Napa cabbage salted, then rubbed with a paste of chilli flakes, garlic, ginger and salted seafood, and left to ferment.
Kimchi goes back well over a thousand years as salted vegetables; chillies turned it red much later. Families still make a winter's supply together at kimjang, and most Korean homes keep a separate refrigerator just for it.
It changes as it ages: crisp and bright when young, sour and deep when old — which is when it goes into stews.