Koshering the Kitchen / Countertops and Sinks

Kitchen countertops are generally cold, but sometimes hot ḥametz 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” (see 10:8 above).

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 Pesaḥ foods until twenty-four hours have elapsed since the last time hot ḥametz 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 Pesaḥ 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. Some think that it is possible to kosher marble countertops by burning alcohol on them, but the koshering strength of alcoholic spirits is less than that of boiling water, and therefore boiling water should be poured on the countertop. Cleaning countertops with a steam cleaner is as effective as pouring boiling water on them, but where hagala in a kli rishon is required, it is ineffective.¹

footnotes: ¹ SA 451:20 states that one can kosher the tables on which pots are placed by pouring boiling water on them (and does not rule leniently based on the principle that koshering method is determined by main usage, which in this case is with cold food). MB 114 ad loc. cites Rabbeinu Yeruḥam that one must kosher such a table according to its most intense usage, i.e., a kli rishon removed from the flame. Therefore, one must pour boiling water over a scorching stone on the table, effectively koshering it on the level of a kli rishon removed from the flame. However, as we saw in 10:9 above, in extenuating circumstances one may kosher a utensil based on its main usage; in this case merely washing the table would suffice.Practically, even one relying on the lenient opinions should at least pour boiling water on the countertop or cover it with an oilcloth. Those who act stringently both pour boiling water and cover the table, preferring not to rely solely on a covering that may slide around. It is worth mentioning the concern raised by some that cheaper countertops made of compressed stone have the status of earthenware, on which hagala is ineffective. However, even earthenware can be koshered by merely washing it, as long as the majority of its usage is with cold items. Additionally, it seems more likely that compressed stone countertops do not have the same status as earthenware vessels; see Hagalat Kelim 13:1. Nevertheless, there are better grounds for covering this type of countertop. See also Sidur Pesaḥ Ke-hilkhato 8:2 and Piskei Teshuvot 451:44.See Hagalat Kelim 13:433 regarding koshering a countertop with alcohol. We do not condemn one who uses this method, as long as he cleaned the countertop well, since be-di’avad cleaning a countertop, whose primary usage is cold, with cold water is effective. Cleaning with the alcohol alone, however, is ineffective.

In general, the status of a sink is similar to that of a countertop, though in one respect it is less strict because it usually contains soap, which befouls the tastes of foods, and in another respect, it is more strict (if made of porcelain), because many poskim say that porcelain has the status of earthenware, which does not release tastes through hagala.

There are two accepted practices for koshering sinks. Those who are lenient clean the sink well and then pour boiling water all over it. Before pouring boiling water on a sink or countertop, 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 countertop, starting with the areas closest to the sink and moving further away. 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 in order to separate between the sink, which has absorbed ḥametz, and the Pesaḥ utensils. These people are also careful not to use boiling water in the sink during Pesaḥ.²

footnotes: ² Its most intense form of absorption is as a kli rishon removed from the flame, since sometimes one places pots of boiling-hot ḥametz in it. One who wants to kosher it based on its most serious usage must place a scalding stone in boiling water and pour the water onto the sink. However, according to many poskim, a porcelain sink has the status of earthenware and cannot be koshered via hagala. In such a case, one must cover the walls of the sink with a plastic insert or aluminum foil. They are also careful not to fill the sink with boiling water, lest the taste absorbed in the walls of the sink become absorbed in the Pesaḥ utensils. Even if the sink is not ben yomo and tastes absorbed in it are thus foul, according to Rema 447:10 even this is forbidden on Pesaḥ.Those who are lenient rely on SA 451:6 that we follow the main usage, which in the case of a sink is with cold foods. This method is thus effective even if the sink is made of earthenware. Additionally, according to Knesset Ha-gedola, porcelain is akin to glass, which does not absorb at all, and not earthenware. Moreover, since there is usually residual dish soap in the sink, any ḥametz taste absorbed into the sink would have been foul from the outset, so the sink would not need to be koshered. And even if we assume that the sink absorbed flavorful ḥametz, it would turn foul once twenty-four hours had elapsed. Even though according to Rema foul-tasting ḥametz is forbidden on Pesaḥ, the present case involved absorption that is, at worst, third degree (nat bar nat bar nat), and, as we have seen, MB 447:98 states that one may be lenient about foul tastes where there is no existing custom, and there is no existing custom about nat bar nat bar nat. Sidur Pesaḥ Ke-hilkhato 8:1 and Hagalat Kelim 124-127 write more about koshering sinks.

Koshering the Kitchen / Grates, Burners, and Stovetops

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 Pesaḥ, because of the seriousness of the ḥametz prohibition (Rema 451:4; MB ad loc. 34). Alternatively, one may wrap thick aluminum foil around the bars on which pots sit, so that there is a barrier between the Pesaḥ pots and the parts of the grates that came into contact with ḥametz. 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.³

footnotes: ³ Throughout the year, we cook both meat and dairy pots atop the grate because taste is not transferred through dry metal. For example, if a hot meat pot touched a hot dairy pot, as long as both pots were dry in the spot that they touched, both pots are kosher. Similarly, even if the grate absorbed the taste of meat, once it dries the taste does not transfer to a dairy pot. Even if a drop of dairy spilled onto the grate in the same spot that meat liquid had previously spilled, the pot remains kosher, since the flame is constantly heating the grate, and whatever liquid had previously spilled on it has already been incinerated. Due to the stringent nature of the ḥametz prohibition, light libun is required but not heavy libun, since technically the grates need not be koshered at all. Kaf Ha-ḥayim 451:82 (citing Ma’amar Mordechai) concurs that le-khatḥila grates should undergo libun, but be-di’avad they are not prohibited. Ḥazon Ovadia p. 75 states that hagala is sufficient to kosher grates, but SAH maintains that light libun is necessary. I believe that covering the grates with aluminum foil is as effective as light libun and perhaps even heavy libun, since it completely separates the grate from the pots, so that even if some liquid spills, it would not connect the grate and the pot.

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, based on the principle of ke-bole’o kakh polto.

Koshering the Kitchen / Ovens

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, but since heavy libun will cause them serious damage, they may not be koshered (see above 9:7). One must therefore buy special baking trays for Pesaḥ, while the ḥametz trays must be cleaned and put away like all other ḥametz utensils. If one does not have Pesaḥ 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 Pesaḥ.⁴

footnotes: ⁴ Some are stringent and insist that ovens cannot be koshered for Pesaḥ, due to a concern (present in older ovens) that crumbs would fall into the door of the oven before Pesaḥ and mix into the Pesaḥ food. The solution to this problem is to clean the door of the oven with a lot of soap, thereby befouling the taste of any crumbs stuck there and rendering them unfit for a dog’s consumption. Others are stringent out of concern that perhaps food touched the walls of the oven, which would mean the oven would need to be koshered with heavy libun – impossible without damaging the oven. But most poskim rule that ovens can be koshered since the oven itself rarely comes into contact with food and only absorbs steam from the food. Light libun at the oven’s highest temperature would certainly kosher it. Even if some ḥametz spilled and its taste was absorbed in the walls of the oven, we have seen that SA (451:6) permits koshering utensils (and ovens) based on the main usage. Even MB (451:48) is lenient in such a case, provided that one performs light libun. We can also add the opinion that the absorption of ḥametz before Pesaḥ is considered heteira bala, for which light libun is effective even le-khatḥila (see above 10:6). Finally, we may factor in the opinion that ke-bole’o kakh polto applies to the temperature of the libun (see above 10:5), so heating the oven at its highest setting is effective.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 Pesaḥ tray to the insufficiently koshered racks. One need not wait twenty-four hours before koshering them, since light libun releases and incinerates the taste absorbed in the utensil. See Sidur Pesaḥ Ke-hilkhato 8:3, which treats this issue at length and explains the entire process of koshering an oven.For ovens that self-clean at 500ºC and incinerate all dirt, since they heat to a temperature that certainly would cause obsolete alloys to spark or redden (see above 10:5), this self-cleaning qualifies as heavy libun and koshers the oven. Baking trays may also be koshered at this heat, but manufacturers’ instructions caution that leaving trays in such heat can ruin them. Consequently, they cannot be koshered by this method (see above 10:7).

Koshering the Kitchen / Warming Trays (Shabbat “Plata”s)

Sauce from ḥametz food occasionally spills from pots onto the warming tray (“plata”), and since the plata is a heat source, the ḥametz is absorbed with the intensity of a kli rishon on the flame. On other occasions, dry ḥametz dishes (such as porridges, kugels, and quiches) fall onto the plata, which constitutes absorption through fire and must be koshered through libun.

A blekh (a metal sheet that is placed atop a gas range on Shabbat) can be koshered through libun if there is no alternative, even though it will warp and become damaged. But when it comes to an electric warming tray, libun is liable to melt the electrical wires and ruin it. Therefore, one must clean it, heat it for an hour, and then cover it with aluminum foil to separate the plata from the Pesaḥ pots.⁵

footnotes: ⁵ emSidur Pesaḥ Ke-hilkhato 8:5 states that one should heat up the plata for an hour and then pour boiling water on it, since it has the status of a kli rishon on the flame. It is also good to cover it with aluminum foil. Hagalat Kelim 13:381 states that one may heat it up or cover it with aluminum foil. I believe that the primary solution is to cover the plata with aluminum foil, since it absorbs like a kli rishon on a flame and possibly even like a direct flame, whereas it is doubtful that the standard heat of a plata would reach the boiling point. R. Mordechai Eliyahu also writes that a plata must be covered with aluminum foil.

Koshering the Kitchen / Microwave Ovens and Dishwashers

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 ḥametz 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 ḥametz may have spilled onto the turntable.⁶

footnotes: ⁶ I have written in accordance with the currently accepted ruling. R. Mordechai Eliyahu rules that one must also take care to cover any food that he heats up on Pesaḥ. Conversely, R. Nachum Rabinovitch writes that it is sufficient to simply clean the microwave and place a barrier between the turntable and the food. R. Henkin also agreed with R. Rabinovitch.(The accepted practice for switching between meat and dairy use is as written above. Alternatively, one may hermetically seal all food, or at least one of the types [meat or dairy]. One may also use perforated covers, one designated for meat and one for dairy, every time he heats food in the microwave, which allows steam to escape but prevents it from going into the food. In either of these last two options, one must place a barrier between the food and the turntable. According to R. Rabinovitch, simply cleaning the microwave suffices, even if one did not cover the food.)

Dishwashers: 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 ḥametz is released, ke-bole’o kakh polto. Regarding the racks, le-khatḥila 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 ḥametz utensils before using the machine with Pesaḥ 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.⁷

footnotes: ⁷ The highest temperature of the water in the dishwasher is c. 80ºC. A dishwasher absorbs at the level of irui from a kli rishon (see above 10:8), since the water is heated by an element (the kli rishon) and then sprayed at the dishes. Thus, ke-bole’o kakh polto applies. Nevertheless, the custom is to kosher all utensils in a kli rishon on a flame; thus, Igrot Moshe OḤ 3:58 states that one should place a scorching hot stone in the dishwasher. When this is difficult, one may perform hagala using the mechanism of absorption, because most poskim maintain that one must perform hagala using boiling water only when koshering a kli rishon used on the flame; when koshering a utensil that absorbed via irui from a kli rishon, the hagala water only needs to reach yad soledet (see above ch. 10, n. 10). This is certainly the case vis-à-vis the dishwasher, which is koshered at least at the same temperature at which it absorbed. Technically, the racks may be koshered in this manner, but since they actually came into contact with food, some authorities ruled that they must be koshered via hagala in boiling water, or at least via pouring boiling water on them (Igrot Moshe). Additionally, some authorities consider the dishwasher to be akin to a kli rishon on the flame; according to these authorities, one must kosher the dishwasher at the intensity of a kli rishon on the flame. According to these authorities, one may only be lenient vis-à-vis the walls of the dishwasher, which do not usually come into contact with food, but not vis-à-vis the racks (R. Pfeiffer’s Kitzur SA, Basar Be-ḥalav vol. 2, explanations 6 and 7). Notwithstanding this stringent view, the mainstream opinion is that the absorption was at the level of irui; therefore, when alternatives are difficult, one may kosher the racks inside the dishwasher. This is the opinion in Hagalat Kelim 13:225-228. Additionally, several authorities maintain that the principle of ke-bole’o kakh polto applies to the temperature of the absorption in a kli rishon, so certainly the dishwasher’s highest setting is sufficient to kosher the trays (see SAH 451:25 and Sidur Pesaḥ Ke-hilkhato 1:4).Igrot Moshe maintains that if the body of the dishwasher is made of porcelain, it cannot be koshered (this is very uncommon; see also below n. 11 that there are those who are lenient, especially since the food does not touch the walls and it is likely that the dishwashing detergent ruined any taste even before it was absorbed. Thus, there is room to be lenient, as with a sink). See also Sidur Pesaḥ Ke-hilkhato 8:32, which rules stringently and requires one to use a white-hot stone to kosher a dishwasher. Piskei Teshuvot 451:25 states that there is concern about koshering plastic, as some poskim maintain that it is impossible to kosher plastic (ibid. 53). However, the mainstream opinion and the view of most poskim is that plastic can be koshered via hagala, plus this is a situation of uncertainty regarding a rabbinic prohibition, as twenty-four hours have elapsed since the dishwasher’s last use. Hagalat Kelim 13:91 concludes that poskim maintain that plastic utensils can be koshered. R. Dov Lior is lenient regarding all types, as I have written.

Koshering the Kitchen / 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 Pesaḥ 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.

One may kosher a tablecloth used for ḥametz by laundering it in a washing machine.

Those who wish to knead dough for Pesaḥ must prepare a different surface, because it is difficult to kosher tables for kneading dough.

A table on which no hot ḥametz foods were placed throughout the year must be cleaned well, but there is no need to cover it.⁸

footnotes: ⁸ SA 451:20 states that the custom is to pour boiling water on the tables, since ḥametz soup would sometimes spill onto the table. MB 114 adds in the name of Responsa Mahari Weil §193 that since sometimes hot quiches are placed on the table, it absorbs taste on the level of kli rishon, so one would need to kosher it with a white-hot stone. Additionally, it states in par. 17 that one must perform hagala on kneading tablets since dough is routinely left on the tables until it turns into ḥametz, making them comparable to a container for storing sourdough (“beit se’or”). Rema states that the custom is to avoid Pesaḥ use of tables that were used for kneading ḥametz, since they would need to be koshered via light libun. Rema also states in par. 16 that the custom is to kosher a beit se’or via light libun.It is clear that there is a difference between their tables, made of thick, strong wood that could withstand a koshering process involving boiling water and white-hot stones, and our tables, made of fiber board or plywood covered in Formica, wood veneer, or an alternative. Technically, when necessary one may follow the main use of the table, which is with cold items; therefore, SA states, “the general practice is to pour boiling water on the tables,” implying that this is not an absolute requirement. Even according to Rema, who says that the koshering method follows the most severe usage, if the table is separated from the Pesaḥ food by a nylon or paper covering, there is no concern that the food absorbed in the table will pass through the barrier, especially if one is careful not to place boiling hot pots directly on the table, only atop a plate or trivet. Moreover, since our tables are more fragile, people rarely place boiling hot pots directly on the table, so the concern that the table will absorb ḥametz on the level of a kli rishon is more implausible.

Koshering the Kitchen / The Refrigerator and Kitchen Cabinets

Because they are used with cold food, the only concern is that some ḥametz crumbs might remain there. Therefore, cleaning them is what koshers them. In hard to reach places where ḥametz 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 ḥametz that got stuck there. Aḥaronim therefore ruled that the shelves should be covered with paper or cloth (MB 451:115). However, there is no concern that ḥametz remained in smooth shelves like those used today. Therefore, once they have been cleaned properly, they need not be covered with paper or cloth.

Koshering the Kitchen / Pots, Skillets, Silverware, and (Non-Earthenware) Bowls

We detailed the laws relating to hagala of pots in the previous chapter. The principle is that intensity of koshering must match the intensity of absorption (see above 10:8), but the custom, le-khatḥila, is to kosher everything through hagala in a kli rishon (ibid. 9). Before koshering a pot one must clean it (ibid. 10). We have already learned how to perform hagala in practice (ibid. 12), and how to kosher a large pot that cannot be inserted into another pot (ibid. 13).

According to Shulḥan Arukh, skillets are koshered for Pesaḥ through hagala, and during the rest of the year they are koshered through libun. According to Rema, they are koshered through light libun for Pesaḥ as well (ibid. 4). Non-stick or Teflon frying pans cannot be koshered, since people fry in them without using oil that has been brought to a sizzle, which means that such pans require heavy libun. Since this procedure ruins them, they cannot be koshered.

Though eating utensils absorb principally as a kli sheni, the custom is to kosher them through hagala in a kli rishon on the flame. This is because the custom, le-khatḥila, is to kosher all utensils in a kli rishon on a flame. Even if one sometimes uses a fork in a pot on the flame, it may be koshered through hagala because it will be damaged by libun and is batel be-rov (as explained above 10:9 n. 11).

Koshering the Kitchen / Blenders and Mixers

Electrical appliances such as blenders and mixers are occasionally used to mince and mix hot and sometimes sharp foods. Regarding such appliances, one must follow the established principles and always relate to two problems: 1) ḥametz may have gotten stuck in crevices and holes; 2) the taste of ḥametz may have been absorbed into the walls of the appliance. If such an appliance was used with cold, non-sharp foods only, there is no problem of absorption, but there is still concern that food particles got stuck in its crevices. It must therefore be cleaned thoroughly. If there are grooves in which food particles remain, the appliance may not be koshered; alternatively, it may be soaked in soapy water or in some other agent that renders the residual food unfit for canine consumption.

Mixers have holes designed to provide ventilation for the motor, so that it does not overheat. Flour and pieces of dough splatter into these holes, and there is concern that, when used with Pesaḥ foods, pieces of ḥametz will fall into the food. In order to kosher a mixer, one must open the motor compartment and clean it thoroughly, or plug up the holes completely. This rule applies to any appliance about which there are similar concerns. If such an appliance was used with hot foods, and one was not cautious about ḥametz throughout the year, there is concern that it has absorbed the taste of ḥametz. Therefore, one must perform hagala on all parts that came into contact with hot food. And if such an appliance was used with sharp foods, and one was not cautious about ḥametz throughout the year, even if the foods were always cold, there is concern that contact with the strong sharpness caused the taste of ḥametz to be absorbed by the appliance. One must therefore perform hagala on all parts that came into contact with food (see SA YD 96:1; Kaf Ha-ḥayim ad loc. 1). If the appliance was used for kneading dough, according to the Sephardic custom hagala is necessary, and according to Ashkenazic custom light libun is needed (based on SA 451:17).

Koshering the Kitchen / Other Utensils

Silver goblets: It is proper, le-khatḥila, 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 (as explained above 10:14). 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 ḥametz 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.⁹

footnotes: ⁹ This matter is unclear. Since there is no liquid present and the challah reached the temperature of yad soledet, perhaps it should be considered to have absorbed the taste of challah as though by means of direct fire, meaning that the lid would need heavy libun – a process that it certainly will not be able to withstand. On the other hand, since there is no liquid present the taste of the challah may not become absorbed into the lid at all, just as taste does not pass between two dry pieces of metal. The custom is to be lenient, especially once factoring in the opinion that ḥametz throughout the year has the status of “heteira,” and thus hagala is effective where normally libun would be (see above 10:6) and that once twenty-four hours passed since its use, it becomes a doubt relating to a rabbinic law. However, since there was definitely ḥametz on the urn, the lid should undergo hagala in boiling water.

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.

Toaster: This requires heavy libun, and since it is liable to be damaged in the process, it should not be koshered.

Kneading Utensils: Rema maintains that such utensils le-khatḥila require light libun, but since they are likely to be damaged, they should not be koshered (451:16, 17). According to Shulḥan Arukh, it is possible to kosher them via hagala. Le-khatḥila, the custom is to be stringent, in keeping with Rema’s ruling (Kaf Ha-ḥayim 451:196, 263).

False Teeth: These should be cleaned thoroughly before the onset of the ḥametz 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 Pesaḥ. Some believe that due to the gravity of the ḥametz prohibition, they must be koshered in a kli rishon or kli sheni¹⁰.

footnotes: ¹⁰ Among the lenient opinions are: ResponsaBeit Yitzḥak YD 1:43:12, Melamed Le-ho’il OḤ  93, R. Zvi Pesaḥ Frank, and Yabi’a Omer 3:24. Responsa Maharsham 1:192 is lenient regarding meat and dairy but is stringent vis-à-vis Pesaḥ, insisting that they be koshered by irui of boiling water. Tzitz Eliezer 9:25 states that technically one need only scrub them well, but there are stringent opinions that insist on performing hagala in either a kli rishon or kli sheini

Koshering the Kitchen / Earthenware and Porcelain Utensils

If earthenware absorbs ḥametz hot, even via a kli sheni, hagala is not effective. Although libun would effectively burn the taste absorbed in the utensil, the Sages forbid koshering earthenware utensils through libun because there is concern that they will crack (see above 10:7). If used cold, however, one may kosher them by washing them thoroughly. If a ḥametz beverage was allowed to sit in such a vessel for twenty-four hours, one may kosher it by soaking it in water for three consecutive days (ibid. 14).

China, clay, and ceramic utensils are considered earthenware.

Regarding porcelain which, though made like earthenware, has a smooth surface like glass, most poskim maintain that it has the status of earthenware, and there is no way to kosher it. This is the halakha (MB 451:163; Kaf Ha-ḥayim ibid. 305). However, some poskim believe that since the surface of porcelain is smooth like glass, it does not absorb at all. When there are additional doubts, their lenient opinion is taken into account.¹¹

footnotes: ¹¹ Shiyarei Knesset Ha-gedola OḤ  451, Hagahot Beit Yosef 30 states that the universal custom is to use porcelain on Pesaḥ even if it was used for ḥametz throughout the year, since porcelain is like glass which does not absorb. He was stringent for himself, as per the opinion of Radbaz, but did not rule stringently for others. She’elat Yaavetz 1:67 also permits it. Pri Ḥadash states that one may only be lenient if he has authentic porcelain, but nowadays, since there is much counterfeit porcelain, all agree that one must be stringent. This is also the opinion of Maḥzik Berakha 451:10, as quoted in Kaf Ha-ḥayim 451:305, and Kol Mevasser 1:80. This is the accepted custom. However, one may be lenient if there are other doubts, as explained by the Aḥaronim cited in Hagalat Kelim 13:368 and Yabi’a Omer YD 1:6 and 7:10.When porcelain breaks, one can see that its inner texture is coarse, like earthenware, and its outer texture is smooth. There are also porcelain utensils that are smooth on the inside and coarse on the outside. It seems that if a utensil like this absorbed in its coarse area, everyone would agree that it has the status of earthenware. Nowadays, most dishes are made of tempered glass, which is sand-based and has a hard texture like glass, even though it is not always smooth as glass. I am often asked whether such dishes can be koshered via hagala if they were used for non-kosher or for milk and meat. In my humble opinion, these dishes should be considered like glass, since when they break one can see that they are made of dense material – like glass, not like porcelain. They thus have the status of quality glass utensils that can withstand the hagala process, as will be explained in the next section. Even the Ashkenazic custom is to be lenient when necessary to kosher such a utensil from forbidden taste it absorbed. To dispel all doubt, one should kosher the utensil with hagala three times (it is not necessary to use three separate refills of water), since according to Itur this would even work for earthenware. It seems that even according to the custom of SA glassware does not need to be koshered, since today’s dishes are not so smooth that they should undergo triple hagala. (I have not mentioned any particular brand names since companies constantly change the composition of their products; I have referred specifically to utensils whose hard texture is similar to that of glass.)

Koshering the Kitchen / Glassware

Leading Rishonim take diametrically opposed positions regarding the status of glass utensils.

According to Rabbeinu Tam, Rosh, Rashba, Ran, and many others, glass is smooth and hard, and even if it had been used to hold boiling hot foods, it does not absorb their tastes. Therefore, even if glass utensils were used with boiling-hot ḥametz throughout the year, they may be rinsed thoroughly and used on Pesaḥ. This is the position adopted in SA 451:26. Similarly, glass utensils may be used alternately for hot meat and hot dairy foods, as long as they are cleaned well in between.

According to Smag, Smak, Mordechai, Agur, and Terumat Ha-deshen, glass, because it is made of sand, has the status of earthenware, which is also made of sand and which absorbs tastes but does not release them. Therefore, if one uses glass utensils with hot ḥametz foods, there is no way to kosher them for Pesaḥ. This is the position adopted by Rema.

There is also a third position, which maintains that glass utensils have the same status as metal utensils, which can absorb and release when boiling hot. However, since glass utensils are fragile and liable to break during hagala, there is no way to kosher them for Pesaḥ (Or Zaru’a, Shibolei Ha-leket).

In practice, many Sephardim follow Shulḥan Arukh’s opinion that glass utensils do not absorb and thus may be rinsed thoroughly and used on Pesaḥ. However, there are important Sephardic authorities who are stringent in this regard, Ben Ish Ḥai among them (Year One, Tzav 14). In Ashkenazic communities, some follow Rema’s stringent ruling while others adopt the middle opinion, allowing glass to be koshered via hagala on the grounds that today’s glass is stronger than in the past and capable of enduring hagala. There is even more of a tendency to be lenient with tempered glass cookware (like Pyrex), which is fire resistant. Some rule that hagala should be performed three times on glassware. In practice, Ashkenazic Jews do not kosher glass utensils for Pesaḥ through hagala, in keeping with Rema, and only under pressing circumstances rely upon the lenient position. With regard to prohibitions other than ḥametz, the tendency is to rely upon the lenient poskim, waiting twenty-four hours from when the utensil last contained hot food and performing hagala three times.¹²

footnotes: ¹² Among Ashkenazic poskim who permit hagala on glassware if there is no concern that it will break are: R. Shlomo Kluger in Responsa Tuv Ta’am Va-da’at, third edition 2:25 and Responsa Maharam Schick YD 141. Tzitz Eliezer 9:26 leans toward permitting one to kosher glassware via hagala and quotes R. Zvi Pesaḥ Frank that one may kosher tempered glass cookware for Pesaḥ, but should do so via triple hagala, since according to Itur triple hagala works even for earthenware vessels if twenty-four hours have elapsed since their last use. According to these poskim, even those who adopt SA’s lenient ruling vis-à-vis glassware would agree that any glassware strong enough to withstand the heat of a kli rishon must be koshered via hagala, out of concern that these utensils may have absorbed taste at such high temperatures. This is the opinion of Responsa Yaskil Avdi 4:14. See also Hagalat Kelim 13:59 for a detailed list of the opinions regarding glassware and 13:375 for the opinions about tempered glass cookware.

Koshering the Kitchen / Enamel and Plastic Utensils

Enamel utensils are made of metal and coated with a thin layer of enamel for aesthetic reasons. The inside of the pot is usually colored white, while the outside is decorated with different colors. Enamel is made of sand like glassware, but it is processed differently. Great uncertainty arose regarding such utensils. At first, poskim were uncertain because the craftsmen kept enamel’s composition secret. Then, when it became known that enamel is made of sand, uncertainly arose again as to whether such utensils have the status of earthenware.

In practice, the poskim rule that one may perform hagala on enamel utensils like all other metal utensils, and some recommend performing hagala three times. Yet regarding Pesaḥ, some instruct not to perform hagala on enamel utensils in light of the severity of the ḥametz prohibition.¹³

footnotes: ¹³ emResponsa Ḥatam Sofer 113 states that enamel is koshered via light libun. R. Shlomo Kluger rules stringently that one may not kosher enamel even via libun, since it might get damaged in the process (Tuv Ta’am Va-da’at, first edition §183). Ktav Sofer YD 78 permits koshering enamel via triple hagala. SHT 451:191 quotes Ḥatam Sofer and then states that many great authorities were more stringent in this matter when it came to Pesaḥ. This is also the view of Maharsham 1:53. Aderet rules that one may kosher such utensils via hagala, but out of respect for Ḥatam Sofer states that one should use triple hagala (which according to Itur works even for earthenware vessels once twenty-four hours have elapsed since they were last used). This is also the opinion of AHS YD 121:27. R. Mordechai Eliyahu states that one may kosher these utensils for Pesaḥ via hagala, and preferably triple hagala

Plastic utensils that have absorbed the taste of boiling hot food are koshered via hagala with boiling water, like all other utensils. This is true of all types of metal, such as silver, copper, iron, aluminum, etc., as well as utensils of leather, wood, and bone. It is earthenware alone that the poskim say cannot be koshered, because, due to its unique composition, it is very absorbent, but does not release all that it absorbs. And some poskim say that glassware has the same status as earthenware. However, Igrot Moshe (OḤ 1:92) states that one should not perform hagala on utensils made of plastic or other synthetic materials not mentioned by the Rishonim, since such materials might be like earthenware, which does not release what it has absorbed. Nonetheless, the overwhelming majority of Aḥaronim agree that hagala is effective on plastic utensils, and this is the halakha. Utensils made of hard plastic are koshered through hagala in a kli rishon on the flame, whereas plastic utensils that are liable to be damaged in a kli rishon on the burner can be koshered at the same level they absorbed the ḥametz.¹⁴

footnotes: ¹⁴ Those who ruled leniently are: ResponsaḤelkat Yaakov 2:163, Seridei Esh 2:160, Tzitz Eliezer 4:6, and many others. This is also what Hagalat Kelim states in 13:91. Sidur Pesaḥ Ke-hilkhato 9:25 assigns greater weight to the stringent opinions, and states that triple hagala seemingly works according to everyone (based on the opinion of Itur that triple hagala is effective even on earthenware vessels once twenty-four hours have elapsed since their last use, although it seems that one needs to change the water between each stage of hagala; see Sidur Pesaḥ Ke-hilkhato 9:25 n. 10). It seems proper to wait twenty-four hours, ensuring that any absorbed taste is foul, in which case hagala is only rabbinically required, and one may be lenient in a case of uncertainty about a rabbinic law.