Which Items Can Be Kashered?
All utensils, equipment, dishes and cutlery which come in contact with non-Passover food must undergo a purging process known as Hechsher Keilim, aka “Kashering”.
Items fashioned from certain materials or fashioned in a certain manner may not be Kashered:
- Earthenware
- China
- Pottery
- Concrete
- Cement
Glass According to the Ashkenazic custom, glass cannot be Kashered under normal circumstances (there are unique circumstances under which they may be Kashered, beyond the scope of this primer. Please consult your Rabbi.)
Plastic While some authorities do not allow plastic to be Kashered, many others do allow.
Items which have nooks and crannies and cannot be cleaned properly including (but not limited to), pots and pans with rolled “lips”, colanders, sifters, and some dishwashers cannot be Kashered with Irui or Hagala (see below for definitions).
Any item which may get ruined through the Kashering process may not be Kashered. This can apply to light plastics which may bend, glass which can shatter, sheet pans and hotel pans which require libun gamur, or any item which is not heat resistant. This is out of concern that one may not Kasher it properly out of concern of breaking this equipment.
The basic premise behind Kashering is known as “K’bol’o, kach polto” — the very manner in which the item became non-permissible is the manner in which we Kasher to make it permissible.
Methods of Kashering
Irui — pouring or spraying boiling water. This method is used for items which only became non-Kosher or Chametz via indirect heat, such as sinks, counters, and tables on which hot Chametz such as pasta, soup, or toast may have been placed or spilled on. Every spot needs to be hit with a direct flow of boiling water. It is not sufficient to pour the water in one spot and allow it to spread out.
You do not have to Kasher the whole utensil at once. If you run out of water or need a break, you can do so. When using the Irui method, all items being Kashered should not be used for 24 hours prior to Kashering.
Hagala — Immersing in boiling water. This method is used for pots, pans, flatware, cups, and most small utensils that may be Kashered. The water should be boiling when items are immersed. You do not have to Kasher the whole utensil at once. If you run out of water or need a break, you can stop in the middle. This is especially important for large items that cannot be submerged at one time.
When Kashering a large pot, fill the pot and boil. When the water reaches a boil, using a tongs, place a rock in the fire under the pot. When the rock is heated, place the rock in the pot and the water will boil over, Kashering the rest of the pot.
Libun Kal — Light scorching. There are several methods that can be used:
ONE: Heat with a torch until the opposite side is hot to the touch (around 190°F depending on the density of the metal). This method can be used for items requiring Irui (use of blow torches is not recommended without specialized training.)
TWO: Heat with a torch until the opposite side can singe paper (around 375°F, depending on the density of the metal). This method is applicable to items requiring Hagala or when Libun is only required as a stringency.
THREE: Dry heat. Heat oven to 550°F (or 500°F if that is the highest temperature) for 2 hours. This method is predominantly used for Kashering standard ovens that do not have a self-clean cycle, or warming boxes and drawers. This method does NOT apply to ovens in which food is baked directly on the racks or the floor of the oven. If food is baked directly on the racks or floor of the oven, it will require Libun Chamur.
Libun Chamur — Intense scorching. Heat with fire until the item is glowing (around 900°F). This method is used for grills, pizza ovens, broilers, etc. The generally accepted custom is that the self-cleaning cycle qualifies as Libun Chamur.
NOTE — Continuous clean, steam clean, aqua clean etc. do not qualify as any type of Kashering. Such ovens should be treated as non self-clean ovens.