The Oven: In a conventional oven, gas or electric, the oven must be completely clean before kashering can begin. Oven cleaner may be necessary to remove baked on grease. If a caustic type of oven cleaner (such as Easy-Off) was used to clean the oven and some stubborn spots remain after the caustic cleaner has been applied a second time with similar results, the remaining spots may be disregarded. Once the oven and racks have been cleaned, they may be kashered by Libbun Kal. Turning the oven to the broil setting for forty (40) minutes satisfies the requirement of Libbun Kal. In a gas oven the broil setting will allow the flame to burn continuously. In a conventional electric oven the highest setting, broil or 550oF, kashers the oven.
In a continuous cleaning oven, one cannot assume that such an oven is clean because the manufacturer claims it to be continuously clean. A visual inspection is required. Since caustic or abrasive oven cleaners, e.g. Easy-Off, cannot be used without destroying the continuous clean properties of the oven, a non-abrasive, and non-caustic, cleaner must be used to clean the oven. Grease spots will usually disappear if the top layer of grease is cleaned with Fantastic and a nylon brush. Then the oven should be turned on to 450oF for an hour so that the continuous clean mechanism can work. If the spots don't disappear the oven should be left on for a few hours to allow the continuous clean mechanism to deep clean. If the spots do not disappear, the spots should be removed with oven cleaner or steel wool. If the spots are dark spots that crumble, they can be disregarded. In all of the above cases the oven should then be kashered by turning the oven to the broil setting for forty minutes.
In a self-cleaning oven, the self-cleaning cycle will clean and kasher the oven simultaneously. This is true for convection ovens with a self-cleaning feature as well. The oven need not be cleaned well before the process begins because everything inside of the oven is reduced to ash. The oven door and rubber around the door should, however, be completely clean before beginning the self-clean cycle.
The Cooktop: On a gas range the cast iron or metal grates upon which the pots on the range sit may be inserted into the oven after they have been thoroughly cleaned. (If one has a self-cleaning oven one need not clean the grates first.) The grates can be kashered simultaneously with the oven. The rest of the range should be cleaned and covered with a double layer of heavy-duty aluminum foil. The burners themselves do not need Kashering or covering, just cleaning. The drip pans should be thoroughly cleaned and need not be kashered. Kashering a Glass, Corning, Halogen or Ceran electric range top for Pesach is a very difficult task. The elements of the stove can be turned on until they come to a glow. The burner areas are now considered Kosher for Pesach. However, the rest of the cook top presents a serious Kashering problem. The unheated area of glass top ranges cannot be covered with foil like conventional or porcelain tops. Since glass tops are made of tempered glass, and are not meant to be covered, there is a risk that the glass cooktop will shatter if it is covered. Therefore, one should check with the company before attempting to kasher a Corning stove top through iruy pouring boiling hot water. In an electric cooktop, one only needs to turn the burners on the high heat setting for a few minutes in order to kasher them, since the burners come to a glow in a few minutes. The remaining cooktop areas should be covered. The knobs with which the gas or electricity is turned on should be cleaned. No other process is necessary to kasher the knobs.
The Broiler: The broiler pan and grill cannot be kashered by just turning on the gas or electricity. Since food is cooked directly on the pan or grill, they must be heated to a glow in order to be used on Pesach. An alternate method is to replace the pan with a new pan and Kasher the empty broiler cavity by cleaning and setting it to broil for forty minutes. If one does not intend to use the broiler on Pesach, one may still use the oven, even without Kashering the broiler, provided that the broiler has been thoroughly cleaned. Similarly, other cooktop inserts such as a griddle or a barbecue broiler would require “Libbun Gamur”- heating the surface to a red glow before usage. If not, the insert should be cleaned and covered and not used for Pesach
Microwave Ovens are difficult to kasher as they are generally made with plastic on the inside. Fortunately, many do not heat up the oven walls enough to cause a real kashrus concern. Clean the microwave and do not use for 24 hours. Then boil a cup of water on the highest setting for 10 minutes. Then quickly insert your hand and touch the oven ceiling. If it is burning hot, the microwave should not be used for Pesach. If it is relatively cool (or even warm) the oven may be used and has just been kashered. The glass plate (if you have one) should be covered with saran wrap.
Metal Utensils that have been used for cooking, serving or eating hot Chametz may be Kashered by cleaning them thoroughly, waiting twenty-four (24) hours and then immersing them, one by one, into a Kosher for Pesach pot of water which has been heated and is maintaining a rolling boil when the vessel is immersed. Note that we do not kasher pans coated with Teflon
The utensils undergoing the Kashering process may not touch each other on the way in to the pot. 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 one by one. The process is finalized by rinsing 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 tong in a different position so that the boiling water will touch the initially gripped area. The entire utensil does not have to be kashered at once; it may be done in parts.
Please watch out for utensils that are rusty or difficult to clean properly. Even silverware made of two parts (a handle and a blade, for instance) should most often not be kashered.
A non-Kosher for Pesach pot may also be used for the purpose of Kashering, provided that it is thoroughly clean and has not been used for twenty-four (24) hours. However, it is the custom to make the pot Kosher for Pesach before using it for Kashering. This can be accomplished by cleaning the pot, leaving it dormant for twenty-four (24) hours, filling the pot completely with water, waiting until the water comes to a rolling boil, and throwing in a hot stone or brick which has been heated on another burner. The hot rock will cause the water to bubble more furiously and run over the top ridge of the pot on all sides at one time. The pot is now kashered.
Ashkenazim today do not kasher Glass Utensils for Pesach. Arcolac, Pyrex, Duralex & Corelle should be treated as glass for Kashering purposes. Plastic Utensils are not kashered.
Sinks are generally made from china, corian, porcelain, stainless steel or granite.
- China sinks cannot be kashered at all.
- Porcelain or corian sinks should also be considered like a china sink, since there is a controversy whether these materials can be kashered. These sinks should be cleaned, not used for twenty-four hours, and completely lined with contact paper or foil. The dishes that are to be washed should not be placed directly into the sink. They must be washed in a Pesach dishpan that is placed on a Pesach rack. Alternatively, a sink insert can be purchased, allowing for the placement of either milchig or fleishig dishes directly into the sink. It is necessary to have separate dishpans and racks for Milchig and Fleishig dishes.
- Stainless steel sinks can be kashered by the following method. Clean the sink thoroughly. Hot water should not be used or poured in the sink for twenty-four (24) hours prior to Kashering. It is recommended that the hot shut-off valve under the sink be turned off twenty-four (24) hours before Kashering. Kashering is accomplished by pouring boiling hot water from a Pesach kettle/pot over every part of the stainless steel sink. The poured water must touch every part of the sink including the drain and the spout of the water faucet. It is likely that the Kashering kettle will need to be refilled a few times before the Kashering can be completed.
- Granite sinks can be kashered like a stainless steel sink.
Countertops Made of granite may also be kashered. Formica countertops should be cleaned and kashered by pouring boiling hot water (iruy) on to the counter tops. The same goes for tables with synthetic tops. Wood tables could theoretically be kashered with boiling water, but the custom is to clean and cover them.
Separate dishtowels should be purchased for Pesach to avoid confusion with dirty chametzdik towels.
(This section was prepared using sections from an article by Rabbi Moshe Heineman. Not all of the psak, however, is that of the Star-K)