Kimchi keeps fermenting in your refrigerator. It gets more sour week by week, and that is the culture working rather than the jar going bad. Cooks prize the older, sourer batches for stews and fried rice. If it smells sharp and sour it is doing its job; trust looks and mold, not tang.
The ferment is led early by Leuconostoc species and later by Lactobacillus, the same family of lactic acid bacteria research associates with a more varied gut community.
It is a multi-vegetable dish, not just cabbage. A standard build carries napa cabbage, radish, scallion, garlic and ginger, so one serving spreads several different plants across your week.
Vitamin K at 54% DV and vitamin C at 24% DV per cup, for about 23 calories. The chili and the cabbage do most of that work.
Two honest caveats. 747mg of sodium per cup, roughly 32% of the daily limit, so it is a side rather than a bowl. And most commercial kimchi contains salted shrimp or fish sauce, so it looks like a vegetable dish while not being a plant-based one. Read the label if that matters to you.