10 – The Principles of Kashering Kelim

01. Kashering Kelim

The Torah commands that if a Jew wishes to use a non-Jew’s kelim (vessels, cookware, cutlery, dishes, etc.) that had been used for non-kosher, they must render them kosher – or “kasher” them – by the same means they were used with forbidden food, as it is written: “any article that enters fire, you shall pass through fire…and anything that does not enter fire, you shall pass through water” (Bamidbar 31:23). The Sages derive from here that kelim must be kashered in the manner that they are used. If they are used with fire, then they are kashered via libun, in fire. If they are used with boiling water, then they are kashered through hagala in boiling water. If they were only used cold, then they are kashered by rinsing them in cold water (Avoda Zara 74b; 76b). Thus, there are three types of kashering: libun, hagala, and rinsing.

The Sages explained that when one cooks a non-kosher food in a pot, its taste is absorbed in the walls, and if one later cooks a kosher food in the same pot, the non-kosher taste will be released from the walls of the pot and enter the kosher food, rendering it forbidden. To remove the taste absorbed in the walls, the pot must be kashered in the same way that it absorbed the taste. This is the well-known principle: “as it absorbs, so it releases” (“ke-bole’o kakh polto”; Pesaḥim 30b). It is necessary to clarify that whenever the Sages spoke of taste absorbed into the kli, they also referred to taste that got stuck to the walls of the kli due to the strength of the cooking or the fire. It was only about two hundred years ago that a method for manufacturing soap, which can clean kelim thoroughly, was discovered. Prior to that, even when they tried to clean kelim using substances like lye and ash, whose effects are similar to that of soap, fatty residue of foods almost always remained stuck to the walls. In addition, since the walls were generally rougher, more taste adhered to them than nowadays. Thus, the directive of this mitzva, to kasher kelim in the manner by which they absorbed taste, refers to taste that adhered to and was absorbed into the walls of the kelim (as explained in detail in Peninei Halakha: Kashrut 32, n. 1).

Kashering kelim for Pesaḥ is just like kashering kelim after they were used for non-kosher food. To make them kosher for Pesaḥ, they must be kashered with the same methods by which they were used. Ḥametz utensils that one does not wish to make kosher for Pesaḥ must be cleaned normally and put away in a closed place so that nobody inadvertently uses them during Pesaḥ (SA 451:1; see also above 6:4, where we learned that such kelim should not be sold).

02. “As It Absorbs, So It Releases” (“Ke-bole’o Kakh Polto”): Between Hagala and Heavy Libun

Let us further explain the principle of “as it absorbs, so it releases” (“ke-bole’o kakh polto”; Pesaḥim 30b). If a kli was used for food that is not hot, since the residual food adheres loosely to the kli, it can be removed easily, by rinsing it in cold water. This is called hadaḥa (rinsing).

If the kli was used with hot liquids, for instance, a pot in which a ḥametz dish was cooked or a ladle or spoon inserted into a pot in which ḥametz was cooked, the taste of the food adheres to and is absorbed by the kli, and only boiling water can cause its release. This is hagala.

If a kli was used directly on a fire – as in the case of roasting spits or baking trays – since there is no liquid to soften the adhesion of the food to the walls, the taste becomes absorbed strongly into the kli, and boiling water is not powerful enough to cause the release of the taste from the walls of the kli. They must be kashered using the method by which they absorbed the taste – through fire, namely, libun.

We must add that absorption through fire takes place only when the food is directly on the fire, for example, in the case of a knife used to cut a pastry that is on the fire. However, if the pastry was removed from the fire and then cut with the knife, even though the pastry is dry, since it is no longer on the fire, the knife’s absorption is deemed weaker, and it can be kashered by means of hagala (Issur Ve-hetter Ha-arokh 58:27; Erekh Ha-shulḥan 94:13).

Before kashering with hagala, it is necessary to clean the kelim, since the boiling water is not powerful enough to remove all the food residue stuck to the walls of the kli. With respect to libun, however, there is a dispute among the Rishonim: Some say that one must clean the kelim before libun as well, because fire, too, is not powerful enough to remove all the food residue stuck to the walls of the kli. Others say that fire is powerful enough to destroy anything stuck to the kli, so it is not necessary to clean kelim that will be kashered by libun. This is the accepted halakhic ruling.[1]

[1]. According to Rashba (Torat Ha-bayit Ha-katzar 4:4), it is necessary to clean roasting spits thoroughly before libun, because libun does not incinerate all of the flavor adhering to the kli. This is also the view of Rabbeinu Yeruḥam, Orḥot Ḥayim, and Pri Ḥadash. Tur states that it is not necessary to clean roasting spits before libun, because the fire incinerates all residual food and flavor adhering to and absorbed within the kli. This is also the view of Me’iri, Hagahot Maimoniyot, and Issur Ve-hetter Ha-arokh, and many Aḥaronim accept this view in practice, including: Taz 451:7; Knesset Ha-gedola; MB ad loc. 24.

03. Kashering Kelim that Absorbed Ḥametz Before the Onset of the Prohibition

We have learned that if a kli absorbs a forbidden food by means of fire, it must be kashered by fire. This principle applies only when non-kosher food has been absorbed. For example, if one roasts non-kosher meat on a spit, the spit must be kashered through libun, because the non-kosher food was absorbed by means of fire. However, if at the time of absorption the meat was kosher, and only later became non-kosher, the kli may be kashered through hagala. Thus, if the meat of a korban was roasted on a spit, after a day passes, the meat of the korban becomes notar and may not be eaten, and the flavor absorbed by the spit is also notar. Therefore, the spit may not be used until it has been kashered. However, since the meat was permitted to eat at the moment its flavor was absorbed in the spit, it is not necessary to perform libun, and it is sufficient to perform hagala in boiling water. This is because hagala releases almost all of the flavor, and whatever is not released is considered weak flavor. When forbidden food was absorbed, even this weak flavor must be removed, but when the initial absorption was of something permitted, it is sufficient to remove the main part of the flavor by means of hagala (Avoda Zara 86a; Ramban and Ritva ad loc.).

The leading Rishonim disagree about ḥametz: Some say that the absorption of ḥametz throughout the year is considered the absorption of permissible matter (heteira bala), since ḥametz may be eaten all year round. Consequently, there is no need to kasher anything for Pesaḥ via libun, as even kelim used in fire, like roasting spits and baking pans, can be kashered by means of hagala. Others say that ḥametz is considered a forbidden food (issura bala); even though it may be eaten le-khatḥila all year round, it is always considered forbidden vis-à-vis Pesaḥ, as even something that became ḥametz before Pesaḥ is called ḥametz and is forbidden to eat on Pesaḥ. Therefore, roasting spits and baking trays must be kashered by means of libun. This is the accepted halakhic ruling (SA 551:4). However, where there are other reasons to be lenient, the lenient position is relied upon (MB 451:28).[2]

[2]. Those who adopt the lenient view that the absorption of ḥametz throughout the year is considered the absorption of permissible matter are: Rambam, Raavad, Rabbeinu Tam, Rid, Raavan, Raavyah, Itur, Sefer Ha-teruma, Or Zaru’a, Roke’aḥ, Yere’im, Shibolei Ha-leket, Smag, Issur Ve-hetter Ha-arokh, Tashbetz, and others. Those who adopt the stringent view are: Ramban, Rashba, Rosh, Ran, Ritva, Nimukei Yosef, Me’iri, Rabbeinu Yeruḥam, and Maharil, and it is inferred from Rif as well.

04. Defining the Difference between Absorption through Liquid and Absorption through Fire: The Status of a Frying Pan

As we learned (section 2), the difference between pots used for cooking, which are kashered by means of hagala in boiling water, and baking trays and roasting spits, which are used for baking and roasting and are kashered by means of libun, is that the absorption through cooking is mild, whereas absorption through fire is intense. This is because the objective of cooking is to mix together the liquids in the dish, so it becomes softer and more flavorful. Since cooking is liquid-based, its absorption is milder. In contrast, the objective of baking and roasting is to minimize the liquid in the food, thus hardening it. Therefore, its absorption is more intense.

Even if a dish cooked in a pot was burned, the pot is kashered by means of hagala, since the initial absorption was through liquid, and, moreover, we follow the main purpose of the kli, which is made for cooking, not baking (Rosh).

Accordingly, a skillet or frying pan is kashered by means of hagala, because the purpose of the oil placed in the frying pan is to make the food more liquid. This is the difference between baking and frying: baking dries out the pastry, whereas frying makes it more liquid. This is the view of most Rishonim (Rosh, Raavyah, Mordechai, and Sha’arei Dura).

But some say that since people often fry with small amounts of oil, the oil is often used up, and the absorption is dry, via fire. Moreover, sometimes there are parts of the frying pan that were not coated in oil even initially, and there the absorption is by means of fire. Therefore, a frying pan or skillet has the same status as a baking tray, and it is kashered by means of libun (Rashba, Rabbeinu Yoel).

In practice, one may kasher a skillet or frying pan for Pesaḥ by means of hagala. Le-khatḥila it is best to kasher it with light libun, which is how it is used all year. This is also the easiest way to kasher it, as it entails heating up the empty skillet until it reaches the temperature of light libun (as described in the next section; regarding Teflon skillets, see section 9 below).[3]

[3]. According to Rashba (Torat Ha-bayit 4:4), Rabbeinu Yoel, and Maharam Ḥalawa, kashering of a skillet in which food was fried with only a bit of oil is by means of libun. According to Raavyah, Rosh (Pesaḥim 2:7), Rabbeinu Yeruḥam, Agur, Shibolei Ha-leket in the name of Ge’onim, Mordechai, Hagahot Maimoniyot, and others, it is by means of hagala. (According to Rabbeinu Tam, Or Zaru’a, Ra’ah, and Ohel Mo’ed, only a kli that is completely surrounded on all sides by the heat of a fire – like a roasting spit or baking tray inside an oven – requires libun. Accordingly, even if one did not place oil in the base of the skillet, it is kashered by means of hagala.)

The Rishonim do not distinguish between Pesaḥ and other prohibitions, but SA (YD 121:4; 451:11) is stringent with regard to other prohibitions, requiring libun, but lenient with respect to Pesaḥ, ruling that hagala is sufficient. The Aḥaronim explain that with regard to Pesaḥ R. Karo combines the opinion that hagala is sufficient with the view that ḥametz before Pesaḥ is considered a permitted food (above, section 3), and thus rules leniently that one may kasher a frying pan for Pesaḥ via hagala (Gra, Ḥok Ya’akov, Ḥida, Ma’amar Mordechai, Nahar Shalom, Erekh Ha-shulḥan, and many others). Against them, Pri Ḥadash (YD 121:8) states that since, in practice, we rule that ḥametz absorbed before Pesaḥ is considered a prohibited food, kashering a skillet for Pesaḥ requires heavy libun. This is also the view of Pri To’ar.

According to Rema (451:11), technically one may kasher a skillet for Pesaḥ by means of hagala, but it is proper to be stringent and kasher it by means of light libun. This is the practice le-khatḥila. (Regarding light libun, see the next section.)

Some say that when there is no sizzling, bubbling oil in the skillet, the skillet has the status of a baking tray (Pri Ḥadash 451:11, SAH 36). It seems from the Rishonim that even if the skillet was coated with a bit of oil, since the oil is supposed to be absorbed into the food as part of the frying process, unlike baking, which is supposed to dry out the food, it is kashered by means of hagala (Rosh and others; so states AHS 451:13. Kaf Ha-ḥayim 451:70 gives a different parameter – that if there was enough liquid present in the skillet to coat something that touched something that was in the skillet [“tofei’aḥ al menat le-hatfi’aḥ”], the skillet can be kashered by hagala).

Regarding a pot used to prepare jachnun, kugel, or kubana, or a frying pan used to prepare malawach, I initially thought that if no sizzling oil is placed in them, they are kashered by means of libun. In practice, however, it seems to me that the result is determinative: If the food remains moist, as in the case of kugel, it is considered “cooked,” and the kli is kashered by means of hagala. If the result is more pastry-like, as in the case of typical kubana and malawach, the kli is kashered by means of libun. If the result is something in between, as in the case of soft kubana and jachnun, one may kasher them by means of hagala, as we can factor in the opinion that ḥametz before Pesaḥ is considered a permitted food, as explained in section 3 above. (See Peninei Halakha: Berakhot 6:11, n. 10.)

05. Libun

The Sages said that libun is the insertion of a kli into fire until “they shed their outer layer” (Avoda Zara 76a) or until the kli gives off sparks (y. Avoda Zara 5:15). Since iron generally does not peel or spark when placed in fire, it seems that the Sages’ intent was that libun should cause the food adhering to the kli to peel off from it or that the food will give off sparks.

Many maintain that libun requires heat that can incinerate and destroy any food that can adhere to the kli, until it is shed in the form of sparks – even though the fire on which ḥametz was roasted or baked never reached such an intense heat (Pri Megadim). This is a temperature or 350-400oC.

Some rule leniently, maintaining that the principle of ke-bole’o kakh polto applies to the temperature of the fire at the time of absorption. The temperature at the time of absorption is the temperature at which kashering can take place. Thus, for example, if a kli absorbed flavor at a temperature of 200oC, it can be kashered at 200oC. In their view, a baking tray that absorbed a forbidden taste in an oven can be kashered in that oven at the same temperature. In practice, halakha follows the stringent view, but in times of need, it is possible to be lenient. Therefore, if a kli is needed, or if following the stringent view might ruin the kli, one may rely on the lenient view.

There is also light libun (libun kal), which entails heating a kli by fire to the point that a piece of straw placed on the opposite side of the kli would become singed from the heat, or a fine thread stretched out over the wall of the kli would become singed and snap from the heat. Light libun is not effective where regular libun is required, but it is more effective than hagala at extracting the flavor absorbed in the kli, and it also incinerates some of the flavor absorbed in and stuck to the kli. When it is uncertain if libun is necessary, one may suffice with light libun. Light libun can be performed by putting a kli in an oven and heating it at the highest temperature for about half an hour.[4]

[4]. Regarding libun, Avoda Zara 86a states: “until they shed their outer layer.” This is cited in She’iltot, Behag, Rif, Rambam, and others. Yerushalmi Avoda Zara 5:15 states: “libun requires that it gives off sparks.” This is cited by Rosh, Tur, and SA 451:4. This is not a dispute, however. Rather, these are two different indicators of libun. So states Pri Megadim 442, Mishbetzot Zahav 1.

At first glance, it seems that the metal of the kli itself must spark and shed a layer, but metals generally do not spark or shed layers due to fire, and according to experts, they did not do so in the past, either. Therefore, it seems that the meaning is that the foods that remained stuck to the kelim would burn, char, and shed layers or burst and release sparks. This is similar to the explanation of R. Pfeiffer (Darakh Kokhav, p. 310), and many works cite his explanation (Ma’adnei Asher, Issur Ve-hetter 159; Hora’ah Berura, YD 121:59; Divrei David, vol. 1, YD 10). Even though nowadays, when we have soap, foods do not remain stuck to kelim, the requirement of kashering remains as it was (Peninei Halakha: Kashrut 32:7-8).

As I wrote above, there is a dispute among Aḥaronim with regard to libun. Many maintain that it requires a fixed temperature that would produce sparks if there is food stuck to the kli. These include: Pri Megadim 441, Eshel Avraham 30; Responsa Maharam Schick, OḤ 213; R. Frank’s Mikra’ei Kodesh: Pesaḥ 1:80:7; Igrot Moshe, YD 1:60. Some adopt the lenient view that libun requires the same temperature at which the kli absorbed the forbidden food. These include: Responsa Arugat Ha-bosem, OḤ 119; Minḥat Yitzḥak 3:66; Tiferet Tzvi 1:30; and Nitei Gavriel (Pesaḥ 1:75, n. 3) in the name of R. Aharon Kotler and R. Y. B. of Brisk. The accepted ruling is the stringent one, as this is the view cited in contemporary works of halakha. However, since according to many the absorption of ḥametz throughout the year is considered the absorption of permissible matter (heteira bala), in which case even hagala would be effective, in times of need one may rule in accordance with the lenient view of libun, namely, that it requires the same temperature at which the kli absorbed the ḥametz. This is certainly the case more than 24 hours after the absorption, as then the flavor is spoiled, and in cases of uncertainty we follow the lenient view. In addition, since nowadays metal kelim are cleaned thoroughly with soap, there is no concern that the forbidden food will impart flavor, and the kashering requirement is based on the kli’s use with forbidden foods (Peninei Halakha: Kashrut 32:7-8). In cases of other forbidden foods, where the rationale of heteira bala (i.e., ḥametz absorbed throughout the year is considered permissible matter, so even kelim used in fire can be kashered by means of hagala) does not apply, one may only be lenient in the case of a significant loss (ibid. 33:6).

Rabbeinu Avigdor, one of the Rishonim (cited in Hagahot Maimoniyot on MT, Laws of Forbidden Foods 17:5), has an even more lenient view: Libun consists of burning a fire under the kli to the point that if one places a piece of straw on it, it will be singed. This is what the Sages meant by “until it gives off sparks.” In practice, the consensus is not to adopt his leniency, and this form of libun is called “light libun,” which is more effective than hagala. When there is uncertainty about whether a kli requires libun, many rule that it may be kashered with light libun (Terumat Ha-deshen §130; Rema 451:4). Another advantage of light libun is that it is effective for crevices that are hard to clean and that hagala does not kasher (MB 451:33). Nowadays, these kelim can be cleaned with soap, which renders everything stuck in the crevices unfit for a dog’s consumption.

The poskim further write that there is an even lighter form of libun, namely, heating the kli to the temperature of “yad soledet bo,” i.e., at which the hand reflexively recoils (Levush; Taz 451:8; SAH 10). This seems to refer to anything above 70oC. Pri Megadim (451, Eshel Avraham 30) states that this form of libun is effective for food absorbed into a kli rishon after it had been removed from the fire.

06. The Principles of Hagala

As we have learned, kelim used for cooking must be kashered by means of hagala. However, there are different temperature levels in cooking, and the operative principle is: ke-bole’o kakh polto.

A kli rishon on the flame: The highest level of intensity of cooking, and as it is used for ḥametz, so it is kashered: in boiling water, in a kli rishon on a flame. Even if the water in the kli rishon on the fire was not boiling when it was used for ḥametz, it must boil during kashering, because it is impossible to estimate the temperature at which the kli absorbed ḥametz, so to dispel uncertainty, it must undergo hagala in boiling water.

A kli rishon removed from the flame: A kli that was heated over a flame and then removed, or if the flame beneath it was then extinguished, still can cook a bit. Therefore, kelim that became forbidden in this manner can be kashered in a kli rishon that is no longer on a flame if the water in it remains very hot.

Liquid poured (“irui”) from a kli rishon: This has the capacity to cook the surface layer (“kedei klipa”) of a food item. Kelim that became forbidden through irui can be kashered by pouring boiling water over them from a kli rishon.

A kli sheni: If a dish that was cooked on a fire was poured into another kli, the second kli is called a kli sheni. The poskim disagree about whether it is necessary to kasher kelim that were placed in a kli sheni. In practice, the ruling is that they must be kashered by means of hagala in a kli sheni (SA 451:5).

Some are even stringent regarding a kli shlishi and beyond (i.e., kelim at least twice removed from the kli in which the food was cooked), maintaining that as long as the food remains at the temperature of yad soledet bo, a kli into which it was inserted must be kashered. Even though most poskim are lenient and maintain that it is sufficient to rinse them, due to the gravity of the ḥametz prohibition, le-khatḥila the custom is to kasher them by means of hagala (SAH 451:34).

A kli that is used at a temperature that never reaches yad soledet bo, that is, it remains under 45oC, even a kli rishon, does not require hagala, and it is sufficient to rinse it.

Le-khatḥila, many have the custom to kasher all kelim used with hot ḥametz foods in a kli rishon on the fire, even if they were used only for irui or as a kli sheni, as we are concerned that they were once used as a kli rishon, but that this was forgotten. (See Rema 451:6; Kaf Ha-ḥayim 451:107.) However, when the level of forbidden use is certain, it is not necessary to kasher the kli using a higher level of hagala.

07. What Determines the Type of Hagala: Main Use or Most Intense Absorption?

Often, the same kli is used at different levels of severity. How is such a kli kashered? Some are stringent, maintaining that every kli must be kashered based upon its most intense usage, so if it was once used in fire, even though it is normally used in boiling water, it must be kashered by means of libun. Likewise, a kli that was once used with boiling water but is normally used with cold water must undergo hagala, for otherwise the kli will be kashered based on majority usage, not based on most intense usage (She’iltot, Raavyah, Mordechai, Issur Ve-hetter Ha-arokh).

In contrast, many authorities are lenient and maintain that the requirement to kasher depends on how that kli is used. Therefore, if it is normally used in boiling water, but occasionally used on a flame, it is kashered by means of hagala. If it is normally used with cold water but occasionally used with boiling water, it is kashered by means of rinsing (Rabbeinu Tam, Ramban, Rashba, Ran, SA 451:6). At first glance, this is problematic: How can kashering a kli based on its majority usage eliminate the flavor it absorbed during its more intense usage? The answer is that after 24 hours, flavors absorbed into and stuck to kelim become foul, and they consequently can no longer render forbidden foods that come into contact with them (as will be explained in the next section). Therefore, the requirement of kashering is based on the kli’s majority use (Rashba, Rama Mi-Fano).

In practice, the custom le-khatḥila is to be stringent and to kasher every kli according to its most intense usage. Under extenuating circumstances, we are lenient and kasher it according to its primary use. When there is concern that kashering it based on its most intense use will ruin the kli, for example, in the case of a kli that is used in fire in a minority of its usages, and which is likely to be damaged by libun, one may kasher it le-khatḥila by means of hagala, in accordance with its primary use.[5]

[5]. The rationale of those who adopt the stringent view is obvious: Since the kli once absorbed through more intense usage, it must be kashered accordingly. This is the view of She’iltot, Raavyah, Mordechai, Hagahot Maimoniyot, Terumat Ha-deshen, Issur Ve-hetter Ha-arokh, and Maharil. On the other hand, the Talmud implies that we follow the kli’s majority usage, so cups that are usually used for cold are kashered by means of rinsing (Avoda Zara 75b), even though they are occasionally used for hot. Knives that are usually used with boiling water are kashered by means of hagala (Pesaḥim 30b) even though they are occasionally used to slice meat that is on the fire. This is the view of Rabbeinu Tam, Ramban, Rashba, Ra’ah, and Ran. Likewise, many infer that this is the view of Rif and Rambam, as cited in Beit Yosef 451:6. This dispute pertains to kashering kelim that absorbed prohibited foods as well.

In practice, SA 451:6, 25, rules in accordance with the lenient view. According to Rema the custom is to be stringent and kasher the kelim according to their more intense usage, but we are lenient be-di’avad. According to SAH 451:27-28, such kelim should not be used on Pesaḥ. Only be-di’avad, if they were used after being kashered according to majority usage, the food is kosher. However, it seems from SHT ad loc. 144 that one may kasher a kli according to majority usage when it is difficult to kasher it according to its more intense use. Additionally, if kashering it according to its more intense use might damage the kli, according to Beit Meir ad loc. 11 (cited in SHT 51) one may kasher it according to its majority use.

Many Sephardic poskim wrote that we follow the majority usage (SA 451:6; Rama Mi-Fano; Gan Ha-melekh; Pe’ulat Tzadik; Zivḥei Tzedek, R. Yosef Messas, Yabi’a Omer 10, YD 58; Or Le-Tziyon 3:10:10-11). However, several Sephardic poskim wrote that le-khatḥila the practice is to be stringent according to the most intense usage (Knesset Ha-gedola; Shulḥan Gavo’ah; Kaf Ha-ḥayim 451:100; R. Ḥayim David Ha-Levi’s Mekor Ḥayim 186:6). SA 451:20 also states that the custom is to kasher tables by means of irui, in accordance with the more intense usage. Since we find some Sephardic poskim who ruled that one should be stringent le-khatḥila, and many Ashkenazic poskim ruled that one may be lenient when necessary, in order to minimize the differences, I wrote that we follow the stringent view le-khatḥila and that we are lenient when necessary. Therefore, forks that are sometimes used in fire should be kashered by means of hagala, since they can be damaged by libun. There is an additional reason to be lenient and require only hagala – the fork that was used in the fire is batel in the majority of forks that were not.

Several Aḥaronim wrote that we determine majority and minority usage based only on use with ḥametz that requires kashering; a kli that is primarily used for cold food that is not ḥametz but was once used for ḥametz in boiling water must undergo hagala. However, if most of the ḥametz usage was cold, as in the case of a table or countertop, even though it was occasionally used with hot ḥametz, it can be kashered with cold water, in accordance with its majority usage. So state Pri Megadim YD 91, Siftei Da’at 3; Beit Efrayim ḤM 17; Ḥazon Ish OḤ 119:15; Shevet Ha-Levi 6:116:3 (and in R. B. Frankel’s notes to §91, he is lenient and maintains that majority use is determined by all usage, including permitted use).

08. Foods Cooked in Kelim That Were Not Kashered

If one mistakenly cooked on Pesaḥ in a ḥametz pot that was not kashered, if 24 hours have not elapsed since ḥametz was last cooked in the kli, the dish is forbidden on Pesaḥ and must be destroyed. If 24 hours have passed, the dish is kosher be-di’avad, as there is a rule that anything that imparts foul taste does not render a food forbidden, and after 24 hours, the flavor absorbed in and stuck to the kli has become foul. Consequently, the taste of the foul ḥametz does not render the dish forbidden (SA 447:10, YD 103:5).

If the one who cooked in a ḥametz pot on Pesaḥ knew that it had not been kashered but transgressed and cooked in it on Pesaḥ, then even if 24 hours have passed since ḥametz was cooked in it, since he transgressed and cooked in a ḥametz pot that was not kashered, the Sages penalize him and render the cooked food forbidden to him and to anyone for whom he cooked. However, others, for whom he did not intend to cook, may eat from it, since in fact there is no ḥametz flavor that renders it forbidden.

Others are stringent, maintaining that even if one accidentally cooked on Pesaḥ in a ḥametz pot, even if 24 hours have passed since ḥametz was cooked in it, the dish is forbidden, because ḥametz on Pesaḥ is treated more stringently than other prohibitions, and just as even the tiniest quantity of ḥametz renders a mixture forbidden, so too, even its befouled taste renders a mixture forbidden (Rema; above, 7:5, n. 5).[6]

[6]. As explained in Peninei Halakha: Kashrut 34:2, it is impossible to calculate with precision how much flavor was absorbed in or stuck to the walls or how much flavor they release, as some kelim, like earthenware, absorb a lot; others, like wooden kelim, absorb less; and there are still others, like metal kelim, in which the flavor only adheres to the walls. Some flavors are absorbed or adhere more strongly, and others less so. Some foods have a very strong flavor, and others have a weak flavor. Since there is a constant uncertainty that can never be resolved, the halakhic ruling is that in order to avoid uncertainty, one must consider the entire wall of the kli as though it is filled with the flavor of the dish, and during cooking, it is all released into the dish. Since the contents of almost all of our pots and kelim are not sixty times the volume of the wall, with all its thickness, if kosher food was cooked in them within 24 hours of cooking non-kosher food, the kosher food is rendered forbidden by the non-kosher flavor that it absorbed.

This is the status of earthen and wooden kelim even today, and this is also the status of glass and metal kelim that were not cleaned with soap, as generally accepted. However, as explained in Peninei Halakha: Kashrut 32:4-8, unlike earthen and wooden kelim, metal and glass kelim do not absorb flavor into their very substance. Consequently, if they were cleaned with soap, as generally accepted today, they do not impart flavor. Therefore, be-di’avad, if one accidentally cooked in a clean ḥametz pot, even within 24 hours, the dish is kosher. Nevertheless, there is still an obligation to kasher it (ibid. 7), so if one took a pot that was used to cook ḥametz within the past 24 hours and purposefully cooks Pesaḥ food in it, even though no flavor that would render it forbidden was imparted into the dish, due to the Sages’ penalty, the dish is forbidden to the cook and to anyone on whose behalf he cooked the dish (Rashba, Ritva, Radbaz, Knesset Ha-gedola, Pri Megadim, and others, as explained in Peninei Halakha: Kashrut 32:3, n. 3, toward the end).

09. Cleaning and Preparing Kelim for Hagala

A kli must be cleaned before undergoing hagala, for although boiling water extracts the flavor absorbed in and stuck to the kli, it does not clean the kli of residual food stuck to it. If one kashers a kli via hagala without first cleaning it, he must clean it and then redo the hagala (SA 451:3).

If the kli has cracks and crevices from which it is hard to remove food residue, it must be cleaned with a lot of soap, until it is certain that the residual food on it is not fit for a dog to eat, and then hagala may be performed. Likewise, if a pot has handles, one must clean around the handles with a lot of soap so that the food residue that may have been left there is completely befouled.[7]

Handles of kelim must also be kashered because when metal vessels are heated during cooking, the heat spreads to the handles, and if they reach the temperature of yad soledet bo, the entire kli, including its handles, is considered as a kli in which a forbidden food was cooked, and the entire kli must be kashered. Its handles can be kashered through irui from a kli rishon, because their use and absorption are not as intense as a kli rishon over fire (Rema 451:12). The handles of wooden kelim also must be kashered, even though they do not get so hot, because sometimes the cooking food drips or sprays onto the handles, and its flavor becomes absorbed in and stuck to the handles. Therefore, both the kli and its handles must undergo hagala (SA 451:12; MB ad loc. 68).

Kelim that are likely to be damaged by the kashering process may not be kashered. This is why earthen kelim cannot be kashered; since earthenware absorbs a lot of flavor, hagala cannot cause the release of all the flavor it absorbed. Libun could kasher an earthenware kli, as libun incinerates all the flavor that the kli absorbed, but since libun is likely to make an earthenware kli shatter, there is concern that libun will not be performed properly. Therefore, the established halakha is that there is no way to kasher an earthenware kli. The only way to kasher an earthenware vessel is to return it to the kiln, where it is impossible to protect it from the full force of the kiln’s fire. Then, if the kli survives, it is as though it has been made anew (SA 451:1; MB ad loc. 13, 14).

Likewise, baking trays, Teflon skillets, and Wonder Pots (an Israeli invention used for baking cakes on stovetops), since they absorb taste through fire, cannot be kashered, as the prevailing custom accords with the stringent view (in section 5) that requires a temperature of 350-400oC to kasher them, and at such a temperature, they will likely become warped to the extent that most people would prefer to simply throw them out. However, as we learned (ibid.), in times of need one may rely on the lenient view that kelim used in fire can be kashered at the temperature they were used to bake or roast, and at such a temperature, they will not be ruined.[8]

[7]. SA 451:3 states that the solution for crevices is to perform libun at the place of the crevices to incinerate the food residue there. The poskim wrote that a wooden knife case, since it will burn up during libun, cannot be kashered (Rema, Taz, MA, MB, etc.). It stands to reason that they did not mention the solution of rinsing it in soap because it did not exist, so libun was the only solution for food residue in crevices.

[8]. The accepted ruling is that baking trays must be kashered by means of heavy libun, and since this is likely to ruin them, they should not be kashered for Pesaḥ (Or Le-Tziyon 3:10:2; Be-ohalah Shel Torah 1:18; Sidur Pesaḥ Ke-hilkhato 8:40; Hagalat Kelim 5:6; 13:315). The same applies to Wonder Pots and Teflon skillets. However, in times of need, one may be lenient and kasher them at the temperature at which they absorbed flavor, as we learned in section 5 that in times of need one may rely on the lenient view that kashering temperature hinges on the temperature at which the absorption by fire took place. We also learned in section 3 that one may factor in the view that ḥametz is considered “heteira bala” and can be kashered by means of hagala. This leniency is reinforced by the opinion of Shulḥan Gavo’ah 451:31 and Responsa Tiferet Adam, OḤ 16, that when one coats a baking tray with oil, the tray has the status of a pot that absorbed through liquid and is kashered by means of hagala. Ḥazon Ovadia: Pesaḥ, p. 134, states that one who wishes to rely on this view may do so. It seems that they mean to say that because of this oil, the pastry does not stick to the kli, and it can therefore be removed easily from the tray. Therefore, its absorption is not considered to be by means of fire. There is room to say that in a case that one is careful to place a baking sheet between the pastry and the tray, according to this view, there is no absorption through fire, and so it can be kashered by means of hagala. In the case of baking sheets, perhaps other poskim would concur with this view.

10. Waiting Twenty-Four Hours before Hagala

It is customary not to perform hagala on a kli until 24 hours have elapsed since the last time it was used with forbidden food  (i.e., until it is no longer “ben yomo”), because for 24 hours the taste that is absorbed into and stuck to the kli remains flavorful, and if the boiling water used for hagala is not sixty times larger than the volume of the walls of the kli, the hagala water may absorb the forbidden taste and cause it to be reabsorbed in the walls and re-stuck to the sides, rendering the hagala ineffective. But after 24 hours, the taste absorbed into and stuck to the kli becomes foul, and then the kli can be kashered even if the water is not sixty times its volume, because the kli releases a foul taste into the water, and such a taste will not render the kli forbidden, even if it is reabsorbed. For a kli is only rendered forbidden if the flavor it absorbs initially is good, in which case it remains forbidden even once the absorbed flavor has become foul. However, if at the time of its absorption and adhesion to the kli the taste was foul, the kli is not forbidden.

Another reason for this 24-hour delay is our concern that meat and dairy kelim will undergo hagala in the same water, release good meat and milk flavor into the hagala water, and if the hagala water is not sixty times the volume of either the meat or the dairy, the flavors will not be batel be-shishim. Rather, these flavors will mingle and then render all of the hagala water, as well as any kelim that undergo hagala in it, forbidden, as they will have absorbed the flavor of basar be-ḥalav (the forbidden mixture of milk and meat). However, once 24 hours have elapsed, the flavors of milk and of meat that are released by the kelim is foul and will not render the hagala water and the kelim that underwent hagala in it forbidden, since noten ta’am li-fgam is permitted (SA 452:2; MB ad loc.).

The common practice at public hagala stations is not to rely on the presumption that everyone waited 24 hours before performing hagala. In order to avoid problems, liquid soap is added to the hagala water, thereby immediately rendering any taste released by the kelim foul, so even if it is reabsorbed into the kelim, since it is foul, it does not render kelim forbidden.

Technically, it is possible to perform hagala on metal and glass kelim that were cleaned with soap without waiting 24 hours, since they do not release flavor. However, le-khathila the custom is to wait 24 hours or add liquid soap in the case of glass and metal kelim, like in the case of wooden kelim.[9]

[9]. According to Rashi, Sefer Ha-eshkol, Yere’im, Ramban, and others, during the entire time that the kelim are in the boiling hot hagala water, the kelim release flavor and do not absorb from the hagala water. Consequently, there are no grounds for all the concerns mentioned above. However, Tosafot, Or Zaru’a, Rosh, Rashba, Smak, and others are concerned about everything mentioned above, and this is the custom, as written in SA and Rema 453:1-2 and in MB 1 ad loc. Thus, one who wishes to perform hagala must ensure that one of two conditions is met: 1) The kelim have not been used for 24 hours, so flavors they release are foul (or liquid soap, which befouls all flavors, has been mixed into the hagala water). 2) The hagala water is sixty times the volume of the kli’s walls, so that any taste released into the water is batel be-shishim.

According to Issur Ve-hetter Ha-arokh, if one kli after another is inserted into the hagala water, the flavor that is released by them is batel, one by one, and we do not combine all the kelim together. However, according to Rashba, the kelim are ḥozer ve-ne’or, so if the hagala water is not sixty times the volume of the walls of all the kelim inserted into the hagala water, all of the aforementioned concerns apply. This is the accepted custom (MB ad loc. 13). The custom, le-khatḥila, is also to kasher only kelim that have not been used for 24 hours, lest the hagala water have less than sixty times the volume of the walls of the kelim (MB ad loc. 20).

All of these principles also applied to metal kelim that were not cleaned with soap, as was the standard practice until modern times. Nowadays, however, when we clean these kelim with soap, and there is no longer any concern that a layer of residual food remains on them, there is no concern that they will release flavor into the hagala water. Only in the case of wooden and earthen kelim is there concern that they will release flavor (Peninei Halakha: Kashrut 32:4-8). Nevertheless, the accepted ruling is to wait 24 hours, in accordance with time-honored custom, or to put soap in the hagala water, as is necessary for wooden and earthen kelim and for glass and metal kelim that were not cleaned properly.

Some maintain that hagala can only be performed in water, as other liquids do not adequately cause the release of flavor (Ramban, Ritva, Me’iri). Others maintain that hagala can be performed in other liquids as well (Rashba). Rema 452:5 rules that hagala should le-khatḥila be done in water, and be-di’avad, it can be done in other liquids. Based on this, several Aḥaronim wrote that le-khatḥila ash should not be mixed into the hagala water (MB, Pri Ḥadash, Ḥok Yaakov). Nevertheless, the accepted ruling nowadays is to mix liquid soap into the hagala water. Apparently there is no concern as the liquid soap does not alter the consistency of the water (so states Sidur Pesaḥ Ke-hilkhato 7:76).

Regarding whether one may perform hagala on Pesaḥ: As we learned above (7:5), according to the majority of Rishonim and SA, who maintain that even on Pesaḥ something that imparts foul flavor does not render the mixture forbidden, it is permissible to perform hagala as long as the kelim have not been used for 24 hours, for then the flavor absorbed in and adhering to the kli is foul. According to Rema, who is concerned about the view that something that imparts foul flavor renders a mixture forbidden on Pesaḥ, one may not perform hagala on Pesaḥ. Only libun, which incinerates the taste in and on the kli, may be done to kasher kelim on Pesaḥ. However, one may perform hagala on clean metal and glass kelim on Pesaḥ, since they do not release ḥametz flavor into the hagala water. (See Peninei Halakha: Kashrut 32:6-7.)

11. Hagala in Practice

For the purposes of hagala, any kitchen pot can be used, as long as it is clean. The hagala water must actually be boiling.

The entire kli is left submerged in the water for about three seconds. Le-khatḥila, the custom is to rinse the kelim in cold water immediately after hagala, but this is not an absolute requirement (SA 452:7; MB 34). Therefore, when it is difficult to rinse the kelim in cold water, there is no obligation to make an extra effort to do so.[10]

Sometimes the immersion of kelim cools the water to the point that it stops boiling. In this case, the kelim should be left in the water until it returns to a boil. If one inserts two kelim simultaneously into boiling water, one must shake the kelim to ensure that the boiling water circulates between them (based on SA 452:3-4).

If a kli cannot be immersed in its entirety into the water, it may be immersed one half at a time (SA 451:11).

Many have the custom le-khatḥila to perform hagala in boiling water even on kelim that were used for irui or as kli sheni (above, section 6).

In brief, this is the procedure of hagala: First, one cleans the kli and boils water in a large, clean pot. Any kli that requires hagala is then inserted into the boiling water for about three seconds. The kli is now kosher. The custom is to add liquid soap to the hagala water or to wait 24 hours from last use with ḥametz or forbidden foods before performing hagala; for kelim that are not clean, it is obligatory to do so. Le-khatḥila, the kli is rinsed in cold water after hagala.[11]

[10]. All concur that hagala water is intended to cause the release of flavor absorbed in kelim. Many Rishonim wrote that the kli should be left in the hagala water until it releases everything it absorbed into the water (Rif; Rambam, MT, Laws of Ḥametz and Matza 5:23; Raavad, Ramban, Rashba, Ran, and others). Raavyah and Tur (452:1) stated that the custom is to insert and remove the kelim immediately. Aḥaronim explain that this is so that they do not reabsorb what they released (MB 452:4). Pri Ḥadash 452:6 explains that the custom is simply to insert and remove the kli immediately, against most Rishonim, and Jewish custom is itself considered Torah. In contrast, Taz and Eliya Rabba state that even according to Tur and the prevailing custom, one must leave it in the water a bit. SAH 452:4 explains that this means “leaving it a very little while.” It seems that this means about three seconds.

The Rishonim also wrote that one should rinse the kli with cold water after hagala, to remove from the kelim what they released and so that the heat of the water does not cause the taste released during hagala to be reabsorbed or get re-stuck (Rambam, Raavyah, Rashba, and many others; Me’iri states that instead of rinsing in cold water, one may dry the kli to wipe off anything that was released and then stuck loosely to the surface of the kli). However, the Rishonim wrote that rinsing in cold water is not essential for the hagala to be effective, as it is not mentioned in the Talmud. Aḥaronim explained that this is because the custom is to perform hagala on kelim that have not been used for 24 hours. (See MB 452:34.)

[11]. Although the custom of Ashkenazic communities and some Sephardic communities is to avoid using hagala to switch kelim from meat to dairy and vice versa, when kashering kelim for Pesaḥ one may switch them from meat to dairy even le-khatḥila (Ḥatam Sofer, YD 110; see Peninei Halakha: Kashrut 33:9, n. 11).

12. Kashering Pots by Means of Hagala

Hagala of a pot must be performed in a large kli into which the entire pot can fit. It is not sufficient to boil water inside the pot, because it is likely that during the course of the year some dishes sprayed out or boiled over the sides of the pot, in which case the flavor of ḥametz was absorbed into and adhered to the pot’s upper lip – and the lip is not kashered by boiling water inside the pot.

If there is no large kli in which hagala can be performed, one should fill the pot that one wishes to kasher with water and bring it to a boil, and at the same time, boil water in a small kli. When the water in the pot boils, insert the small kli into the boiling water in the pot, which will cause a lot of water to spill over every side of the pot, thus kashering its lip. (See Avoda Zara 76a, and see SA 452:6.)

When it is possible to remove the handles of the pots, some are scrupulous to remove them and clean them. Alternatively, one may clean around them with plenty of soap, until it is clear that any flavor that may have been in the crevices has been befouled. Then one performs hagala (above, section 10). Pots that have a metal fold along the rim do not require any special treatment.[12]

[12]. Some have the custom of going over the edges and lid of the pot with a blowtorch in order to incinerate the residue that may be found under the folds of metal along the rim and lid of the pot. However, this is unnecessary, as whatever residue may have been trapped there is extremely foul with age and constant rinsing with soap, as we discovered upon examination. We also found that whatever accumulates around the handles is exceedingly foul, so there is no need to remove the handles, since rinsing with soap certainly befouls any flavor completely.

Regarding hagala of a large pot that is kashered by boiling water in it: It can be suggested that one should cause the water to overflow by pouring boiling water into it from an electric kettle. However, the solution I suggested, using a small kli with boiling water, is preferable, because when pouring the water, it cools down slightly, whereas the entirety of the small kli is boiling hot and is itself a kli rishon, and so does not cool down.

Kashering a pot by causing it to overflow onto its outer walls is effective for a kli that absorbed ḥametz through overflow, but a kli that is regularly inserted into another kli and absorbed ḥametz flavor there – as in the case of a ladle – absorbed in a kli rishon, and hagala by the overflow method is not effective. Instead, it must be kashered through complete immersion in boiling water (MB 452:31).

13. Absorption through Pickling (“Kvisha”) and Its Kashering

Kelim into which cold ḥametz has been placed are kashered by rinsing them. For example, beer mugs are kashered for Pesaḥ by rinsing them, even though beer is ḥametz, because as long as the ḥametz in a kli has not reached the temperature of yad soledet, its residue adheres only loosely to the kli, and it can be removed by rinsing. Certainly, then, plates and bowls into which ḥametz cakes were placed are kashered by cleaning them, because in addition to the fact that the pastries are not hot, they are also dry, and without moisture, flavor does not adhere to a kli. However, one must remove crumbs that may remain on the kelim.

But if the beer was left in a mug for 24 hours, according to many, this constitutes kvisha (“pickling,” or the absorption of taste through prolonged soaking) occurs, and the Sages said: “kavush ki-mevushal” (pickling is akin to cooking). That is, pickling imparts flavor into foods just as cooking does, and according to many, it even imparts flavor into kelim (Peninei Halakha: Kashrut 35:9). Therefore, it is forbidden on Pesaḥ to use kelim in which beer was left for 24 hours.

Kelim that have absorbed taste via kvisha can be kashered through hagala in boiling water, for if hagala is effective on kelim used for cooking, it certainly works on kelim used for pickling. Moreover, since kvisha is a milder form of absorption, one may kasher such kelim by soaking them in water for three 24-hour periods – that is, by soaking the kli in water for 24 hours, replacing the water, soaking it for another 24 hours, replacing the water again, and soaking it for another 24 hours. Of course, it is generally faster and easier to kasher these kelim by means of hagala in boiling water, but kelim that are liable to be damaged by boiling water may be kashered in this manner.

An alcoholic beverage like whiskey, according to some poskim, has the effect of kvisha and imparts the flavor of the whiskey into the kli within 18 minutes. Thus, if one wishes to use this kli on Pesaḥ, he must first kasher it by means of hagala or by soaking it in water for three 24-hour periods.[13]

[13]. The Talmud (Ḥullin 111b) states: “Shmuel said: Pickled [food] (kavush) is like cooked [food] (mevushal).” Some explain this to mean that pickling food in a sharp or briny liquid causes the absorption of flavor, much as cooking does, but merely soaking in water or another liquid that is neither sharp nor briny does not cause absorption like cooking (Rashi, Rashba, and many others infer that this is Rambam’s view). But according to most poskim, soaking in any liquid is considered like cooking (Rabbeinu Tam, Tosafot, Raavad, Or Zaru’a, Rosh, Mahari Weil, Ritva, SA YD 105:1). Some say that in order to be considered like cooking, the pickling must last for three days (Raavyah, Maharam Rothenburg, Yere’im), but according to most poskim, it must last only 24 hours (Rosh, Mahari Weil, Sha’arei Dura, SA YD 105:1, and others). With regard to sharp liquids, some say that even pickling in a sharp liquid only causes absorption after 24 hours (Issur Ve-hetter Ha-arokh, Shakh, Taz), and some say that it begins causing absorption in the amount of time it would take to bring it to a boil (“shi’ur hartaḥa”; SA YD 105:1, MA, Binat Adam, and others). The Aḥaronim are uncertain how long the “shi’ur hartaḥa” is: 10, 18, or 24 minutes.

There is a dispute among the poskim regarding the degree to which kelim absorb taste via kvisha. Some maintain that kelim absorb taste from kvisha just as from cooking (Issur Ve-hetter Ha-arokh, Shakh, and Pri Megadim). Others maintain that kvisha causes kelim to absorb flavor only in their outermost layer (Taz). Still others maintain that only wooden and earthenware kelim absorb flavor through kvisha, but not metal kelim (Kereti U-feleti, Erekh Ha-shulḥan). Above I adopted the stringent view, because this is the accepted ruling, and so it is proper to accept it in practice le-khatḥila. As a matter of technical law, however, the halakha follows the lenient view with respect to glass and metal kelim.

Even though an earthenware kli that absorbed ḥametz during the cooking process cannot be kashered through hagala, if such a kli absorbed flavor through kvisha, it can be kashered by means of hagala or by soaking it for three days, as explained in SA 451:21.

Chapter Contents