In continuation of the discussion of vessels where the prohibition of cooking applies even though the vessels are not actually on the fire itself, the Mishna teaches:
A stew pot [ilpas] and a pot that were removed from the fire while they were still boiling, even if they were removed before Shabbat, one may not place spices into them on Shabbat itself. Even though the pot is not actually standing on the fire, the spices are still cooked in it because the pot is a primary vessel, i.e., a vessel whose contents were cooked on the fire.
However, one may place the spices into a bowl or into a tureen [tamḥui], which is a large bowl into which people pour the contents a stew pot or a pot. Bowls and tureens are both secondary vessels and food placed into them does not get cooked. Rabbi Yehuda says: One may place spices into anything on Shabbat except for a vessel that has in it something containing vinegar or brine of salted fish.
The Gemara offers two different versions of a discussion between Rav Yosef and Abayye who quotes Rabbi Hiyya – either as saying that salt cooks even in a secondary vessel or else that it can never get cooked, even in a primary vessel.
It is difficult to articulate a precise and unequivocal definition of cooking salt, because the concept of cooking, in general, is not clear in the Talmud. In any case, water with even a very small quantity of salt requires a significantly higher temperature to reach boiling. Since salt boils only at a very high temperature or after cooking for a long time, its cooking is said to be like “cooking the meat of an ox.”
As far as the halakha is concerned, sprinkling salt into a primary vessel after it was taken off the fire is permitted, as per the second version in the Gemara, because halakha tends to be established according to the second version. Moreover, in that version Rav Naḥman and Abayye are in agreement. Other authorities state that putting salt even into a secondary vessel is prohibited (Rema). According to that approach, the first statement in the Gemara is accepted (Taz). (Rema; Rambam Sefer Zemanim, Hilkhot Shabbat 22: 6; Shulḥan Aruk, Oraḥ Ḥayyim 318:9).