Wednesday, 7 September 2022

What is a 'Kosher Kitchen'?


Keeping a kosher kitchen is considered by many to be the baseline of religious Judaism. Many families keep kosher (at least at home) even if they keep little else, often to the strictest standards. This has likely served to preserve Jewish identity for generations, forcing us to stay together and form communities.

Apart from avoiding eating non-kosher food, the laws of kashrus also forbid cooking in utensils previously used for non-kosher. We also may not cook meat in utensils previously used for milk or vice versa. As we shall see, this has a clear source in the Torah, but it can nevertheless be difficult to understand the rationale. As always, I will attempt to provide clarity of the underlying principles as well as some practical ramifications.

Midianite Utensils

The Biblical source for these laws is the command given regarding the utensils taken as spoils from the war against the Midianites, prior to entering Eretz Yisrael:

וַיֹּאמֶר אֶלְעָזָר הַכֹּהֵן אֶל אַנְשֵׁי הַצָּבָא הַבָּאִים לַמִּלְחָמָה זֹאת חֻקַּת הַתּוֹרָה אֲשֶׁר צִוָּה ה' אֶת מֹשֶׁה: אַךְ אֶת הַזָּהָב וְאֶת הַכָּסֶף אֶת הַנְּחֹשֶׁת אֶת הַבַּרְזֶל אֶת הַבְּדִיל וְאֶת הָעֹפָרֶת: כָּל דָּבָר אֲשֶׁר יָבֹא בָאֵשׁ תַּעֲבִירוּ בָאֵשׁ וְטָהֵר אַךְ בְּמֵי נִדָּה יִתְחַטָּא וְכֹל אֲשֶׁר לֹא יָבֹא בָּאֵשׁ תַּעֲבִירוּ בַמָּיִם:

במדבר לא, כא – כג

Elazar the Priest said to the men of the army, who come in to war, "This is the law of the Torah that Hashem commanded Moshe: The gold, silver, copper, iron, tin and lead – anything that comes into contact with the fire, you shall pass into the fire and purify, however it must be cleansed in water of sprinkling. Anything that does not come into contact with fire, you shall pass into water."

Bamidbar 31:21-3

The "water of sprinkling" is the water containing the ashes of the Parah Aduma (Red Heifer), and is needed to cleanse the utensils from ritual impurity caused by contact with a dead body. However, Chazal understand that the purification through fire serves a more mundane purpose – the purging of any non-kosher taste absorbed into the utensils. If a utensil were to be used subsequently without undergoing the required purging, this taste could be ejected into other food, rendering it non-kosher.[1]


Elsewhere, we are commanded to purge any leftover taste of a sin offering from the utensils in which it was cooked. Here, the Torah also teaches us the law of earthenware utensils:

וּכְלִי חֶרֶשׂ אֲשֶׁר תְּבֻשַּׁל בּוֹ יִשָּׁבֵר וְאִם בִּכְלִי נְחֹשֶׁת בֻּשָּׁלָה וּמֹרַק וְשֻׁטַּף בַּמָּיִם:

ויקרא פרק ו פסוק כא

"An earthenware utensil in which it will be cooked must be broken. If it was cooked in a copper vessel, it must be purged and rinsed with water."

Vayikra 6:21


Chazal learn from here that food absorbed in an earthenware utensil can never be purged (completely).[2] For this reason, the only option is to destroy the utensil.[3]


The Rambam writes that if non-kosher meat was cooked in an earthenware utensil, and this utensil was not destroyed but was instead used to cook kosher meat, this meat becomes non-kosher. If however it was used to cook a different type of food (i.e. not meat), this food is only forbidden to eat if the taste of the (non-kosher) meat is detectable within it.[4]

The reason for this distinction is straightforward to understand. Use of non-kosher utensils only affects the food cooked in them if significant 'non-kosher taste' is transmitted to the kosher food. If this kosher food is not meat, it is possible to determine whether a significant taste is present by means of a simple 'taste test.'[5] However, if kosher meat was cooked in the utensil, the taste of non-kosher meat may not be detectable due to its similarity to the taste of the kosher meat. The 'taste test' is therefore not reliable in this instance.

The Rambam's source for this distinction comes from a gemara that discusses cases where small amounts of non-kosher food fall into kosher food inadvertently. However, this gemara has a solution for the case of non-kosher food falling into kosher food of the same type – the non-kosher food is nullified as long as the volume of the kosher food is sixty times larger.[6]

The Rambam does not give this solution in the case of the food cooked in the non-kosher utensil, presumably because in this case assessing the respective volumes is also not practical. There is no way of knowing how much non-kosher food became absorbed in the utensil.[7] We can only be lenient in the unlikely event that the volume of the kosher food is sixty times larger than the volume of the entire utensil.[8]

The Anachronism

The fundamental principle behind all of the above does not appear to be true in the world today. We use pots to cook a variety of food, and if these pots have been washed in between, we never taste any hint of the previous dish in the current one. Any amount of food that does get absorbed into a utensil is insignificant, and certainly considerably smaller than a sixtieth of the kosher food cooked in it subsequently.[9]

This fact shows that absorption into standard utensils has changed significantly since the war against the Midianites, and since the time of Chazal. This change can easily be explained based on improved quality both of the pots that we use (being smoother and without significant deformities), and of the detergents used to clean them.

The logical conclusion is therefore that the standard utensils of today can be kashered simply by washing them thoroughly with soap. There should be no problem with using the clean utensils of a non-Jew, and not even any need to keep separate dishes for meat and milk. Could this really be true?

As I am sure the vast majority of readers will know, the rabbinic consensus today is not so lenient. Few discuss the possibility that the rules followed for centuries are no longer relevant. Even those who do, are fearful of making significant changes to these rules, and bend over backwards to justify maintaining at least the majority of them.[10]

For me, the most ironic part of this is that even following the old rules to the letter should lead to significant leniencies. Even in the past, if it were possible to determine that no significant taste had been transmitted to food cooked in a non-kosher pot, this would be sufficient in order to allow consumption of the food. There should be no difficulty in making such a determination nowadays.[11]

Intentional Nullification

While many of the justifications given for following the old rules appear spurious at best, there is one point which is worthy of discussion. Even if no taste absorbed in a utensil will ever be significant enough to forbid the food cooked in it, does this necessarily mean that intentionally causing a transmission of this small amount of food is permitted?

The usual rule is that we may not 'nullify a prohibition intentionally' (אין מבטלין איסור לכתחילה). Would the use of a non-kosher utensil, causing the forbidden taste absorbed in it to become nullified within the kosher food cooked, fall under this prohibition?

This exact question is already debated by the rishonim. The Rashba writes that if the amount of non-kosher food absorbed into a utensil is so small that its taste will never be noticeable in other food, cooking in this utensil is permitted and there is no issue of 'nullifying a prohibition intentionally.'[12] However, the Ra'ah strongly disagrees.[13] The Shulchan Aruch rules leniently in accordance with the Rashba,[14] while other poskim advocate stringency.[15]

It would therefore appear that there is some basis for continuing to be particular about using only kosher utensils, and for keeping separate utensils for meat and milk.[16] However, when things go wrong and the wrong utensils are used inadvertently, this should rarely render the food non-kosher.[17]

[1] See for example Avoda Zara 75b.

[2] Pesachim 30b

[3] Returning the shards to the furnace will remove the absorbed taste and it is then possible to recraft a new utensil. See Zevachim 96a.

[4] Hilchos Ma'achlos Asuros 17:1

[5] This test would have to be administered by a reliable non-Jew (see footnote 11 below for details).

[6] Chulin 97a-b

[7] See Radvaz on the Rambam, who gives this explanation.

[8] See Shulchan Aruch, Yoreh Deah 98:4.

[9] See for a study (in Hebrew) on amounts of food that do get absorbed into utensils. Although the study concludes that such absorption does take place, it concedes that the amount is certainly less than a sixtieth (although as we have written above, this is clear without the need for this study). At the end of the article, letters from various contemporary poskim are added, some of which support the position that I put forward here.

[11] The classic way to make this determination was to ask a non-Jewish expert cook to taste some of the food and to tell us if he could discern the relevant taste. Although the Ashkenazi practice was not to rely on the testimony of a non-Jew (see Rema, Yoreh Deah 98:1), Sefardi tradition does accept such testimony. Once a Sefardi eats the food, relying on the non-Jew, and confirms that there is no non-kosher taste, an Ashkenazi can take the word of the Sefardi. In reality, as today we know that neither the non-Jew or the Sefardi will discern any non-kosher taste, this whole process can be dispensed with and the food should be permitted without the need for any 'taste test.'

[12] Toras HaBayis, Bayis 4, Sha'ar 4.

[13] Bedek HaBayis there.

[14] Yoreh Deah 99:7; 122:5

[15] Shach and Taz there. See also Bi'ur HaGra

[16] Although it is also quite possible that even the stringent rulings of the Shach and Taz were only relevant in their times. In a world when most non-kosher utensils were capable of imparting taste to food, they felt that it would not be appropriate to make a distinction regarding exceptional cases. Today, when utensils never impart taste to food, it is harder to justify this stringency.

[17] The utensil may need kashering in the traditional manner, or may even need to be discarded when kashering is not possible, based on the stringency discussed above.

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