas Yitzchak 3:67).
Natural rubber has the same status as wooden vessels and is subject to hag’alah. Synthetic rubber is akin to plastic (Igros Moshe O.C. 2:92).