The Principles of Koshering Utensils
Though the walls of pots and other vessels appear solid and impervious, they actually absorb the taste of food cooked in them. It is impossible to measure how much taste the walls of a pot absorb and how much they release back into the food; some vessels absorb more than others do, such as earthenware, and some less, such as utensils made of metal. However, according to halakha, we do not take into consideration the degree of taste the utensils absorbed; rather, any utensil in which non-kosher food was cooked, is forbidden to be used to cook kosher food without first koshering it by means of removing the minute taste absorbed in it. The same applies to utensils in which foods made of chametz was cooked; in order to use such utensils during Pesach, one must first remove the taste of the chametz.
In general, however, if one be-di’avad
(a level of performance that ex post facto satisfies an obligation in a less-than-ideal manner) forgot that the pot absorbed the taste of forbidden food and cooked another food in it, the food in question remains kosher, provided it was a mistake. But if one knows that a pot had absorbed a non-kosher taste, but cooks kosher food in it anyway, the food is prohibited.
Therefore, in practice, anyone who wishes to use a pot in which chametz food was cooked, must first kosher it. Similarly, one must kosher the countertop, sink, oven and stove, before Pesach.
Releasing through the Same Method as Absorption (“Ke-bole’o Kakh Polto“)
The most basic principle of koshering cooking utensils is that forbidden taste is released from the vessel in the same manner that it was absorbed: “ke-bole’o kakh polto.” There are two principal media through which utensils absorb taste: 1) through direct heat of fire, without a liquid medium, requiring it be koshered by means of heavy libun, that is, heating the vessel by fire until it gives off sparks or becomes red hot, or 2) absorption through a liquid medium, requiring immersion in boiling water (hagala). This also entails differing degrees: liquids in a kli rishon on a flame, kli rishon not on a flame, irui from a kli rishon, and a kli sheni. ‘Ke-bole’o kakh polto’.
Another basic principle: If a utensil absorbed the taste of a prohibited food on two different levels, for example, a spoon that sometimes absorbed chametz in a kli rishon on a flame, and other times as a kli sheni, it is koshered according to its most intense usage – i.e., in boiling water. However, when it is difficult to do so, or if there is a concern that the utensil will be damaged, it can be koshered in accordance with its primary use. For example, a fork usually used with liquids or in a kli sheni, but sometimes is stuck into food in an oven, in which case it absorbs through fire, since libun is liable to damage the fork, we go according to the letter of the law, i.e., the fork is koshered according to its primary use – in boiling water.
Cleaning the House
There is a significant difference between cleaning the house for Pesach, and cleaning the kitchen. When cleaning the house, the goal is that a crumb of chametz the size of kezayit (an olive) should not remain. But when cleaning the kitchen and its utensils, the goal is that no chametz whatsoever (kol she’hu) remain, lest it gets mixed in food for Pesach. And as is well-known, chametz on Pesach is forbidden even b’kol she’hu. And when it comes to cooking utensils, even the taste of chametz absorbed in them should not remain, lest the taste of chametz, kol she’hu, get mixed in Pesach foods while cooking or baking.
There are some people who do not grasp this fundamental difference and clean their house meticulously, but arrive to Seder night completely exhausted; others compound their mistake – they are meticulous in cleaning their house, but are negligent in cleaning their kitchen.
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. Because they absorb through fire, they require heavy libun (heating a vessel by fire to the point that absorbed taste is incinerated), 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.
With regard to baking trays, however, we are stringent and require heavy libun. However, if one conducts light libun on a tray, he may place a disposable tray inside of the multi-use tray, and certainly atop the racks. It is best to cover the racks with aluminum foil, so that if something spills onto them it will not connect the Pesach tray to the insufficiently koshered 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. The baking trays of such ovens may also be koshered at this heat.
Grates and 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 chametz. Be-di’avad, the food remains kosher even if cooked on grates that did not undergo libun.
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.
The Law of Food that has Fallen under the Grates
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. 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, one may cut off the side that has come into contact with the enamel and eat the rest.
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. One should wait twenty-four hours between the last chametz cooking and beginning to cook for Pesach (this heating is considered light libun, which is sufficient for it according to the vast majority of poskim).
Sinks and Counter-tops
There are two accepted practices for koshering them: Those who are lenient clean them well and then pour boiling water all over them. Before pouring boiling water on a sink or counter-top, it must be dried well, so that the boiling water touches it directly and is not 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 counter-top, starting with the areas closest to the sink and moving further away. To do so, one can also use a steam machine, whose steam heat reaches one hundred degrees (and has the status of pouring boiling water from a kli rishon, namely the vessel in which food was cooked).
Those who are stringent, in addition to pouring boiling water on the sink, put a plastic insert in it or line it with thick aluminum foil.
If the marble counter-top is fragile, and as a result, one is careful not to place boiling pots directly on it – even those who are stringent can suffice by pouring boiling water on it, without covering it with an oilcloth or aluminum foil (see, Peninei Halakha: Pesach 11: 1-2).
Warming Tray (Shabbat Platta)
It should be thoroughly cleaned, and heated on the highest heat for two hours, and covered with aluminum foil.
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 rotating plate and the food that will be heated in the microwave, because chametz may have spilled onto the rotating plate, and when using it on Pesach, place the food in a plastic container or a thick, perforated carton, separating between the rotating plate and the foods being heated on Pesach.
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 (taste is released from a vessel in the same manner that it was absorbed). 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. However, those who follow the lenient approach have authorities on whom to 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 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 (Peninei Halakha: Pesach 11:8).
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.
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 in the past, people would cover them with paper. 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.
Electric water heaters
Electric water heaters and Shabbat water heaters (that are placed on the platta) 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 places 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.
Toaster: This requires heavy libun, and since it is liable to be damaged in the process, it should not be koshered. If it is a small toaster, it can be koshered in the same way as a baking-oven, and used on Pesach with disposable trays.
Silver goblets: It is proper, le-khatĥila, 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, but when necessary, one may clean them and perform hagala.
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 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.
The status of braces is similar to that of one’s teeth; just as one thoroughly brushes his teeth before Pesach, so should he brush around the braces.
This article appears in the ‘Besheva’ newspaper, and was translated from Hebrew. Other interesting and informative articles by Rabbi Melamed, including all of his highly acclaimed series of books “Peninei Halakha” in Hebrew, and some in English, can be found at: