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Weekly Halacha

Using One Oven for Meat and Dairy

Using one oven for both meat and dairy demands vigilance lest one transgress any of the laws pertaining to basar-b’chalav. Ideally, separate ovens for meat and dairy are the solution for preventing basar-b’chalav mix ups, and many people do have separate ovens for that very reason. Those who do not, however, should familiarize themselves with the answers to the following questions.

Question: May an oven be used for meat and dairy dishes at the same time?

Discussion: It is prohibited to bake uncovered[1] meat and dairy dishes in one oven for the following three reasons:

    1. The meat may come into actual contact with the dairy or vice versa, either through touching, or when particles from one dish splatter onto the other.

    2. When two foods are baked or roasted simultaneously in one oven, they absorb each other’s aromas (reicha).

    3. When moist foods or liquid mixtures are baked in an oven, steam (zei’ah) is emitted, carrying the taste of one food to the other.

If, b'diavad, one cooked meat and dairy dishes in the same oven simultaneously, he must consult a rav to determine whether the food may be eaten or not[2].

Question: May an oven be used for meat and dairy dishes that are baked consecutively?

Discussion: The first two problems mentioned above—items touching or splattering each other, and reicha—do not apply, since the meat and dairy dishes will not be in the oven at the same time. We are, however, still concerned with the issue of zei’ah. This is because whenever moist foods (as opposed to “dry” foods like a potato) are baked in an oven, steam is emitted. When, for instance, uncovered meat is cooked in an oven, the steam emitted carries the taste of the meat and “deposits” it onto the walls and roof of the oven. When moist dairy foods or liquid mixtures are subsequently cooked uncovered in the same oven, their steam rises, absorbs the meat taste from the walls and roof of the oven, condenses, and falls back into the dairy dish. The dairy dish is now prohibited as basar b'chalav.

The poskim debate whether or not we need to be concerned with this problem. Some hold that there is no issue of zei’ah when baking or roasting inside a closed oven, since the oven’s heat is intense enough to completely dry out and evaporate the steam which rises from the food even before it reaches the walls or roof of the oven[3]. Thus no steam is deposited onto the walls or roof of the oven to later condense and fall back into the dairy food. According to this opinion zei’ah is never a problem for foods baking inside a hot oven[4], and it is, therefore, permitted to use the same oven for meat and dairy consecutively, even l’chatchilah, as long as the surface of the oven roof and walls is free of any meat spills or residue. Many people follow this opinion[5].

But other poskim are more stringent. In their opinion we can not or do not know for certain that all of the steam will be evaporated before being deposited onto the oven walls or roof, and it is, therefore, still possible that some meaty steam will enter the dairy food[6]. [Note, however, that even according to the strict opinion, this problem affects only most gas ovens. With electric ovens or other ovens where the heating element is on top, zei’ah would be no problem since the steam will definitely dry up and vanish before it reaches the walls and roof of the oven[7] ]. To avoid this eventuality, one should adhere to the following procedure:

First, determine the primary use of the oven—is it going to be used mainly for meat, or for dairy dishes? For the sake of this Discussion, let us assume that the primary use of the oven will be for meat dishes. For halachic purposes, this oven now becomes a “meat oven,” in which liquid or solid meat dishes will be roasted and baked, covered and uncovered. [To later use the oven for dairy dishes, one should line the racks with aluminum foil. The foil should be changed when dairy dishes are placed in the oven.]

Before using this oven for dairy, one must first make sure that the oven is completely clean from any meat spills or residue. Once that is ascertained, a dairy dish (or a parve food which will be eaten with dairy) may be placed into the oven as long as one of the following two conditions is met: 1) The dairy dish is thoroughly covered; 2) The dairy dish is not moist. Since, generally, only moist or liquid dishes produce steam[8], there will be no way for the meat steam which found its way onto the walls and roof of the oven to be released from the walls and roof and enter the dairy dish, as occurs when moist dishes are cooked.

Question: According to the stringent opinions mentioned earlier, what can be done so that an uncovered, moist dairy food or liquid mixture can be baked l’chatchilah in a meat oven?

Discussion: Before moist dairy foods can be baked in a meat oven[9], the oven needs to be properly koshered. There are different opinions as to whether our ovens can be koshered and what means may be used to kosher them[10]. Some poskim maintain that there is no easy, practical[11] way to kosher our ovens, since an oven cannot be koshered unless sparks are actually seen during the koshering process[12]. Other poskim are of the opinion that our ovens can be koshered only through a self-cleaning cycle, which heats the oven to approximately 900°F[13]. But the majority of poskim[14] hold that heating the oven at its highest setting for one hour is sufficient to kosher an oven for consecutive use of meat and dairy, and many households follow this opinion[15].

To review: Whether or not zei’ah is a concern when cooking uncovered, moist dairy inside a meat oven is debatable. There are many who follow the more lenient opinion and use their oven for meat and dairy consecutively, as long as they ascertain that there are no spills or residue on the surface of the oven[16]. Still, in deference to the more stringent opinions mentioned earlier, it is appropriate, at the very least, to kosher the oven by heating it at its highest temperature setting for one hour before using for moist, uncovered dairy, or for parve food which will be eaten with dairy[17]. Obviously, having two separate ovens for meat and dairy, or self-cleaning an oven between meat and dairy, avoids all of these halachic concerns.

Note: Challah may be baked in the same oven that was used to roast uncovered meat, even though the challah may be eaten with dairy. Challah dough does not produce enough steam to release the meat steam that was deposited onto the walls and roof of the oven[18]. The oven should first be thoroughly cleaned from any visible meat residue. Preferably, the racks should be changed or covered with foil.

Question: Do the halachos mentioned earlier concerning meat and dairy in the same oven apply to microwave ovens as well?

Discussion: No, they do not. All poskim would agree that it is forbidden to use the same microwave oven for meat and dairy consecutively. The air space, roof and walls of a microwave oven do not become hot enough for us to assume that the steam that is emitted from the foods will be “burned” before being deposited onto the walls or roof of the oven. In addition, microwave ovens are small, compact units, which quickly fill up with steam from the food being warmed in them.

Koshering a microwave between meat and dairy or dairy and meat is halachically problematic. Some poskim[19] permit koshering a microwave by first scrubbing it clean, waiting twenty-four hours[20], and then placing a cup of water inside the microwave and heating it for 5-10 minutes, until thick steam fills the oven[21]. Other poskim, however, are wary of permitting this procedure, and it is not recommended to rely on the lenient opinions[22].

Even if koshering a microwave would be allowed, the poskim discourage using the same microwave for both meat and dairy, since it is a long-standing custom[23] that we do not kosher utensils from meat to dairy or vice versa. The poskim also recommend not to use the same microwave for meat and dairy even if one is careful to keep all of the food covered while being cooked or warmed in the microwave[24].

It is clear, therefore, that those who need to use a microwave for both meat and dairy foods should make every effort to get two separate microwave ovens and designate one for meat and the other for dairy.

1. Technically, if one of the foods is tightly covered, they can both bake in the oven at the same time; see Y.D. 108:1. Practically speaking, however, this is not a good idea, for if the cover slips off or is lifted off inadvertently, or if one of the foods spills over, the food might very well be forbidden to eat, even b'diavad (see Kesav Sofer 54 and Igros Moshe, Y.D. 3:10).

2. Since, b'diavad, there are several factors that must be taken into account, such as the type of oven, the proximity of the foods to each other, the amounts of the foods in question, the type of foods (“sharp” or bland) and other factors.

3. In addition, the walls and roof of the oven are hot enough so that immediately upon impact any steam or condensation will burn and fizzle out and will not remain in the walls or roof of the oven.

4. It must be stressed that these poskim surely reckon with zei’ah as a factor rendering a food item dairy or meaty, but they maintain that inside a closed oven there is no zei’ah as explained above.

5. See She’alas Ya’avets 1:193, quoted by Yad Efrayim, Y.D. 97:2, Maharsham 3:208. See Sefer Zikaron Yad Moshe Tzvi ha-Levi, pg. 201, where Rav B.Y. Wosner proves from several sources that this is the opinion of most poskim and the prevalent custom.

6. Beis Shelomo, Y.D. 164; Igros Moshe, Y.D. 1:40; Minchas Yitzchak 5:20; Chelkas Ya’akov 2:136.

7. Igros Moshe, Y.D. 1:59.

8. Igros Moshe, Y.D. 1:40 based on Pischei Teshuvah 92:6. This is a generality, since most solid foods do not produce much steam. If, in fact, a fair amount of steam was detected rising from a solid food, then we need to be concerned with it as we would be with a liquid food.

9. The following procedure is for using the oven l'chatchilah. B'diavad, there are several possible heterim that allow dairy food that was baked in a meat oven (or vice versa) to be eaten. See Maharsham 3:26; Igros Moshe, Y.D. 1:40; Yabia Omer, Y.D. 5:7. A rav should be consulted.

10. The poskim discuss the following issues: 1. Are our ovens—which are made from metal but coated with porcelain—considered klei cheres which cannot be koshered without libun chamur? 2. Is it sufficient to kosher an oven by heating it with fire from an external source, or does the fire have to originate inside the oven? 3. Since most of our baking is done in pans, may we rely on libun kal since the food does not (usually) touch the actual oven surface? 4. Even if libun chamur is required, must sparks actually be seen during the libun?

11. Although an oven can be koshered by using a blowtorch, this is a dangerous and cumbersome process which should be undertaken only by a professional who is also well-versed in the halachah.

12. Sha'ali Tziyon 2:20; She'arim Metzuyanim B'halachah 116:2; Badei ha-Shulchan 92:8, s.v. l’chatchilah. See also Igros Moshe, Y.D. 1:60.

13. Rav M. Feinstein (oral ruling, quoted in Sefer Hilchos Pesach, vol. 1, pg. 181, and in Ohalei Yeshurun, vol. 1, pg. 72 and 77); Minchas Chein, pg. 29. When koshering the oven from meat or dairy to parve, half of the self-cleaning cycle (about an hour and a half) is sufficient; Rav M. Stern (quoted in Pischei Halachah, Kashruth, pg. 114).

14. Rav Y.E. Henkin (written responsum published in ha-Darom, vol. 15); Rav A. Kotler (oral ruling, quoted in Sefer Hilchos Pesach 1, pg. 180); Yesodei Yeshurun, vol. 6, pg. 157; Minchas Yitzchak 3:66 (see, however, 5:20, where he is hesitant); Chazon Ovadyah, pg. 73:4; Rav M. Stern, Pischei Halachah, Kashruth, pg. 114).

15. See Seder Pesach K'hilchaso, pg. 64, who quotes many poskim as allowing this leniency.

16. Another practical suggestion is to place some foil under the meat item being baked so that whatever spills over will not land directly on the racks or the oven floor but on the foil. The foil is then removed before the dairy item is inserted.

17. Some poskim additionally recommend that twenty-four hours elapse after using the oven for meat before the oven is used for dairy.

18. Igros Moshe, Y.D. 1:40; 1:59.

19. Rav M. Feinstein (oral ruling, quoted in Sefer Hilchos Pesach, pg. 182); Rav S. Wosner (mi-Beis Levi, Nissan 5753); Teshuvos v'Hanhagos 2:212; Yalkut Yosef (O.C. 451), pg. 360.

20. Scrubbing the microwave and waiting 24 hours before koshering a microwave is required, since the koshering process of a microwave is hagalah, not libun kal, and a through cleaning and a wait of 24 hours are prerequisites of hagalah; see Mishnah Berurah 451:22, 452:20 and Rama, Y.D. 121:2.

21. This leniency does not apply to microwave ovens with a browning element or to convection microwave ovens.

22. See Shevus Yitzchak, Mikrogal, pg. 57, quoting Rav Y.S. Elyashiv; The Laws of Kashrus, pg. 234.

23. Quoted by Mishnah Berurah 509:25. See The Daily Halachah Discussion to 29 Cheshvan for the details concerning this custom.

24. Shevus Yitzchak, Mikrogal, pg. 57, quoting Rav S.Z. Auerbach and Rav Y.S. Elyashiv.

Weekly-Halacha, Text Copyright © 2011 by Rabbi Neustadt, Dr. Jeffrey Gross and

Rabbi Neustadt is the Yoshev Rosh of the Vaad Harabbonim of Detroit and the Av Beis Din of the Beis Din Tzedek of Detroit. He could be reached at

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