Bishul 15 - Kli Sheini 2; Kalei Habishul (Klal 20 Siman 4) Hilchos Shabbos - S0512

We are continuing in siman 4, which discusses kli sheini. Yesterday, we learned an introduction and today we will read it inside.

The Chayei Adam writes that if kli rishon is the container which was on the fire, kli sheini is when those contents are poured into another container. The Chayei Adam writes that kli sheini does not perform bishul, even if the temperature inside of the pot is yad soledes bo. However, there are items which cook easily, known as kalei habishul, which do cook in a kli sheini. We are not experts in determining which items cook in a kli sheini and which do not, so cooking in a kli sheini becomes a safeik deoraysa. Therefore, one should be careful and refrain from placing anything still relevant to bishul into a kli sheini, out of concern that the kli sheini will cook the item. If the kli sheini is no longer yad soledes bo, it cannot cook even kalei habishul and there is no concern of bishul.

The Mishnah Berurah points out that the Gemara gives a list of items which definitely do not cook in a kli sheini. These include water and olive oil. The Chayei Adam’s conclusion to be machmir out of safeik does not apply to these items, since the Gemara already tells us that they do not cook in a kli sheini. Therefore, one can add water or olive oil to a food item in a kli sheini. 

On the other hand, the Chayei Adam gives salt and onions as two examples of items about which a person should be careful. Onions are straightforward, but we need to explain the concept of bishul as it applies to salt. Halacha differentiates between two types of salt. One type is salt which is mined from salt caves, which is then ground up into the salt we use. This type of salt is considered kalei habishul. The other type of salt is when seawater is heated until the water evaporates. The latter salt is considered cooked, so we can apply the concept of ain bishul achar bishul and it is muttar to add to a kli sheini. Therefore, the Chayei Adam writes that one should not pour previously uncooked salt into food which is a kli sheini, and certainly should not place the salt in the container and then pour the kli rishon on top of it, as that would be irui kli rishon. 

Summary
Kli sheini is defined as the container into which a kli rishon food is transferred. 
It does not have the power of bishul because the walls of the container are not hot, they cool the food as the food transfers heat into them.
However, if the item is defined as kalei habishul, items which cook easily, it will cook in a kli sheini. The Chayei Adam holds that we do not know which items are considered kalei habishul and which are not, so out of safeik, one must be machmir and refrain from adding any food which is not fully cooked to a kli sheini.
Some exceptions are water and olive oil, since the Gemara explicitly states they are not kalei habishul.
Additionally, if the item was previously fully cooked, we apply the concept of ain bishul achar bishul and it is muttar to place in the kli sheini.