Bishul Kli Shlishi

Igros Moshe (OC IV #74.4) Question Should one  be concerned for the view of the Chaye Adam that everyone agrees that a kli sheini cooks if it is hot to burn the hand (yad nekeves). Furthermore to be concerned also that a kli shlishi cooks when it is that hot? Answer  It is impossible to know what the accepted practice is in this issue since we are strict with everything because we are concerned it might cook since there are things that cook in a kli sheini that we don’t know and thus this distinction is not relevant on a practical level. Concerning a hot kli shlishi (yad nekeves) it is not relevant since we are lenient and simple assume that nothing is cooked in a kli shlishi. However we should not learn from this to be lenient for a kli sheini.  It is possible that even the Chaye Adam  would rule that there is no prohibition  for a kli shlishi  even if very hot (yad nekeves)  But it is not clear there is such a thing.

Igros Moshe (OC IV #74.16) I personally am strict  for myself and don’t put instant coffee or sugar in a kli shlishi however according to halacha there is no need to be strict

Igros Moshe (OC IV #74.17) Question Is it permitted to place uncooked salt in a kli shilishi? Answer In my humble opinion as I have written before we don’t find that any cooks in a kli shlishi. Salt is is viewed l’chumra to be cooked when placed in a kli sheini so obviously it is not viewed even l’chumra to be cooked in a kli shlishi especially when the law is clear that salt is permitted even in a kli rishon. 

Igros Moshe (OC IV #74.18) Tavlin is permitted in kli sheini onion is considered tavlin according to Aruch HaShulchan while the Taz prohibits it. Because there is a question whether onion and garlic are tavlin that is permitted in a kli sheini it is best to be strict like the Taz but only because there are things that cook in a kli sheini that we don’t know about. Nonetheless there is no problem with a kli shlishi. Lemon is prohibited in a kli sheini  but is permitted in a kli shlishi. Concerning coffee and cocoa they are considered tavlin and can be placed in a kli sheini  according to the Mishna which says tavlin can be placed in a kli sheini since they won’t be cooked.  I am surprised by the Aruch HaShulchan who is strict not to put them in a kli sheini or kli shlishi. The Mishna Berura prohibits coffee in a kli sheini because there are things which are cooked by a kli sheini. However the Mishna clear excludes Tavlin from being cooked in a kli sheini. This makes sense for tea leaves not to consider them as tavlin since they don’t give flavor but just color, however coffee and cocoa are clearly tavlin and therefore their question is puzzling. The best approach is to be strict with a kli sheini but to permit putting them in a kli shlishi.