The Kashering Primer

Rabbi Eli Gersten

How to Make Your Kitchen Kosher-for-Passover, Even if You’re not a Rabbi

One of the most daunting preparations we make for Pesach is kashering, a process to prepare chametz utensils for Pesach use. As with all areas of halachah, those who are unsure of how to apply the rules of kashering to their situation should consult an Orthodox rabbi.

The Torah (Bamidbar 31:23) requires kashering utensils acquired from a non-Jew, as they are presumed to have been used in non-kosher cooking (and will have absorbed non-kosher flavor). Since chametz on Pesach is also forbidden, the Talmud applies the laws of kashering to chametz as well. There are four basic methods of kashering. The prescribed method depends on the utensil and how it was used.

Utensils used directly in the fire (e.g. BBQ grate), must be kashered by placing them into fire. This process has the effect of burning away any absorbed taste. To qualify as a complete libun, metal must be heated until it glows. A self-clean cycle of an oven (approx. 850°F) also qualifies as libun. There is no need to wait 24 hours before libun, though it is advised. There is no need to scrub the utensil before performing libun, since the fire will burn off residue, but some cleaning is advised.

HAGALAH (Boiling)
Utensils that were used to cook nonkosher liquid can be kashered with hagalah (boiling in water). To prepare the utensil for hagalah, the utensil must be thoroughly cleaned. Only utensils that can be scrubbed clean should be kashered. Items that have narrow cracks, crevices, deep scratches or other areas that cannot be cleaned, cannot be kashered for Pesach. The following, for example, cannot be kashered for Pesach: pots with rolled lips, bottles with narrow necks, filters, colanders, knives (or other utensils) where food can get trapped between the blade and handle. After cleaning, the utensils should then be left idle for 24 hours. To kasher, every part of the utensil must make contact with boiling water. This process can be done in parts. For example, a large spoon can be immersed into a pot of boiling water for 10 seconds, turned over and then the remainder immersed. When the utensil is removed from the boiling water, it should be rinsed off in cold water. While strictly speaking these utensils may be kashered in a clean non-Pesach pot that was not used for 24 hours, the minhag, however, is to kasher the pot first, by boiling water in the pot and discarding.

IRUY KLI RISHON (Poured Boiling Water)
If the utensil only came in contact with hot liquid being poured on it (iruy), it can be kashered in the same manner. If the utensil came in contact with hot chametz solids, then one should kasher by pouring boiling water accompanied by an even melubenet, a heated stone. For example, if hot pasta fell into a sink, stones should be heated on the stove, and moved around the surface of the sink while boiling water is poured over them. In this way, the water will remain boiling on the surface of the sink. The stones may need to be reheated several times, since they cool down quickly. In all other aspects the process is identical to hagalah.

LIBUN KAL (Light Burning)
In certain cases, libun kal is sufficient. This can be accomplished by heating in an oven at 550° F for one hour. This method of kashering can be used in place of hagalah. It is also used when the need for libun is only an added stringency.

Ceramic, such as china, and enamel coated pots cannot be kashered. It is the custom of Ashkenazim not to kasher glass as well. Some poskim do not permit kashering plastic or other synthetic materials for Pesach; however, the opinion of the OU rabbanim is that it may be kashered, if there is a need. Ask your rabbi for guidance. Composite stone (e.g. quartz counters) which is made mostly of stone, but is held together with resin, can be kashered. As a rule, materials such as metal, wood, stone, natural rubber, and fabric can be kashered.


It is recommended that one not wait until erev yom tov to run the self-cleaning cycle to kasher an oven, as this is known to be hard on the oven and repairs may be required.

Some newer self-cleaning ovens employ Aqualift technology that cleans at low heat; they should be considered like non-self-cleaning ovens. see The Modern Kitchen below.

Please note that kashering may discolor oven racks and stovetop burners. If racks have rubber wheels, the wheels may melt. Replacement racks for Pesach should be ordered well in advance of the holiday.

The Kashering Checklist

The Modern Kitchen


Libun Gamur – Burning
Hagalah – Boiling
Iruy Kli Rishon – Poured Boiling Water
Even Melubenet – Heated Stone

1.Refrigerators, Freezers, Food Shelves & Pantries: Clean & Cover These areas should be thoroughly cleaned, paying special attention to the edges where crumbs may get trapped. The surfaces should be lined with paper or plastic. Note: Refrigerators and freezers will operate more efficiently if holes are poked in the lining to allow air flow.

2. Dishwashers: Hagalah (boiling in water) Kashering of dishwashers is a complicated process and should only be done in consultation with a halachic authority.

3. Stainless Steel Sink: Iruy (pouring boiling water) Remove drain. [It is recommended that the drain be replaced. If this is difficult, it may be used if the drain has large holes that can be completely scrubbed clean]. It is preferable to kasher a sink by pouring boiling water in conjunction with an even melubenet (a heated stone). In lieu of kashering with a heated stone, some will place a rack on the bottom of the sink, or use a sink insert.

4. The Sink Faucet: (including instant hot) Iruy (pouring boiling water) Detach any filters or nozzles.

5. Countertops:

Stainless Steel, Granite, Composite Stone (E.G. Quartz) Or Formica Countertops: Iruy (pouring boiling water) OR Covering it is preferable to kasher a countertop by pouring boiling water in conjunction with an even melubenet. There are different opinions as to whether formica (or plastic) countertops can be kashered for Pesach.

Ceramic Tile Countertops: Cannot Be Kashered & Must Be Covered
The counter should be covered with a water resistant covering.

6. Stovetops:

Gas Stovetop: Libun (Burning) & Cover The stovetop surface and grates should be cleaned well and not used for 24 hours. The stovetop surface should be covered with foil. The stovetop grates can be replaced or they should be burned out in the oven @ 550° F for one hour.

Electric Stovetop: Libun (Burning) & Cover The stovetop surface should be cleaned well and covered with foil. The burners should be turned on until they glow red.

Glass Stovetop: Cannot Be Kashered & Must Be Covered* The stovetop surface should be cleaned well and not used for 24 hours. During Pesach, pots should not be placed directly on the stove surface, but rather an aluminum (or other metal) disk should be placed directly under the pot. *The entire glass top surface should not be covered as this might cause it to overheat and crack.

7. Ovens:

Self-Cleaning Ovens: Libun (burning) Remove any visible food. Complete self-cleaning cycle with racks in place.

Non-Self-Cleaning Oven: Libun (burning) Clean all surfaces (walls, floor, doors and racks) thoroughly with a caustic cleanser (e.g. Easy Off). Pay special attention to thermostat, oven window, and edges of the oven chamber. Black discoloration that is flush with the metal need not be removed. Oven should not be used for 24 hours. Place racks in the oven and turn the oven to broil (highest heat) for 60 minutes. A broiler pan that comes in direct contact with food should not be used. Note: The method of kashering described above is based on the ruling of Rav Aharon Kotler zt’l. However, Rav Moshe Feinstein zt’l ruled that the oven must either be kashered with a blow torch, or an insert should be placed in the oven. Consult your rabbi for guidance.

8. Warming Drawers: Libun (burning) Typically warming drawers do not get to libun kal temperature. Therefore, unless one is experienced in kashering with a torch, warming drawers are not recommended for use on Pesach.

9. Microwaves: Hagalah (boiling in water) (for those who kasher plastic) The microwave must be cleaned well and not used for 24 hours. Glass turntable should be removed and replaced with new kosher-for- Passover surface. A styrofoam cup should be filled with water and boiled in the microwave for 10 minutes. The cup should be refilled and moved to another spot and the process repeated for 10 more minutes. Cardboard or contact paper should be taped over the glass window pane for the duration of Pesach.

10. Metal Tea Kettle: Hagalah (boiling in water) The same treatment for pots applies here. Although it is uncommon for anything but water to be put into a tea kettle, nevertheless it must be kashered. Tea kettles often sit on the stove, and it is common for them to get spritzed with hot food.

11. Electric Mixer: Not Recommended Because of the difficulty in cleaning out the housing of the mixer from fine particles of flour, one should not use their year-round mixer on Pesach. The mixer blades, though, can be cleaned and kashered with hagalah.

12. Silverware, Pots & Other Small Items: Hagalah (boiling in water) Rolled lips, seams or cracks that cannot be cleaned will require torching of those areas. Utensils should be immersed one at a time into a pot of boiling water that is on the fire. Water should be allowed to return to a boil before the next item is placed in the pot. The pot can be non-Passover, provided it is clean, has not been used for 24 hours, and water is first boiled in the pot and discarded. Larger items can be submerged in the water one part at a time. Utensils should then be rinsed in cold water.

13. Keurig Coffee Maker: Hagalah Or Iruy (pouring boiling water) (for those who kasher plastic) The coffee maker must be cleaned well and not used for 24 hours. Remove K-cup holder and perform hagalah or iruy on K-cup holder. Run a Kosher-for-Passover K-cup in the machine (this will kasher the top pin).

14. Hot Water Urn, Water Cooler: Iruy (pouring boiling water)

Urn only used for heating water: Run hot water through the water tap for 10 seconds, while pouring boiling water from a kettle over the water tap.

Urn also used to warm food (e.g. to warm challah): Not recommended. Must be put away for the holiday.

Water Cooler In addition to pouring boiling water over tap, replace water bottle.

15. Baby High Chair Covered The tray should be covered with contact paper. The seat, legs and bars should be wiped down with a soapy rag.

16. Tablecloths, Kitchen Gloves, Aprons & Other Fabric Items: Wash Fabric items can be kashered by washing them with detergent in a washing machine set on “hot.” Items should be checked to make sure no pieces of food remain attached.

17. Tables: Covered Although wooden tables can be kashered, the common custom is to clean tables well and then cover them.


Rabbi Eli Gersten
Rabbi Eli Gersten serves as OU rabbinic coordinator and recorder of OU policy.

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