I haven't tried making saurkraut in years, and the last few times I tried I got moldy cabbage, not saurkraut.
This time I'm trying my new favorite secret ingredient, whey leftover from skyr production. It seems to be doing the trick so far. I got some preshredded cabbage, since I'm lazy, and added a tablespoon of kosher salt and a 3-4 tablespoons of whey, along with some caraway seeds. We're into day 2 at room temperature, and it's really starting to smell like saurkraut, with no mold in sight (knock on wood). If it survives until tomorrow, it goes in the fridge thenceforth.
I may be trying some more fermentation experiments over the coming weeks, so we'll see how they turn out too.