This is the approved revision of this page, as well as being the most recent.
- If something permitted was cooked with something forbidden in a kli sheni after the fact the food is permitted. Some are strict unless there is a case of great loss.
- If something forbidden was cooked in a pot or utensil that was a kli sheni the pot or utensil needs to be koshered. Some poskim hold it doesn't need to be koshered.
- The Rama Y.D 94:7 holds that a solid item in a kli sheni is a kli sheni and there's no difference between a solid and a liquid after they landed.
- If something permitted was cooked with something forbidden in a kli shelishi after the fact the food is permitted.
- A solid piece of food that is picked up on a fork or with one's hand is considered a kli rishon until it is placed on the plate or bowl.  As it is being placed down on the plate or bowl that is considered iruy. After it settles it is considered a kli sheni.
Not Yad Soledet Bo
- A kli rishon that isn’t yad soledet bo one shouldn’t use initially for something that isn’t kosher. After the fact it could make something non-kosher up to a klipah.
- A kli sheni that isn’t yad soledet bo one shouldn’t use initially but after the fact it doesn’t make something non-kosher at all.
- Roasting something forbidden together with something permitted will make the permitted thing forbidden up to the thickness of a Etzbah where they touched.
- A food which absorbed a taste of something forbidden can't forbid something else with roasting unless it is fatty. Ashkenazim assume that all foods might be fatty.
- Shulchan Aruch Y.D. 105:2. The Rashba Torat Habayit 1b quotes someone who says that just like a kli sheni doesn't cause Bishul (Shabbat 40b) it doesn't cause any transference of taste. The Rashba himself disagrees based on Chullin 8a and Chullin 8b. He held that even though a kli sheni doesn't cause bishul it does cause a transference of taste. The Tur 105:2 understands that the Rashba himself would say that a kli sheni could only transfer taste up to a klipah but himself argues that perhaps it transfers taste completely. The Shulchan Aruch Y.D. 105:2 cites the lenient opinion who says that it doesn't transfer taste as well as the Rashba that it transfers taste up to a klipah. He says initially one should be strict for the Rashba. Shach 105:5 and Taz 105:4 cite the Maharshal who holds that a kli sheni can transfer taste completely and advise being strict. Badei Hashulchan 105:39 is strict unless there is a great loss in which case one can rely on Shulchan Aruch. Chachmat Adam 59:6 says that a klipah is necessary unless there is a loss.
- Based on the dispute cited above, the utensils that were made non-kosher because of a kli sheni should not require koshering according to the lenient opinion and should require koshering according to the Rashba. Shulchan Aurch 105:2 is initially strict for the Rashba. Therefore, Minchat Yakov 33:6, Rabbi Akiva Eiger 105:6, Badei Hashulchan 105:39, and Horah Brurah 105:28 write that one should be lenient to kosher something that became non-kosher because of a kli sheni unless it is a loss. Yabia Omer OC 3:24:1 implies this as well. His proof is from the Rif Pesachim 8b, Rosh Pesachim 2:7, Shulchan Aruch O.C. 451:5, Tur and Bet Yosef Y.D. 121:3-5 who say that a kli sheni requires koshering.
- Horah Brurah 105:29 writes that even though some are strict regarding a kli sheni there's no need to be strict regarding a kli shelishi. Shevet Halevi 8:181 agrees. Badei Hashulchan cites the Pri Chadash who is strict. See Chatom Sofer YD 95.
- Badei Hashulchan 106:21 outlines three approaches as to why the food while in the air is still considered a kli rishon. 1) According to the Maharshal (Yam Shel Shlomo Gid Hanesheh 44, Kol Habasar 75) any solid food (Gush) is considered a kli rishon. 2) Solid food that is in the air that didn't land is considered a kli rishon.(Chazon Ish 9:5) 3) Any food that is in the air that didn't land is considered a kli rishon. (Shach 105:5)
- Shach 105:7 citing Darkei Moshe 105:4 clarifies that a hot food that is placed on a plate or bowl is considered iruy while it is being placed down. However, after it settles it is considered a kli sheni.
- Pri Megadim M”Z 105:4 writes using a kli rishon even if it isn’t a yad soledet bo it is an issue even after the fact. That’s the implication of Torat Chatat 23:3 and 33:1. Badei Hashulchan 105:2 s.v. lechatchila cites the Pri Megadim and seems to agree.
- Pri Megadim M”Z 105:4 writes that the Shach and Taz conclude that if a kli sheni isn’t yad soledet bo it doesn't make something forbidden at all after the fact. But initially it is an issue up to a klipah. Badei Hashulchan 105:2 s.v. lechatchila cites the Pri Megadim and seems to agree.
- There are three opinions of how far roasting can transfer taste. The Rashba thinks that essentially it could only transfer up to the thickness of a peel. But he is strict for the opinion of Tosfot for any question of Biblical nature. Tosfot Chullin 99b s.v. ad and Rosh Chullin 7:24 hold that it could transfer up to the thickness of a netila, which is an Etzbah. Lastly, the Ri Halavan (cited by) holds that roasting can transfer taste completely just like cooking. Shulchan Aruch follows the Rashba. Maharshal follows the Ri Halavan but the Shach disagrees.
- The Rashba cited by Shulchan Aruch 105:7 holds that taste absorbed in a food can't impart taste with roasting unless it is fatty. Maharshal in Yam Shel Shlomo Chullin 7:45 and Isur Vheter LMaharshal siman 37 writes that ein beluah yotzei blo rotev only applies to tata gavar or two pieces next to one another but it doesn't apply to tzeli or melicha. He explains that he is following the Ri Halavan that tzeli and melicha transfer taste completely just like cooking. Shach 105:18 quotes the Maharshal and disagrees.