Can I cook ramen or tradition soup on Shabbos?
Firstly, instant soups contain in them many different ingredients, and although some of them were pre-cooked, some other added ingredients might not be pre-cooked. It is hard to state a general Halacha about instant soups, as these things change from one company to another and from production to production. Some argue that some of the ingredients might also be considered Kali Habishul (items that can be cooked very easily), which even pouring from a Kli Sheini (second vessel) is able to cook them. Others maintain that the spices (like finely diced parsley), even though they are finely crushed, are different than other foods and one may place them even in a Kli Sheini. Either way, as the precise ingredients and method of production is unclear, one should avoid pouring hot water even from a Kli Sheini.
The same concerns apply with ramen: If one wants to cook items that were not precooked, this could be touching on Bishul, or cooking items which are Kali Habishul, or at the least a Rabbinical prohibition that it seems like cooking.
There is an additional concern that possibly the items were only baked and not cooked, and some opinions hold that there is “cooking after baking” even in a Kli Sheini.
Even if the noodles were already pre-cooked together with the other dehydrated items, there is still a concern that possibly there are items mixed in that were not cooked.
Therefore, for those who are lenient to use Kli Shlishi on Shabbos, as is the common custom, one can place them in a Kli Shlishi (third vessel of hot water that was transferred), or even better, pour from a Kli Shlishi on them.
Shulchan Aruch Admur Hazaken (O.C. 318:11-12).
Shemiras Shabbos Kehlchasa 1 footnote 185*.
See also Shabbos Kehalacha vol. 1 page 286.
Halacha Berurah 318: 122