German food question - Does Rotkohl in a jar need to be cooked?

It's edible straight from the jar, but that's not the usual way. It gets a lot more soft and tasty if you cook it about half an hour. Give some oil and chopped onion in a pot and stew it for a minute, then add the cabbage, but no water in addition. Then you can add a lot of different spice, at first a bay leaf, some pepper, nutmeg, cinnamon, clove, pimento, even ginger, if you like, but just a pinch of everything. You can also sugar it, if you want to. Let it cook gently, but don't forget to stir, and don't let it scorch. If it gets too dry, you can add a little bit of water.

I drain it and add to a pan I have sauteed an onion, a bit of grated apple and few caraway seeds, warm it threw and serve, it is cooked before it is jarred and then sealed with heat to preserve, as a chef and of German heritage (I am a descendant of Martin Luther, the Lutheran), I use to make it as a chef it is popular all over the Northern European countries, from Scandinavian to Austria, and made very much the same, give or take a few ingredients.

If you are serving it with a hot meal then warm it through. It doesn't need to 'cooked' as such.

It's fine to serve it straight from the jar with a salad or in a sandwich.

refrigerate and eat it cold!