Kashering from Meat to Dairy and Vice Versa
Parsha Halacha – Parshat Va’eira – Shabbat Mevorchim Shevat
Kashering from Meat to Dairy and Vice Versa
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In the Torah portion of Va’eirah, Aharon performs the sign that he is a G-dly messenger by turning his staff into a tanin (snake[1]) and then turning the snake back into a staff again.[2]
This article will discuss the permissibility of kashering meat utensils for the purpose of using them for dairy or vice versa.
The Custom Not to Kasher
The Magen Avraham writes[3] that it’s customary not to kasher meat utensils in order to use them with dairy or vice versa.
The Reason
The reason for the custom (as quoted in the name of Rabbi Mordechai Yaffe[4]) is that, were it permissible to kasher in this manner, one might keep only one utensil for both meat and dairy and kasher it constantly from one to the other. This can be problematic as one may forget what the current status is and use it for dairy when it is was actually most recently used for meat or vice versa.
The Source
A basis for this custom can be found in the Talmud[5] which says that a butcher shouldn’t keep one knife and use it for both kosher meat and for forbidden fats[6] (by washing it in between) as he may forget and use it to cut meat after cutting the fats without washing it in between.
Another Reason
Another possible reason for this custom is that, were it permissible to kasher a meat utensil to be used for dairy (or vice versa), one may forget and kasher these items within 24 hours of their use when, in fact, one must wait 24 hours before kashering.[7]
Although a similar argument can be made regarding kashering from non-kosher to kosher, in such case we aren’t strict since otherwise we would have to discard the utensil. In the case of dairy and meat, however, when the utensil can simply be used for its current use (instead of kashering and switching it), we are strict and do not kasher.[8]
This reason only applies when kashering in boiling water (hagalah). When kashering by direct heat, e.g. a blowtorch (libun), however, there is no need to wait 24 hours[9]and, as such, it would be permissible (according to this opinion) to kasher from meat to dairy or vice versa.
Some Disagree
The Pri Chadash (Rabbi Chizkiyahu Da Silva of 17th-century Italy and Israel) writes[10] that he doesn’t see a basis for this custom as we don’t make decrees that aren’t mentioned in the Talmud. As such, he permits such kashering.
Similarly, the Chida (of 18th-century Israel and Italy) writes[11] that “In our countries we kasher dairy utensils that haven’t been used that day to use for meat and vice versa. We are not concerned with the strict opinion on this matter.”
In Practice
The custom of not kashering from meat to dairy or vice versa is brought down in the Ba’er Heitev (Yoreh De’ah 121:3), in the Mishnah Berurah (Laws of Pesach 451:19), and in many other sources and is therefore the accepted custom.[12] This applies even to kashering through direct heat (libun).[13] (But see below regarding the Shulchan Aruch HaRav.)
If one did kasher from meat to dairy or vice versa, the kashering “works” (bedieved/ post facto) and the utensil may be used for the other “type.”[14]
Exceptions
The poskim write that in the following cases one may kasher from meat to dairy or vice versa:
· If one is selling the utensil to someone else, the utensil may be kashered to be used for the opposite type.[15]
· If the utensils haven’t been used in 12 months.[16]
· One may kasher a utensil from meat or dairy and turn it into a pareve utensil. One may then decide to use it for meat or dairy as they wish.[17]
· In a case of need.[18]
· When one is kashering for Pesach, one may then switch it from meat to dairy or vice versa.[19]
· Some say that one may kasher an oven from meat to dairy and vice versa.[20]
· Some say that one may make the utensil treif and then switch it for the opposite use.[21] The Shulchan Aruch HaRav, however, doesn’t seem to agree with this idea.[22]
Pareve
If a pareve utensil became dairy or vice versa, one may kasher it back to being pareve.[23]
Opinion of the Alter Rebbe
It’s noteworthy that the Shulchan Aruch HaRav doesn’t mention the custom of not kashering from meat to dairy or vice versa in the laws of Yom Tov which is where it is quoted in the Magen Avraham.[24] It is possible that the Shulchan Aruch HaRav follows the opinion of the Sha’ar HaMelech (see above) who allows kashering when using direct heat (libun) and since in the laws of Yom Tov the discussion is about kashering through libun, this custom doesn’t apply.
May we merit to cleanse ourselves from our impurities!
Wishing you a Shabbat Shalom UMevorach and a Chodesh Tov!
Copyright 2025 by Rabbi Aryeh Citron
[1] Many opinions say that tanin means a snake (Rashi, Ibn Ezra, and Da’at Zekeinim) or a water snake (HaKetav VeHakabbalah).
Some say that tanin is a large sea creature (see Genesis 1:21).
According to Rabbi Yosef Bechor Shor, it means a crocodile (see Ezekiel 29:3).
[2] Exodus 7:8 - 13
[4] The Magen Avraham writes that he heard this in the name of Rabbi Mordechai Yaffe. It is noteworthy that Rabbi Yaffe is the author of the Levush, and I haven’t found this explanation in the Levush.
[6] The butcher would sell those fats to gentiles (Rashi).
[7] When kashering from non-kosher, one should wait for 24 hours after it was used before kashering as otherwise the “kashering water” can become non-kosher from the flavor emitted by the utensil being kashered. This would then render the utensil once again not kosher unless the flavor was nullified in the water which was 60 times the volume of the utensil. This doesn’t apply when kashering from meat to dairy since the flavor emitted is a permissible one. (This principle is called Nat bar Nat Leheteira.)
In practice, it is best to wait 24 hours even when kashering from meat to dairy (according to those who permit this kashering) so as not to differentiate between different types of kashering. In addition, if one were to kasher a meat utensil within a dairy pot (or vice versa) and both were used within 24 hours, that could render both items non-kosher. See Shulchan Aruch HaRav 452:14 and 15.
(Regarding not causing even a slight mixture of meat and dairy flavors in the first place (אין עושין נ"ט בר נ"ט לכתחילה), the Shulchan Aruch HaRav 452:13 (in a marginal note) says that this doesn’t apply when the flavor is emitted from a utensil and is three times removed from its source. I.e., one from the meat to the utensil, one from the utensil to the water, and then from the water into the kashering pot.)
[8] Sha’ar HaMelech by Rabbi Isaac Nunis Blimonte of 18th-century Turkey, Laws of Yom Tov 4:8.
Rabbi Blimonte quotes the (Hagahot Rabbeinu Peretz on) Sefer Mitzvot Kattan, 198, as a source that permits kashering from meat to dairy as long as it wasn’t used for meat on that day.
[9] The reason for the difference is that, when kashering through boiling, the flavor can re-enter the pot and utensil after it comes out into the water. Whereas when kashering though heat (libun) the flavor is burned in its place and cannot re-enter the utensil. (See Shulchan Aruch HaRav 451:10). See Mishnah Berurah 451:76 who implies that one may kasher with libun during the 24 hours after use.)
[10] Yoreh De’ah, 97:1.
[11] Orach Chaim 409:2.
[12] See Pri Megadim in Eshel Avraham 452:13 and in the sources quoted in Piskei Teshuvot 451:16.
[13] Pri Megadim, Eshel Avraham, 451:30.
[14] Responsa of Maharsham, vol. 2, 241.
[15] Kitzur Shela quoted in ibid.
[16] Ibid.
[17] Ibid. in the name of the Butchatcher Rov. I heard from Rabbi Avraham Wosner of Monsey that this change can take place even after one pareve use.
[18] Pri Megadim, Eshel Avraham 452:13.
[19] Chatam Sofer, quoted in Mishnah Berurah, Laws of Pesach 451:19.
[20] Shulchan Aruch HaRav 494:16. See Hilchot Bassar Bechalav by Rabbi Dovid Hofstedter, page 563.
[21] Pri Megadim, Eshel Avraham 409:11.
[22] See Shulchan Aruch HaRav 452:21 that אֵין לְהַבְלִיעַ אִסּוּר לְכַתְּחִלָּה עַל דַּעַת שֶׁיַּגְעִילוֹ וְיַפְלִיטוֹ אַחַר כָּךְ (“Initially, it is forbidden to cause a forbidden substance to be absorbed with the intent that afterwards hag’alah will be performed and the forbidden substance will subsequently be purged.”)
[23] Responsa Maharsham, ibid.
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2 Iyyar 5785
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