If a potato or any parve permissible food item is cooked in liquid with a forbidden substance why does it take on the identity of just taste (tam k'ikker) rather than becoming a new entity which is chatika nases nevela?
Please put references in shulchun aurach to where you are talking about– EfraymNov 29, 2022 at 23:53
Without a reference, it's hard to know exactly what you are talking about.
Firstly, Ch'n'n isn't exactly a "new item". We are still talking about taste.
The general situation these two concepts come up is in the situation of transferring taste. If the potato is removed from the unkosher liquid and put into another liquid, how do we determine whether that second liquid becomes unkosher?
As is commonly known, we need 60 against the non-kosher food to nullify its taste. However, this is an originally kosher potato, so what do we measure 60 against?
Generally speaking, the Mechaber holds that in this case (depending on other factors which I won't go into), we only need to measure against the amount of non-kosher substance that got absorbed by the potato. The Rama holds that we need to measure against the whole potato - we treat it as if it is a neveila (and this is derabbanan).
So, I think you might have Rama and Mechaber backwards, although hard to tell without more information and sources in the question. I recommend learning Shulchan Aruch Yora Deah 92:2-3 and commentaries to get a good handle on these halachot.