Question: [Wednesday, 11th Teves, 5782]
I guess I was never made aware of this, but a Shabbos guest of mine told me that it is forbidden to bake fish and meat simultaneously in the same oven. What do I now do with the fish and meat that was baked together simultaneously in the same oven?
It is correct that it is forbidden to bake fish and meat in the same oven, simultaneously. However, if the fish and meat were both hermetically covered in a way that vapor was not released during the baking, then everything remains permitted. Furthermore, even if only one was covered and the only other was uncovered, seemingly both remain permitted. If, however, both the fish and the meat were uncovered, then both the meat and fish are forbidden.
Explanation: It is forbidden to eat meat and fish together due to danger, and this danger applies whenever the flesh or gravy of meat and fish mix together. Now, since vapor commonly carries the actual substance of the product, when one bakes the uncovered meat and fish in the same oven, the vapor of the meat enters into the fish and the vapor the fish enters into the meat, hence rending them both forbidden. [This issue has become mainly relevant today by the modern-day ovens, although by ovens of medieval times there was no issue of vapor being that the ovens were very large and contained large chimney holes which allowed before falling back onto the foods.] For this reason, it is imperative that one never bake fish and meat at the same time in the same oven, and at the very least, if one needs to, one is to make sure that they are both hermetically covered. If they are both covered then since no vapor can escape, then there is no worry of intermingling of the two gravies. In the event that only one is covered, then while there is no worry that the covered product will release vapor, the uncovered product will release vapor and it thus can prohibit the covered product as a result. However, in truth one can argue that since by mixtures of meat and fish the Poskim rule that only if the two substances actually mix do they become forbidden, and not through mere absorbance of taste, therefore by fish and meat even the covered food remains permitted as it only absorbs the taste of the vapor of the other food through its cover and not the actual vapor.
Sources: See regarding baking fish and meat simultaneously in same oven: Rama Y.D. 116:2 that one may not do so due to Reicha, although Bedieved it is permitted; Rama Y.D. 108:1 regarding baking under the same roofing which causes Zeiah, which is Mamashus to travel; See regarding the issue of vapor: Michaber and Rama Y.D. 92:8; 108:1; See regarding the status of today’s ovens: 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; See regarding 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; Vetzaruch Iyun from Kaf Hachaim 108:32 who explains that the Zeiah case which prohibits is if both the Heter and Issur are uncovered; See regarding that by fish and meat there is no prohibition of taste: Implication of Michaber 95:1 and Chulin 111a “One who roasts fish in a meat pot may eat it”; Taz 95:3 “One can learn from here that there is no danger in eating fish that contains the taste of meat through being cooked in a Ben Yomo pot of meat”; Issur Viheter 39:26 “All secretion of taste of meat that is absorbed in a vessel into fish is not Bedieved forbidden due to danger”; Rashal Kol Habasar 9; Kneses Hagedola 116:18; Minchas Yaakov 57:1 concludes “The custom is to be lenient [even initially-Kaf Hachaim 116:20] if the pot is clean”; Peri Megadim 95 M.Z. 3 defends the ruling of the Taz ibid; Lechem Hapanim 116:3; Beis Lechem Yehuda 116:4; Chochmas Adam 68:1; Eidos Biyihosef 2:46; Divrei Hilel 2:32; Daltei Teshuvah 95:5; Ikareiy Hadat Y.D. 14:10; Zechor Leavraham 3:186; Darkei Teshuvah 116:27; Kaf Hachaim 116:20; Sheivet Halevi 6:111 writes it is the custom of the world to be lenient.