“Question: What exactly is the issue with eating roasted meat on Seder night? And can roasted chicken be eaten?
Discussion: The Mishna in Pesochim (Perek 4 Mishna 4) rules that in areas where the minhag is not to eat roasted meat on leil haseder it is forbidden to do so. The reason given (Rashi on the aforementioned Mishna Pesochim 53b) is because it appears that one is eating korbon pesach outside [of Yerushalayim, which is forbidden]. In other words, if one is seen eating roasted meat on Seder night, and roasting is one of the characteristic properties of the korbon pesach (see Mishna Pesochim Perek 7 Mishna 1; also Mishna Zevochim Perek 5 Mishna 8) it may be assumed that this individual is eating korbon pesach, and others will follow his example and come to sacrifice the korbon pesach outside of the Beis Hamikdosh, which is of course forbidden min hatorah because of shechutei chutz (and punishable by kores). Because of this, various places had the minhag to refrain from eating roasted meat on Seder night, to avoid the possibility of this misunderstanding.
The Shulchan Aruch (Orach Chayim Siman 476 se’if 1) quotes the din of the Mishna; namely that in places where the minhag is not to eat roasted meat on leil haseder it is forbidden to do so. Additionally, the Shulchan Aruch (ibid se’if 2) rules that even roasted beef or poultry cannot be eaten on leil haseder [even though the korban pesach cannot be brought from these species, and there is less room for misunderstanding] in places that have the custom to refrain from roasted meat.
It is clear from the Mishna (Pesochim ibid) and Shulchan Aruch (ibid) that this prohibition only applies in areas that have this minhag. The Shulchan Aruch and Remo do not elaborate and specify which areas have this minhag, and which do not. The Magen Avraham (Siman 476) does write that in “these lands” [obviously discussing Europe, but more specifics are unclear] the minhag is indeed to refrain from eating roasted meat on both nights of Seder.
The Mishna Berura (Siman 476 s.k. 1) elaborates on the ruling of the Shulchan Aruch and says that even if the meat was not roasted on an open fire but was roasted in a pot without additional liquids this is included in the prohibition and may not be eaten on leil haseder (the Mishna Berura explains that even though this method of cooking is dissimilar to the korbon pesach that had to be spit roasted specifically, and being roasted in a pot would invalidate it ; there is still reason to prohibit meat roasted in a pot because of onlookers who are not aware of this distinction and may still come to assume that the meat being cooked is actually korbon pesach). Additionally, even if meat was first boiled [which is certainly permitted] and then roasted in a pot, it is forbidden to be eaten. However, if the meat was first roasted and subsequently boiled, it is permitted to be eaten on leil haseder. [I.e. the second cooking process determines the status of the meat.]
Conclusion: As we have discussed, the issue with eating roasted meat on Seder night is because it may appear to an onlooker that one is eating korbon pesach outside of Yerushalayim, which could result in tragic consequences (i.e. that the onlooker may come to sacrifice a korbon pesach outside of the Beis Hamikdosh which is prohibited min hatorah and punishable by kores).
Regarding eating roasted poultry, the Shulchan Aruch clearly writes that in a place that has the custom to refrain from roasted meat, it is also forbidden to eat roasted poultry (even though the korbon pesach obviously cannot come from poultry.)
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