Koshering for Pesach Made Easy

Rules for simple koshering of the kitchen for Pesach * A utensil that rarely comes into contact with fire – if it is difficult to do ‘libun’, it can be koshered according to its main use * New self-cleaning ovens that clean themselves at high temperatures do not need additional cleaning and koshering * To kosher marble countertops and sinks, it is enough to pour boiling water on them, but many people have the custom of covering them * Today’s tables do not require boiling water poured on them * The main cleaning for Pesach is in the kitchen

“Ke-bole’o Kakh Polto”

The most basic principle of koshering cooking utensils is that forbidden taste is released from the utensil in the same manner that it was absorbed: “ke-bole’o kakh polto.”  In other words, the utensil must be koshered in the same way that it was used inadvertently, or with chametz. There are two main modes of by fire, and its koshering is done by heavy libun. 2) Boiling water, and its koshering is by ‘hagala’ in boiling water.

There are differing levels in this as well: kli rishon on the flame (the utensil in which the food is cooked), a kli rishon removed from the flame, irui (liquid poured from a kli rishon) and a kli sheni. ‘Ke-bole’o kack polto’.

When are Foods Prohibited?

Le-khatchila (from the outset), one should not use a utensil that was used in a prohibited way, or with chametz, without koshering it in the same way that it was used. However, be-di’avad (after the fact), if a pot that was not koshered was accidentally used, usually, the food in which it was cooked is kosher, since the prohibited taste is undetectable. The reason is that after twenty-four hours have elapsed, the prohibited taste absorbed in it does not taste good. But if one consciously used the utensil without koshering it, our Sages fined such a person – that the food cooked in it is forbidden. The same holds true for Pesach – anyone who unintentionally used a utensil or the marble countertop without koshering – it can be used be-di’avad, but if it was done intentionally – the food is forbidden (Peninei Halakha: Pesach 7: 5, footnote 5).

A Utensil that Absorbed Chametz on Two Levels

If a utensil absorbed chametz on two levels, such as a spoon that sometimes absorbed chametz in a kli rishon on the fire, and occasionally by way of a kli sheni – it is koshered according to its more severe use – i.e., in boiling water on the fire. However, when it is difficult or likely to cause damage, we go according to its majority use. For example, a fork that is usually used as a kli rishon or sheni, whose koshering is done in boiling water, but occasionally is used to check to see if a cake or pastry in the oven is cooked on the inside, in which case its absorption is by fire – since libun is liable to damage the fork, we go according to the letter of the law, and kosher the fork according to its majority use in boiling water.

Koshering a Baking Oven

To kosher an oven, clean it thoroughly and run it at its highest setting for half an hour.

It is difficult to kosher baking trays. Given that they absorb through fire, they require heavy libun, but since heavy libun will cause them serious damage, they may not be koshered. One must therefore buy special baking trays for Pesach, while the chametz trays must be cleaned and put away like all other chametz utensils. If one does not have Pesach trays, he may use disposable trays. However, he must also kosher the racks along with the oven and cover them with aluminum foil, and only then he may place the disposable trays on the racks.

Ovens that self-clean at a temperature of 500ºC need not be cleaned before koshering because such intense heat is considered heavy libun and is sufficient to kosher the oven for Pesach.

A toaster that comes directly in contact with food placed in it, requires heavy libun, and since it is liable to be damaged in the process, it should not be koshered. If it is a small oven, it can be koshered the same way as a baking oven, and for Pesach, disposable trays should be used.

Koshering the Gas Burners

Throughout the year, people usually use the same stovetop grates for both meat and milk, because even if some meat or dairy food spills onto them, the flame incinerates and befouls whatever has spilled. However, people customarily perform light libun on such grates for Pesach, because of the seriousness of the chametz prohibition. Alternatively, one may wrap thick aluminum foil around the bars on which pots sit, so that there is a barrier between the Pesach pots and the parts of the grates that came into contact with chametzBe-di’avad, the food remains kosher even if cooked on grates that did not undergo libun (as is the case throughout the year with regard to meat and milk).

The areas of the grates that do not come into contact with the pots, the enamel cook top beneath the grates, and the burners must be cleaned well of all residual food. Since none of these parts come into contact with the pots, they need not undergo libun or be covered with foil. Generally, people turn on all the flames for half an hour.

Food that Falls On the Burners

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 cook top 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 thoroughly and that no meat and dairy foods have spilled on it in the past twenty-four hours, one may eat what falls there.

Electric Ranges and Ceramic Burners

Electric ranges: Clean thoroughly and run on the highest setting for half an hour.

Ceramic burners: These look like smooth and unbroken glass surfaces on which pots are placed directly. They are koshered by cleaning and then heating on the highest setting for half an hour, based on the principle of ke-bole’o kakh polto.

Marble Countertops and Sinks

Kitchen countertops are generally cold, but sometimes hot chametz foods or boiling pots from the stove are placed on them, and if some sauce spills on the countertop, it is absorbed at the level of a “kli rishon removed from the flame.”

In order to kosher a countertop, one must first clean it well, paying special attention to crevices and making sure that no food remains stuck in them.

Marble countertops should ideally be koshered by pouring boiling water over them while placing a scalding hot stone or piece of metal on them. By doing so, the water is brought to a boil and reaches a koshering level of a kli rishon removed from the flame. However, it is difficult to bring metal to such a heat in private homes, and doing so could damage the countertop. Therefore, the general practice is to suffice with pouring boiling water on the countertop. In this case, one should make sure not to use the countertop for Pesach foods until twenty-four hours have elapsed since the last time hot chametz foods were on the countertops. Instead of pouring hot water, one may also cover the countertops entirely with oilcloth or thick foil in order to separate between the countertops and the Pesach utensils.

Those who are stringent do both – they pour boiling water on the countertop and then cover it with linoleum or thick foil.

Fragile countertops, on which boiling pots are never placed, can be koshered by merely cleaning and pouring boiling water on them.

Warming Trays (Shabbat “Plata”s)

 They must be cleaned thoroughly, heated for an hour, and then covered with aluminum foil to separate the plata from the Pesach pots.


The common practice is to kosher a microwave oven in four steps: 1) cleaning it thoroughly of any residual food resulting from spillage or vaporization; 2) waiting twenty-four hours so that the absorbed taste becomes foul; 3) heating a container of water in it for three minutes (since microwave ovens absorb chametz via vapor that rises from food as it is heated); 4) placing something as a barrier between the turntable and the food that will be heated in the microwave, because chametz may have spilled onto the turntable.


The filter, where residual food often gets stuck, must be cleaned thoroughly. Then the dishwasher should be run at its hottest setting, so that any absorbed chametz is released, ke-bole’o kakh polto. Regarding the racks, le-khatchila 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, one may perform hagala by running them through the dishwasher’s 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 a flame. 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 to rely.

Dining Room 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 the level of kli rishon. However, today’s tables are more delicate and fragile, and would be damaged, warped, or defaced by boiling hot water.

Therefore, the mainstream approach is to clean the table well and affix nylon or paper to it, creating a set 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 directly on the table.


 Because they are used with cold food, the only concern is that some chametz crumbs might remain there. 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 substance that will befoul the crumbs and render them unfit for animal consumption.

 Kitchen Cabinets

When kitchen cupboards were made of natural wood, they often had cracks that were difficult to clean completely from chametz that got stuck there, therefore people were accustomed to cover the shelves with paper or cloth. However, there is no concern that chametz remained in smooth shelves like those used today. Therefore, once they have been cleaned properly, they need not be covered with paper or cloth.

Other Utensils

 Silver goblets: It is proper, le-khatchila, to perform hagala on silver goblets used for kiddush wine and other hard drinks, because crumbs sometimes fall into the goblet along with these strong drinks, which, according to some poskim, causes their taste to be absorbed into the goblet after eighteen minutes.

Plastic baby bottles: It is better to replace them because they absorb tastes at a level of irui from a kli rishon. When necessary, one may clean them and perform hagala.

Electric water heaters, urns, samovars, and hot water kettles must undergo hagala, because chametz crumbs may have fallen into them, causing their taste to be absorbed. Hagala in this case means filling the device to the top with water, boiling it, and then pouring it out through the opening generally used to dispense the water. Before hagala, it is good to clean out the stone deposits that accumulated inside. If one puts challah loaves on the lid of the urn to warm them before the Shabbat meal, hagala should be performed on the kettle and its lid. 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, Retainers, and Braces

 These should be cleaned thoroughly before the onset of the chametz prohibition. They need not undergo hagala, because people do not normally put boiling foods or liquids in their mouths; just as they are used for both meat and dairy when cleaned in between, so can they be used on Pesach.

Braces that are stuck on the teeth for a few months are like the teeth themselves, and just as one cleans his teeth well before Pesach, so too, must he clean with a toothbrush around the braces.

Cleaning the House

There is a huge difference between cleaning one’s house for Pesach, and cleaning the kitchen. In cleaning the house, the goal is not to leave a crumb of chametz the size of an olive, so that we will transgress by means of it the prohibitions of “bal yera’eh” or “bal yimatze“; whereas cleaning the kitchen and its utensils, the goal is not to leave even the smallest amount of chametz, lest it get mixed in with other Pesach food. As is known, chametz on Pesach is forbidden ‘b’kol she’hu’ (even the slightest amount). And when it comes to the utensils used to cook in, there should also be no trace of the taste of chametz stuck or absorbed in the utensils.

This article appears in the ‘Besheva’ newspaper, and was translated from English. Other interesting, informative, and thought-provoking articles by Rabbi Melamed can be found at:

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