[Q] When did we start to eat KIMCHI?

[A]In Samkuksagi (historical records of the three kingdoms), there was a record about nabchae which refered to an official process that King Shimun went through to welcome his queen.
In the record, "jang" "hae" were found. Given, "hae" means salting (mostly vegetables), hae is likely to refer to all pickled fish and Kimchi.
There is no way to figure out what kind of food hae was but plausible assumption is that it was a kind of pickled vegetable such as "jangachi"