Koshering the Oven
In order to kosher an oven, one must clean it well and heat it at its highest temperature for half an hour.
It is difficult to kosher oven trays and pans, because they absorb through fire and require libun chamur, but since libun chamur will cause them serious damage, they are not to be koshered. One must therefore buy special oven trays and pans for Pesach, while the chametz Pesach trays and pans must be cleaned and stored away like all other chametz utensils. If one doesn’t have trays and pans appropriate for Pesach, it is possible to use disposable trays and pans. One should kosher the rack with the oven, and cover it with aluminum foil, and then place the disposable trays on the rack.
Some authorities are stringent and insist that ovens cannot be koshered for Pesach, due to a concern (that was present in older ovens) that crumbs would fall into the door of the oven before Pesach and mix into the Pesach food. The solution to this problem is to clean the door of the oven with a lot of soap to ruin the taste of any crumbs stuck there and render them unfit for a dog’s consumption.
Contrary to the oven itself, the racks of the oven must be koshered with libun chamur. However, if one conducts libun kal on the entire oven, including the racks, it is sufficient to place disposable pans on top of the racks on Pesach. One should also cover the racks with aluminum foil, so that if something spills onto the racks, it will not “connect” the pan with the Pesach food to the insufficiently koshered racks.
Koshering the Stovetop
Throughout the year, people usually use the same stove grates for both meat and milk, because even if some meat or dairy food spills onto them, the fire emanating from the burner will burn and spoil whatever has spilled. However, people customarily perform libun kal on such grates for Pesach, because of the seriousness of the chametz prohibition (Rama 451:4; Mishna Berura 34). Another possibility is to wrap thick aluminum foil around the areas of the grates where pots rest, in order to separate between the parts of the grates where chametz food was placed and the Pesach pots. However, bediavad, if a person did not perform libun on the grates and cooked food on them during Pesach, the food is kosher.
The areas of the grates that do not come into contact with the pots, as well as the enamel surface underneath the grates, and the tops of the burners, must be cleaned well of all food particles. But since none of these parts come into contact with the pots, they need not undergo libun or be covered with aluminum foil. Generally, people turn on all the burners for about half an hour.
It is also important to know that throughout the year one should be stringent and refrain from eating food that has fallen onto the enamel surface under the grates, because meat and dairy foods spill there, and the enamel becomes not kosher. If one knows that the enamel has been cleaned well, and that no meat and dairy foods have spilled onto it in the past twenty-four hours, it is permissible to eat food that falls there. But when these two conditions have not been met, one should be stringent and refrain from eating whatever comes into contact with this enamel, because it might have absorbed the taste of meat and milk. If a thick piece of food falls there, it is possible to cut off the side that has come into contact with the enamel and eat the rest.
Electric burners should be cleaned thoroughly and heated to the highest heat setting for half an hour.
Ceramic burners are equipped with a surface similar to glass which itself heats up, and pots are placed directly upon it. To kosher, they must be cleaned well and heated to their highest temperature for half an hour. One should wait twenty four hours between the last cooking of hametz and the first Pesach cooking.
In practice, there are two customs for koshering a sink. Those who are lenient clean the sink well and then pour boiling water all over it. Before pouring boiling water on a sink, or a marble countertop, it must be dried, so that the boiling water will touch it directly, and will not be cooled by any cold water on its surface. For this reason, one must first pour the boiling water on the sink and then on the marble countertop, starting with the areas close to the sink and then moving further away.
Those who are stringent, in addition to pouring boiling water on the sink, put a plastic tub in it, or line it with thick aluminum foil in order to separate between the sink, which has absorbed chametz, and the Pesach utensils.
An electric hotplate should be cleaned well and heated to its maximum for two hours, and then covered with aluminum foil.
The metal sheet that people place over the burners of a gas stove (blech) can be koshered in two ways: 1) clean it and heat it with libun kal. 2) clean it, and heat it up as is done on Shabbat for two hours, and additionally cover it with aluminum foil.
The Microwave Oven
The common practice is to kosher a microwave oven in four stages: 1) Cleaning it thoroughly of any food particles that may remain as a result of spilling or vaporization. 2) Refraining from using it for twenty-four hours so that the absorbed taste becomes pagum. 3) A microwave oven absorbs chametz via vapor that rises from food as it is heated. One therefore koshers a microwave oven by heating a small bowl of water in it for three minutes. 4) Because some chametz may have spilled onto the rotating plate, something should be put on this plate to separate between it and the foods that will be heated during Pesach.
The filter must be cleaned properly, because food often gets stuck there. Then the dishwasher should be run at its highest temperature, so that it will emit any chametz in the same manner it was absorbed, k’bol’o kach polto. Regarding the trays, l’chatchila they should undergo hagala or irui with boiling water, or be replaced. If it is difficult to kosher them through hagala or to replace them, it is possible to perform hagala on them by rinsing them inside the dishwasher at its longest and hottest setting.
In any event, one must wait twenty-four hours after the last load of chametz utensils before using the machine with Pesach utensils.
Some take a stringent approach to dishwashers and consider them to have the status of a kli rishon on the burner. This means that to kosher a dishwasher one must put a white-hot piece of metal in it in order to boil the water. However, those who follow the lenient approach have authorities on whom they can rely.
The Dining Table
In the past, people would kosher their tables by pouring boiling water over them, and some took the stringent approach of pouring boiling water onto a white-hot stone on the table, so that the koshering would be at a level of kli rishon. However, today’s tables are more delicate and fragile, and if people pour boiling water on them, they become damaged – sometimes they swell, or their outer layer strips off.
Therefore, it is most important to clean the table well and to affix nylon or paper to it in order to create a constant barrier between the table and Pesach utensils and foods. In addition, a tablecloth should be spread over the nylon or paper, and it is a good idea to avoid placing boiling hot pots on the table, even when it is properly covered.
The Refrigerator and Kitchen Cupboards
Because these places are cold, our only concern is that some chametz crumbs might remain in them, and therefore cleaning them is what koshers them. In hard to reach places where chametz crumbs may have gotten stuck, one must pour soapy water or some other disinfectant that will render the crumbs unfit for animal consumption.
Once, when kitchen cupboards were made of natural wood, they often had cracks, and it was difficult to clean out the chametz that was stuck there. Achronim therefore ruled that the shelves should be covered with paper or cloth (Mishna Berura 451:115). However, when it comes to smooth shelves like the ones used today, there is no reason to be concerned about chametz remains. Therefore, after they have been cleaned properly, there is no obligation to cover them with paper or cloth.
Plastic Baby Bottle: It is good to use a new baby bottle during Pesach, because they absorb tastes at a level of irui from a kli rishon. When necessary, it is possible to clean them and perform hagala on them.
Stovetop Water Urn: An urn (maycham) used to heat water for Shabbat must undergo hagala, because chametz crumbs may have fallen into it, causing their taste to be absorbed. Before hagala, it is good to clean the urn of stone deposits that have accumulated inside. Even if one customarily puts challah loaves on the cover of the urn to warm them before the Shabbat meal, performing hagala on the kettle and its cover is sufficient.
Thermos: After cleaning it properly, hagala should be performed on it. If this is difficult, pouring boiling water into it and around its opening is sufficient.
False Teeth: These should be cleaned well before the onset of the chametz prohibition. It is not necessary to subject them to hagala, because people do not normally put boiling foods or liquids in their mouth and just as people with false teeth rely on cleaning alone between eating meat and dairy foods, one can do the same for Pesach. Yet some Poskim maintain that due to the gravity of the chametz prohibition, false teeth must be koshered in a kli rishon or kli sheni.
The law regarding braces attached to teeth for months at a time is similar to normal teeth, and just as normal teeth should be cleaned well before Pesach, so too, the area around the braces should be cleaned with a toothbrush.