Question: Can I add sauces and spices to hot food on Shabbos?
Answer: There is a big difference as to whether the sauces or spices are raw or have previously been cooked, whether the food is a davar gush, solid food such as a thick cholent or davar lach, food with significant liquid and if the food is in the keli rishon, pot that was on the flame or keli sheni, e.g. one’s plate.
The Shulchan Aruch (OC 318:9) writes that while one can’t place salt directly into a keli rishon, one may do so in a keli sheni. The Rema, however, writes that ideally one shouldn’t even add salt to hot food in a keli sheni (See Shabbos 42b). Nonetheless, the Mishna Berura (318:64;71) writes that as regular table salt has been cooked already (in its processing), one would be allowed to add salt to a pot off the flame as we follow the rule, ein bishul achar bishul, food can’t be cooked again. Nonetheless, he writes one should ideally only add it to a keli sheni.
The Shulchan Aruch (OC 318:9) writes that one shouldn’t add raw spices such as pepper into a keli rishon, though the Mishna Berura (318:65) allows one to add spices to a keli sheni.
The Mishna Berura (318:45;65) writes that as davar gush retains its heat for longer than liquid, it should be treated as a keli rishon. Thus, one shouldn’t add spices, etc.
Nonetheless, R’ Moshe Feinstein (Igros Moshe OC 4:74 Bishul 5) and R’ Yehoshua Neuwirth (Shemiras Shabbos Kehilchasa 1:58) write that one may add ketchup and other cooked sauces (See Meor Hashabbos 1:267) even on a davar gush.In conclusion, one should avoid adding anything to the pot and shouldn’t add spices to a hot solid food.