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Koshering Utensils


This week’s article will begin discussing the laws of Pesach – which utensils can be koshered, and how. We will take a look at the sources and resulting halachos for various kinds of vessels. Can earthenware be koshered, and if so – how? What about porcelain or glass? Are marble or other natural stone any different? And what about engineered Caesarstone? Does the ownership and use make any difference? How is a taboon koshered? Can chametz dishes remain in the breakfront over Pesach? And what happens to the taste of chometz absorbed in earthenware or ceramic dishes that remain in a Jew’s possession over Pesach? Of this and more in the coming article.

Forbidden Taste

This week’s parasha discusses kosher and non-kosher foods: which animals may be consumed, and which may not. One of the halachos we learn from this week’s parasha appears in the pasuk: “These are the ones that are unclean for you, among all creeping creatures; anyone who touches them when they are dead will be unclean until evening” (Vayikra 11:31). This pasuk seems to present a contradiction (Toras Kohanim 2:12; Chulin 112b and more): either we distance ourselves from the unclean, or they are, as the pasuk defines, “for us”. Chazal answer that “the unclean” prohibits anything that receives taste or was mixed in with forbidden foods, and the words “for you” teach us that if it was cooked or mixed in a way that does not affect the taste, it is permitted for consumption.

Similarly, the pasuk: “And they shall be an abomination for you” (Vayikra 11:11) teaches us another halacha (Toras Kohanim 3:8) “an abomination — for you”: if the reptile gave its flavor to something, it becomes an abomination, but if the flavor is unapparent – it may be “for you”.

Absorbed Flavor

The Torah teaches us that when used with heat (cooking or baking for example) a vessel absorbs the flavor of the food that was cooked inside. Chazal call this flavor ta’am habaluah – “absorbed flavor”.

Note: halacha is not necessarily aligned with laboratory findings. This explain the allergy warning on food labels which may seem contradictory to their kashrus status: a pareve item may have an alert for milk; Pesach products may have a warning for gluten. While the kashrus agency can ascertain that the possibility these allergens are present is greatly diminished, since the presence of these elements is measured by kashrus standards and not scientific standards, the component may be present in a medically dangerous amount (depending on the severity of the allergy) but not in a halachically prohibited one.

Immersion in Boiling Water

In last week’s parasha we read: “An earthenware vessel in which it is cooked shall be broken, but if it is cooked in a copper vessel, it shall be scoured and rinsed in water” (Vayikra 6:21). The Torah teaches us that an earthenware vessel that was used for cooking the Chatos offering must be broken and cannot be koshered through immersion in boiling water (once the time-span for eating a sacrifice has passed, the remaining meat or flavor is given the status of non-kosher food). However, if it was cooked in a metal vessel, the vessel can be koshered by immersion in boiling water. Since this removes the absorbed flavor from the pot, the next food that is cooked inside does not become unkosher.

In general, most utensils that were used for forbidden foods – either by mixing milk and meat, forbidden foods, or to be made kosher for Pesach, can be koshered. However, the method for koshering may vary.

Although we don’t customarily transfer utensils from dairy to meat during the year, before Pesach or for Pesach it may be done. Additionally, some substances such as earthenware or enamel cannot be made kosher ever. Utensils that were used to cook directly on a fire (without the medium of water) — e.g., a baking pan or grill — need to be koshered with a blowtorch (libun) which must be applied until the utensil is red hot. A utensil that will be ruined in such intense heat cannot be made kosher.

This week’s article will focus on those utensils which cannot be made kosher, with the focus on the approaching holiday of Pesach: what can be done with them, what can be done in extenuating circumstances when these dishes must be used, and what is the halacha post facto, if they were already used.

We’ll start with ceramic (called by Chazal klei cheres) which are the source for these halachos. In next week’s article we will continue to vessels made of glass and bone, ending with modern eating utensils and their materials – porcelain, china, plastic, Pyrex, rubber and others.


Earthenware vessels cannot be made kosher, and cannot be transferred from dairy to meat, or from chometz to Pesach. The prohibition to kosher them is twofold:

  1. Earthenware cannot be made kosher through immersion in boiling water as we read in last week’s parasha: “An earthenware vessel in which it is cooked shall be broken” (Vayikra 6:21). The Gemara derives from this pasuk that earthenware vessels can never be changed (Paschim 30b). Flavor that was absorbed in pottery cannot be removed from it.
  2. Libun – blowtorching or heating until a utensil is red hot (approximately 500 degrees Celsius) does remove flavor, and earthenware can, technically be koshered this way. However, since the utensil will probably be ruined from the intense heat, Chazal were concerned this koshering method would not be executed properly. Therefore, Chazal forbade using libun to kosher earthenware (Pesachim 30b).

Defining Earthenware

Earthenware vessels are made of clay mixed with water and fired in a kiln (usually heated between 800-1200 degrees Celsius). Earthenware or pottery is a porous material which absorbs anything cooked inside and gives the next dish a strong taste of the previous one.

The vessel’s quality greatly depends upon the materials used to create it and the heat used for drying it. These factors determine how absorbent the final product will be.

The Gemara (Psachim 30b, Avoda Zara 33b) discuss several types of pottery. With regard to Pesach, all pottery or earthenware that absorbed chometz is forbidden. Regarding forbidden wine there are several types of pottery with which we are more lenient.

Practically, the Mishna Brura (451:18) rules that any earthenware vessel created from earth and dried in a kiln or oven fall in the same category as pottery. However, sun-dried earthenware can be koshered with boiling water. Caesarstone is a world-famous company that produces quartz countertops and surfaces from a combination of roughly 90 percent natural quartz and 10 percent polyresin. The Chazon Ish is stringent here, maintaining that only natural stoneware can be made kosher with hag’ala (immersion), but earthenware or engineered stone, despite being dried in the sun and not in an oven, are seen as pottery which cannot be koshered. However, Rav Eliyashiv (Siddur Pesach Kehilchaso, chapter 9:7); Rabbi Shlomo Zalman Auerbach (Halichos Shlomo Pesach, chapter 3:4); and Rav Yisroel Yaakov Fisher (Even Yisroel 7:21) rule leniently, aligning with the Mishna Brura’s opinion.

Earthenware Tableware

The Shulchan Aruch (OC 451:1; YD 105:2) rules that earthenware utensils that were used for cooking cannot be koshered. Chazal refer to this utensil as a kli rishon (literally “first utensil”) — a utensil used for cooking, baking or roasting food or liquid. When hot food or liquid is transferred from the kli rishon into a second utensil the second utensil is called a kli sheni. A kli shlishi is the third utensil into which hot food or liquid is transferred.

If the chometz or forbidden food came in contact with an earthenware vessel that had the status of a kli sheni the vessel’s status is subject to widespread dispute among the poskim. Opinions range from completely forbidding koshering it, to permitting it with haga’la, ending with permitting use without any koshering at all because the heat of a second dish does not absorb flavor. (See Shulchan Aruch YD 105:2; Rama 451:1; Magen Avraham, ibid footnote 3; Chok Yaakov; Pri Chadash; Kaf Hachaim ibid footnote 17, 20; Ben Ish Chai 96:1:14, and others.)

Practically, both Ashkenazi and Sfaradi authorities follow the opinions of the Mishna Brura (451:11) and Kaf Hachaim (451:20). Preferably, one should be stringent and not use non-kosher or chometz pottery even if it was only used as a kli sheini. Furthermore, if hot kosher food was placed on such a dish, the food would become forbidden, lechatchila. Where stringency involves large financial loss or conflicts with the joy of Yom Tov, one can be lenient and rely upon those who permit it. This permit is applicable only after the utensil has not been used for 24 hours with the forbidden food. The Mishna Brura adds (Sha’ar Hatziyoun, footnote 10) that if it was used as kli shlishi, one can be lenient even within 24 hours of use.

Today, since it is common for food to be poured directly from a pot or kettle into a ceramic bowl or mug, koshering pottery is forbidden by all authorities since we are afraid that the vessel does not have the status of a kli sheni. The same is obviously true for a ceramic mixing spoon which is often used to mix food in a boiling pot on the fire.

It is important to note that where the dish is used in a microwave it gains the status of kli rishon just like a pot and therefore, koshering is impossible.

If the ceramic or china is particularly expensive and the dish was mostly used as a kli sheini or shlishi, the case may be presented to a rabbi for ruling. It is important to ensure the case is presented properly and mention if the dish was used in a microwave or in a heating drawer.


Ceramic or pottery that touched hot non-kosher or chometz foods cannot be koshered or made kosher for Pesach. Where this involves significant loss or conflicts with simchas Yom Tov there is room for leniency if the food was on a dish that had the status of a kli sheini (i.e. no food was poured on it directly from a pot) and 24 hours have passed from the forbidden use, it may be used. Additionally, if the piece was used as a kli shlishi – i.e. the food was served on serving dishes and from there to the dish in question, where extremely necessary the vessel may be used even before 24 hours passed from the forbidden use.

Firing Again

The Shulchan Aruch (OC 451:1) notes that placing earthenware in a kiln or furnace used for firing pottery can kosher it, enable transfer from dairy to meat, or from chometz to Pesach. A regular oven, though, cannot be used for this purpose, despite the fact it may reach the required temperature for libun. The Mishna Brura explains (footnote 14) that since ceramic gets very hot in a kiln and kilns cannot be opened before they have reached a certain temperature due to concern of breaking or shattering, there is no concern that the vessel will be removed before it is fully koshered. However, in an oven, where it takes much longer to reach the proper temperature, we are concerned that it might be removed before it is fully koshered.

A self-cleaning oven that can reach 500 degrees Celsius in which all grime and oil becomes soot is seen as libun chamur. Since the oven is locked while self-cleaning and it is impossible to remove the dish before the cycle is completed, one can kosher ceramic vessels in a self-cleaning oven if there is no concern that they will be damaged.

Earthenware on Pesach

What happens to chametz pottery which has absorbed flavor of chometz? Must it be disposed together with the chometz? And after Pesach do become chometz she’avar alav haPesach – chometz that has been in a Jew’s property over Pesach, which is forbidden to use?

The Shulchan Aruch rules (OC 451:1) that one may keep vessels earthenware in his possession after thorough cleaning, despite the cooked-in chometz. Furthermore, a utensil, which due to pikuach nefesh or a mistake, was used on Pesach with chometz in Jewish property (i.e. the dish has absorbed the flavor of chometz on Pesach) may be kept in one’s property over Pesach, and may be used after Pesach.

If the last scenario occurred on the last day of Pesach, the vessel must remain without use for 24 hours before it is used after Pesach for chametz.

Storing Chometz Dishes

The Shulchan Aruch rules that chametz dishes should be cleaned thoroughly and stored out of reach over Pesach. Preferably, the storage room or space should be locked, and the key hidden away to prevent mistaken use. The Mishna Brura explains (footnote 8) that when one has to search for the key it gives him time to recall that the utensils are chometz.

Therefore, dishes that were not koshered for Pesach should not be left in a breakfront or china closet despite serving only as display pieces. If they are displayed on a shelf so high that a ladder must be used to access them, the Mishna Brura writes (451:7) that we do not challenge one who leaves them in their place. Hiding one’s chametz dishes is much preferred. One can be more lenient if the utensils were not used for cooking or did not come in direct contact with boiling chometz (as is the case with most decorative dishes).

Next week’s article will deal with modern equivalents of pottery as well as other materials – porcelain, China, plastic, etc.: when is koshering permitted, and what can be done in extenuating circumstances.


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