Materials that can be koshered are materials which absorb—but which also emit. When, for example, something unkosher is cooked in a metal pot, the pot absorbs the unkosher substance. When the pot is ‘koshered,” that substance is emitted.
Which materials fall within this category?
Metals can be koshered. This applies to all pure metals, such as gold, silver, copper, iron, tin and lead (which are mentioned in the text of the Torah), and other metals, such as aluminum, steel, and so forth, which are not specifically mentioned there.
Even if the metal vessel contains an area that is partly painted, the vessel can be koshered.
Other Materials that Can be Koshered
They are: Teflon; Stone (this refers to actual stone, not “stoneware); Wood; Plastic; Bone (this refers to actual bone, not “bone china”); and Rubber.
Koshering Handles and Covers
Handles of utensils—must be koshered. This applies, even if the handle is a separate component and attached to the utensil with screws or the like.
When the handle is made of metal, whatever the pot absorbed—is absorbed by the handle as well, since metal is a conductor of heat. (In the language of the sages: “If part of the utensil is hot—it is all hot.”)
When the handle is made of, let us say, wood, the heat is not conducted to the handle. However, there is still the possibility that food fell or splattered onto the handle. There is also the possibility that somebody touched the handle while he or she had hammets on the hands. So, the handle must be koshered.
The cover of a pot must be koshered, even if food within the pot never touched the cover. Reason: the vapors within the pot carry the taste throughout the pot and into the cover.
To view a list of materials that cannot be koshered for Passover, click here
To view an extensive list of kitchen utensils and appliances and how they are koshered, click here