Napa cabbage is the main ingredient in fermented Korean kimchi. We’ve heard from several of you who are planning a first go at making your own batch of kimchi. Way to go! Leave your Napa Cabbage unwashed and uncut until you are ready to use it. Seal the head of Napa cabbage in a large plastic bag and store it in the fridge. It should stay fresh for about a week. Discard any outer leaves that have yellowed before cooking with it.