Utensils that are used during the year for chometz may not be used to prepare food for Pesach unless they have been properly kashered. Cloth (not plastic) tablecloths, towels, potholders, bibs, and aprons used year round with chometz should be washed thoroughly with detergent in hot water and may then be used for Pesach even if the stains do not come out. Synthetic material such as Terylene, or rayon (which is made of chemically processed natural fibers), which only withstand a warm water cycle may be used on Pesach after they have gone through a warm washing with detergent but only if there are no visible stains after they have been cleaned.
Surfaces upon which only cold chometz has been placed during the year, such as pantry shelves and refrigerators, should be thoroughly washed and rinsed to ready them for Pesach use. It is advisable to go over the surface with bleach or some other liquid (e.g., Fantastik) that will make any edible crumbs inedible upon contact. Surfaces that are used for hot chometz during the year must, in addition, be kashered.
Granite, marble, Caesarstone, wood (if it has a smooth surface), and stainless steel countertops can be kashered by pouring boiling water on them (irui). Make sure the counter was not in direct contact with hot chometz for the 24-hour period preceding the kashering. It is best to use an electric water heater that is plugged in and boiling the water as it is being poured over the counter, but any pot of boiling water that is taken off the fire with a rolling boil is also acceptable. A removable electric hot water kettle is also acceptable. The entire area should have the hot water poured directly on it. Pour over the countertop in a systematic way to be certain that you reach all areas with the hot water. Surfaces that cannot be koshered for Pesach, such as Formica and ceramic tiles, should be covered with non-absorbent material such as contact paper, cardboard or aluminum foil (it is best to use a few layers of aluminum foil, as it tears easily).
To kasher a stainless steel or granite sink, first clean it and then keep hot water off it for 24 hours. Then pour boiling water over its entire surface in a systematic fashion to make sure that every spot is hit directly with the boiling water. It is not sufficient to pour on one spot and let the water run down the sink. The same rules apply to koshering sinks as to kashering countertops (see above). After kashering, the sink or countertop should be rinsed with cold water. China, corian and porcelain sinks cannot be kashered; dishes should not be placed directly into such a sink. They must be washed in a Pesach dishpan that sits on a Pesach rack. It is necessary to have separate dishpans and racks for milchig and fleishig dishes. Another option is to fully line the sink with a tin or plastic insert, contact paper or aluminum foil.
Metal utensils that are used with liquid (soup pots, cutlery, serving utensils, kiddush cups, etc.) can be kashered by first cleaning them thoroughly, not using them for 24 hours, and finally, completely immersing them in a kosher for Pesach pot of water that has been heated and is maintaining a rolling boil when the vessel is immersed. The metal utensil being kashered should be submerged in the boiling water for about fifteen seconds. This should be followed by rinsing in cold water immediately upon removal. The entire item does not need to be in the hot water at one time. One may kasher half of the utensil and then reimmerse to kasher the other part. Just make certain that the second immersion overlaps the part that was already kashered and no part of the utensil was left unkashered. Each item should be kashered one at a time.
The utensils undergoing the kashering process may not touch each other. In other words, if a set of flatware is being kashered for Pesach, one cannot take all the knives, forks and spoons and put them in the boiling water together. They should be placed into the boiling water separately. A suggestion for kashering is to tie the pieces of silverware to a string loosely, leaving seven centimeters between each piece, and immerse the string of silverware slowly, making sure the water keeps boiling. Remove the string of silverware and rinse the kashered items in cold water. If tongs are used to grip the utensil, the utensil will have to be immersed a second time with the tongs in a different position so that the boiling water touches the initially gripped area. An alternative method, especially useful for larger pots, is to clean the pot inside and out, leaving it dormant for 24 hours, filling the pot completely with water, waiting until the water comes to a rolling boil, and using a pair of tongs to throw in a hot stone or brick that has been heated on another burner. The hot stone will cause the water to bubble more furiously and run over the top ridge of the pot on all sides at once. (Use caution, as the hot water may spray in all directions.) You can also pour boiling water (from a kettle or hot water heater) into the center of the pot and have the water spill over the edges. The kashering process is finalized by rinsing the pot in cold water.
A pot that is not kosher for Pesach may also be used for koshering, but it is the custom to make the pot kosher for Pesach first.
After the Pesach kashering process has taken place, the status of these newly kashered utensils may be changed from milchig to fleishig or vice versa or to pareve.
Braces, bite plates and retainers should be brushed thoroughly before Pesach and they may be used. Dentures and metal fillings do not pose a halachic problem on Pesach since food or drink that reaches them is not yad soledes bo.
Kashering countertops, sinks (irui), and metal utensils put in boiling water (hag’oloh), use a method of kashering that removes the absorbed flavor from the material.
There is a fundamentally different method of kashering, which is more powerful and destroys the chometz inside the material. This is called libbun gamur. Libbun gamur is the method used for kashering an electric range or self-cleaning oven.
To kasher an electric range, first scour it thoroughly. Then turn on the burner to the highest temperature setting for 15 minutes, or until it gets red-hot.
Gas grates should be put in a self-cleaning oven for kashering. Another method of kashering the grates is to place pots of water or a blech on all the grates and turn the flames on for 10 minutes. The heat is spread across the area all the way to the end of each grate and they are kashered that way. Make sure to remove the knobs if you are using a blech to cover the grates. Sometimes the heat is so intense that the knobs on the side melt and they can be hard to replace.
Glass-top stoves (Corning, Halogen or Ceran electric smooth top ranges) can be kashered in the area of the burners only. The most practical thing to do is to change the entire glass top for Pesach. If you wish to kasher the burners, they should be turned to high for 15 minutes. The area in between burners and around the grates cannot be kashered and you may want to cover it with foil or some other material to avoid running the risk that whatever falls on those areas cannot be eaten on Pesach. However, covering those areas may cause the glass or special material to crack. Since the area beyond the burner is not kasherable, any pot placed on the burner should not touch those areas not kashered. It is advisable to place a disk over the burner area (the disk should not extend beyond the burner area so that it does not reach the part of the glass top that is not kasherable). Any pot placed on the burner can then extend beyond the area of the burner since it will not come in direct contact with the glass top. If, however, a spill reaches the disk and the area beyond, the pesachdik pot and food and the disk may now be unusable for Pesach. If in spite of these problems, you still wish to use the glass top, it is advisable to place trivets over the unkashered area so that you have a place to put down the pesachdik pots.
A non–self-cleaning oven should be cleaned with a special oven cleaner such as Easy Off and not used for 24 hours. After this time, it should be turned on to the maximum setting for forty minutes. This will kasher the oven, but not the broiler or the racks, which come in direct contact with food. The broiler pan cannot be kashered. If the area of the broiler is cleaned with oven cleaner, you can kasher the rest of the oven and leave the clean broiler pan itself non-pesachdik in the oven while baking pesachdik food in the oven as long as the broiler area and the oven are two separate systems and the vapors of the oven do not reach into the broiler area. If the broiler pan is replaced, the broiler can be kashered in a similar fashion as the oven. If one wants to kasher the pan or racks, libun gamur (glowing hot metal) is required. Placing the racks and pan in a self-cleaning oven is the most practical way to kasher them.
Warming drawers cannot be kashered because the heat setting does not go high enough to constitute libbun. The warming drawer should be cleaned, sealed, and not used for Pesach. If it is part of an oven, the rest of the oven can still be kashered and used for Pesach.
Many microwave ovens without browning elements or convection can be kashered. If the walls do not exceed 120 degrees Fahrenheit during cooking, it is certainly cool enough and one only needs to clean it well. Otherwise, to see whether your microwave gets too hot, cook a potato in it for about five minutes and then open the door before it has finished its cycle. Then immediately check the temperature of the ceiling and walls. If you can keep your hands there for 15 seconds, the oven walls never reached yad soledes bo and they have not become treif or chometzdik. Many microwave ovens are able to pass this test. If yours does, just clean the oven walls very well with a cleanser so that the surfaces are clean. Any residual food matter should become pagum from the bleach or cleansing agent. (Lechumro, place a cup or bowl of water inside and boil for at least twenty minutes.) Then put in a new glass tray or cardboard on the bottom.
Self-cleaning ovens may be operated on the cleaning cycle and then used. It is preferable to kasher a self-cleaning oven and use it for Pesach than to kasher a regular oven in the way described above. Self-cleaning is considered libbun gamur, whereas the kashering of an oven by turning on to the highest temperature is libbun kal.
A grill cannot be kashered by just turning on the gas or electricity. Since food is roasted directly on the grill, it requires libbun gamur, which means that it must be heated to a glow in order to be used. This can be done either by using a blowtorch (which should only be done by qualified and experienced personnel) or by sandwiching the grates between charcoal briquettes and setting them on fire. Alternatively, the grates of the grill can be replaced. The part of the grill cavity that is level with the grate must also be kashered by heating it to a glow. This is because food is likely to have touched that area during barbecuing. The empty grill cavity must be kashered by cleaning, closing the hood and setting it to broil for forty minutes.
Inserts such as griddles that come into direct contact with food are treated the same as a grill. Therefore, they too would require application of direct heat until the surface glows red. Otherwise, the insert should be cleaned and not used for Pesach. If the grill has side burners, they should be treated like cooktop grates (assuming no food has been placed directly on them).
It is easiest to determine that the metal has been brought to a glow in a darkened room. Often, it is more practical to purchase a new grill for Pesach.
Dishwashers technically can be kashered if they have a stainless steel interior. You will still need to change all the racks. After waiting 24 hours, run a complete cycle with soap. You will also need to replace all rubber or plastic parts. In practice, it is impractical and difficult to kasher dishwashers and it is not recommended.
Kitchen items that cannot be kashered: A mixer, blech, plata for Shabbos, bread machine, Crock-Pot, sandwich maker, toaster/toaster oven, waffle iron, enameled pot, and anything made of china, Corelle, Arcolac, CorningWare, Melmac, plastic, porcelain, Pyrex, Silverstone, stoneware, synthetic rubber, or Teflon. These items should be washed thoroughly and put away in a completely sealed off area until after Pesach. It is advisable to go over the surfaces of the item with bleach or some other liquid that will make any edible crumbs inedible upon contact. One can also put bleach and water in a spray bottle and spray into the hard-to–reach areas such as in a toaster.
Glass was expensive and hard to obtain a century ago and it was customary to kasher drinking glasses by immersing them in cold water for three 24-hour periods. This is accomplished by submerging the glasses for 24 hours. The water should then be poured out and replenished and let sit for another 24 hours. This procedure should be repeated a third time, for a total of 72 hours. This procedure of submerging cannot be used for Pyrex or glass that was used directly on the fire or in the oven. In general, kashering glasses is not recommended anymore. Wherever glasses are readily available for purchase, special glasses for Pesach are preferable. Arcoroc and Corelle should be treated as glass for kashering purposes.
It’s important to note that where libbun kal helps, certainly libbun gamur is good; where hag’oloh helps, surely libbun kal is good; where irui helps, certainly hag’oloh and libbun work.
It is recommended that the following items be bought new for Pesach and not kashered: drinking glasses, baby bottles, blech, plastic colander, dishwasher, water pitchers, hot water urn that was used around chometz, Crock-Pot, china, CorningWare, Pyrex, sandwich maker, toaster, and toaster oven.
People may put hot food in the refrigerator but it is usually done in a way that would not cause the racks or shelves to absorb chometz. Hot food might be put in after being placed in a container, a pot or pan but it is unlikely that the food would be put directly on the shelf while hot. Even if the pot or pan in which the food was cooked in is still hot, and placed on the rack or shelf, as long as there is no liquid or moisture under the utensil to transmit the flavor of chometz from the walls of hot pot to the cold surface, the cold surface cannot absorb any chometz flavor.
 It is easier to have control of a smaller, lighter pot and a smaller pot doesn’t take so long to reach a rolling boil. Some people try to use large pots since they hold a lot of water. Large pots of hot water, however, can be more dangerous, are bulky and one has less control pouring the water exactly where one wants it to go. Besides, the larger the pot, the longer it takes to reach a boil.
 An electric kettle usually has a cut-off switch that turns off the power as soon as it starts to boil. If that cut-off switch is broken or if you figured out how to by-pass it, and the water continues to boil until the kettle is removed from the base, that kettle is perfect for kashering because the water gets so hot that one can hear it boiling while pouring it over the sink and counters.
 Formica is kasherable from treif flavor it absorbed but ceramic tiles are not. Neither is kasherable for Pesach.
 It is easiest to check if the metal has turned red hot in a dark room. Some coils have a material over them that hide the red hot metal underneath. In a dark room it is possible to see the glow of the red hot metal. Some metals never turn red hot but they reach the same temperature and that is also good enough.
 Often the grates self kasher every time the flame is on and there is a pot on the grates. The area under the pot will be kashered automatically. The kashering of grates mentioned above, is likely unnecessary, but it should be done anyway to be sure that the full length of the grates are kashered, even the part that is not generally under the pot.
 The trivets may touch the unkashered area. Since the trivets and unkashered area are dry, no flavor passes between them. The pot is only touching the Pesachdik trivet. It is important to avoid a situation that hot liquid connects the pot to the trivet and the trivet to the unkashered area.
 Some people place pizza or other food directly on the racks on occasion. If so, they need libbun gamur and the racks should be koshered in a self-cleaning oven. If you always place pans on your racks and there is no spillage of food onto the racks (if that is possible), you can leave the racks in the oven and libbun kal (which will be defined later on) is sufficient.
If there is an occasional spillage and food is not regularly placed on the racks, a libbun kal is acceptable bedeieved. In other words, if you are the one responsible for kashering then you should make sure to do a libbun gamur. However, if someone else kashered it with a libun kal and you know that most of the time the rack was used with a pan or some other separation between the food and the rack, then you can rely on the kashering process of libun kal and eat the food. See Shulchan Aruch O.C. 451:6 where the various opinions are mentioned. The Ramo is concerned about even an incidental absorption of flavor whereas the Mechaber rules that one only need to be concerned about the way the item is used the majority of the time. The appropriate kashering method is dependent on how the utensil is used the majority of the time. (This is true according to the minhag that kashering should only be done on a utensil that is an eino ben yomo. If you are unsure if the item is a ben yomo or there is some extenuating circumstance permitting one to kasher a ben yomo, all opinions agree that the kashering method must match the method in which the flavor had gone into the utensil in the last 24-hour period.)
כתב המחבר בהלכות פסח סימן תנ”א ס”ו כל כלי הולכין בו אחר רב תשמישו הלכך קערות אע”פ שלפעמים משתמשין בהם בכלי ראשון על האש כיון שרב תשמישן הוא בערוי שמערה עליהן מכלי ראשון כך הוא הכשרן. וברמ”א שם ויש מחמירין להגעיל קערות בכלי ראשון וכן הוא המנהג. ובגר”ז כתב (תנ”א סכ”ז) ולענין הלכה יש להחמיר לכתחילה כסברא האחרונה וכן נוהגין ואין לשנות עכ”ל. וע”ש בסכ”ח. ובמ”ב ס”ק מ”ז כתב להדיא דבדיעבד סמכינן אדיעה ראשונה וכ”ד המקור חיים. ומש”כ דאם הוא בן יומו גם המחבר מודה לרמ”א, כ”כ המ”ב שם ס”ק מ”ו וז”ל אם ידוע שתוך מעת לעת השתמשו בו בחמץ בכלי ראשון ממש אע”פ שעיקר תשמישו תמיד הוא ע”י עירוי או בכלי שני צריכין הגעלה בכלי ראשון אלבא דכו”ע ואם ע”י האור צריך ליבון עכ”ל. ומלשון המ”ב משמע דאם הוי ספק אי הוי ב”י ס”ל למחבר דאזלינן בתר רב תשמישו, וצ”ע דלכאורה הוי ספק דאורייתא ועיין בחזו”א דעמד ע”ז (סימן קכ”ב סק”ד) וכתב דנראה דגם בספק יש להחמיר ובעינן ידוע שלא נשתמש תוך מעל”ע שימוש החמור ואף שהוא מועט מ”מ לא שייך כאן למיזל בתר רובא דאין שימוש המועט מקפח שימוש הרוב, וכ”ה ברמ”ע שם דספק הוי ספיקא דאורייתא אלא שבסוף דברי הרמ”ע לא משמע כן, ואפשר דבעינן שיהא לבו מסתפק בדבר וסתמא לא חיישינן כיון דלא שכיח עכ”ל. הרי היכא דלבו מסתפק בדבר ס”ל דהוי ספיקא דאורייתא ולכאורה ממ”ב משמע דכשלבו מסתפק ס”ל למחבר דאזלינן בתר רב תשמישו אם לא דנימא דהמ”ב מיירי בסתמא ודוחק לומר הכי.
דין זה שאזלינן בתר רב תשמישו באב”י שייך בכל הכשר כלים, אמנם לענין הכשר כלים לפסח יש להקשות דהרי חמץ בפסח במשהו, ולא מהני ביטול בפסח, וכיון דדין אינו ב”י כמשהו, איך משתמשים בכלים שנבלעו בהם טעם חמץ במקרה והוא אינו ב”י, והרי לא הועילה ההכשרה למיעוט תשמישו, וי”ל כיון דהגעלה יהא קודם זמן איסור, טעם החמץ כבר נתבטל במים בהגעלה קודם זמן האיסור ולכן אינו אוסר במשהו כשמשתמש בכלי בפסח. ולא שייך בזה חוזר וניעור בדבר שאינו אלא טעם של בליעות, דאף הרמב”ם (עיין סימן תמ”ז ס”ד) מודה שטעם חמץ שאין בו ממשות שנתבטל קודם הפסח אינו חוזר וניעור כמבואר במ”ב סימן תמ”ז ס”ק כ”א, והכא הרי טעם החמץ כבר נתבטל במים לפני הפסח.
I’ve been googling the question regarding koshering silicone mats and pot holders, etc. for Pesach. They can withstand the heat of boiling but I cannot find anything in writing…
Please see the following link https://dinonline.org/2018/03/19/kashering-silicone-for-pesach/
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