The status of Pareve foods baked simultaneously with meat or cheese:[1]

*Waiting six hours after eating the Chezkat Besari foods: The focus of this Halacha is solely on the subject of whether a food that was cooked with meat or dairy utensils may be eaten with the opposite food. The subject of whether one is required to wait six hours after consuming such food was discussed in the previous chapter, in which we ruled that one is not required to wait. See there for full details!

Background: The subject of baking Pareve foods together with meat or cheese, and its subsequent status in whether it remains Pareve, is affected by many different aspects. These include: 1) Reiach, or the smell of the meat/cheese penetrating the Pareve. 2) Zeiah, which is the vapor of meat/cheese penetrating the Pareve.[2] 3) Mamashus, which is having the meat/cheese contact the Pareve contact that is in the oven and hence receive forbidden taste. In the types of ovens that existed in previous times, which were very large in size and/or contained a large hole [the size of a pot] which allowed the vapor to escape, there was no concern of Zeiah, although the other concerns were still relevant. [These typical medieval ovens did not contain a Zeiah concern as they were too large[3], or had a wide-open vent which released the vapor, and their only concern was that of Reicha.] However, our ovens today which are a small closed off box, contain a serious Kashrus concern of Zeiah upon the vapor of the food hitting the ceiling of the oven.[4] Accordingly, the status of a Pareve food cooked with meat/cheese in the same oven is as follows:

The law if foods uncovered:[5] If uncovered bread[6] [or other Pareve food] was baked simultaneously with uncovered meat or dairy in the same oven, then the Pareve food becomes meaty/dairy and is forbidden to be eaten with the opposite food.[7] [If the food was then mixed with the opposite food, everything is forbidden unless it contains 60x.[8]]

Foods covered:[9] If both[10] the Pareve food and meat or dairy are properly covered to the point that they will not release vapor [and the oven was clean of any meat or dairy residue[11]], then the Pareve remains Pareve and may be eaten even initially for the opposite food. [If the Pareve food is doubly wrapped, such as two sheets of tinfoil wrapping, then the food remains Pareve even if the meat/dairy food is uncovered.[12]]

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[1] Michaber 97:3; See “A Semicha Aid for Learning the Laws of Taaruvos” Chapter 108 for a full analysis of this subject!

[2] There are two possible ways of understanding the prohibition of Zeiah: 1) Due to Nitzuk Chibur [See Admur 451:41 and Levush 93 who learns that the vapor prohibits due to the law of Nitzuk Chibur] 2) Due to Mamashus [See P”M 92 M.Z. 29 and O.C. 441 A.A. 44 and Yad Yehuda 92:52 who learns that the prohibition of Zeiah is due to Mamashus falling back inside.]

[3] A large oven negates a Zeiah concern as a) It dissipates the Zeiah evenly everywhere, and by the time it reaches the oven roof, there may be no vapor left; b) the oven roof would not get hot to the point of Yad Soledes, and the vapor was below Yad Soledes by the time it hit the oven, thus avoid any issue of Zeiah. This applies even if the oven contains no vents during the cooking or baking.

[4] See Igros Moshe Y.D. 1:40 in length for the Zeiah concerns in our ovens and that they have the same status as a pan placed over two uncovered foods, brought in Rama 108:1; Maharsham 3:208; Minchas Yitzchak 5:20; Chelkas Yaakov 2:136; Kinyan Torah 1:24; Badei Hashulchan 92:166; Darkei Halacha p. 242

The reason: As the roofing is very close to the food and it is hence just like the case of a cover on two pots. Now, this prohibition of Zeiah is either due to Nitzuk Chibur [See Admur 451:41 and Levush 93 who learns that the vapor prohibits due to the law of Nitzuk Chibur] or due to Mamashus [See P”M 92 M.Z. 29 and O.C. 441 A.A. 44 and Yad Yehuda 92:52 who learns that the prohibition of Zeiah is due to Mamashus falling back inside.] Thus, although some Poskim entertain that perhaps our ovens today do not have a Mamashus prohibition, as the vapor will not fall back down [Shut Beis Hayotzer], nevertheless, it would still be forbidden due to Nitzuk Chibur.

[5] Michaber ibid; Rama 108:1; See “A Semicha Aid for Learning the Laws of Taaruvos” Chapter 108 Halacha 2I and 3A for a full analysis of this subject!

[6] This refers to a case that the bread nevertheless remains Kosher, such as it was made into a special shape, or is a small amount. See Chapter 6!

[7] The reason: As a) Reicha: We rule that initially one must suspect that the smell of a food penetrates another food and transfers taste into it. Thus, since one is able to eat the Pareve food plain, or with the food it was baked with, therefore it has the status of Lechatchilah and may not be eaten with the opposite food. [Shach 97:4; 108:2; Chavas Daas 97:10; P”M 97 S.D. 4; Aruch Hashulchan 97:13; Kehilas Yehuda 97:3; Zivcheiy Tzedek 97:27; Kaf Hachaim 97:39] However, Bedieved, due to this reason alone, if this food became mixed with the opposite food, everything remains permitted, if Zeiah is not applicable. Furthermore, this worry of Reicha only applies if the oven was small, or was large but closed, and neither food was covered, If, however, one of the foods were covered, or if the oven was large and open, then the food remains Pareve and may be eaten with the opposite food. [Michaber 97:3] b) Zeiah: In modern ovens today, the vapor of the meat/milk have nowhere to escape or dissipate due to the small size of the ovens and therefore the Pareve food absorbs actual Mamashus vapor from the meat/milk, and becomes meaty/dairy. This would apply even if one of the foods are covered [but not both] and this would apply even Bedieved, that if one mixed the once “Pareve” food with the opposite food, 60x is required. [Michaber and Rama 92:8; Tur 92 in name of Rosh Kalal 20:26] 

[8] See Michaber and Rama 92:8; Tur 92 in name of Rosh Kalal 20:26

[9] Michaber ibid

[10] If only one food was covered: See Admur 447:10 and Michaber 108:1 that it suffices for even one of the foods to be covered, however, that is regarding Reicha. However, regarding Zeiah, so long as the vapor of one of the foods hits the other food, it is forbidden, and thus both foods must be covered. Accordingly, if either the Pareve or meat/milk food is uncovered, then seemingly the Pareve food becomes meaty/dairy as it is similar to the case of Rama 92:8 where the uncovered milk pot prohibits the even covered meat pot, as the vapor travels towards it. Similarly here, the vapor travels from the meat to the covered Pareve, and makes it meaty. [See chapter 95 Halacha 1 in Q&A regarding if we apply Nat Bar Nat in such a case] Furthermore, even if the meat or milk was covered while the Pareve was uncovered it becomes meaty/dairy as perhaps the vapor of the uncovered travels to the covered food, becomes meaty, and then returns back to the uncovered food and makes it meaty. [See Peri Toar 92:16; P”M 92 M.Z. 29; Degul Mirivava 92 regarding that the dairy uncovered pot also becomes forbidden even if the meat pot was covered.] This especially applies according to Admur 451:41 [and Levush 93] who learns that the vapor prohibits due to the law of Nitzuk Chibur, and hence it is as if one poured meat onto a Ben Yomo dairy pot, in which the Rama 95:3 rules it is forbidden. [This is unlike the P”M ibid and O.C. 441 A.A. 44 and Yad Yehuda 92:52 who learns that the prohibition of Zeiah is due to Mamashus falling back inside.] Vetzaruch Iyun from Kaf Hachaim 108:32 who explains that the Zeiah case which prohibits is if both the Heter and Issur are uncovered.

[11] Otherwise, the vapor of the residue will penetrate the covered Pareve, as explained in Rama ibid

[12] The reason: As the vapor only becomes absorbed in the external covering, and the internal covering does not absorb from the external one, being there is no moisture in-between, and is similar to two dry pots touching each other. [See Taz 92:29; 97:3]

[13] Kehilas Yehuda 97:3; Zivcheiy Tzedek 97:26; Kaf Hachaim 97:37